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Year 10.5 of John’s Freezer: WTF?

Posted in Freezermas, tagged , , on August 20, 2022| 3 Comments »

2021-2022: “over and over again & again” sums it up. I do love this band I “discovered” in 2021 though. Finding new music has been a joy for me through these tough recent years.

The pandemic goes on; my life goes on; but it has been another rough 1+ years. I have hardly done any hands-on anatomy as I’m hardly on campus at all, and my team’s work has mostly shifted into digital modelling for now (more about that below; it is not a bad thing though). My main news for 2021-2022 falls into the categories of Life Stuff, and Work Stuff to summarise here. “WTF” sums it up as it has been a… strange time; very challenging at a personal level, due to the Life Stuff.

Stomach-Churning Rating: stuff is weird, but nothing truly stomach-churning is here

Life Stuff: It’s been about the same as 2020-2021; summarised here. Thankfully, no major grief from losing people/pets close to me, this time. But my heath has been really awful instead — my epilepsy returned in May 2021, much to our surprise, after 2 years of remission. I suspect dehydration was a cause, as I later found out that I’d been chronically dehydrated, which came as a shock. I’ve since learned to step up my hydration routine, and I feel better. Right now I’m >5 months seizure-free, after a very hard time of monthly seizures for ~5 months in a row, including a scary one after a flight from Phoenix-London, in which I woke up in a toilet stall at Heathrow baggage claim, very disoriented and alone, eerily with no one in that large men’s loo area. My taxi driver was wondering why I was so late… I am glad I didn’t fall and hurt myself with no one around. Fingers crossed that doesn’t happen again. But on top of that, I’ve been fighting a longstanding chronic illness (details are not necessary) at the same time, and that got very bad in April 2022, sending me to hospital with severe internal infection; very life-threatening, painful and frightening. Again, right now I feel that I’m in recovery, and grateful for some good (overall) care from the NHS. Owing to these health problems though, plus the pandemic and financial challenges, I’ve not been travelling and don’t foresee much of that for my near future. Which also means not enough real holiday; “staycations” in my house just aren’t enough, as I’ve been here for ~2.5 years. I’m starting to do more fun things, finally, again, and that led to this blog post (first one in almost one year). I feel I have some energy to do things that I enjoy again.

Walking tinamou bird XROMM animation

Work Stuff: Mostly that has been pretty good, with a caveat. The DAWNDINOS project still dominated my work life, much to my pleasure. Indeed, just this week I tied the final ribbon on that, formally, with submission of my final grant report to the EU/ERC. The grant ended on March 31, 2022 and I was VERY, VERY sad to have to bid farewell to my team, who I hugely enjoyed working with for those 5.5 years. Now comes the caveat to “work is good”, which is that suddenly I have no funding (feast-to-famine) and “just” one PhD student (Vittorio LaBarbera; reinforcement learning simulations of locomotion); MRes student Georgia Wells just finished; and a Research Fellow (Dr. Masaya Iijima). It looks like I’ll be doing more undergrad research projects than postgrad for awhile, but we’ll see. The grant funding lottery can be hard to predict. Regardless, there’s a lot of fun science going on! With DAWNDINOS, since last summary we’ve cranked out a bunch of cool papers on archosaur locomotor biomechanics — find them here. #25-31 are the newer ones I haven’t blogged about anywhere yet; #25, 28 and 30 are blogged about by Dr. Ashleigh Wiseman here; and #30 (which is, in part, a summary of DAWNDINOS to date) got SICB conference coverage here.

Muscle-bound Euparkeria hindlimbs from our DAWNDINOS paper #28; picture by Oliver Demuth.

DAWNDINOS paper #26 with DAWNDINOS postdoc Dr. Delyle Polet was a serendipitous one inspired by him giving a seminar to our lab when he first came to the UK, and it struck me that his method for using biomechanical simulations with the “Murphy number” (related to pitch moment of inertia; MOI) to test how animals move would work really well with a long-bodied, hefty Triassic pseudosuchian (= large pitch MOI) such as Batrachotomus, whose results we could compare with known fossil trackways of similar archosaurs (e.g., Isocheirotherium). We found evidence for it using at least two running gaits, which was pretty surprising.

Walking/running Batrachotomus 2D simulation, matching tracks (blue+red).

And just this week we published another “spin-off” paper (also see van Beesel primate shoulder-modelling studies #17,#29) adapting our 3D digital modelling methods to another taxon. This one came out of left field for me (I’d never expected I’d work on sharks!) but actually fits very well with my research interests in giant animals, biomechanics and palaeontology. We reconstructed the giant shark Otodus megalodon from the best fossils available (including a Belgian vertebral column somewhat neglected since the 1860s), finding that it was ~16m long and >60,000 kg; but this is not the largest it could get, as a vertebra ~50% larger is known! This paper got a LOT of nice press attention, and the video below is perhaps the best science communication release I’ve been involved with (all kudos go to Catalina Pimiento and the animation team she commissioned). Very importantly, the key data are free to use.

Explanatory video by @cookedillustra, Ian Cooke-Tapia

LATE ADDITIONS: But it wasn’t all #DAWNDINOS-related research! I was very pleased to have Dr. Chris Basu’s PhD work with me on giraffid locomotor biomechanics published in PNAS. We showed, with experiments and computer simulations, that Giraffa has unusually low overall leverage (“effective mechanical advantage”; EMA) for its forelimbs during walking (and presumably all gaits/speeds); and even its cousin Okapia does, to a degree; and the extinct giant giraffid Sivatherium too. This is because of its long limbs, which one might look at and call it “cursorial adaptation” but our analysis reveals the tradeoffs of that; as limb length goes up, EMA goes down, and that negatively impacts athletic abilities. All the more reason to be wary of simplistic length-speed conclusions from extinct animals (calling T. rex!). This, with the similar paper on elephant EMA we published in 2010, is one of my papers I’m proudest of; even though neither (curiously) got much (if any) media/other attention. So it goes.

Above: OpenSim simulation of left forelimb of Giraffa during walking; in ~real-time, representing one ground-contact (stance) phase. Green arrow = ground-reaction force (GRF); red lines = major muscle lines of actions (the simulation activated/deactivated them, producing forces to counter the GRF). EMA is the ratio of the muscles’ leverage vs. GRF leverage around joints; it is ~0.3 in a giraffe vs. ~1.0 in a horse. EMA tends to be larger in larger mammals, up to horse-sized, then it gets weird in really big animals.

We also scienced the hell out of salamanders. Four papers, all involving Fire salamanders Salamandra salamandra! Three stemmed from my past PhD student Eva Herbst’s work: one explaining a new method to measure joint mobility; another applying that to walking salamanders in vivo and ex vivo; and the third comparing similar data to the Permian ‘giant’ salamander-relative Eryops, showing that its hip and knee joints were about as mobile as a Fire salamander’s. The fourth paper used video analyses of Fire salamanders in a theoretical model and simulation (with other animals) to demonstrate how multi-legged locomotion is controlled. It’s great to have these studies (partly from my old NERC grant on tetrapod locomotor evolution) out after ?5+ years; now Fire salamanders are among the salamanders whose locomotion we understand best. And we have more data still…

Above: Hindlimb configurations in S. salamandra (A) from rotoscoping of in vivo walking, during (B) mid-swing, (C) toe-on,(D) mid-stance, and (E) just before toe-off. These limb configurations were recreated in E. megacephalus (F) with three different knee spacing options: (G–J) tight knee spacing; (K–N) intermediate knee spacing; and (O–R) larger knee spacing, based on the amount of knee spacing present in the rotoscoped salamander at the null pose. S. salamandra configurations in (B–E) were scaled to E. megacephalus knee B.

Oh and I did some science consulting! “Prehistoric Planet” rocked the casbah; glad to see it out ~3 years after I began offering some critiques on the animations. I hope one scene I commented on eventually sees the light of day, as it wasn’t in the final programme. Similarly, “Dinosaurs: The Final Day” did well, and I gave the same kind of input. My experiences with these shows have inspired me to blog someday about how to become, and do, science consulting for documentaries, so watch for that. I may work in some commentary on what it means to be an invisible minority in that context, as I have thoughts.

Blink and you’ll miss me waving my arms about how Carnotaurus might have waved its arms!

There’s a lot of fun science to come, and that keeps me going. We’ve finished initial biomechanical models of 13 extinct archosaurs for DAWNDINOS, and those will become papers on modelling and simulating locomotor function, ultimately testing how performance differed between Pseudosuchia and Dinosauriformes/Dinosauria; and how locomotion evolved (e.g., bipedalism). Some examples in progress are below; these don’t show the muscles or external dimensions reconstructed. Stay tuned in 2022 and beyond for all that! Beyond this, time will tell what I’ll be doing, but DAWNDINOS is going to keep me very busy for plenty of years, and that is good fun for me.

Top image: top to bottom = Postosuchus (pseudosuchian), Heterodontosaurus (ornithischian dinosaur), Riojasuchus (pseudosuchian), Silesaurus (dinosauriform); Bottom image: Gracilisuchus (pseudosuchian), Lago/Marasuchus (dinosauriform), Coelophysis (theropod dinosaur). These are from ongoing studies with DAWNDINOS team members and collaborators around the world. All use 3D scans of the actual fossil material of one main specimen, wherever possible.

See you in 2023!?

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Simulating Dinosaur Locomotion And Wrestling With Scepticism

Posted in Biomechanics, Exalting Archosauria, tagged , , , , , , , on September 22, 2021| 6 Comments »

We released a publication that, for me, comes full circle with research that started my career off. Back in 1995 when I started my PhD, I thought it would be great to use biomechanical models and simulations to test how extinct dinosaurs like Tyrannosaurus rex might have moved (or not), taking Jurassic Park CGI animations (for which the goal was to look great) into a more scientific realm (for which the goal is to be “correct”, even at the cost of beauty). “It would be great”, or so I thought, haha. I set off on what has become a ~26 year journey where I tried to build the evidence needed to do so, at each step trying to convince my fairly sceptical mind that it was “good enough” science. For my PhD I mainly focused on reconstructing the hindlimb muscles and their evolution, then using very simple “stick figure”, static biomechanical models of various bipeds to test which could support fast running with their leg muscles, culminating in a 2002 Nature paper that made my early career. I since wrote a long series of papers with collaborators to build on that work, studying muscle moment arms, body/segment centre of mass, and finally a standardized “workflow” for making 3D musculoskeletal models. And gradually we worked with many species, mostly living ones, to simulate walking and running and estimate how muscles controlled observed motions and forces from experiments. This taught us how to build better models and simulations. Now, in 2021, our science has made the leap forward I long hoped for, and the key thing for me is that I believe enough of it is “good enough” for me, which long held me back. This is thus my personal perspective. We have a press release that gives the general story for public consumption; here I’ve written for more of a sciencey audience.

Skeleton of the extinct theropod Coelophysis in a running pose, viewed side-on. Image credit: Scott Hocknull, Peter Bishop, Queensland Museum.

Stomach-Churning Rating: 1/10: just digital muscles.

Earlier in 2021, we simulated tinamou birds in two papers (first one here), the second one revealing our first ever fully predictive simulations, of jumping and landing; detailed here and with a nice summary article here. That research was led by DAWNDINOS postdoc Peter Bishop and featuring new collaborators from Belgium, Dr. Antoine Falisse and Prof. Friedl De Groote. Thanks to the latter duo’s expertise, we used what is called direct collocation (optimal control) simulation; which is faster than standard “single-shooting” forward dynamic simulation. The simulations also were fully three-dimensional, although with some admitted simplifications of joints and the foot morphology; much as even most human simulations do. The great thing about predictive simulations is that, unlike tracking/inverse simulations (all of my prior simulation research), it generates new behaviours, not just explaining how experimentally observed behaviours might have been generated by neuromuscular control.

OK, so what’s this new paper really about and why do I care? We first used our tinamou model to predict how it should walk and sprint, via some basic “rules” of optimal control goals. We got good results, we felt. That is the vital phase of what can be called model “validation”, or better termed “model evaluation”; sussing out what’s good/bad about simulation outputs based on inputs. It was good enough overall to proceed with a fossil theropod dinosaur, we felt.

Computer simulation of modern tinamou bird running at maximum speed. Grey tiles = 10 cm.

And so we returned to the smallish Triassic theropod Coelophysis, asking our simulations to find optimal solutions for maximal speed running. We obtained plausible results for both, including compared against Triassic theropod footprints and our prior work using static simulations. Leg muscles acted in ways comparable with how birds use them, for example, and matching some of my prior predictions (from anatomy and simple ideas of mechanics) of how muscle function should have evolved. The hindlimbs were more upright (vertical; and stiff) as we suspect earlier theropods were; unlike the more crouched, compliant hindlimbs of birds.

TENET: Thou shalt not study extinct archosaur locomotion without looking at extant archosaurs, too!
Computer simulation of extinct theropod dinosaur Coelophysis running at maximum speed. Grey tiles = 50 cm.

We observed that the simulations did clever things with the tail, swinging it side-to-side (and up-down) with each step in 3D; and in-phase with each leg: as the leg moved backward, the tail moved toward that leg’s side. With deeper analyses of these simulations, we found that this tail swinging conserved angular momentum and thus mechanical energy; making locomotion effectively cheaper, analogous to how humans swing their arms when moving. This motion emerged just from the physics of motion (i.e., the “multi-body dynamics”); not being intrinsically linked to muscles (e.g. the big caudofemoralis longus) or other soft tissues/neural control constraints (i.e., the biology). That is a cool finding, and because Coelophysis is a fairly representative theropod in many ways (bipedal, cursorial-limb-morphology, big tail, etc.), these motions probably transfer to most other fully bipedal archosaurs with substantial tails. Curiously, these motions seem to be opposite (tail swings left when right leg swings backward) in quadrupeds and facultatively bipedal lizards, although 3D experimental data aren’t abundant for the latter. But then, it seems beavers do what Coelophysis did?

Tail swings this-a-way (by Peter Bishop)
Computer simulation of extinct theropod dinosaur Coelophysis running at maximum speed, shown from behind to exemplify tail lateral flexion (wagging). Grey tiles = 50 cm.

The tail motions, and the lovely movies that our simulations produce, are what the media would likely focus on in telling the tale of this research, but there’s much more to this study. The tinamou simulations raise some interesting questions of why certain details didn’t ideally reflect reality: e.g., the limbs were still a little too vertical, a few muscles didn’t activate at the right times vs. experimental data, the foot motions were awkward, and the forces in running tended to be high. Some of these have obvious causes, but others do not, due to the complexity of the simulations. I’d love to know more about why they happen; wrong outputs from such models can be very interesting themselves.

Computer simulation of modern tinamou bird (brown) and extinct theropod dinosaur Coelophysis (green) running at maximum speed. Grey tiles = 10 cm for tinamou, 50 cm for Coelophysis.

Speaking of wrong, in order to make our Coelophysis walk and run, we had to take two major shortcuts in modelling the leg muscles. The tinamou model had standard “Hill-type” muscles that almost everyone uses, and they’re not perfect models of muscle mechanics but they are a fair start; it also had muscle properties (capacity for force production, length change, etc.) that were based on empirical (dissection, physiology) data. Yet for our fossil, because we don’t know the lengths of the muscle fibres (active contractile parts) vs. tendons (passive stretchy bits), we adopted a simplified “muscle” model that combined both into one set of properties rather than more realistically differentiating them. It was incredibly important, then, that we try this simple muscle model with our tinamou to see how well it performed; and it did OK but still not “perfect”, and that simple muscle model might not work so well in other behaviours. That was the first major shortcut. Second, again because we don’t know the detailed architecture of the leg muscles in Coelophysis, we had to set very simple capacities for muscular force production: all muscles could only produce at most 2.15 body weights of force. This assumption worked OK when we applied it to our simulation of sprinting in the tinamou (vs. average 1.95 body weights/muscle in the real bird), so it was sufficiently justifiable for our purposes. In current work, we’re examining some alternative approaches to these two shortcuts that hopefully will improve outputs while maximising realism and objectivity.

Computer simulation of extinct theropod Coelophysis running at maximum speed, shown alongside running human (at 4 m/s) for scale and context. Image credit: Peter Bishop.

If you pay close attention, our simulations of Coelophysis output rather high leg-forces, and it’s unclear if that’s due to the simple muscle model, the simple foot modelling, or is actually realistic due to the more vertical (hence stiff) hindlimbs; or all of these. Another intriguing technical finding was that shifting the body’s centre of mass forwards slowed down the simulation’s running speed, as one might expect from basic mechanics (greater leg joint torques), but unlike some prior simulations by other teams.

Computer simulation of extinct theropod Coelophysis shown alongside running human for scale and context. Shown from above to illustrate tail wagging behaviour. Image credit: Peter Bishop.

Users of models and simulations are very familiar with catchphrases like “all models are wrong, but some are useful” or the much more cynical (or ignorant) “garbage in, garbage out”; or the very dangerous attitude that “if the mathematics is correct, then the models can’t be that wrong” (but if the biology is wrong, fuggedaboutit!). These are salutary cautionary tales and catechisms that keep us on our toes, because the visual realism that realistic-looking simulations produce can seduce you into thinking that the science is better than it is. It’s not a field that’s well-suited for those fearful of being wrong. I’ll never think these outputs are perfect; that is a crazy notion; but today I feel pretty good. This was a long time coming for me, and it is satisfying to get to this stage where we can push forwards in some new directions such as comparing simulations of different species to address bigger evolutionary questions.

The wrestling with scepticism never ends, but we can make progress while the match goes on.

from WWE… I could not resist

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Evolutionary Biomechanics of Dinosaur Legs

Posted in Better Know A Muscle, Biomechanics, Exalting Archosauria, Freezermas, tagged , , , , , on March 19, 2021| 6 Comments »

The blog is back! Briefly. With dinosaurs. Back in 2005, I published a paper in which I used a “SIMM” 3D musculoskeletal biomechanical model of Tyrannosaurus rex to analyse its muscle actions and infer a relatively upright hindlimb pose. This was an outcome from my NSF-funded postdoctoral research at Stanford University, in which engineers kindly taught me how to use SIMM (handing me a loaded gun?). Part of my plan all along was to build multiple such models along a rough evolutionary sequence to revisit old questions I had with past, qualitative functional morphology papers from 2000 onwards, and see if biomechanics could quantitatively reveal more about the functional evolution of dinosaur hindlimb muscles. So I got data for modelling some extinct dinosaurs (theropods Dilophosaurus, Allosaurus, Velociraptor) and living birds (Struthio, others) and published nuggets of that but held others back…

Stomach-Churning Rating: -1/10; dinosaurs!

I handed these 3D model data off to my PhD student Vivian Allen in ~2007, charging him with the task of making more models to flesh out the phylogeny and finish what I’d started. And he sure did. He graduated, did a couple of postdocs with me, and we gradually massaged his thesis chapter on this topic into a draft paper. Easier said than done, though! That’s why 14 more years have passed.

Viv came up with some clever tools in MATLAB software code (from which he became a very competent programmer and went on to a successful career in that!) to boil complex data on muscle leverages (moment arms) across a wide range of joint motion for the hindlimbs for each taxon.

These data then were fed into further code that took the results from all models, ultimately 13 of them from an Australian freshwater crocodile to two living birds and 10 extinct dinosaurs plus close cousin Mara/Lagosuchus (Figure 1). The code expressed these leverages as changes in ancestral values along the main branch of the evolutionary tree from early (Triassic) “ruling reptile” Archosauria (represented here just by the croc as a proxy) to modern birds, and 9 main ancestral “nodes” in between. Our code tracked both how each of 35 hindlimb muscles we modelled evolved in its leverage, as well as overall “average” leverage of functional groups around the hip, knee and ankle joints.

So, back and forth we went for some 10 years playing with the models (see Video below), data and code, and the paper describing the whole thing, slowly closing in on a final version but also sometimes distracted by our other projects and Real Life Stuff like health and children, and concerns about how we conducted this study (i.e. a lot of fiddling).

Figure 1: Evolutionary tree of dinosaurs and their relatives as used in the study, showing all 13 models, species names, and names of groups along the bottom (red nodes) of the tree. Averostra and Avetheropoda were ancestral groups of theropod dinosaurs that the study inferred had particular specialisations of the hindlimb muscles. Right hindlimbs in side view. The limbs are all straightened vertically into a baseline reference posture but the study investigated variation in muscle function across a wide range of limb poses.

Then I got a new grant “DAWNDINOS” that changed the scene for me, refocusing my team’s energies onto the Triassic (and early Jurassic) and the evolutionary biomechanics of diverse archosaurs’ locomotion, assessed with both LOTS of experimental studies of living crocs and birds, and LOTS of predictive simulations of locomotion. Stay tuned for much more on that from our team, but we’ve already published some key steps here. Most notably, we developed an improved protocol for modelling and simulating our animals, as shown by Bishop et al.’s 2021 study of the early theropod Coelophysis bauri (also appearing in the current paper). Awkwardly for me, that new method rendered our old models and methods a bit obsolete (although still fine), so I pushed to publish this current paper with Viv, and brought collaborator Dr. Brandon Kilbourne on board to aid in some final stats, figures and more. That finally did it, and now we’ve published the paper in Science Advances. Deep breath.

Video: Rotating movies of 3 musculoskeletal models from this study. Models have been posed into representative limb orientations illustrating a gradual or stepwise transformation from more upright to more crouched.

Well what’s the paper about, then? We used our 13 models and processed evolutionary functional patterns to test three main questions (hypotheses) about muscle leverage, making educated guesses at what might prevail from early Archosauria to Aves:

  1. Hip extensor / flexor (i.e. femur retractor/protractor) moment arm ratios remained constant. We weren’t sure what to expect, as these antagonists both seem to change a lot on the whole lineage, so we went with this prediction.
  2. Knee flexor / extensor ratios decreased; i.e. the flexors (“hamstrings” etc.) weakened and/or extensors (equivalent of our quadriceps) strengthened their leverage. Anatomy of the knee joint and muscles around it suggests this, plus since Gatesy’s 1990-onwards studies we’ve expected archosaurs to shift from more ‘hip-based’ to more ‘knee-based’ locomotion as we get closer to avian ancestry.
  3. Hip medial (internal) long-axis rotator / abductor (i.e. pronators of the limb vs. those that draw the leg away from the body) ratios increased. This idea comes right from my paper w/Gatesy in 2000, where we surmised that archosaurs shifted from relying on hip adductors (in crocs/other quadrupeds) to abductors (in bipedal dinosaurs; like humans) to medial rotators (‘torsional control’ as in birds today) during weight support.

Moreover, we reconstructed the evolution of 35 muscles’ actions across ~250 million years, which was a new step.

Here’s a summary of what we found (Figure 2):

Figure 2: Short visualization/explanation of the study’s main insights. Pictures by palaeoartist Jaime Headden: https://qilong.wordpress.com/about/ in left side view, including “muscled” and silhouette images. Right side images include representative hip, knee and ankle muscles from the study. Changes such as the enlargement of muscles in front of the hip that straighten the knee, and reduction of the caudofemoralis longus muscle that runs from the tail to the back of the thigh, are evident.

So, overall hypothesis 1 about hip extensors/flexors ended up complicated; rejected because hip flexor leverage actually increased. Furthermore, we found that around the ancestral nodes for early theropod dinosaurs (Neotheropda through Avetheropoda; around 200 Mya), there were peaks in muscle leverage (size-normalized) that surprised us, and persisted despite many different analyses we threw at them over the years. As far as we could tell, these peaks that kept appearing for various muscles’ actions were “real” (estimates). Which meant these ancestors may have had specialised high leverage relative to both their own ancestors and descendants; the peaks got reversed in evolution. These ancestors had some other weird anatomical and functional traits, such as tightly articulated hip joints early on (which they lost later), increased body size in the later forms, more ‘macropredatory’ ecology (e.g. eating sauropods?), and a centre of mass of the body that was shifted forwards (due to big arms and heads/necks). This weirdness is a cool unexpected finding that showed up for the other hypotheses too, and it needs some more investigating. A ‘failed’ hypothesis test led to neat insights.

Figure 3. From the paper– showing our main results for changes in moment arm ratios across archosaurian ancestors. Hip extensors/flexors decreased then increased; knee flexors/extensors decreased; and hip medial rotators/abductors decreased then had a series of increases.

Hypotheses 2 and 3 found good support, on the contrary, overall (Figure 3). We seem to have been able to quantify the shifts from hip-based to knee-based, and abductor-based to medial-rotator-based, muscle actions. I find that very satisfying. Ankle weight support (extension) capacity also increased, which fits morphological changes fairly well. If you’re into archosaur limb muscle form and function, there’s a lot more food for thought in the paper.

Funnily enough, ~20 years has been sufficient time that we could have had plenty more models in this study if we’d delayed it even longer and re-re-re-analysed our data. But we had to draw the line somewhere and not infinitely revise with every new model we’ve been creating. With the current state of musculoskeletal modelling in my group, we could have more than doubled our sample size and fleshed out the most important gaps such as in the crocodile-lineage (extinct Pseudosuchia) and other Triassic forms plus elsewhere. A big challenge remains having some nice 3D-preserved early fossil birds beyond Archaeopteryx; e.g. so many nice Chinese ones are too flat (e.g. joints we need) to reliably model here. It’s something that can still be done and is worth doing, but I suspect the general trends we’ve found along the dinosaur lineage are “correct”.

What’s personally important to me about this paper is (1) how it not only bridges a huge morphofunctional gap across archosaur evolution in scientific terms, and (2) how we’ve completed a long-delayed project with stubbornness (and during a pandemic!), but also (3) how it bridges my past career from my PhD and postdoc to the present work with DAWNDINOS. We’re now forging well beyond what this new paper has done in terms of truly testing, as best we can (estimate) so far, how limb muscles of archosaurs functioned and evolved, and how these contributed to particular behaviours and performance (maybe even palaeoecology and evolutionary success/extinction?). The current paper is just simple modelling of muscle leverage, but leverage is only one (very important!) piece of muscle function and performance. With fully dynamic, anatomically integrative, physiologically and physically representative biomechanical computer simulations that predict what living and extinct archosaurs could or could not do, we can do even better. So watch for that! Hopefully it won’t all take 20 years, or 250 million.

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Guest Post: The Strangest-Looking Animals of All Time

Posted in Biomechanics, Guestsicle, tagged , , , , , , on September 22, 2020| 2 Comments »

Our special guest post this week comes from Dr. Liz Clark of Yale University in New Haven, Connecticut, USA. She continues to bring biomechanics-fu to echinoderms– the weird marine critters like seastars and sea urchins. Including fossils, as you’ll see today! You may remember her from blog posts such as “Guest Post: Brittle Star Arms Are Weird“.

Stomach-Churning Rating: 1/10; echinoderms are inoffensive.

Imagine that you’re stuck in a cardboard box on the beach, holding a small stick. Could you use the stick to move yourself forward? What would you do? You could try digging into the sediment ahead of you to pull yourself along. You could try rowing side to side, as if you were in a rowboat. Or maybe it’s not possible and you’d give up, decide to stay put, and wave your stick in the air for help.

Believe it or not, this is a strange-but-important dilemma that some paleobiologists- like me!- have been wrestling with for generations. My research specialty is in the biomechanics of locomotion– how organisms use their bodies to get from one place to the next (through walking or swimming, for instance). We can learn a lot about an animal by studying their locomotion, such as why their body is shaped the way that it is, or what role they occupy in their ecosystem. Animal motion is a major inspiration for robotic design, and I work with engineers to apply the novel insights on animal locomotion from my research to create new kinds of devices.

Studying the biomechanics of motion in living organisms is (relatively) straightforward. We can use high-speed cameras, motion capture software, and 3D imaging tools to visualize and understand how organisms move in real-time, informing our inferences about how they perform certain tasks. Inferring locomotion in fossil organisms, on the other hand, is tricky since we can’t observe the organism’s behavior like we could if the organism were alive. Instead of being able to watch the organism move, we’re left with a snapshot of the animal frozen in place in a rock. We’re also missing a lot of physical information: locomotion in most animals requires soft tissue and hard skeletal structures, but typically with fossils, only the hard structures get preserved.

However, we can often garner some insights from living organisms to determine the locomotion strategies that fossil organisms use. Most organisms in the fossil record look at least somewhat similar to organisms alive today. If our fossil has four legs, for instance, we can study locomotion in living tetrapods (four-legged animals) to help us create a framework for deriving inferences about locomotion in our extinct tetrapod fossil animal. But for some really strange-looking animals- ones without obvious modern analogues- we’re not so lucky. For me, this is where the fun begins.

Figure 1: Stylophorans! Here are four fossilized stylophorans from the Helderberg Group of the Early Devonian (YPM 036413)

So getting back to the cardboard box and the stick. These are metaphorical examples of the different locomotion strategies that have been proposed for a group of fossil animals known as stylophorans (Figure 1). Stylophorans are extinct organisms related to sea stars and sea urchins, but with a body structure unlike any organism on the planet today. They have a large, relatively flat body called a theca (i.e., the cardboard box), and a long, thin segmented tail known as the aulacophore (i.e. the stick) (Figure 2). They’re known in the paleontological community as some of “the strangest-looking animals of all time.”

Figure 2: Stylophoran anatomy. The “theca” is the body cavity, and the “aulacophore” comprises of the proximal aulacophore, the stylocone, and the distal aulacophore.

By reconstructing stylophoran locomotion, we can unlock the mechanics of a unique system for motion and its potential applications to engineering. We can also understand more about how this organism lived and functioned in its ancient ecosystem. And, by developing a new approach to understand locomotion in stylophorans, we can apply this strategy to analyze locomotion and movement in other unusual fossil animals as well!

For years, scientists have been documenting the incredible array of stylophoran diversity in the fossil record and making their best predictions about how they would have been able to move (or not!). These predictions are based on their morphology– the structure of an organism’s body. For stylophorans, that means the shape and structure of the theca and aulacophore. There are a variety of stylophoran thecal shapes, ranging from ovoid in Enopleura to trapezoidal in Ceratocystis to almost crescent-shaped in Cortnurnocystis. There’s a similarly wide array of aulacophore morphologies as well.

Figure 3: Left: One half of the concretion within which the stylophoran fossil we analyzed is preserved. Right: The 3D digital image of the stylophoran fossil, created by micro-CT scanning the fossil specimen.

We developed a new approach using 3D imaging (Figure 3) to create a digital model of a stylophoran specimen. We used the model to test if several different locomotion strategies that had been proposed before were physically possible or impossible for a stylophoran to actually perform.

First, we used a micro-CT scanner to image a fossil stylophoran. This outputs a digital 3D picture of the stylophoran fossil that we can look at and analyze on a computer. Next, we developed a program to calculate the joint centers- the point at which one skeletal structure rotates relative to another-within the digitized stylophoran’s aulacophore (Figure 4). This created a digital marionette– a rig of our stylophoran fossil that flexes at the junctures between aulacophore segments as it would have in life. We then rotated each segment at the joint center to calculate the aulacophore’s total range of motion– a reconstruction of how far the aulacophore could flex in each direction (Figure 5).

Figure 4: A look into some of the nuts and bolts of the 3D model we created. Tri-colored axes demarcate where the joint centers are in the proximal aulacophore. 

We used this 3D range of motion model to evaluate several locomotion strategies that had been previously hypothesized for this group of stylophorans. One hypothesis suggested that these stylophorans dug their aulacophores into the substrate– sediment on the ocean floor- to pull themselves forward. Another suggested that they moved the aulacophore side to side in order to push themselves along. We found that the first hypothesis would have been impossible to conduct based on the range of motion we calculated, but the second strategy was theoretically possible! We’ll need to do more work to see how likely it was that stylophorans would have actually used this technique. Nevertheless, through this investigation, our team produced the first objective, data-driven methodology for analyzing locomotion in fossil invertebrates, which is a big step in the right direction for the study of fossil invertebrate biomechanics! Our technique can be applied to study other organisms with rigid skeletons as well, like crabs, insects, or sea stars, for instance, and we’re looking forward to seeing our technique used to uncover more interesting locomotion strategies!

Figure 5: A snapshot of the 3D model where we can observe how dorsal and ventral range of motion compare to the originally preserved orientation of the aulacophore (highlighted in green).

Do you want to know more? You can! We published a paper on this topic here!

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Crimbo Crocodylian Capers

Posted in Croc-cicles, Exalting Archosauria, tagged , , , , , , on December 17, 2019| 3 Comments »

Ho ho ho! The vagaries of the scientific publication system today brings forth TWO open access papers on crocodylian functional anatomy, evolution and biomechanics, from my team with others’; including our DAWNDINOS project in part. Get ready to bite down on the science! I’ve loved crocodylians throughout my life– “dacadile” was among my first words, for a beloved stuffed croc toy, and “Alligators All Around” was an early favourite song (it’s still GREAT).

One of the many large adult alligators in St. Augustine, Florida.

Stomach-Churning Rating: 1/10; bones and movies of awesome behaviours.

First, I am so relieved and pleased to finally publish an experimental study I began over 17 years ago. This is my most-delayed paper ever, due to my own perfectionism, overcommitment and failures at funding it more broadly. But published is published and I’m glad to see it out. We collected a large experimental dataset from 15 species of Crocodylia at the St Augustine Alligator Farm Zoological Park (a conservation/education centre) in Florida. (No matter how you species-ify them, that’s a good chunk of diversity; roughly half or more.) This was a non-invasive study of 42 individuals ranging from 0.5 to 43 kg in body mass (hatchlings to adults). Larger adults were too dangerous or too slow to work with. It took 3 years (2002, 2004, 2005) of data collection to assemble this, with some twists and turns (including a close brush with Hurricane Katrina), and then a lot of analysis and reanalysis; and I’d do it all very differently if I did it today but that’s a moot point. So what’s the paper about?

Adorable Siamese crocodile family “cuddling”. Crocs are great parents! IIRC, that is the father shown.

Some Crocodylia (the inclusive modern name for all crocs, caimans, gharials, gators) are known to use what we call asymmetrical gaits: “mammal-like” footfall patterns in which the left and right limbs do not move as mirror images of each other. In particular, these gaits include galloping (rotary or transverse; either way a “4-beat” pattern with left-right hind- followed by right/left forefoot contacts) and bounding or half-bounding (the former being the most extreme, with left-right hind- and then forefoot contacts as synchronous pairs). Often people just say that crocs can “gallop” but this confuses/conflates the issue and omits that they can use these faster bounding gaits. Regardless, we’ve known about these gaits at least since HB Cott’s 1961 photographic documentation of them in Nile crocodiles; and more detailed studies of Australian freshwater and saltwater crocodiles in the 1970s-2000s. But very often, scientists and popular natural history accounts ascribe the asymmetrical gaits to only a few species or young individuals.

“Freshie” croc bounding in the wilds of Australia; credit Kent Vliet.

Osteolaemus dwarf African crocodile getting marked up for study.

That’s where we came in. We had access to a huge collection of captive Crocodylia and a very supportive institution (with coauthors from there as a result). I wanted to know which Crocodylia do use asymmetrical gaits, having a very strong suspicion from the literature that Alligatoroidea, the alligator and caiman lineage, don’t use them, whereas their cousins the “true crocodiles” in Crocodyloidea do. And I wanted to test how body size interacted with this ability, as prior accounts hinted that asymmetrical gaits got lost with increasing size or in adults. Finally, I was interested in what the benefits of asymmetrical gaits were– did they give those that used them marked boosts in performance, especially maximal speed? Answering that would help understand why these gaits are used.

Cuban crocodile Crocodylus rhombifer in preparation. A gorgeous but aggressive species that we handled carefully.

So we walked and ran our subjects across some platforms past video cameras and collected about 184 useful trials or strides of gait across level ground at a wide range of speeds; and a LOT of not-so-useful data (mostly subjects just sitting and pouting). We found that, yes, most Crocodyloidea we studied could bound or gallop; and no Alligatoroidea did. In the latter case, we didn’t use as large a sample of subjects as we could have, partly because it already seemed evident that alligators did not use asymmetrical gaits, and partly because those alligatoroids we did try to coax to move quickly either only used symmetrical gaits (e.g. trotting) or would only sit and fight or hiss. And we found that bigger animals moved at least relatively more slowly and less athletically, and perhaps even more slowly in absolute terms (metres/second).

Most intriguingly to me, it didn’t matter what gait alligatoroids or crocodyloids used. They all could move at roughly similar top speeds if they wanted to; less than 5 m/s or 11 mph. It’s just that crocodyloids tended to use asymmetrical gaits, especially bounding, at top speeds– but not always: some even chose to trot at their top speeds. We don’t know why, and we still don’t know why asymmetrical gaits are chosen but they likely have other benefits such as acceleration and manoeuvrability.

It’s a thrill to finally be able to share the huge dataset, including a gigantic file of videos (with some highlights shown here), with the paper, closing this study at last. It should be very useful to anyone studying Crocodylia or wanting to educate people about locomotion. I’m a bit tired of hearing that galloping is a mammalian behaviour when we know so well that many species of animals do it, or something like it. And it was absolutely thrilling to see five species of Crocodylia bound or gallop when they hadn’t been properly documented to do it before– enough anecdotes, here’s cold hard facts from video on what happens. What remains is a mystery: did Crocodylia have this ability to use asymmetrical gaits as an ancestral trait, as almost everyone assumes (and thus alligators and caimans have lost or essentially never express the ability), or did crocodiles uniquely evolve this ability more recently? I would join most scientists in wagering on the former; and there are good reasons to suspect the ability goes deeper into extinct Crocodylomorpha.

(my favourite video is below!)

Want more cool videos? Try my Youtube channel— or if you want ALL of the videos, go here!

Next, Torsten Scheyer was kind enough to invite me to join his team in studying a fossil I’ve long been fascinated by: the “giant caiman” Purussaurus mirandai, from the Miocene (~6 million years ago?) of Venezuela, in the Urumaco Formation‘s very weird biota. Purussaurus has been known of for >125 years but Torsten’s team noticed that Purussaurus (mirandai) specimens tended to add one of their trunk vertebrae to their hip girdles (sacrum; normally only two vertebrae in Crocodylia but here three), and that the shoulder and hip girdles had unusual bone morphology (straighter, more vertical relative to the body). So they asked me to help interpret these features. And here’s the paper!

Infographic by Torsten Scheyer’s team– click to emcroccen!

Three-vertebra sacrum and other traits of Purussaurus; with living caiman bones for comparison. E (bottom): inwards-facing femur head. (see paper for more info)

It became evident that, together, those odd traits conveyed a signal that the skeleton was transformed to aid in supporting the huge body against gravity. For example, I found it quite interesting how the head of the femur (thigh bone) was oriented more directly into the hip socket in multiple specimens, more like a dinosaur’s hip, and specialised for support and fore-aft motions. I used Haley O’Brien et al’s data to estimate just how big P. mirandai might have been and it came out as perhaps 3000 kg and 8 metres total length; as we’d thought, among the largest Crocodylia (and there are larger Purussaurus known, too).

Reconstruction of Purussaurus and morphology of the girdles. (see paper for more info)

The team also put a cool “evo-devo-biomechanics” spin on the study. It is well known that the regional identities of vertebrae (e.g. neck, trunk, sacrum, tail) are largely determined by Hox (homeobox) regulatory genes, early in development. So changes of vertebral identity intimate changes of genetic controls. Crocodylia don’t normally add a trunk vertebra to their sacrum, and only a few fossil crocodyliforms (extinct cousins) ever did either, but we noticed that some specimens of Crocodylia would at least partially make this transformation in pathological states (below). Hence the controls to make these changes exist and sometimes manifest in living crocs, but it’s probably not an “easy” transformation to achieve. One could speculate that under intense selection, such as that imposed by giant body size and some degree of activity on land, that transformation could more easily get permanently “fixed” in a species.

Palaeosuchus palpebrosus (Cuvier’s dwarf caiman) with pathological partial-three-vertebra-sacrum; and lots more morphology. (see paper for more info)

As a nice tie-in to the asymmetrical gait study above, we can safely infer that the giant Purussaurus wasn’t a fast animal on land, by any means. But its skeleton is consistent with it having found novel ways to maintain the ability to stand and move on land, even if slowly.

Happy holidays! Santa Jaws is watching you– be good!

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Darwin Day 2019: Some Papers In Evolutionary Biomechanics

Posted in Biomechanics, Exalting Archosauria, Freezermas, Frozen Mammals, Two-Dog-Night Tetrapods, tagged , , , , , , , , , on February 12, 2019| 1 Comment »

Today is the 210th anniversary of Charles R. Darwin’s birthday so I put together a quick post. I’d been meaning to blog about some of our latest scientific papers, so I chose those that had an explicit evolutionary theme, which I hope Chuck would like. Here they are, each with a purty picture and a short explainer blurb! Also please check out Anatomy To You’s post by Katrina van Grouw on Darwin’s fancy pigeons.

Stomach-Churning Rating: 1/10 science!

First, Brandon Kilbourne at the Naturkunde Museum in Berlin kindly invited me to assist in a paper from his German fellowship studying mustelid mammals (otters, weasels, wolverines, badgers, etc.; stinky smaller carnivorous mammals). Here we (very much driven by Brandon; I was along for the ride) didn’t just look at how forelimb bone shape changes with body size in this ecologically diverse group. We already knew bigger mustelids would have more robust bones, although it was cool to see how swimming-adapted and digging-adapted mustelids evolved similarly robust bones; whereas climbing ones had the skinniest bones.

The really exciting and novel (yes I am using that much-abused word!) aspect of the paper is that Brandon conjured some sorcery with the latest methods for analysing evolutionary trends, to test how forelimb bone shapes evolved. Was their pattern of evolution mostly a leisurely “random walk” or were there early bursts of shape innovation in the mustelid tree of life, or did shape evolve toward one or more optimal shapes (e.g. suited to ecology/habitat)? We found that the most likely pattern involved multiple rates of evolution and/or optima, rather than a single regime. And it was fascinating to see that the patterns of internal shape change deviated from external shape change such as bone lengths: so perhaps selection sometimes works independently at many levels of bone morphology?

Various evolutionary models applied to the phylogeny of mustelids.

Then there, coincidentally, was another paper originating in part from the same museum group in Berlin. This one I’d been involved in as a co-investigator (author) on a Volkswagen (yes! They like science) grant back about 8 years ago and since. There is an amazing ~290 million year old fossil near-amniote (more terrestrial tetrapod) called Orobates pabsti, preserved with good skeletal material but also sets of footprints that match bones very well, allowing a rare match of the two down to this species level. John Nyakatura’s team had 3D modelled this animal before, so we set out to use digital techniques to test how it did, or did not, move—similar to what I’d tried before with Tyrannosaurus, Ichthyostega and so forth. The main question was whether Orobates moved in a more “ancestral” salamander-like way, a more “derived” lizard-like way (i.e. amniote-ish), or something else.

The approach was like a science sledgehammer: we combined experimental studies of 4 living tetrapods (to approximate “rules” of various sprawling gaits), a digital marionette of Orobates (to assess how well its skeleton stayed articulated in various motions), and two robotics analysis (led by robotics guru Auke Ijspeert and his amazing team): a physical robot version “OroBOT” (as a real-world test of our methods), and a biomechanical simulation of OroBOT (to estimate hard-to-measure things in the other analyses, and matches of motions to footprints). And, best of all, we made it all transparent: you can go play with our interactive website, which I still find very fun to explore, and test what motion patterns do or do not work best for Orobates. We concluded that a more amniote-like set of motions was most plausible, which means such motions might have first evolved outside of amniotes.

OroBOT in tha house!

You may remember Crassigyrinus, the early tetrapod, from a prior post on Anatomy To You. My PhD student Eva Herbst finished her anatomical study of the best fossils we could fit into a microCT-scanner and found some neat new details about the “tadpole from hell”. Buried in the rocky matrix were previously unrecognized bones: vertebrae (pleurocentra; the smaller nubbins of what may be “rhachitomous” bipartite classic tetrapod/omorph structure), ribs (from broad thoracic ones to thin rear ones), pelvic (pubis; lower front), and numerous limb bones. One interesting trait we noticed was that the metatarsals (“sole bones” of the foot) were not symmetrical from left-to-right across each bone, as shown below. Such asymmetry was previously used to infer that some early tetrapods were terrestrial, yet Crassigyrinus was uncontroversially aquatic, so what’s up with that? Maybe this asymmetry is a “hangover” from more terrestrial ancestry, or maybe these bones get asymmetrical for non-terrestrial reasons.

The oddly asymmetrical metatarsals of Crassigyrinus.

Finally, Dr. Peter Bishop finished his PhD at Griffith University in Australia and came to join us as a DAWNDINOS postdoc. He blasted out three of his thesis chapters (starting here) with me and many others as coauthors, all three papers building on a major theme: how does the inner bone structure (spongy or cancellous bone) relate to hindlimb function in theropod dinosaurs (including birds) and how did that evolve? Might it tell us something about how leg posture or even gait evolved? There are big theories in “mechanobiology” variously named Wolff’s Law or the Trajectorial Theory that explain why, at certain levels, bony struts tend to align themselves to help resist certain stresses, and thus their alignment can be “read” to indicate stresses. Sometimes. It’s complicated!

Undaunted, Peter measured a bunch of theropod limb bones’ inner geometry and found consistent differences in how the “tracts” of bony struts, mainly around joints, were oriented. He then built a biomechanical model of a chicken to test if the loads that muscles placed on the joints incurred stresses that matched the tracts’ orientations. Hmm, they did! Then, with renewed confidence that we can use this in the fossil record to infer approximate limb postures, Peter scanned and modelled a less birdlike Daspletosaurus (smaller tyrannosaur) and more birdlike “Troodon” (now Stenonychosaurus; long story). Nicely fitting many other studies’ conclusions, Peter found that the tyrannosaur had a more straightened hindlimb whereas the troodontid had a more crouched hindlimb; intermediate between the tyrannosaur and chicken. Voila! More evidence for a gradual evolution of leg posture across Mesozoic-theropods-into-modern-birds. That’s nice.

Three theropods, three best-supported postures based on cancellous bone architecture.

If you are still thirsty for more papers even if they are less evolutionary, here’s the quick scoop on ones I’ve neglected until now:

(1) Former PhD student Chris Basu published his thesis work w/us on measuring giraffe walking dynamics with force plates, finding that they move mostly like other quadrupeds and their wobbly necks might cost them a little.

(2) Oh, and Chris’s second paper just came out as I was writing this! We measured faster giraffe gaits in the wilds of South Africa, as zoo giraffes couldn’t safely do them. And we found they don’t normally go airborne, just using a rotary gallop (not trot, pace or canter); unlike some other mammals. Stay tuned: next we get evolutionary with this project!

(2) How do you safely anaesthetize a Nile crocodile? There’s now a rigorous protocol (from our DAWNDINOS work).

(3) Kickstarting my broad interest in how animals do “extreme” non-locomotor motions, we simulated how greyhounds stand up, finding that even without stretchy tendons they should, barely, be able to do it, which is neat. Expect much more about this from us in due time.

(4) Let’s simulate some more biomechanics! Ashley Heers, an NSF research fellow w/me for a year, simulated how growing chukar birds use their wing muscles to flap their way up steeper inclines (“WAIR” for devotees), and the results were very encouraging for simulating this behaviour in more detail (e.g. tendons seem to matter a lot) and even in fossil species; and finally…

(5) Hey did you ever think about how bone shape differs between hopping marsupials (macropods) and galloping artiodactyl (even-toed) mammals? We did, in long-the-making work from an old BBSRC grant with Michael Doube et al., and one cool thing is that they mostly don’t change shape with body size that differently, even though one is more bipedal at faster speeds—so maybe it is lower-intensity, slower behaviours that (sometimes?) influence bone shape more?

So there you have the skinny on what we’ve been up to lately, messing around with evolution, biomechanics and morphology.

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Pre-Submission Manuscript Scrutiny

Posted in RANT, tagged , on November 26, 2018| 5 Comments »

This one goes out to the scientists. These days perhaps more than ever we live and die, career-wise, by the publication. Right or wrong as “publish or perish” may be, personally I enjoy writing papers– it hits my creative and intellectual buttons in fun ways. I also like to read and think about ways to write better papers, and am always improving (and making mistakes to learn from). Here are some I’ve come up with over the years, especially relating to the digital era and other aspects of modern science publishing but also to focus on the “forgotten fringes” of preparing a paper for submission to a journal. These are details that I find many authors forget, or do at the last minute, or don’t consult coauthors on, that matter and should be more of a focus. I won’t focus on good writing style or other important aspects of prose, or many things I’ve covered in my “mission statement” or elsewhere. The points I’ll make here are more specifically tactical and technical.

Stomach-Churning Rating: 0/10; the only anatomy here is that of a manuscript submission. Maybe that will excite you too?

So you’ve analysed some cool data and come up with a good story to encapsulate it, you chose a journal that suits it (and your belief system), and you’re closing in on clicking that serotonin-inducing “Submit” button. Did you think of these things yet?

  • Coauthor order: Did you discuss it earlier when doing the work? Oh dear, you should! Assuming you’re doing a multi-authored manuscript, that’s vital, and I’ve been burned by forgetting to do it properly until too late in the game before. It’s best to establish (1) who is doing what in terms of the research (all the way through writing up and submitting), and (2) who thus is where in author order, before having any draft of a manuscript at all. That may change as the research evolves, but it should be an explicit discussion with all involved—including, perhaps, those *not* listed as coauthors (but acknowledged, or even not), if there is reason they might be expecting otherwise. Yes, these days we all win by collaborating and co-author order may not matter for some coauthors, but it does not hurt to discuss it openly whereas it can lead to ill will if skipped. Think about details like: who’s the corresponding author(s)? You can have 2 at many journals, so maybe spread that around. Who’s the senior author? (that tradition may vary in different countries and fields) Again, you can even explicitly list ~2 senior authors (with asterisks by their names). Credit should be given where it is due; that’s all. Which leads very directly to…
  • Author contributions: This is a huge neglected area. And it matters tremendously, not just in terms of the above socio-political issues (or ego) but in terms of responsibility. If something seems wrong with a paper these days, we must turn to the “Author contributions” section to see who needs to explain what happened; although blame can be far from a simple issue. In cases of accusations of scientific error or misconduct that is vital. More positively, this section, thoughtfully considered, spreads credit around and shows potential employers who has the skills that paid the bills on that paper; or on grant/award applications/nominations who was/were the mastermind(s). If the journal oddly doesn’t have such a section online/in the manuscript format guidelines, add it to the end of the MS anyway! In tandem with item #1 above, this should be openly laid out, discussed, and explicitly agreed on before any submission—and the earlier in the process of research, the better. Detail not just who originated the idea, collected and analysed the data, and wrote the paper but the nitty-gritty of every step (“XX did CT scans… XX did segmentation of the scans…”), if space allows. The author contributions should make sense in terms of item #1, too. Minimally the senior author should be involved in conceiving the study (which IS important!) and editing + approving the final text; otherwise they probably should not be an (senior) author at all. Honorary coauthors, well, I’ve said plenty about those here before and they still make me grind my teeth.
  • Data availability/accessibility: If you’re active in science now you must know about the principles of Open Science, and all journals worth their salt are changing rapidly to adjust to evolving perspectives on this issue. You should be thinking about how you’ll share your data while you collect it. This is “Good Research Practice”. Metadata are data too, and should follow with their data. It takes time and that’s annoying perhaps, but think of this: what is someone going to do if they want to use the data from this paper 50 years from now? If it’s not in the Supplementary/Supporting Information online, or in a big database like Figshare/Dryad/OSF/etc, one may have cause to worry that it will vanish within 5 years. We all still see “data are available on request” in papers these days (that was the old way), and I won’t get into that debate here, but the writing is on the wall that the old ways are fading. Hence evolving one’s research practice to make sharing data part of one’s philosophy and publication practice, AND (here’s the clincher) promoting its value in other aspects of science (e.g. CVs, hiring, promotion, awards…) are only going to be looked back upon fondly by future scientists. We do also need top-down leadership for this sea-change to happen; and it will have a big impact when it settles in.
  • Funding: This is massively important. Be sure to ask all coauthors to specify if anyone needs to be thanked for funding the work. Double-check it for your own funders, and thank whomever did directly or indirectly contribute to the research; even if small amounts. (They all like being thanked, regardless of why they are being thanked, if they deserve it) Many funders don’t allow you to credit a paper to the grant (thus showing productivity) unless they are explicitly thanked here or in the Acknowledgements section. And on that note:
  • Acknowledgements: “Thank broadly!” Slow down and brainstorm here: did you get advice, tools or data from colleagues, undergraduate helpers (who didn’t quite make coauthorship—but we should try to help them get there!), or anyone else? Did you amend your reviewed paper to thank reviewers (or pre-print commenters)? Did you thank museums and other institutions (or even websites) that helped with resources? Be creative in this section because hey, it’s nice to see yourself thanked. I think this section is really important as human beings. Extra little tip: get rid of “We would like to thank” here; just “We thank”. No need to ask for permission or waffle with thanks.
  • Paper keywords: Most journals ask for some keywords to include with the paper, often during the submission process (as with item #2 above). So it is easy for the corresponding author to be the only one involved in this, which is not ideal. I try to add keywords to the manuscript draft (between authors and abstract, as usual) in the early editing process, to consider with the rest of the paper. While database searching is sophisticated these days, a good general strategy still is to choose words that aren’t in the title or strongly featured in the abstract. Broader terms, to draw in readers from overlapping research areas or questions, should be used; e.g. I tend to throw in “biomechanics” or “scaling” or “anatomy” and so on. Keywords should not be an afterthought.
  • References/Bibliography: A lot of people writing papers don’t check their references at all (I forget sometimes too)—errors easily creep in here, especially from naughty reference managers that corrupt formatting or even page numbers and years. I try to clear my head/eyes and skim the references in a near-final draft to add italics where needed, double-check journal details, and tidy up other formatting. Some journals do this for you later, but some do not. It’s wise to ensure it’s done as well as you can; messy references can lead one to doubt other aspects of care that went into the science.
  • Reviewers: Editors have a sucky job, to be honest. Finding and chasing down reviewers is not fun, but it is the service that editors provide, often for free. Please help them and, where feasible, recommend ~5 reviewers (include current emails) without conflicts of interest who can evaluate your paper. Do that in the online submission, or in the cover letter if there isn’t a spot for it there. Always do it; don’t leave it open to editors (even though they may not use any of them!). Rarely, you might have cause to ask for an excluded reviewer(s) if they won’t give you a fair shake or you otherwise have evidence to indicate they have a conflict of interest, so note that on submission and maybe justify it directly (without libel!). Excluded reviewer requests are almost always followed. All of these things should be discussed with coauthors well in advance to agree on them. Google-Scholaring around might find some names you forget. And as you build your list, think about selecting (1) non-white male status quo (i.e. not me), (2) early career researchers, and (3) scientists from outside the USA+UK. Think outside the box—maybe someone from slightly outside your field, with complementary expertise, could give a good perspective? Aim for some fair diversity; like item #3 above, this is increasingly becoming Good Practice, and rightly so.
  • Cover letter: As an editor and author, I don’t like them. Maybe I should more, but I think they tend to be overwrought and/or redundant these days. I don’t think the authors, title, journal, abstract (or even bite-sized summary, perhaps), or anything else mentioned elsewhere in the manuscript submission (e.g. recommended reviewers) should be in a cover letter, usually. The goal is brevity. You may not need to do a cover letter at all; check the journal to see if it is mandatory. The best usage is to explain why the paper fits the journal criteria; and perhaps nothing else. That may not be sufficiently clear in the paper itself. Keep in mind that editors reading cover letters are busy and do not want a 2-page screed about how awesome your paper is; but may want help (~1 succinct paragraph; plain English; very different from the Abstract or don’t bother) deciding if it is right for review. But if the cover letter doesn’t seem necessary, skip it. Get co-author input though, if unsure.
  • Pre-prints: Hey, that’s a new thing for us non-physicists! I don’t have a problem with them; some people do. I also haven’t gotten much out of them before, but that might be my fault or bad luck. But who cares what I think? You should think about them. Maybe try submitting your paper with one and trying it out; disseminate it via social media and see what happens? Almost all journals now allow pre-prints to be submitted before/with the manuscript. There may be little to lose in using them, but as I keep repeating, ensure you talk about it with coauthors first.

Those are some things I keep thinking of as I write, edit and review papers. What else? (the focus here is on the “bookends” surrounding the Abstract/Introduction and the Discussion/Conclusions)

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Guest Post: Brittle Star Arms Are Weird

Posted in Guestsicle, tagged , , , , , on October 25, 2018| 4 Comments »

Our special guest post this week comes from Dr. Liz Clark of Yale University (you may have heard of it?) in New Haven, Connecticut, USA. She is bringing some biomechanics-fu to echinoderms– the weird marine critters like seastars and sea urchins. Did you see her 9-awesome-things-about-echinoderms blog post on Anatomy to You? You should. And you should check this out– and check out our new paper on this topic, which just came out! Remember: all images below can be clicked to zoom in. That’s so fun!

Eversible Stomach-Churning Rating: 2/10; no Uni sushi here.

I remember the first time I saw one. I was at the Duke Marine Lab staring at a chunk of dredged-up oyster shells in a glass dish, when all of a sudden a mass of big, black spines obscured my view. I looked up from the microscope to see a creature with a round body the size of a nickel and a flurry of long, skinny, spiny arms skulking hurriedly across the dish. It wasn’t quite a spider- the five-fold symmetry gave its echinoderm affinity away- but it wasn’t quite a starfish, either. Starfish appear graceful as their tiny tube-feet make hurried and unseen movements underneath them to transport them slowly across the sand- appearing nearly motionless to the naked eye. This animal, on the other hand, was making rapid, whip-like strikes with its arms so that it clambered forward, rapidly and fearlessly scaling the uneven terrain of the shells in a bold attempt to escape the dish. I was hooked. I had to know who this monster was, and learn as much about it as I could.

Brittle star arm set up to study its ossicle-joint mobility with CT scanning (below).

That was the day I was introduced to the brittle star. The name “brittle star” is a bit of a misnomer, since they are really anything but. Brittleness implies rigidity and stiffness, suggesting they have a delicate nature with the impossibility of repair or to adapt, which couldn’t be farther from the truth. Their long arms are incredibly flexible, each made of around 100 tiny segments that allow them to bend in any direction or loop them around in circles. I bet that their name comes from the ease at which they can cast off their arms, which they do intentionally to escape predators or pesky researchers trying to grab them, which deceitfully suggests fragility when in fact their arms are incredibly sturdy and packed with powerful muscles. They can flawlessly regenerate their arms, and, in the meantime, even after they lose several of them, they adjust their strategy for locomotion so that they keep prowling across the seafloor unphased. Their physical flexibility and ability to repair and adapt in the face of damage makes them anything but brittle. The Japanese name for brittle star roughly translates to “spider-human-hand,” which I think much more accurately captures the ethos of this group.

Brittle stars have internal skeletons, and each segment of their arms are made of a cluster of small skeletal elements (ossicles). Researchers in the past have made the assumption that differences in the shape of these ossicles between species change how they move, but I wasn’t so sure. So, John and I decided to work together to figure it out.

We didn’t dive into the freezer for this one- sorry to disappoint all of the diehard fans of John’s freezer out there (but in my defense can you imagine how tough it would have been to even find them in the sea of rhinos, giraffes, and crocs?!). [JOHN: awwwwwww!! It’s more of a wall keeping in the wildlings, than a sea right now though!] Instead we ordered some brittle stars off the internet! The first thing we did was make some measurements of how flexible the arms of brittle stars are when they’re alive. Then we digitized their skeletons by micro-CT scanning them so we could see the articulations between the ossicles and the segments in 3D. We scanned them in a few different positions so we could see the articulations between the ossicles as their arms bend. Then we incorporated all of that data into a 3D model that allowed us to visualize what’s going on in the inside of brittle star arms as they move them around.

We made several different models using this strategy to see if different ossicle shapes change how their arms move. We looked at the differences between arm ossicles in two different species– Ophioderma brevispina and Ophiothrix angulata, which represent two of the three different major morphologies of brittle star arms.  We also looked at the difference in the movement mechanics at the tip and base of the arms in O. brevispina, since the ossicles at the tip are thin and elongated compared to wide and flat at the base.

We found that the tip of the arm of Ophioderma brevispina was more flexible than the base due, at least in part, to the shape of the ossicles. We also found several major differences between the two species, including the location of their joint center and the degree to which they could laterally flex. However, none of these differences were easily attributable to any specific morphological feature that set Ophiothrix angulata and O. brevispina apart, which cautions against making assumptions of brittle star functional capabilities by only looking at the shape of the ossicles. We also found that some of the smaller ossicles within each segment shift their position to accommodate arm flexion, when they were originally thought to limit the motion of the arm! We only looked at a few individuals of two species, but the methods for model-building we developed provide a framework to incorporate a broad sample of brittle star species in the future. We’re curious if the results we found stand when more brittle stars are brought into the mix!

It was incredible to take the journey from initially being surprised and captivated by the movement of these animals to eventually building 3D digital models to discover how they are able to do so. It made me realize that opportunities to be inspired by the natural world are around every corner, and that there are so many interesting questions out there that are still unanswered. Thanks to John and our other team members Derek Briggs, Simon Darroch, Nicolás Mongiardino Koch, Travis Brady, and Sloane Smith for making this project happen!

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Harryhausen’s in the House!

Posted in Geeking Out, Museums are Cool, tagged , , , , , on June 23, 2018| 6 Comments »

If you’re in London, you still have almost one week left to hurry to the Valence House in Dagenham and see a great exhibit on Ray Harryhausen’s dinosaurs and other cool “Dynamation” stop-motion models and art!

This blog post is a photo tour of what I saw, in case you cannot go.

Like it? Click it. Bigger pic.

Stomach-Churning Rating: 1/10 nice stop-motion animation models. Medusa won’t hurt you here.

I loooooooooooove Ray Harryhausen’s work, ever since I was a child and saw “Jason and the Argonauts” and many other films, plus “Clash of the Titans” once it came into theatres. There is the attention to detail in anatomy and locomotion, and the wondrous fantastic nature of even the more mundane creatures he animated, and the rich mythology that he drew from to inspire his creations. Modern CGI is great in a different way, but nothing I can think of in recent special effects truly beats (1) the skeleton battle in ‘Jason, and (2) the Medusa encounter in ‘Clash (to name what might be my top two faves). And so when I learned that several of the original (restored) models from those films were on exhibit in northeastern London, I requested to go there with my family for Fathers Day. Results:

Boom! Ole’ stony-gazed, snaky-haired gorgon of yore.

No deadly bow here, but the rattlesnake tail is.

Medusa concept art by Harryhausen; the “bra” was there for American censors but Ray thought it looked wrong and removed it in the final version.

Look out, Jason! Here come the Children of the Hydra! Yep, original (restored) articulated models. Joints are visible. They look ready to kick some Iolcusian butt!

Context of the exhibit- local chap befriended Harryhausen and convinced him to let him restore his models; and so here we are. On with the dinosaurs! (and other palaeo-things)

Gwangi model made in resin; non-poseable but made around time of the “Valley of Gwangi” film to help design the poseable models.

Gwangi climactic scene in church; concept art by Harryhausen.

Other ‘Gwangi characters: “Eohippus” (Hyracotherium), Ornithomimus and boy.

Cowboy lassoing an Ornithomimus as per the movie scene in ‘Gwangi? Yes please. (Harryhausen original)  Jurassic Park had its T. rex lurching out of a forest to grab a Struthiomimus, intentionally mirroring the scene in ‘Gwangi where the titular Allosaurus–Tyrannosaurus hybrid chomps the Ornithomimus.

Poseable “Eohippus” original- with real fur! Great Dynamation too; very lifelike in the film.

Original Harryhausen concept art of the “Eohippus” show demo.

Suddenly, Ceratosaurus! (from “One Million Years BC”)

Styracosaurus original resin model. (from “One Million Years BC”)

Old school Polacanthus art by Alan Friswell. SPIKEY!

Old school Iguanodon art by Alan Friswell. MUSCLEY!

Panoply of archosaurs by Alan Friswell: pterodactyl, Tenontosaurus (made for the Frame Store special effects company in 2001) and tyrannosaur head (made at age 9).

Pterodactyl made at age 12, so don’t laugh.

Back to the fantastic beasts– original poseable hydra from ‘Jason!

Original Pegasus from ‘Clash! What a seamless blend of fur and feathers.

Original R2, I mean Bubo, from ‘Clash!

I forget the scene (the 1-eyed fates in ‘Clash?) but I like it. Original Harryhausen concept art.

Lunar leader from “First Men in the Moon.” (original)

Non-original (but based thereon) model by Alan Friswell, of nautiloid thingy from “Mysterious Island”.

Fiji mermaid by Alan Friswell.

“Hand of Glory” by Alan Friswell.

Pithecanthropus by Alan Friswell. Very Harryhausen in spirit.

Oddly, but somehow appropriately, there are ?350 year old whale bones on display in the hall next door, with a mysterious history.

WW2 bomb shelter in a “Victory Garden” outside the House. And the house is supposedly haunted. So take care when you visit…

What can I say? I loved it! Almost a religious experience; like seeing holy relics. Awesome in every sense of awesome.

Downside: you cannot grab the precious Dynamation models and play with them hands-on. I wanted to enact a furious Hydra-Gwangi battle. But alas, only in my imagination…

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Papers Seen In 2017

Posted in Biomechanics, Croc-cicles, Exalting Archosauria, Two-Dog-Night Tetrapods, tagged , , , , , , , , , on November 25, 2017| Leave a Comment »

As 2017 approaches its end, there have been a few papers I’ve been involved in that I thought I’d point out here while I have time. Our DAWNDINOS project has been taking up much of that time and you’ll see much more of that project’s work in 2018, but we just published our first paper from it! And since the other two recent papers involve a similar theme of muscles, appendages and computer models of biomechanics, they’ll feature here too.

Stomach-Churning Rating: 0/10; computer models and other abstractions.

Mussaurus patagonicus was an early sauropodomorph dinosaur from Argentina, and is now widely accepted to be a very close relative of the true (giant, quadrupedal) sauropods. Here is John Conway’s great reconstruction of it:

We have been working with Alejandro Otero and Diego Pol on Mussaurus for many years now, starting with Royal Society International Exchange funds and now supported by my ERC grant “DAWNDINOS”. It features in our grant because it is a decent example of a large sauropodomorph that was probably still bipedal and lived near the Triassic-Jurassic transition (~215mya).

In our new study, we applied one of my team’s typical methods, 3D musculoskeletal modelling, to an adult Mussaurus’s forelimbs. This is a change of topic from the hindlimbs that I’ve myopically focused on before with Tyrannosaurus and Velociraptor [in an obscure paper that I should never have published in a book! pdf link], among other critters my team has tackled (mouse, elephant [still to be finished…], ostrich, horse, Ichthyostega… dozens more to come!). But we also modelled the forelimbs of Crocodylus johnstoni (Australian “freshie”) for a key comparison with a living animal whose anatomy we actually knew, rather than reconstructed.

Mussaurus above; Crocodylus below; forelimb models in various views; muscles are red lines.

The methods for this biomechanical modelling are now standard (I learned them from their creator Prof. Scott Delp during my 2001-2003 postdoc at Stanford): scan bones, connect them with joints, add muscle paths around them, and then use the models to estimate joint ranges of motion and muscle moment arms (leverage) around joints. I have some mixed feelings about developing this approach in our 2005 paper that is now widely used by the few teams that study appendicular function in extinct animals. As a recent review paper noted and I’ve always cautioned, it has a lot of assumptions and problems and one must exercise extreme caution in its design and interpretation. Our new Mussaurus paper continues those ruminations, but I think we made some progress, too.

On to the nuts and bolts of the science (it’s a 60 page paper so this summary will omit a lot!): first, we wanted to know how the forelimb joint ranges of motion in Mussaurus compared with those in Crocodylus and whether our model of Mussaurus might be able to be placed in a quadrupedal pose, with the palms at least somewhat flat (“pronated”) on the ground. Even considering missing joint cartilage, this didn’t seem very plausible in Mussaurus unless one allowed the whole forearm to rotate around its long axis from the elbow joint, which is very speculative—but not impossible in Crocodylus, either. Furthermore, the model didn’t seem to have forelimbs fully adapted yet for a more graviportal, columnar posture. Here’s what the model’s mobility was like:

So Mussaurus, like other early sauropodomorphs such as Plateosaurus, probably wasn’t quadrupedal, and thus quadrupedalism must have evolved very close to in the Sauropoda common ancestor.

Second, we compared the muscle moment arms (individual 3D “muscle actions” for short) in different poses for all of the main forelimb muscles that extend (in various ways and extents) from the pectoral girdle to the thumb, for both animals, to see how muscle actions might differ in Crocodylus (which would be closer to the ancestral state) and Mussaurus. Did muscles transform their actions in relation to bipedalism (or reversal to quadrupedalism) in the latter? Well, it’s complicated but there are a lot of similarities and differences in how the muscles might have functioned; probably reflecting evolutionary ancestry and specialization. What I found most surprising about our results was that the forelimbs didn’t have muscles well-positioned to pronate the forearm/hand, and thus musculoskeletal modelling of those muscles reinforced the conclusions from the joints that quadrupedal locomotion was unlikely. I think that result is fairly robust to the uncertainties, but we’ll see in future work.

You like moment arms? We got moment arms! 15 figures of them, like this! And tables and explanatory text and comparisons with human data and, well, lots!

If you’re really a myology geek, you might find our other conclusions about individual muscle actions to be interesting—e.g. the scapulohumeralis seems to have been a shoulder pronator in Crocodylus vs. supinator in Mussaurus, owing to differences in humeral shape (specialization present in Mussaurus; which maybe originated in early dinosaurs?). Contrastingly, the deltoid muscles acted in the same basic way in both species; presumed to reflect evolutionary conservation. And muuuuuuch more!

Do you want to know more? You can play with our models (it takes some work in OpenSim free software but it’s do-able) by downloading them (Crocodylus; Mussaurus; also available: Tyrannosaurus, Velociraptor!). And there will be MUCH more about Mussaurus coming soon. What is awesome about this dinosaur is that we have essentially complete skeletons from tiny hatchlings (the “mouse lizard” etymology) to ~1 year old juveniles to >1000kg adults. So we can do more than arm-wave about forelimbs!

But that’s not all. Last week we published our third paper on mouse hindlimb biomechanics, using musculoskeletal modelling as well. This one was a collaboration that arose from past PhD student James Charles’s thesis: his model has been in much demand from mouse researchers, and in this case we were invited by University of Virginia biomechanical engineers to join them in using this model to test how muscle fibres (the truly muscle-y, contractile parts of “muscle-tendon units”) change length in walking mice vs. humans. It was a pleasure to re-unite in coauthorship with Prof. Silvia Blemker, who was a coauthor on that 2005 T. rex hindlimb modelling paper which set me on my current dark path.

Mouse and human legs in right side view, going through walking cycles in simulations. Too small? Click to embiggen.

We found that, because mice move their hindlimb joints through smaller arcs than humans do during walking and because human muscles have large moment arms, the hindlimb muscles of humans change length more—mouse muscles change length only about 48% of the amount that typical leg muscles do in humans! This is cool not only from an evolutionary (mouse muscles are probably closer to the ancestral mammalian state) and scaling (smaller animals may use less muscle excursions, to a point, in comparable gaits?) perspective, but it also has clinical relevance.

Simulated stride for mouse and human; with muscles either almost inactive (Act=0.05) or fully active (Act=1). Red curve goes through much bigger excursions (along y-axis) than blue curve), so humans should use bigger % of their muscle fibre lengths in walking. Too small? Click to embiggen.

My coauthors study muscular dystrophy and similar diseases that can involve muscle stiffness and similar biomechanical or neural control problems. Mice are often used as “models” (both in the sense of analogues/study systems for animal trials in developing treatments, and in the sense of computational abstractions) for human diseases. But because mouse muscles don’t work the same as human muscles, especially in regards to length changes in walking, there are concerns that overreliance on mice as human models might cause erroneous conclusions about what treatments work best to reduce muscle stiffness (or response to muscle stretching that causes progressive damage), for example. Thus either mouse model studies need some rethinking sometimes, or other models such as canines might be more effective. Regardless, it was exciting to be involved in a study that seems to deliver the goods on translating basic science to clinical relevance.

Muscle-by-muscle data; most mouse muscles go through smaller excursions; a few go through greater; some are the same as humans’.

Finally, a third recent paper of ours was led by Julia Molnar and Stephanie Pierce (of prior RVC “Team Tetrapod” affiliation), with myself and Rui Diogo. This study tied together a bunch of disparate research strands of our different teams, including musculature and its homologies, the early tetrapod fossil record, muscle reconstruction in fossils, and biomechanics. And again the focus was on forelimbs, or front-appendages anyway; but turning back the clock to the very early history of fishes, especially lobe-finned forms, and trying to piece together how the few pectoral fin muscles of those fish evolved into the many forelimb muscles of true tetrapods from >400mya to much more recent times.

Humerus in ventral view, showing muscle attachments. Extent (green) is unknown in the fossil but the muscle position is clear (arrow).

We considered the homologies for those muscles in extant forms, hypothesized by Diogo, Molnar et al., in light of the fossil record that reveals where those muscles attach(ed), using that reciprocal illumination to reconstruct how forelimb musculature evolved. This parallels almost-as-ancient (well, year 2000) work that I’d done in my PhD on reconstructing hindlimb muscle evolution in early reptiles/archosaurs/dinosaurs/birds. Along the way, we could reconstruct estimates of pectoral muscles in various representative extinct tetrapod(omorph)s.

Disparity of skeletal pectoral appendages to work with from lobe-fins to tetrapods.

Again, it’s a lengthy, detailed study (31 pages) but designed as a review and meta-analysis that introduces readers to the data and ideas and then builds on them in new ways. I feel that this was a synthesis that was badly needed to tie together disparate observations and speculations on what the many, many obvious bumps, squiggles, crests and tuberosities on fossil tetrapods/cousins “mean” in terms of soft tissues. The figures here tell the basic story; Julia, as usual, rocked it with some lovely scientific illustration! Short message: the large number of pectoral limb muscles in living tetrapods probably didn’t evolve until limbs with digits evolved, but that number might go back to the common ancestor of all tetrapods, rather than more recently. BUT there are strong hints that earlier tetrapodomorph “fishapods” had some of those novel muscles already, so it was a more stepwise/gradual pattern of evolution than a simple punctuated event or two.

Colour maps of reconstructed right fin/limb muscles in tetrapodomorph sarcopterygian (~”fishapod”) and tetrapod most recent common ancestors. Some are less ambiguous than others.

That study opens the way to do proper biomechanical studies (like the Mussaurus study) of muscle actions, functions… even locomotor dynamics (like the mouse study)– and ooh, I’ve now tied all three studies together, tidily wrapped up with a scientific bow! There you have it. I’m looking forward to sharing more new science in 2018. We have some big, big plans!

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