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Archive for the ‘Two-Dog-Night Tetrapods’ Category

We’d been wanting to do a family holiday in Ireland for years and so we finally did. I’d been to Dublin twice before for work visits and we wanted a more rural experience. On others’ recommendations, we started in the city of Cork. With some sleuthing and asking around, I realized that we weren’t far then from gorgeous Killarney National Park, and then it wasn’t far west from there to get to Valentia Island, where incidentally there is something amazing for palaeontology-lovers. There was no detering me at that point from visiting what I’d only read about. I’ll mainly let the images tell the story.

Stomach-Churning Rating: 0/10; fossils and scenery. Kick back and enjoy.

Island map- it really is that simple to get around! The harbour town of Portmagee is damned adorable.

Driving in (no I am the passenger; not taking photo while at the wheel!)- excitement level = 8 and building… “Tetrapod carpark” sign ratcheted up the excitement and was amusing.

Headed to the trail; excitement level = 9…

Looking down onto the site (on the right); excitement level = 9.5; beauty level = 9.5 too!

Now, the site of what is broadly accepted by experts as a ~Late Devonian tetrapod’s fossil trackway(s) was originally described by Stössel in 1995. To me, that feels like a recent discovery but it is 22 years ago. The only other well-preserved, widely-accepted, probably-terrestrial, Late Devonian tetrapod trackways are from the Genoa River site in Australia; described by Warren et al. in 1972. Those trackways even reveal some details of the fingers and toes; these do not. Other tracks are either isolated footprints of minimal scientific value/clarity, subaerial (i.e. underwater), not clearly tetrapod (or now argued to be arthropod or other origin), not Devonian, or controversial for reasons I won’t get into here. Clack and Lucas have reviewed the relevant evidence recently. So there are essentially two places in the world that you can visit to view tracks like these and it was a joy to go visit one set. (Easter Ross, Scotland may be a third site but it is reasonably disputed in age and maker)

There is a big “however,” however- Falkingham and Horner showed how lungfish can produce tracks (with fins and heads together) that look like these– so there is still uncertainty. Without finger and toe impressions, claims of discrete tetrapod tracks can be risky, and it would be wrong to say that the Valentia Island footprints are uncontroversially or 100% certainly tetrapod in origin, although they are Devonian and made by some sort of animal.

Stössel et al. also published a very recent update on these Valentia Island tracks with more information. I wish I’d come across that before I visited (oops!). That study reports on a total of nine(!) trackways from the area, adding to the 1995’s first one (the “Dohilla locality, Do 1”– see diagrams below), and describes them as Middle Devonian (with a radiometric dating of 385 million years old). I’m not enough of a geologist to evaluate that; prior reports had focused on Late Devonian or so.

Rippled sandstone example; near-shore preservation characteristic of the trackway area/Valentia Slate Formation. It’s an alluvial deposit (freshwater floodplain), interpreted to lie inland from the coastal marine deposits. Raindrop impressions and possible mudcracks on the plane of the tracks offer some support that the tracks were made on (moist) land.

The island has plenty of signs advertising the tracks as a tourist destination but happily(?) there are no knick-knack shops stocked with plush tetrapods, or other developments at or near the site. One simply winds down a very narrow road near a radio station and old lighthouse, and parks then walks to see the tracks. No fancy crap; just AWESOME sights to take in, and some good educational information.

Explanatory plaque at the viewing area. Pretty good!

Nice image of where Valentia Island was; although the 385 My age may be exaggerated. It’s not clear how old the tracks are but “Mid-to-Late Devonian” might suffice. Claims that they are the “oldest known” may still be contentious (see references above).

Explanatory signs on the peak above the shore. Given the likely tetrapod trackmakers like Acanthostega-style critters, the adult animal may have been able to breathe air with lungs and underwater with gills.

Enough exposition– let’s expose those tracks! (images can be clicked to enlarge)

My first close-up look at the tracks. Whoa! Small tracks are presumably hand (manus) impressions; larger ones are foot (pes). The tracks go in an alternating fashion (like a salamander’s walk) and the animal was probably going from the bottom-right toward the top-left. Moss and moisture obscured some of the prints that day, sadly. The tracks are oval, with the long axes perpendicular to the direction of travel. There are some pesky geological deformations of the trackway, faults, and other distortions. 145 footprints in total are reported from this one trackway!

Trackway as it turns to the left and gets harder to follow. John-shadow for ~scale. Frustratingly for me, a little rivulet was coming down the hill across the left side of the trackway and hiding much of the detail of the end.

Alternative view of the majority of the tracks; turned ~90 degrees from above two views.

Zoomed-in view of the tracks from head-on (opposite the view in other photos); i.e. western position looking east (ish). I added red and blue dots to roughly outline the right side of the main trackway (red) and the second one (blue), which crosses it and may have been made after it.

Even these nice trackways, viewed by an expert, take some unpacking. Here is some:

Diagram of known tracks at the site by Stössel et al. 2016.

Diagram at view site with extra tail (or body) drag trail crossing the main tracks; described later by Stössel.

I’m not at all a religious person and I don’t really like the term “spiritual” either, but this experience was emotional for me. Awe is certainly the best word to describe what I felt on viewing these tracks. The literature just doesn’t do them justice; nothing beats a first-person experience like this. We were lucky with excellent weather, too, and we were almost alone during the visit so there was pleasant silence in which to contemplate the tracks. I brought my copies of three papers on the trackways and, struggling with the wind, compared them with the visible tracks to understand what other scientists had seen. That amplified the experience enormously for me.

Even if they turn out to be non-tetrapod or younger or something less exciting (“sham-rock”?), it was thrilling to see the Valentia Island tracks and think about what happened >350 million years ago when they were made by our very distant cousins, along the land-water interface of space and time.

(I also feel bad for online reviewers that were disappointed with the site- it’s hard to grasp the scientific importance and/or accept the evidence, even with the decent information available on-site. Even if people know the nice fossil record of dinosaurs, they may not know how good the fossil record of early tetrapods is and how confidently we can figure out what happened in the Devonian emergence of tetrapods onto land. But some visitors clearly got it.)

And, looking at the site myself, I realized how many more tracks might be buried under the cliffs of the site- the first trackway emerges from under a cliff and thus must still be preserved for some distance underground, awaiting future exposure. What more might we learn about that single animal and others that made tracks around the same time? I hope to live to find out. I feel a personal connection now to these tracks, left pondering what story they preserve– and hide. I’m glad I’m able to share my own story with you, and encourage you to make the visit yourself!

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Who needs “Ice Road Truckers” when you have the “John’s Freezer” team on the road with fossils, amphibians, felids and 3D phenotype fun? No one, that’s who. We’re rocking the Cheltenham Science Festival for our first time (as a group), and pulling out all the stops by presenting two events! Here’s the skinny on them, with updates as the week proceeds.

Stomach-Churning Rating: 2/10 for now (just bones), but it could change once the cheetah dissection is under way… 8/10 bloody cheetah bits but only at the end (updated)

Right now, Lauren Sumner-Rooney (of “Anatomy To You” and other fame) is on-site with a rotating team of others from our lab, in the “Free Activity Tents” area of the Imperial Gardens/Square, inside a marquee where we’ll be showing off our NERC-funded tetrapod research all week. This “First Steps” event features not only our past and present work with Jenny Clack, Stephanie Pierce, Julia Molnar and others on Ichthyostega & its “fishapod” mates, but also our “scampering salamanders” research in Spain, Germany and England. I’ve blogged a lot about all that, and won’t repeat it here, but you can see a 3D-printed Ichthyostega skeleton, view the skeleton in a virtual reality 3D environment, see related specimens and engage in kid-friendly activities, and talk to our team about this and other related research.

Ichthyostega 3D printed backbone is born!

Ichthyostega 3D printed backbone is born!

The central themes of that event are how bone structure relates to function and how we can use such information, along with experimental measurements and computer models of real salamanders, to reconstruct how extinct animals might have behaved as well as how swimming animals became walking ones. How did fins transform into limbs and what did that mean for how vertebrates made the evolutionary transition onto land? If you know my team’s work, that encapsulates our general approach to many other problems in evolutionary biomechanics (e.g. how did avian bipedalism evolve?). Added benefits are that you too can explore this theme in a hands-on way, and you can talk with us about it in person. That continues all week (i.e. until Saturday evening); I’ll be around from Thursday afternoon onwards, too. Kids of all ages are welcome!

Ichthyostega 3D print taking shape!

Ichthyostega 3D print taking shape!

Then, on Saturday for our second free event we join forces with Ben Garrod (master of primate evolution, the secrets of bones, and “Attenborough and the Giant Dinosaur”) and RVC’s forensic pathologist Alexander Stoll as well as Sophie Regnault (“sesamoid street” PhD student w/me). As the “Large Animal Dissection” title hints, it’s not the right kind of gig to bring small kids to. There will be blood and stuff— we’ll be dissecting a cheetah together from 10am-4pm. This will involve walking through all the major organ systems, giving evolutionary anecdotes, and plenty more, with an aim to understand how the magnificent adaptations of cheetahs evolved—but also to investigate what problem(s) this animal faced that led to its sad demise. By the day’s end, there will just be a skeleton left. Get a front row seat early for this event, which serendipitously ties into “Team Cat”’s Leverhulme Trust-funded research project (we wanted a big animal and it just happened to be a cheetah; I had hoped for a giant croc or a shark or something but can’t complain!).

Ichthyostega 3D print is ready!

Ichthyostega 3D print is ready!

If you miss these events, please do cry bitter tears of regret. But don’t despair, there will be another “big cat dissection” in the London area in ~November (watch here for details), and plenty more fossil tetrapod stuff to come, plus a LOT more dinosaurs on the horizon!

Guess the bones! (photo by Zoe Self)

Guess the bones! (photo by Zoe Self)

And please come back to this blog post for more pics and stories as the week carries on… For hashtag afficionados, you can follow the fun on Twitter etc. at #firststepsCSF16. What a world we live in!

Update 1: While you’re here, check out our Youtube playlists of tetrapod-related videos:

Lobe-finned fishes

Ichthyostega‘s awesome anatomy

Tetrapod evolution: Tiktaalik to salamanders!

Update 2: Photos of our main stand (about tetrapod evolution)

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Our poster/banner display looks nice.

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Our tent brings in some punters.

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Our bones excite people young and old, sighted and blind.

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Fun with stickers and lab t-shirts.

And…

Update 3: Cheetah meat & greet
Ben, Alex, Sophie and I tackled the cheetah dissection today and it went GREAT! Much better than I’d optimistically expected. Rain didn’t scare the crowds off and neither did the gore, which there was some of (gelatinous spinal cords, lumpy tumors and at least one flying tiny bit of cheetah flesh that landed on a good-natured audience member!). Photos will tell the tale:

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Peek-a-boo!

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Sophie and Alex help us get set up in our tent.

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Our initial rough schedule- although we ended up improvising more after lunch.

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Dissectors assemble!

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The beast revealed. It was skinned by the museum that loaned it to us.

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Alex showing his talent: removing the viscera in one piece from end to end, starting with the tongue.

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Impressive finding of a surgical fixture (plate and wires) on the tibia, which had been used to hold the shattered bone back together long enough for it to heal. Added to the kidney disease and liver-spleen-lung cancer, this cheetah was in the sorriest shape of any cadaver I’ve seen yet.

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Cheetah coming to pieces: (from bottom) lumbar/pelvic region, hindlimb, thorax, forelimb and other bits.

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Dr Adam Rutherford, an eye expert, did a nice dissection of the cheetah’s eye, here showing the tapetum lucidum (reflective membrane), which shows up as light blue colour. Its small size befits the not-very-nocturnal habits of cheetahs.

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The lens of the cheetah’s eye. Now cloudy because of dehydration and crystalization, but still fascinating to see.

Want to see more images and the enthusiastic responses from the audience (we got some great feedback)? Check out Twitter’s #cheltscifest feed, or more simply my Storify condensation of the cheetah-related tweets here.

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[This is the original, unedited text of my shorter, tighter (and I think actually better) News & Views piece for Nature, on the paper described below)

Ambitious experimental and morphological studies of a modern fish show how a flexible phenotype may have helped early “fishapods” to make the long transition from finned aquatic animals into tetrapods able to walk on land.

Stomach-Churning Rating: 1/10. Cute fish. Good science. Happy stomachs!

Photo by Antoine Morin, showing Polypterus on land.

Photo by Antoine Morin, showing Polypterus on land.

Napoleon Bonaparte’s military excursions into Egypt in 1798-1799 led a young French naturalist, Ètienne Geoffroy Saint-Hilaire, to cross paths with a strange fish that had paired lungs and could “walk” across land on its stubby, lobelike fins. In 1802, he dubbed this fish “Polyptère bichir”1, today known as the Nile bichir, Polypterus bichir La Cepède 1803. The bichir’s mélange of primitive and advanced traits helped to catapult Geoffroy into scholarly conflict with the reigning naturalist Georges Cuvier back in France and to establish Ètienne as a leading anatomist, embryologist and early evolutionary researcher of repute even today2. Now, on their own excursion under the very “evo-devo” flag that the discoverer of Polypterus helped raise, Canadian scientists Standen et al.3 suggest how the remarkable plasticity of the skeleton of Polypterus (the smaller west African relative of P. bichir, P. senegalus or “Cuvier’s bichir”) reveals a key part of the mechanism that might have facilitated the gradual transition from water to land and thus from “fishapods” to tetrapods (four-limbed vertebrates).

In a bold experiment, the authors raised 149 young bichirs on land and in water for eight months, then studied how they moved on land vs. in water, and also how the ultimate shape of the skeletal elements of the paired front fin bases differed between the land- and water-raised bichirs. Standen et al.3 discovered that both the form and function of the fins’ foundations transformed to better satisfy the constraints of moving on land. Land-acclimated bichirs took faster steps on land, their fins slipped across the substrate less, they held their fins closer to their body, their noses stayed more aloft and their tails undulated less, with less variable motions overall—behaviours that the authors had predicted should appear to enhance walking abilities on land. In turn, the bones of the neck and shoulder region altered their shape to produce a more mobile fin base with greater independence of fin from neck motion, along with improved bracing of the ventral “collarbone” region. These environmentally-induced traits should have fostered the locomotor changes observed in “terrestrialized” fish and aided the animals in resisting gravity, and they represent a common biological phenomenon termed developmental plasticity4,5. Interestingly, the land-reared fish could still swim about as well as the wholly aquatic cohort, so there was not a clear trade-off between being a good swimmer and a good walker, which is surprising.

Considered alone, the developmental plasticity of bichir form and function shows how impressive these amphibious fish are. But Standen et al.’s study3  ventured further, to apply the lessons learned from bichir ontogeny to a phylogenetic context and macroevolutionary question. The phenotypic plasticity during bichir development, they infer, could have been harnessed during the evolutionary transformation of fins for swimming into limbs for walking, in the “fishapod” ancestors of tetrapods. Indeed, bichirs are close to the base of the family tree of fishes6, and other living relatives of tetrapods have reduced or lost their fins (lungfishes) or adapted to strange deep-sea swimming lifestyles, never walking on land (coelacanths). Thus perhaps bichirs and the “fishapod” lineage share what Geoffroy would have called “unity of type”, today termed homology, of their developmental plasticity in response to a land environment. Surveying the fossil record of early “fishapods” and tetrapods, Standen et al.3 found that the macroevolutionary changes of neck and shoulder anatomy in these gradually more land-adapted animals parallel those they observed in terrestrialized Polypterus, providing ancillary support for their hypothesis.

A further test of the application of Polypterus’s plasticity to fossil tetrapods is naturally difficult. However, the “fishapod” lineage has some exceptional examples of fossil preservation. With sufficient sample sizes (e.g. fossil beds that reveal growth series, such as the Late Devonian Miguasha site in Canada7) and palaeoenvironmental gradients in fish or tetrapods, one could imagine performing a rigorous indirect test. Even small samples could be helpful– for example, the early tetrapod Ichthyostega exhibits some developmental changes in its forelimb suggesting that it became more terrestrial as it grew, whereas the related Acanthostega does not evidence such changes8— this hints at some developmental plasticity in the former animal.

During the Devonian period (~360-420 million years ago), were the “fishapod” ancestors of tetrapods floundering about on land now and then, gradually shifting from anatomy and behaviours that were more developmentally plastic (as in bichirs) to ones that were more canalized into the terrestrialized forms and functions that more land-adapted tetrapods retained? An attractive possibility is that the developmental plasticity could have led to fixation (reduction of plasticity), an evolutionary phenomenon called genetic assimilation, which another intellectual descendant of Geoffroy, Conrad Hal Waddington, promoted from the 1950s onwards9, a concept that now enjoys numerous cases of empirical support10 that this one may eventually join.

The nature of the genetic and developmental mechanism that bichirs use to achieve the observed developmental plasticity is still unclear. If it has a high enough degree of heritability, then it could be selected for in cross-generational experiments with bichirs. With sufficient time and luck raising these unusual fish, the hypothesis that their plastic response to a terrestrial environment can become genetically assimilated could be directly tested. This study could thus become an epic exemplar of how genetic assimilation can contribute not only to microevolutionary change but also to major macroevolutionary events, as was presciently suggested in a seminal review of developmental plasticity4.

This genetic assimilation is the Polypterus study’s reasonable speculation, and one that Geoffroy likely would have applauded, all the more for involving his beloved bichirs. Much as Napoleon’s landfall in Egypt was not a lasting success, bichirs never left wholly terrestrial descendants despite their malleable locomotor system. But the same type of plastic developmental mechanism that bichirs use today to make tentative, floppy incursions of the terrestrial realm might have been harnessed by our own “fishapod” forebears, leaving a far more revolutionary dynasty upon the Earth.

 

References

  1.  Geoffroy, E. (1802). Histoire naturelle et description anatomique d’un nouveau genre de poisson du Nil, nommé polyptère. Annales du Muséum d’Histoire Naturelle 1:57-68.
  2. Le Guyader, H., & Grene, M. (2004) Geoffroy Saint-Hilaire: A Visionary Naturalist. Univ. Chicago Press.
  3. Standen, E. M., Du, T. Y., & Larsson, H. C. E. (2014). Developmental plasticity and the origin of tetrapods. Nature, published online.
  4. West-Eberhard, M. J. (1989). Phenotypic plasticity and the origins of diversity. Annual Review of Ecology and Systematics 20:249-278.
  5. Pigliucci, M., Murren, C. J., & Schlichting, C. D. (2006). Phenotypic plasticity and evolution by genetic assimilation. Journal of Experimental Biology 209(12):2362-2367.
  6. Near, T. J., Dornburg, A., Tokita, M., Suzuki, D., Brandley, M. C., & Friedman, M. (2014). Boom and bust: ancient and recent diversification in bichirs (Polypteridae: Actinopterygii), a relictual lineage of ray‐finned fishes. Evolution 68:1014-1026.
  7. Cloutier, R. (2013). Great Canadian Lagerstätten 4. The Devonian Miguasha Biota (Québec): UNESCO World Heritage Site and a Time Capsule in the Early History of Vertebrates.Geoscience Canada40:149-163.
  8. Callier, V., Clack, J. A., & Ahlberg, P. E. (2009). Contrasting developmental trajectories in the earliest known tetrapod forelimbs.Science324:364-367.
  9. Waddington, C. H. (1953). Genetic assimilation of an acquired character. Evolution 7:118-126.
  10. Crispo, E. (2007). The Baldwin effect and genetic assimilation: revisiting two mechanisms of evolutionary change mediated by phenotypic plasticity. Evolution 61:2469-2479.

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What a week!

My team had a new technician arrive, Kyle Chadwick from Uni. Virginia, and NSF Postdoctoral Research Fellow, Dr. Ashley Heers (see here for an example  of new stuff she’s starting here at the RVC!), started working with me at the RVC, and then these guys showed up…

Salamanders!

Woo hoo!

First a tiger salamander (Ambystoma) paid a visit, for filming an episode of the Windfall Films/PBS documentary “Your Inner Fish” (a la the famous book):

So cute! Tiger salamander, soon to be a TV celebrity.

So cute! Tiger salamander, soon to be a TV celebrity.

Dr. Stephanie Pierce (who was also a coauthor on a great open access croc paper in Proc Roy Soc B this week) was filmed with Prof. Jenny Clack to recap some of our past work on tetrapod locomotion. Watch out for the 3-part series!

And that gorgeous salamander was a star performer in strutting his stuff for the camera to demonstrate the locomotion of modern tetrapods, including some lovely slo-mo footage from our lab cameras:

(if that’s too slow for you, try the normal-speed footage. I’ll admit, salamanders don’t really need slo-mo video for normal walking, but I like it)

So cool!

But then we got a special package… with three frozen fire salamanders (Salamandra salamandra) from colleagues in Germany!

Three new occupants of the freezers, for planning our studies of salamander locomotion

Three new occupants of the freezers, for planning our studies of salamander locomotion

This marks the start of an exciting new period in my team’s work in the lab. I’ve always liked salamanders and newts, and we’ve scanned and modelled plenty (e.g. this old post), but now we’re going to work with live fire salamanders (a first for me)! We are using the dead ones to plan the new studies with the live ones– these new studies will involve lots of high speed videos and force platform analysis (as shown above), in conjunction with XROMM (biplanar fluoroscopy/3D skeletal motion analysis) and other techniques including computer simulations. We got initial approval this week to work with these salamanders, and found a reputable source this week too, so it was definitely Salamander Week in my group!

This research all will feed into our upcoming studies of extinct tetrapods: we’re using salamanders to figure out how salamanders move and what limits their speed and gait, and then we’re using the same sorts of computer tools to try to estimate how extinct tetrapods may have moved and how locomotion evolved, in much more specific detail than our prior work had done, which was mainly about using 3D reconstructions of anatomy to show what those animals could not do. More about the project here.

Watch this space for more scampering salamanders!

UPDATE: And here’s one! Not quite scampering, but…

Setting up our two fluoroscopes for a test run of our gait studies-- but with one of the deceased salamanders. Gotta get a good image  before any live animal work!

Setting up our two fluoroscopes for a test run of our gait studies– but with one of the deceased salamanders. Gotta get good images before any live animal work begins!

An example of the kind of footage we’re aiming for (single 2D fluoroscope view from Nadja Schilling’s team’s research; see XROMM website for more details on the methodology)

UPDATE 2:

I did a CT scan with a normal medical grade CT scanner at the highest resolution we can manage (0.625 mm slices). Check out the results below, which amuse me:

Looks like a toy; too crude resolution. But we can see major structures, and we can very nicely see the “microchip” (which looks HUGE) that was placed in this animal’s back when in captivity, and then another structure is visible near the pelvis which might be another chip or else remains of some food, pathology, or a really odd pelvis– I am not totally sure!

So this is why we tend to use microCT, which can go down to as low as ~5 micron resolution, to get 3D anatomy of animals this small. It’s no surprise to me, but it is fun to see how far we could push our normal CT machine. The results aren’t horrid but wouldn’t have much scientific value for us. They did confirm for us that this specimen is heavily ossified, so the faint images of bone that we are getting in our x-ray fluoroscopes (above) are due to something going wrong with our camera system, not the animal’s immature skeleton. Stay tuned for more updates as the science happens!

UPDATE 3:

20 wonderful adult Fire Salamanders have joined our team and are relaxing over the coming week before we start taking them for walks. Here is one exploring its new home:

Fire salamanderUPDATE 4:

August 11-15, 2014 we are in Jena, Germany using their fancy biplanar radiography system (“x-ray video”) to study our salamanders, at last! Follow the tweets starting here, for more information as it happened! https://twitter.com/JohnRHutchinson/status/500187568416518144

and this video of “Jabba” the corpulent salamander walking-

with a top view, too-

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…a daily picture of anatomy! And today it is five pictures; zza-zza-zee! ♫

Welcome back againagain, (gasp, pant) and again to Freezermas

I’m letting the dogs out today. Science gone barking mad! Hopefully my puns will not screw the pooch.

Stomach-Churning Rating: 4/10; a dog cadaver’s leg (not messy), then just tame digital images of anatomy.

I am working with Rich Ellis, a former MSc student at Univ. Colorado (see his cool new paper here!), for a fun new collaboration this year. He was awarded a prestigious Whitaker Foundation scholarship to do this research, which focuses on how different animals stand up from a squatting position, with the legs about as bent as they can be.

We want to know how animals do this standing up movement, because it is in some ways a very demanding activity. Very flexed/bent limb joints mean that the muscles (and some tendons) are stretched about as far as they ever will be. So this places them at disadvantageous lengths (and leverage, or mechanical advantage) for producing force. We know almost nothing about how any animal, even humans, does this-– how close to their limits of length are their muscles? Which muscles are closest? Does this change in animals with different numbers of legs, postures, anatomy, size, etc? Such fundamental questions are totally unaddressed. It’s an exciting area to blaze a new trail in, as Rich is doing. So far, we’ve worked with quail, humans, and now greyhounds; in the past I did some simple studies with horses and elephants, too. Jeff Rankin from my team and other collaborators have also worked on six species of birds, of varying sizes, to see how their squat-stand mechanics change.  Thus we’ve covered a wide diversity of animals, and now we’re learning from that diversity. “Diversity enables discovery,” one of my former PhD mentors Prof. Bob Full always says. Too true.

Greyhounds are interesting because they are medium-sized, long-legged, quadrupedal, quite erect in posture, and very specialized for fast running. Fast runners tend to have big muscles with fairly short fibres. Short fibres are bad for moving the joints through very large ranges of motion. So how does a greyhound stand up? Obviously they can do it, but they might have some interesting strategies for doing so- the demands for large joint motion may require a compromise with the demands for fast running. Or maybe the two demands actually can both be optimized without conflict. We don’t know. But we’re going to find out, and then we’ll see how greyhounds compare with other animals.

To find out, we first have to measure some dogs standing up. We’ve done that for about 8 greyhounds. Here is an example of a cooperative pooch:

Those harmless experiments, if you follow me on Twitter, were live-tweeted under the hashtag #StandSpotStand… I dropped the ball there and didn’t continue the tweeting long after data collection, but we got the point across– it’s fun science addressing useful questions. Anyway, the experiments went well, thanks to cooperative pooches like the one above, and Rich has analyzed most of the data.

Now the next step involves the cadaver of a dog. We could anaesthetize our subjects and do this next procedure to obtain subject-specific anatomy. But it really wouldn’t be ethically justified (and if I were an owner I wouldn’t allow it either!) and so we don’t. A greyhound is a greyhound as far as we’re concerned; they’ll be more like each other than either is like a quail or a human. Individual variation is a whole other subject, and there are published data on this that we can compare with.

We get a dead dog’s leg — we don’t kill them; we get cadavers and re-use them:

Greyhound hindlimb for CT

We study the hindlimb because birds and humans don’t use their forelimbs much to stand up normally, so this makes comparisons simpler. We’re collecting forelimb data, though, as we work with quadrupeds, for a rainy day.

We then CT scan the leg, getting a stack of slices like this– see what you can identify here:

It’s not so clear in these images, but I was impressed to see that the muscles showed up very clearly with this leg. That was doggone cool! Perhaps some combination of formalin preservation, fresh condition, and freezing made the CT images clearer than I am used to. Anyway, this turned out to be a treat for our research, as follows.

We then use commercial software (we like Mimics; others use Amira or other packages) to “segment” (make digital representations in 3D) the CT scan data into 3D anatomy, partitioning the greyscale CT images into coloured individual objects– two views of one part of the thigh are shown below.

What can you identify as different colours here? There are lots of clues in the images (click to embiggen):

Hindlimb segmentation of greyhound

And here is what the whole thigh looks like when you switch to the 3D imaging view:

Quite fetching image, eh?!

The next steps after we finish the limb segmentation are to apply the experimental data we observed for greyhounds of comparable size by importing the model and those data into biomechanics software (SIMM/OpenSim). We’ve done about 40 models like this for various species. I detailed this procedure for an elephant here.

Then, at long last, science will know how a greyhound stands up! Wahoo! Waise the woof! Stay tuned as we hound you with more progress on this research-as-it-happens. Rich just finished the above thigh model this week, and the rest of the leg will be done soon.

Many thanks to Rich Ellis for providing images used here. And thank you for persevering my puns; they will now be cur tailed.

Happy Freezermas! Sing it: “On the fifth day of Freezermas, this blo-og gave to me: one tibiotarsus, two silly Darwins, three muscle layers, four gory hearts, a-and five stages modelling a doggie!” ♪

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To kick off the New Year just right, our tetrapod team has a new paper in Nature, following up on last year’s Ichthyostega not-so-good-at-walking study (also see here). Yet this paper has a more anatomically descriptive — and also an “evo-devo” — twist to it. For brevity, I’ll let our press release tell the story, since I think it does a good job of it (like I always preach scientists should do, we worked with our PR company to write this together, so we’re happy with how the press release came out). In a nutshell, our study used some very fancy synchotron radiation techniques to image the 3D anatomy of the backbone in early land vertebrates. Our findings surprised even us, and ended up turning around palaeontology/comparative anatomy’s view of how the backbone evolved, giving us a new glimpse into our inner tetrapod.

Stick around for the videos at the end, which are the first four supplementary movies from the paper and are rather pretty (there are two more, for imaging/segmenting afficionados, but they are not as pretty or interesting for most of this blog’s readership). The final figure (Figure 1 from our paper) gives some extra visual context.

The paper is:

Pierce, S.E., Ahlberg, P.E., Hutchinson, J.R., Molnar, J.L., Sanchez, S., Tafforeau, P., Clack, J.A. 2013. Vertebral architecture in the earliest stem tetrapods. Nature, published online [here].

I should note that I’m just 3rd author, so I deserve only modest credit. But I helped. Even though no freezers were involved, or harmed, in the process.

Ichy_vertebrae_final_sm-01

Above image: Julia Molnar‘s illustration of Ichthyostega showing anatomical changes of its spine from front to back, with neural arch/spine in pink, twin pleurocentra in yellow, and intercentrum in green. These four parts, three kinds of bones, made up the backbone of the first land vertebrates. These parts evolved in different ways in later animals, but formed one main bone in all living lineages of vertebrates.

RVC PRESS RELEASE:

Scientists reassemble the backbone of life using a particle accelerator

Research published today (Sunday 13 January 2013) in the journal Nature documents, for the first time, the intricate three-dimensional structure of the backbone in the earliest four-legged animals (tetrapods).

The international team of scientists, led by Dr Stephanie E. Pierce from The Royal Veterinary College and Professor Jennifer A. Clack from the University of Cambridge, bombarded 360 million year old early tetrapod fossils with high energy synchrotron radiation. The resulting high resolution X-ray images allowed the researchers to reconstruct the backbones of the extinct animals in exceptional detail.

The backbone, also known as the spine or vertebral column, is a bony structure found in all tetrapods, along with other vertebrates such as fish. It is formed from many elements or vertebrae all connected in a row – from head to tail. Unlike the backbone of living tetrapods (e.g. humans), in which each vertebra is composed of only one bone, early tetrapods had vertebrae made up of multiple parts.

Lead author Dr Pierce says: “For more than 100 years, early tetrapods were thought to have vertebrae composed of three sets of bones – one bone in front, one on top, and a pair behind. But, by peering inside the fossils using synchrotron X-rays we have discovered that this traditional view literally got it back-to-front.”

For the analysis, the European Synchrotron Radiation Facility (ESRF) in France, where the three fossil fragments were scanned with X-rays, used a new protocol to reveal tiny details of the fossil bones buried deep inside the rock matrix.

Using this new technology, the team of scientists discovered that what was thought to be the first bone – known as the intercentrum – is actually the last in the series. And, although this might seem like a trivial oversight, this re-arrangement in vertebral structure has over-arching ramifications for the functional evolution of the tetrapod backbone. (see here for a now out-of-date image from Wikipedia)

Dr. Pierce explains: “By understanding how each of the bones fit together we can begin to explore the mobility of the spine and test how it may have transferred forces between the limbs during the early stages of land movement”.

But, the findings didn’t end there. One of the animals – known as Ichthyostega – was also found to have an assortment of hitherto unknown skeletal features including a string of bones extending down the middle of its chest.

Professor Clack says: “These chest bones turned out to be the earliest evolutionary attempt to produce a bony sternum.  Such a structure would have strengthened the ribcage of Ichthyostega, permitting it to support its body weight on its chest while moving about on land.”

This unexpected discovery supports recent work done by the same authors that showed Ichthyostega probably moved by dragging itself across flat ground using synchronous ‘crutching’ motions of its front legs – much like that of a mudskipper or seal.

Dr Pierce adds: “The results of this study force us to re-write the textbook on backbone evolution in the earliest limbed animals.”

The next step, the researchers say, is to understand how the backbone aided locomotion in these early tetrapods using sophisticated biomechanical analysis.

The study was funded by the Natural Environment Research Council.

Additional support was provided by the European Research Council and the ESRF, of which the Science and Technology Facilities Council (STFC) is the UK shareholder.

MOVIES:

These are rotating images of the anatomy, colour-coded, of the four species of early tetrapod that we examined for this study. Each shows the same basic pattern of having a “reverse rhachitomous” (pleurocentra in the front, intercentrum in the back; trying to think of a mullet joke…) anatomy. This is opposite the pattern that essentially all studies since famed evolutionary biologist/palaeontologist Edward Drinker Cope coined the term “rhachitomous” in 1878 have portrayed these and related animals as having. And this realization forces a re-examination of how the backbone structures first evolved in tetrapods and which parts (intercentra? pleurocentra? And where?) formed the spines of later animals.

For once, as authors we all felt that this finding really deserved the painfully hackneyed “rewrite the textbooks” label. It changes a lot of what we thought we knew about this classic evolutionary transition of anatomy. Check a vertebrate palaeontology/comparative anatomy textbook and you’ll likely find rhachitomous vertebrae and/or changes of pleurocentra vs. intercentra told in a way that we now are pretty sure is wrong.

You can also see the “sternebrae” (sternal elements; parts of the sternum that evolved independently in later land animals) in the first movie.  This, to my knowledge, is by far the oldest such evidence. I know of ossified sternal plates in Early Permian mesosaurs like Stereosternum, but nothing earlier although perhaps in some synapsid I don’t know, or a basal diapsid of some kind? Chime in in the comments if you know of something I missed. Regardless, the sternebrae in Ichthyostega have nothing to do directly with those convergently evolved in lissamphibians, lepidosaurs, synapsids and archosaurs, although there may be some parallel developmental mechanisms involved and at least similar dermal tissues recruited into ossification patterns. Even so, these sternebrae are further evidence of how that taxon, at least, was beginning to make forays onto land, as they’d have helped it to support its belly on land and breathe.

The segmented PPC-SRµCT of Ichthyostega stensioi MGUH VP 6115 spinning in yaw and roll.

The segmented PPC-SRµCT of Ichthyostega eigili MGUH VP 29017a spinning in yaw and roll.

The segmented PPC-SRµCT of Acanthostega gunnari MGUH f.n. 1227 spinning in yaw.

The segmented µCT of Pederpes finneyae GLAHMS 100815 spinning in yaw.

FIGURE:

Figure 1_Pierce et al

Above: (a,b) How we used to think the vertebrae were composed in early tetrapods like Ichthyostega. (c) How we found that Ichthyostega‘s posterior thoracic vertebrae actually tend to look. (d) Ichthyostega‘s anterior lumbar vertebral morphology. (e) Acanthostega according to Coates’s important description. (f) Our revision of the anatomy of Acanthostega (anterior dorsal). (g) Our new interpretation of Pederpes‘s morphology, from a posterior dorsal. Focus on the yellow vs. green elements. In a,b and e they are in different positions (reversed) compared with our new versions in c,d,f,g.

To put the above figure and movies into broader context, check this Wikipedia image. We think the red/pink bones (pleurocentra) are in the wrong place relative to the blue ones (intercentrum); the ones currently there in this image actually belong to the vertebral unit behind that one, so the pleurocentra should be moved to the front (left end) of each unit. But also look down toward the bottom of the figure. Some of those vertebrae may need to have their blue/pink bits re-examined and interpreted, too. Is it turtles intercentra all the way down?

There you have it! Welcome to your new, revised, irradiated, reverse-rhachitomous inner tetrapod’s vertebrae. Propagation phase-contrast X-ray synchrotron microtomography FTW!!!!

Science media articles arising from this study–

I like to keep track of media stories covering our research, using this blog, so here are some of the stories about this paper. It’s funny… this was one of the most broadly important papers I’ve ever been on, but the coverage was relatively scant. It was too technical. We knew that would be a problem, and really had a hard time putting into words why the study was so surprising even to us! Most writers wanted the “how did the animals move?” angle, which was not what the study was about. I still feel that this angle was not even needed; the study (and again I take minimal credit for it) is exciting without it. To comparative anatomy and evo-devo specialists, anyway. Well, that’s science for you; sometimes it is just too hard to explain its value to the outside world, even when you feel its importance in your very spine… And the press coverage was not terrible by any means; no sour grapes from me. Regardless, we’re glad it has been well received by specialist researcher colleagues we’ve spoken to, and that matters a lot.

NERC’s Planet Earth (nice story from our funder)- “Scientists had fossil backbone backwards”

BBC online (the only story aside from NERC’s that did more than read the press release) “Tetrapod anatomy: Backbone back-to-front in early animals”

Discovery News online– “First Land Animals Shuffled Like Seals” (good, but is sort of mixing up our this study, our 2012 one and Ahlberg et al’s 2005 seal-analogue study; latter two were more about movement. As often happens, a lot of other media stories basically copied this one’s headline/angle.)

Discover 80beats– “Paleontologists Use 3-D Models to Rewrite Evolution” (also in “top stories”)

Popsci– “Particle Accelerator Reveals That First Land Animals Walked Like Seals”

Daily FMail (nice pics)- “Astonishing 3D images reveal the first four-legged land animals in amazing detail – and overturn a century of research” (wins longest headline award)

Red Orbit– “Study Reveals First Ever Images Of Early Tetrapod Backbone And How It Helped In Land Evolution”

Examiner.com– “X-ray study rewrites tetrapod backbone evolution (Photos)”

Everything Dinosaur– “Ichthyostega Gets a Re-Think”

Business Standard– “Scientists recreate earliest quadraped’s backbone” (Proofread, editors! Quadruped.)

Geekosystem– “Early Land-Dwelling Animals Moved About Like Seals, Probably Didn’t Balance Balls on Their Noses” (scores some pts for humour)

…and the PR-copying, non-spellchecking fail of the week award goes to… Physorg! “Scientists reassemble the backbone of life with a particle acceleratorynchrotron [sic] X-rays”

Warming up the acceleratorynchrotron for our next study… 🙂

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Party time! Let the media onslaught begin! We’ve published a paper in Nature on the limb motions of Ichthyostega (and by implication, some other stem tetrapods). Since we did use some crocodile specimens from Freezersaurus (see below) in this study, I figured WIJF could cover it to help celebrate this auspicious event. Briefly. Particularly since we already did a quasi-blog on it, which is here:

http://www.rvc.ac.uk/SML/Research/Stories/TetrapodLimbMotion.cfm

and some juicy fossily images at:

http://www.rvc.ac.uk/SML/Research/Stories/TetrapodImages.cfm

However I want to feature our rockin’ cool animations we did for the paper, to squeeze every last possible drop of science communicationy goodness out of them. So here they are in all their digital glory. Huge credit to Dr. Stephanie Pierce, the brilliant, hardworking postdoc who spearheaded the work including these videos! Dr. Jenny Clack is our coauthor on this study and the sage of Ichthyostega and its relatives- her website is here. Also, a big hurrah for our goddess of artsy science, Julia Molnar, who helped with the videos and other images. Enjoy!

The computer model

The forelimb model

The hindlimb model

We used some of my Nile crocodile collection to do a validation analysis of our joint range of motion (ROM) methods, detailed in the Supplementary info of the paper, which I encourage anyone interested to read since it has loads more interesting stuff and cool pics. We found that a bone-based ROM will always give you a greater ROM than an intact fleshy limb-based ROM. In other words, muscles and ligaments (and articular cartilage, etc.). have a net effect of reducing how far a joint can move. This is not shocking but few studies have ever truly quantitatively checked this with empirical data from whole animals. It is an important consideration for all vert paleo types. Here is a pic of one of the crocodiles from the study, with (A) and without muscles (B; ligaments only):

I’ll close with Julia Molnar’s jaw-droppingly awesome flesh reconstruction from our model. Why Nature wouldn’t use this as a cover pic, I’ll never understand, but I LOVE it! When I first saw it enter my email inbox and then opened it to behold its glory, my squeal of geeky joy was deafening.

(edit: Aha! Fellow Berkeley alum Nick Pyenson’s group made the Nature cover, for their kickass study of rorqual whale anatomy, including a “new” organ! Well, we don’t feel so bad then. Great science– and a win for anatomy!!!)

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