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Posts Tagged ‘sesamoid’

The Bird Knee Challenge

Posted in Anatomy Vignette, tagged , , , , , , , on December 10, 2017| 9 Comments »

An epiphysean Sispyhean task today: solve this mystery that has been bothering me for >15 years. It’s about bird knees. Read on.

Stomach-Churning Rating: 1/10- bones and brief words. Nothing to worry about.

Here is an ostrich. I was interviewing undergrads the other day and looked up to see it, then thought something like: “Oh yeah, that little bit of bone really bothers me. I cannot figure it out.” What little bit of bone?

Right leg, side view, ostrich…

This little bit of bone. Zooming in on that ostrich’s knee:

Who am I? (femur above; tibiotarsus below; “PTE” is the crest of bone with the white arrow on it)

The little bit of bone is not talked about much in the scientific literature on bird knees. But we know it’s there and it is part of the composite bone called the tibiotarsus (ancestral tibia, this bit of bone, and the proximal tarsal [ankle] bones on the other end; the astragalus and calcaneum of earlier dinosaurs).

What is it? We call it something like the proximal tibial epiphysis (PTE for short, here). An epiphysis is an end of a bone that fuses up with the shaft during growth, around the time of skeletal maturity; ultimately ending longitudinal (length-wise) growth of that bone. Mammals almost ubiquitously have them. So do lizards and tuataras. And some fossil relatives. Not much else– except birds, in this particular region (the two ends of the tibiotarsus; also in the foot region; the tarsometatarsus; which also has its share of mysteries such as the hypotarsus; I won’t go there today). You can see the PTE in mostly cartilaginous form if you take apart a chicken drumstick.

This PTE, like other well-behaving epiphyses, fuses with the tibiotarsus in mature birds, forming one bone. But the young ostrich’s knee above shows the PTE nicely; and other living birds show more or less the same thing.

It begs for explanations. I’ve talked about it in a few of my papers. But I’ve always punted on what it really means– does it have anything to do with the patella (they appear at similar times in evolution; we know that much, roughly)? Where does it come from, developmentally? (we sort of know that but more work is needed in different species and in high resolution) When did it evolve? What does it tell us? Why is it there in living birds and almost no other extinct birds/other dinosaurs? Does it have anything to do with why birds, during their evolution, seem to gradually increase the fusion of skeletal elements or ossify new ones (tendons, kneecaps, etc)? Why here and not in the femur or several other long bones of birds? How much do these PTEs vary between (or within) bird species?

This is the challenge in the post’s title. I present to you: solve this puzzle. Developmentally, biomechanically, evolutionarily, genetically, whatever– why does this PTE happen? There are hints– e.g. this paper proposes why growth rates of long bones favour the formation of “secondary centres of ossification” like this. But I’m unable to satisfy myself with any solutions I can find. Maybe you can complete The Bird Knee Challenge?

Have a go at it in the Comments below! There are plenty of papers or even a grant or something involved in sorting out this single mystery; one of the many basic mysteries about animal anatomy.

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Why do ostriches have two kneecaps in each knee?

Posted in Exalting Archosauria, Shiverin' Sesamoids!, tagged , , , , , , , on June 8, 2017| 1 Comment »

Uh oh, a “why?” question in biology! There are many potential, and not mutually exclusive, answers to such questions. Ultimately there is a historical, evolutionary answer that underpins it all (“ostriches evolved two kneecaps because…”). But we like ostrich knees and their funky double-kneecaps (patellae; singular = patella) so we wanted to know why they get so funky. One level of addressing that question is more like a “how?” they have them. So we started there, with what on the surface is a simple analysis. And we published that paper this week, with all of the supporting data (CT, MRI, FEA).

Stomach-Churning Rating: 6/10 because there is a gooey image of a real dissection later in the post, not just tidy 3D graphics.

First author Kyle Chadwick was my research technician for 2 years on our sesamoid evolution grant, and we reported earlier on the detailed 3D anatomy of ostrich knees (this was all part of his MRes degree with me, done in parallel with his technician post). Here, in the new paper with Sandra Shefelbine and Andy Pitsillides, we took that 3D anatomy and subjected it to some biomechanical analysis in two main steps.

Ostrich (right) knee bones. The patellae are the two knobbly bits in the knee.

First, we used our previous biomechanical simulation data from an adult ostrich (from our paper by Rankin et al.) to estimate the in vivo forces that the knee muscles exert onto the patellar region during moderately large loading in running (not maximal speed running, but “jogging”). That was “just” (Kyle may laugh at the “just”– it wasn’t trivial) taking some vectors out of an existing simulation and adding them into a detailed 3D model. We’ve done similar things before with a horse foot’s bones (and plenty more to come!), but here we had essentially all of the soft tissues, too.

Ostrich knee with muscles as 3D objects.

Second, the 3D model that the muscular forces were applied to was a finite element model: i.e., the original 3D anatomical model broken up into a mesh, whose voxels each had specific properties, such as resistance to shape change under loading in different directions. The response of that model to the loads (a finite element analysis; FEA) gave us details on the stresses (force/area) and strains (deformations from original shape) in each voxel and overall in anatomical regions.

Finite element model setup for our study. If you do FEA, you care about these things. If not, it’s a pretty, sciencey picture.

The great thing about a computer/theoretical model is that you can ask “what if?” and that can help you understand “how?” or even “why?” questions that experiments alone cannot address. Ostriches aren’t born with fully formed bony kneecaps; indeed those patellae seem to mature fairly late in development, perhaps well after hatching. We need to know more about how the patellae form but they clearly end up inside the patellar (knee extensor) tendon that crosses the knee. So we modelled our adult ostrich without bony patellae; just with a homogeneous patellar tendon (using the real anatomy of that tendon with the bony bits replaced by tendon); and subjected it to the loading environment for “jogging”.

The right knee of an ostrich hatchling. The patellae have yet to form; indeed there is little bone around the knee region at all, yet.

We then inspected our FEA’s results in light of modern theory about how tissues respond to loading regimes. That “mechanobiology” theory, specifically “tissue differentiation”, postulates that tendon will tend to turn into fibrocartilage if it is subjected to high compression (squishing) and shear (pushing). Then, the fibrocartilage might eventually be reworked into bone as it drops the compression and shear levels. So, according to that theory (and all else being equal; also ignoring the complex intermediate states that would happen in reality), the real ostrich’s kneecaps should be located in the same positions where the FEA, under the moderately large loads we applied, predicts the homogeneous tendon to have high compression and shear. But did the real anatomy match the mechanical environment and tissue differentiation theory’s predictions?

Tissue differentiation diagram displaying the theoretical pathways for transformation of tissues. If tendon (red) experiences high shear (going up the y-axis) and high compression (going toward the left), it should turn into fibrocartilage (purple). Transformation into bone (diagonally to the bottom right) would reduce the shear and compression.

Well, sort of. The image below takes some unpacking but you should be able to pick out the red areas on the bottom row where the patellae actually are, and the yellow shaded regions around some of those patellar regions are where the compression and shear regimes are indeed high and overlapping the actual patellar regions. The upper two rows show the levels of compression (or tension; pulling) and shear, but the bottom row gets the point across. It’s not a bad match overall for the first (“real”; common to all living birds) patella, located on top of the upper knee (femur). It’s not a good match overall for the second (unique to ostriches) patella, located below the first one (and attached to the tibia bone).

FEA results! (click to embiggen)

Kyle says, “Being a part of this project was exciting because of the application of engineering concepts to interesting biological (including evolutionary) questions. Also, it never gets old seeing people’s reactions when I tell them I study ostrich knees.”

The study had a lot of nuances and assumptions. We only looked at one instant in slow running and only at one adult ostrich, not at the full development of ostrich anatomy and loading. That’s harder. We started simple. The tissue differentiation theory is used more for fracture healing than for sesamoid bone formation but there’s some reason to suspect that similar mechanisms are at play in both. And there’s much more; if you want the gory details see the paper.

So did we solve why, or how, ostriches have two kneecaps? We felt that the mechanical environment of our FEA was a good theoretical explanation of where the first patella forms. We originally expected the second patella, which evolved more recently and might be more mechanically sensitive as a result, to be a better match than the first one, but it was the opposite. C’est la science!

Enough models, let’s have some reality! I warned you this post would get messy, and here it is. Left leg (skinned) of an ostrich showing the muscles around the knee. The patellar region would be in the gloved hand of the lucky individual shown.

This study, for me, was a fun experience in moving toward more fusion of “evo-devo” and biomechanical analyses, a research goal of mine lately– but there’s still a ways to go with the “how?” and “why?” questions even about ostrich kneecaps.

We felt that the best conclusion supported by our analyses was that, rather than have homogeneous stresses and strains throughout their knee tissues (e.g. the patellar tendon), ostriches have a lot of regional diversity in how those tissues are loaded (in the condition we modelled, which is adequately representative of some athletic exertion). Look at the complex FEA coloured results above again, the top two rows: there are a lot of different shades of compression/tension and shear; not homogeneous strains. That diversity of regional loading sets those tissues up for potential transformation throughout growth and development. And thus ONE of the reasons why ostriches might have two kneecaps is that the heterogeneous loading of their knee tendon favours formation of heterogeneous tissue types.

Another, compatible, explanation is that these different tissues might have consequences for how the muscles, tendon and joint operate in movement behaviours. In due time there will be more about that. In the meantime, enjoy the paper if this post makes you want to know more about the amaaaaaazing knees of ostriches!

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Open Tuatara

Posted in Anatomy Vignette, Shiverin' Sesamoids!, tagged , , , , , on November 25, 2016| 1 Comment »

A quick heads-up that we just posted on our sister blog Anatomy To You, about a new open-access paper we’ve published on the skeletal anatomy of the tuatara Sphenodon. Lots of cool images you can’t see anywhere else are there!

In focus: The big picture of little bones in tuatara

I give it a Stomach-Churning Rating of 3/10- some picked specimens of tuatara but they’re still cute, not nasty, I’d say.

AND, like the Cool-Whip or vanilla ice cream atop your leftover pumpkin pie, there’s an added delicious bonus: a huge dataset of microCT scans from 19 tuatara specimens, free to access here:

https://osf.io/bds35/

We are VERY pumped up about getting this paper and dataset released, so we are spreading the word as wide as we can!

Sayonara.

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Deck the ‘Nets With PeerJ Papers

Posted in Exalting Archosauria, tagged , , , , , , , , , on December 23, 2014| 7 Comments »

Deck the ‘Nets With PeerJ Papers— please sing along!

♬Deck the ‘nets with PeerJ papers,
Fa la la la la, la la la la.
‘Tis the day to show our labours,
Fa la la la la, la la la la.

Downloads free; CC-BY license,
Fa la la, la la la, la la la.
Read the extant ratite science,
Fa la la la la, la la la la.

See the emu legs before you
Fa la la la la, la la la la.
Muscles allometric’ly grew.
Fa la la la la, la la la la.

Follow the evolvin’ kneecaps
Fa la la la la, la la la la.
While we dish out ratite recaps 
Fa la la la la, la la la la.

Soon ostrich patellar printing
Fa la la la la, la la la la.
Hail anat’my, don’t be squinting
Fa la la la la, la la la la.

Dissections done all together
Fa la la la la, la la la la.
Heedless of the flying feathers,
Fa la la la la, la la la la♪

(alternate rockin’ instrumental version)

Stomach-Churning Rating: 5/10: cheesy songs vs. fatty chunks of tissue; there are no better Crimbo treats!

Today is a special day for palaeognath publications, principally pertaining to the plethora of published PeerJ papers (well, three of them anyway) released today, featuring my team’s research! An early Crimbo comes this year in the form of three related studies of hind limb anatomy, development, evolution and biomechanics in those flightless feathered freaks of evolutionary whimsy, the ratites! And since the papers are all published online in PeerJ (gold open access), they are free for anyone with internet access to download and use with due credit. These papers include some stunning images of morphology and histology, evolutionary diagrams, and a special treat to be revealed below. Here I’ll summarize the papers we have written together (with thanks to Leverhulme Trust funding!):

1) Lamas, L., Main, R.P., Hutchinson, J.R. 2014. Ontogenetic scaling patterns and functional anatomy of the pelvic limb musculature in emus (Dromaius novaehollandiae). PeerJ 2:e716 http://dx.doi.org/10.7717/peerj.716 

My final year PhD student and “emu whisperer” Luis Lamas has published his first paper with co-supervisor Russ Main and I. Our paper beautifully illustrates the gross anatomy of the leg muscles of emus, and then uses exhaustive measurements (about 6524 of them, all done manually!) of muscle architecture (masses, lengths, etc.) to show how each of the 34 muscles and their tendons grew across a more than tenfold range of body mass (from 6 weeks to 18 months of age). We learned that these muscles get relatively, not just absolutely, larger as emus grow, and their force-generating ability increases almost as strongly, whereas their tendons tend to grow less quickly. As a result, baby emus have only about 22% of their body mass as leg muscles, vs. about 30% in adults. However, baby emus still are extremely athletic, more so than adults and perhaps even “overbuilt” in some ways.

This pattern of rapidly growing, enlarged leg muscles seems to be a general, ancestral pattern for living bird species, reflecting the precocial (more independent, less nest-bound), cursorial (long-legged, running-adapted) natural history and anatomy, considering other studies of ostriches, rheas, chickens and other species close to the root of the avian family tree. But because emus, like other ratites, invest more of their body mass into leg muscles, they can carry out this precocial growth strategy to a greater extreme than flying birds, trading flight prowess away for enhanced running ability. This paper adds another important dataset to the oft-neglected area of “ontogenetic scaling” of the musculoskeletal system, or how the locomotor apparatus adapts to size-/age-related functional/developmental demands as it grows. Luis did a huge amount of work for this paper, leading arduous dissections and analysis of a complex dataset.

Superficial layer of leg muscles in an emu, in right side view.

Superficial layer of leg muscles in an emu, in right side view. Click any image here to emu-biggen. The ILPO and IC are like human rectus femoris (“quads”); ILFB like our biceps femoris (“hams”); FL, GM and GL much like our fibularis longus and gastrocnemius (calf) muscles, but much much bigger! Or, perhaps FL stands for fa la la la la?

Data for an extra set of emus studied by coauthor Russ Main in the USA, which grew their muscles similarly to our UK group. The exponents (y-axis) show how much more strongly the muscles grown than isometry (maintaining the same relative size), which is the dotted line at 1.0.

Data for an extra set of emus studied by coauthor Russ Main in the USA, which grew their muscles similarly to our UK group. The exponents (y-axis) show how much more strongly the muscles grew than isometry (maintaining the same relative size), which is the dotted line at 1. The numbers above each data point are the # of individuals measured. Muscle names are partly above; the rest are in the paper. If you want to know them, we might have been separated at birth!

2) Regnault, S., Pitsillides, A.A., Hutchinson, J.R. 2014. Structure, ontogeny and evolution of the patellar tendon in emus (Dromaius novaehollandiae) and other palaeognath birds. PeerJ 2:e711 http://dx.doi.org/10.7717/peerj.711

My second year PhD student Sophie Regnault (guest-blogger here before with her rhino feet post) has released her first PhD paper, on the evolution of kneecaps (patellae) in birds, with a focus on the strangeness of the region that should contain the patella in emus. This is a great new collaboration combining her expertise in all aspects of the research with coauthor Prof. Andy Pitsillides‘s on tissue histology and mine on evolution and morphology. This work stems from my own research fellowship on the evolution of the patella in birds, but Sophie has taken it in a bold new direction. First, we realized that emus don’t have a patella– they just keep that region of the knee extensor (~human quadriceps muscle) tendon as a fatty, fibrous tissue throughout growth, showing no signs of forming a bony patella like other birds do. This still blows my mind! Why they do this, we can only speculate meekly about so far. Then, we surveyed other ratites and related birds to see just how unusual the condition in emus was. We discovered, by mapping the form of the patella across an avian family tree, that this fatty tendon seems to be a thing that some ratites (emus, cassowaries and probably the extinct giant moas) do, whereas ostriches go the opposite direction and develop a giant double-boned kneecap in each knee (see below), whereas some other relatives like tinamous and kiwis develop a more “normal”, simple flake-like bit of bone, which is likely the state that the most recent common ancestor of all living birds had.

There’s a lot in this paper for anatomists, biomechanists, palaeontologists, ornithologists, evo-devo folks and more… plenty of food for thought. The paper hearkens back to my 2002 study of the evolution of leg tendons in tetrapods on the lineage that led to birds. In that study I sort of punted on the question of how a patella evolved in birds, because I didn’t quite understand that wonderful little sesamoid bone. And now, 12 years later, we do understand it, at least within the deepest branches of living birds. What happened further up the tree, in later branches, remains a big open subject. It’s clear there were some remarkable changes, such as enormous patellae in diving birds (which the Cretaceous Hesperornis did to an extreme) or losses in other birds (e.g., by some accounts, puffins… I am skeptical)– but curiously, patellae that are not lost in some other birds that you might expect (e.g., the very non-leggy hummingbirds).

Fatty knee extensor tendon of emus, lacking a patella. The fatty tissue is split into superficial (Sup) and deep regions, with a pad corresponding to the fat pad in other birds continuous with it and the knee joint meniscus (cushioning pad). The triceps femoris (knee extensor) muscle group inserts right into the fatty tendon, continuing over it. A is a schematic; B is a dissection.

Fatty knee extensor tendon of an emu, showing the absence of a patella. The fatty tissue is split into superficial (Sup) and deep regions, with a pad corresponding to the fat pad in other birds continuous with it and the knee joint meniscus (cushioning pad). The triceps femoris (knee extensor) muscle group inserts right into the fatty tendon, continuing on over it. A is a schematic; B is a dissection.

Sectioning of a Southern Cassowary's knee extensor tendon, showing: A Similar section as in the emu image above. revealing similar regions and fibrous tissue (arrow), with no patella, just fat; and B, with collagen fibre bundles (col), fat cells (a), and cartilage-like tissue (open arrows) labelled.

Sectioning of a Southern Cassowary’s knee extensor tendon, showing: A, Similar section as in the emu image above. revealing similar regions and fibrous tissue (arrow), with no patella, just fat; and B, With collagen fibre bundles (col), fat cells (a), and cartilage-like tissue (open arrows) labelled.

Evolution of patellar form in birds. White branches indicate no patella, blue is a small flake of bone for a patella, green is something bigger, yellow is a double-patella in ostriches, and grey is uncertain. Note the uncertainty and convergent evolution of the patella in ratite birds, which is remarkable but fits well with their likely convergent evolution of flightlessness and running adaptations.

Evolution of patellar form in birds. White branches indicate no patella, blue is a small flake of bone for a patella, green is something bigger, yellow is a double-patella in ostriches, black is a gigantic spar of bone in extinct Hesperornis and relatives, and grey is uncertain. Note the uncertainty and convergent evolution of the patella in ratite birds (Struthio down to Apteryx), which is remarkable but fits well with their likely convergent evolution of flightlessness and running adaptations.

3) Chadwick, K.P., Regnault, S., Allen, V., Hutchinson, J.R. 2014. Three-dimensional anatomy of the ostrich (Struthio camelus) knee joint. PeerJ 2:e706 http://dx.doi.org/10.7717/peerj.706

Finally, Kyle Chadwick came from the USA to do a technician post and also part-time Masters degree with me on our sesamoid grant, and proved himself so apt at research that he published a paper just ~3 months into that work! Vivian Allen (now a postdoc on our sesamoid bone grant) joined us in this work, along with Sophie Regnault. We conceived of this paper as fulfilling a need to explain how the major tissues of the knee joint in ostriches, which surround the double-patella noted above, all relate to each other and especially to the patellae. We CT and MRI scanned several ostrich knees and Kyle made a 3D model of a representative subject’s anatomy, which agrees well with the scattered reports of ostrich knee/patellar morphology in the literature but clarifies the complex relationships of all the key organs for the first time.

This ostrich knee model also takes Kyle on an important first step in his Masters research, which is analyzing how this morphology would interact with the potential loads on the patellae. Sesamoid bones like the patella are famously responsive to mechanical loads, so by studying this interaction in ostrich knees, along with other studies of various species with and without patellae, we hope to use to understand why some species evolved patellae (some birds, mammals and lizards; multiple times) and why some never did (most other species, including amphibians, turtles, crocodiles and dinosaurs). And, excitingly for those of you paying attention, this paper includes links to STL format 3D graphics so you can print your own ostrich knees, and a 3D pdf so you can interactively inspect the anatomy yourself!

(A) X-ray of an ostrich knee in side view, and (B) labelled schematic of the same.

Ostrich knee in side view: A, X-ray, and (B) labelled schematic.

3D model of an ostrich knee, showing: A, view looking down onto the top of the tibia (shank), with the major collateral ligaments (CL), and B, view looking straight at the front of the knee joint, with major organs of interest near the patella, sans muscles.

3D model of an ostrich knee, showing: A, View looking down onto the top of the tibia (shank), with the major collateral ligaments (CL), and B, View looking straight at the front of the knee joint, with major organs of interest near the patella, sans muscles.

You can view all the peer review history of the papers if you want, and that prompts me to comment that, as usual at PeerJ (full disclosure: I’m an associate editor but that brings me £0 conflict of interest), the peer review quality was as rigorous at a typical specialist journal, and faster reviewing+editing+production than any other journal I’ve experienced. Publishing there truly is fun!

Merry Christmas and Happy Holidays — and good Ratite-tidings to all!

And stay tuned- the New Year will bring at least three more papers from us on this subject of ratite locomotion and musculoskeletal anatomy!

♬Should auld palaeognathans be forgot, 
And never brought for scans? 
Should publications be soon sought, 
For auld ratite fans!♪

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I Never Met A Fella Who Didn’t Like a Good Patella

Posted in Exalting Archosauria, Shiverin' Sesamoids!, tagged , , , , on November 24, 2013| 21 Comments »

Here, I give you a long-planned post on the patella (“kneecap bone”) of birds, which was my Royal Society Senior Research Fellowship sabbatical project for 2012-13. This is only a brief introduction to the anatomical issues at hand, err, I mean at knee…

Stomach-Churning Rating: 6/10; mostly skeletons/fossils, but there are a few images of the dissection of a guineafowl, which is fresh and meaty.

Archaeopteryx, the Berlin specimen. Helluva fossil, but nary a patella!

Archaeopteryx, the Berlin specimen. Helluva fossil, but nary a patella!

The question I am exploring, first of all, is simply how the patella evolved, because it seems to be present in almost all living birds. However, it is absent in all non-avian dinosaurs, and indeed most Mesozoic birds, too. There is barely a hint of any precursor structure (a “patelloid”) in other reptiles, but lizards evolved their own patella that is quite different (a flattened lozenge, not a rectangular structure lying tightly confined in a “patellar groove” on the femur as it is in birds). Mammals evolved the knobbly, hemispherical kind of kneecap that we’re familiar with, possibly on several occasions (a different story!). So the patella evolved at least three times in the lizard, mammal and bird lineages– and possibly more than once in each of these groups. And that’s about it for almost 400 million years of tetrapod evolution, except for a few very rare instances in fossils and sort-of-patella-like things in some frogs or other weirdos.

Fossil birds exhibit no clear presence of a patella until we come very close to modern birds on the avian stem of the tree of life (see below). And then, suddenly in modern birds, there is a lot of variation and not much good documentation of what kind of patella exists. This makes it challenging to figure out if the patella is ancient for modern birds or if it evolved multiple times, or how it changed after it first evolved– let alone bigger questions of what the patella was “for” (performance benefits, functional consequences, etc.; and developmental constraints) in the birds that first evolved it.

Considering that the patella is such an obvious bone in some birds, and certainly affects the mechanics of the knee joint (forming a lever for the muscles that cross it; homologous to our quadriceps muscles) and hence locomotion, it is a compelling research topic for me.

What follows is a pictorial guide to the patella of some birds, in sort of an evolutionary/temporal sequence (see my earlier post for a recap of some major groups), with a focus on animals I’ve studied more intensively so far (with >10,000 species, there is a lot that could be done):

Gansus, IVPP V15080
The early Cretaceous bird Gansus (from the IVPP in Beijing), represented by many beautifully preserved specimens, all of which lack a patella. This absence is characteristic of other stunningly preserved fossil Chinese birds, indicating that this is almost certainly an ancestral absence of a patella, until…

The famed Cretaceous diving (flightless) bird Hesperornis, from Wikipedia/Smithsonian.  Note the massive, conical/crested patella in front of the  knee (jutting up and overlapping the ribs/vertebrae close to the pelvis; see also below). That elongate patella is characteristic of many diving birds that use foot-propelled swimming; it has evolved many times in this fashion. Other hesperornithiform birds show some transformational states in their anatomy toward this extreme one.
Hesp-patella

Check this out! More Hesperornis (cast), with the femur on the left and the patella on the right. The bloody patella is almost as long as the femur! That’s nuts. With kind permission from the Natural History Museum, London.

Exhibited ostrich skeleton in left side view showing the patella (white arrow).
Exhibited ostrich (Struthio camelus) skeleton in left side view showing the patella (white arrow), on exhibit atThe Natural History Museum at Tring, Hertfordshire, UK. Ostriches are remarkable in that they have this elongate patella (actually a double patella; there is a smaller, often-overlooked second piece of bone) and yet are rather basal (closer to the root of the modern avian family tree)– however, they obviously are specialized in ways other than this double patella, most notably their very large size, flightlessness, and elongate legs. So the unusual patella is more likely linked to their odd lifestyle than a truly primitive trait, at least to some degree (but stay tuned: what happened with the patella in other members of their lineage, the ratites/palaeognaths, is much less well understood!).
Note that ostriches and Hesperornis together hint that the presence of a patella might have been an ancestral trait for living birds, but their patellae are so different that the ancestral state from which they evolved must have been different, too; perhaps simpler and smaller. Hence we need to look at other birds…
Skinned right leg of guineafowl, Numida meleagris.
Skinned right leg of a Helmeted Guineafowl, Numida meleagris, above. That whitish band of tissue in the middle of the screen, on the front of  the knee, is part of what is concealing the patella. That is an aponeurosis (connective tissue sheet, like a thin tendon) of the muscles corresponding to our “quads” or our tensor fascia latae, detailed more below. Guineafowl are fairly basal and well-studied in terms of their bipedal locomotion, so they are an important reference point for avian form and function.
Right guinefowl leg, with patella semi-exposed.
Right guineafowl leg, with patella exposed. Here I’ve peeled away that white band of tissue  and associated muscles, which have been reflected toward the bottom of the screen (AIL and PIL labels corresponding to the anterior and posterior parts of the Iliotibialis lateralis muscle). The tip of the scalpel is contacting the patella. It’s not much to see, but lies atop the bright yellow fat pad that cushions it against the femur. You should be able to see a groove in the end of the femur just above that fat pad, which is where the patella sits and slides up and down as the knee moves/muscles contract. This is called the patellar groove, or sulcus patellaris.
Left leg of a guineafowl (with right tibiotarsus behind it) showing both patellae in articulation; in medial (inside) view. The patella is the little rectangular bit of bone in the top middle of the screen, interposed between femur and tibiotarsus.
Left leg of another guineafowl (with right tibiotarsus behind it, on the left) showing the patellae in articulation; in medial (inside) and cranial (front) views, respectively. The patella is the little rectangular bit of bone in the top middle of the screen, interposed between femur (thigh) and tibiotarsus (shank). With kind permission from the Natural History Museum, London.  
Penguin-patella
Right leg of a Cape Penguin (Spheniscus demersus) from the University Museum of Zoology in Cambridge, showing the big lumpy patella in this wing-propelled diver. They still walk long distances on land, so presumably a patella plays some role in their gait, helping to explain its large size, which like the ostrich and Hesperornis seems to be a novel trait. Notice the groove across the patella, made by the tendon of the ambiens (like our sartorius/”tailor’s muscle”), which crosses from the inside to the outside of the leg via this route. This groove is often considered a useful phylogenetic character in modern birds, as its contact with the patella (sometimes via a hole, or foramen) varies a lot among species.
Buceros skeleton UMZC
A hornbill, Buceros sp., from the UMZ Cambridge museum as well. This displays the possibly-more-typical, little rounded patellar nubbin that many birds have. See below for more.

Buceros knee closeupCloseup of the knee/patella of the hornbill, Buceros sp., from above. Not much to squawk about, patella-wise, but it’s there.

And so we complete our quick tour of the avian patella, in its grand variation and humble beginnings.

Why does an ostrich have a patella and a Tyrannosaurus, Edmontosaurus or Triceratops did not? Why were birds the only bipedal lineage to evolve a patella (mammals and lizards gained a patella as small quadrupeds), and why did some bipeds like kangaroos “lose” (reduce to fibrous tissue, apparently) their patella?

These are the kinds of mysteries my group will now be tackling, thanks to a generous Leverhulme Trust grant on sesamoid bone ontogeny, mechanics and evolution.  My group is now Dr. Vivian Allen as the postdoc, Sophie Regnault as the PhD student, and Kyle Chadwick as the technician and MRes student, along with numerous collaborators and spin-off projects. We’re looking forward to sharing more! But for now, I hope that I’ve engendered some appreciation for the avian patella, as the silly title indicates (“fella” used in the general sense of anyone!). This work is all unpublished, but some of this should be out in not too long, in much more lavish detail! Much as the patella is the “forgotten lever “of the avian hindlimb, it is the fulcrum about which a substantial part of my research group’s activity now pivots.

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A Chance Encounter with Darwin’s Chickens. And Cake.

Posted in Exalting Archosauria, Geeking Out, Museums are Cool, tagged , , , , , , , on May 14, 2013| 8 Comments »

Bovids to the right of me, pinnipeds above, what's a guy to do but squee?

Bovids to the right of me, pinnipeds above, what’s a guy to do but squee?

I’ve been doing some osteological studies of the patella (bone in the major tendon in front of the knee; termed a sesamoid) that have included frequent visits to the Natural History Museum’s avian skeleton collection at Tring. It’s a cute little town, northeast of London, in the green county of Hertfordshire where I live and work. The museum at NHM-Tring is a great old school multi-storey display packed with skeletons and stuffed animals in dark wood cabinets, with many critters hanging from wrought iron railings or other suspensions above (see above). I blogged about the Unfeathered Bird exhibit (and book) that just finished up its tour there yesterday. And I’ll be blogging later, as I keep promising, about the cool things I’ve learned during the past year of my studies of the form, function, development and evolution of the patella.

As an aside, I heartily recommend doing research at the NHM-Tring. It’s away from the bustle (and arduous Tube trip) of the South Kensington NHM, and the curatorial staff are immensely helpful… and there is something else that makes the trip even more enjoyable, but you must read more below to find out about it.

Stomach-Churning Rating: 2/10; 150-year-old dry bones. But an advance warning to (1) diabetics and (2) pun-haters, for reasons that will become evident.

Dr Heather Paxton and Dr Jeffrey Rankin, postdoc researchers working on our collaborative BBSRC chicken biomechanics grant (see thechickenofthefuture.com), explain their science to an attentive Darwin.

Dr Heather Paxton and Dr Jeffery Rankin, postdoc researchers working on our collaborative BBSRC chicken biomechanics grant (see thechickenofthefuture.com), use the Structure & Motion Lab whiteboard to explain their science to an attentive Darwin.

Today I have a short pictorial exhibit of something wonderful I ran into while patellavating in the NHM collections. As often happens while doing museum research, I had a serendipitous encounter with a bit of history that blew my mind a little, and had me geeking out. These things happen because museum collections are stuffed with specimens that, to the right eyes or the right mindset, pack a profound historical whallop. As a scientist who is pretty keen on chickens (Gallus gallus), there are probably no museum specimens of chickens that would get me more excited about than the chickens Darwin studied in his investigations of artificial selection. In fact, most museum specimens of domestic chickens would not be that interesting to me, especially after seeing these ones.

Darwin wielded the analogy between artificial selection and his conceptual mechanism of natural selection in the first ~4 chapters of On the Origin of Species to clobber the reader with facts and try to leave them with no doubt that, over millennia, nature could craft organisms in vastly more complex and profound ways than human breeders could mould them over centuries. While people most often speak of Darwin’s pigeons when referring to Darwin and avians or artificial selection and variation, his chickens appear in The Origin and other writings quite often, too (most prominently, The Variation of Animals and Plants Under Domestication in 1868– more about that here). For example, from my 1st edition facsimile of The Origin from Harvard University Press, pp. 215-216:

“Natural instincts are lost under domestication… It is not that chickens have lost all fear, but fear only of dogs and cats, for if the hen gives the danger-chuckle, they will run… and conceal themselves in the surrounding grass or thickets; and this is evidently done for the instinctive purpose of allowing, as we see in wild ground-birds, their mother to fly away. But this instinct retained by our chickens has become almost useless under domestication, for the mother-hen has almost lost by disuse the power of flight.”

Well told, Mr D!

I am also reminded of how chickens and Darwin have had darker relationships, such as this sad story. Or how evolution via Darwinian mechanisms crosses paths with pop culture in fowl ways, such as how tastes-like-chicken evolved, or how some say that chickens, over great periods of time, have been naturally selected in such a way that they are now heritably predisposed to cross roads, or that the amniote egg preceded the evolution of the genus Gallus by some 325+ million years. I see I am drifting and drifting further away from the topic at hand, so let me segue back to Darwin’s chickens. We’ll take this corridor there:

Inside the avian osteology collection at Tring. Sterlie at it might seem, places like this are fertile breeding grounds for scientific discovery.

Inside the avian osteology collection at Tring. Sterile at it might outwardly seem, places like this are fertile breeding grounds for scientific discovery. And a sterile-looking collection means well cared-for specimens that will persevere for future discoveries.

So anyway, when museum curator Jo Cooper said to me something like “I have some of Darwin’s chickens out over on the other counter, do you want to have a look or shall I put them away?” my answer was quick and emphatic. YES! But only after lunch. I was hungry, and nothing stops me from sating that hunger especially when the sun is out and there are some fine pubs within walking distance! I settled on the King’s Arms freehouse, and had a delicious cheeseburger followed by a spectacularly good apple-treacle-cake with ice cream, expediently ingested while out on their sunny patio. Yum! I cannot wait to have that cake again. What a cake! Darwin’s bushy eyebrows would have been mightily elevated by the highly evolved flavour, which would have soothed his savage stomach ailments. He would have been like:

“Damn, Emma! Holy s___ this is great apple-cake; here, try some! There is grandeur in this tasty cake, with its several flavours, having been originally cooked into a few baking trays or into one; and that, whilst this pub has gone on serving fine food according to the fixed hygiene laws of Tring, from so simple a beginning endless foods most beautiful and most wonderful have been, and are being, devoured.” And Emma, cake then firmly in hand, would have said something like, “My dear Charles, I shall try this enticing dessert, and I am glad to see you so enthused about something other than barnacles. Write a letter to Huxley or Lyell about that cake later. You need to focus on concocting an ending to that big species book of yours, not cakes. It’s been 20 bloody years, dude; cake can wait. End the book on a high note.” And so it must have happened.

Working at a museum collection is like having an extra home/office for a day or more. You get familiar with the environment while working there, and start to settle in and enjoy the local environs while taking work breaks. Or I do, anyway. So this post is also partly about how cake and other provisions are an important part, or even a perk, of life as a visiting museum researcher. Put in some good solid work, then it’s cake time, but where are the cakes? You explore, and you discover them– opening the door of an unfamiliar shop or pub near a museum can be like opening a museum cabinet to discover the goodness inside. Just don’t get them mixed up. Museum specimens: for research; subjects for science. Cakes: for eating; fuel for scientists. Got it?

But I digest digress. This post is not about my lunch. Not so much, anyway, although I did enjoy the cake quite a bit. Back to the chickens. Here, try some!

Darwins-chickens (1)Darwins-chickens (6)

Darwins-chickens (5) Darwins-chickens (4)

Above: Views of Darwin’s chickens laid out at the NHM-Tring.  (all photos in this post can be clucked to emchicken them)

The chickens, much like the pub lunch, did not disappoint in the least. Here I had before me Darwin’s own personal specimens, which I envisioned him dissecting and defleshing himself, studying them in deep introspection, then handing them over to the museum for curation once his lengthy researches were complete (all the ones I studied dated back to around 1863-1868, so they were curated shortly after The Origin was published (1859)). Perhaps the museum gave him some fine sponge-cake in return. There was at least one male and female adult of each of numerous breeds, many of them still bearing the dried flesh of centuries past. This was great for me, as the patella often gets removed and clucked chucked in the bin with its tendon when museum specimens of birds are prepared (much as elephant “sixth toe” sesamoids are). All of the specimens had their honking huge patellae on display, so that’s what a lot of my photos feature. I do so lament that I did not take a photo of the cake. Did I tell you about that cake? Oh… Check out these examples of Darwin’s chickens:

XXXX breed in right side view, with the patella indicated by a red arrow. It is still attached to the tibiotarsus by the patellar tendon (often misnamed the patellar "ligament", but it is just a continuation of the proximal tendon).

African rooster (wild variety? Darwin’s label was not clear) in right side view, with the patella indicated by a red arrow. That patella is still attached to the tibiotarsus by the patellar tendon (often misnamed the patellar “ligament”, but it is just a continuation of the proximal tendon).

Darwin's handwritten label and the well-endowed patella of the Spanish Cock. What? Oh, you. Stop it.

Darwin’s handwritten label and the well-endowed patella of the Spanish Cock. What? Oh, you. Stop it. That has nothing to do with cake, and only cake-related humour is allowed in this post.

Some other fascinating features exhibited by Darwin’s chickens, which he doubtless mulled over while nibbling on fine cakes, included the following:

The hindlimb of a Polish Silver Laced breed, nicely showing the ossified tendons (red arrow) along the tarsometatarsus. Why these tendons turn into bone is one of the great unsolved mysteries of bone biology/mechanics and avian evolution. Check out the famed feather crest here.

The hindlimb of a Polish Silver Laced breed, nicely showing the ossified tendons (red arrow) along the tarsometatarsus. Why these tendons turn into bone is one of the great unsolved mysteries of bone biology/mechanics and avian evolution.

Check out the famed feather crest of the Silver (Laced) Polish here; it gets so extreme in males that they have a hard time seeing, and can get beaten up by other cockerels when kept in mixed breed flocks.

Here on this blog, and of course on the companion blog “Towards the Chicken of the Future,” domestic chickens and wild junglefowl have often come up, most recently with the Dorking Chicken (another of Darwin’s own specimens that I studied) in the “Mystery Museum Specimen” poetry round of late. Dorkings are HUGE chickens; easily twice the weight of even a broiler chicken, up to 4-5kg. The Dorking-characteristic polydactyly featured in that post is also observed at a relatively high incidence in Silkie and Sultan breeds, I’ve learned. Like this one! (I was so patella-focused, or cake-somnolescent, that I missed it while studying at the museum and only noticed it now while browsing through my photos, bereft of cake)

Nice leg of a Sultan hen. There is an extra toe here as in the Dorking chicken; a duplicate hallux (first toe). This is not, as it might at first seem, a pathological condition as in modern "twisted toe"-suffering domestic chickens.

Nice leg of a Sultan hen. There is an extra toe here as in the Dorking chicken; a duplicate hallux (first toe). This is not, as it might at first seem, a pathological condition as in modern “twisted toe”-suffering domestic chickens.

Malays are another giant breed like the Dorking, but with longer and more muscular legs and longer necks, looking much more like a classic, badass wild junglefowl than a fancy, pampered chicken. But here, undressed to the bare bones, it just looks like a skinny chicken leg, albeit perhaps a bit svelte compared to the Dorking or Sultan.

Hindlimb of a Malay breed of chicken, which Wikipedia nicely tells the story of its misnomer (it may originate from Pakistan, not Malaysia!). Can you find the nice patella? Check out Darwin's lovely label, too.

Hindlimb of a Malay breed of chicken, which Wikipedia nicely tells the story of its misnomer (it may originate from Pakistan, not Malaysia!). Can you find the nice patella? Check out Darwin’s lovely label, too.

You may have come across wild-eyed news stories 5 years ago about “OMG Darwin was sooooooo wrong about chickens!”, referring to his writings on the origin of domestic chickens from Red junglefowl. As Greg Laden adeptly wrote, Darwin (say it with me) didn’t really get it very wrong after all. He did quite well, in fact. Some media outlets did get it more wrong, probably inspired by this press release. Oh well; the science they were reporting about definitely was interesting- modern chickens seem to have some of their yellow skin pigmentation-related genes from Grey junglefowl, although they are still largely descendants of Red junglefowl.

Here, have a JUMBLE-fowl, or rather a junglefowl cockerel, with another Darwin label:

Darwin's example of a wild-type chicken; a Red Junglefowl. As he suspected, these Asian birds were the ancestors of domestic chickens, but today evidence suggests that domestication occurred multiple times in Asia and with different wild varieties of junglefowl bred/mixed in different regions.

Darwin’s example of a wild-type chicken; a Red junglefowl. As he suspected, these Asian birds were the ancestors of domestic chickens, but today evidence indicates that domestication may have occurred multiple times in Asia and with different wild varieties of junglefowl bred/mixed in different regions.

Some breeds aren’t so funky inside, of course, but just have cool feather patterns on the outside, like the “pencilling” (dark streaks on white feathers) evident in pencil breeds; also called triple-laced. Like this fine chap below once would have had, before Darwin tore off his feathers and reduced him to a research-friendly naked skeleton:

A Golden Pencil Hamburgh breed of chicken (cockerel), whose skeleton features the leg and a fine articulated patella.

A Golden Pencil(led) Hamburg breed of chicken (cockerel), whose skeleton features the leg and a fine articulated patella.

Also known as the Holland Fowl, several European countries including the UK claim the Hamsburg as an original breed from their respective realm, and no surprise they do- it’s a lovely spangled chicken. Then, later in the 1800’s the Americans got involved in breeding them, too, and it’s all a big mess. They should get together, have some delectable cakes, and just sort it out.

Scaly, still-greasy foot and hindlimb of what Darwin labelled as the male of a "Game" breed.

Scaly, still-greasy foot and hindlimb of what Darwin labelled as the male of a “Game” breed.

We thus close with another leg of another chicken. Darwin was a bit naughty here, or else terminology of breeds has changed a lot since the 1850’s (very possible), as he just labelled this as a “Game” cockerel. Now, Gamefowl is a big category of breeds. I’m guessing this one was either (1) a Cornish/Indian Game variety or (2) an Old or Modern English Game Fowl. Maybe a person who knows their chicken breeding far better than me (that’s not hard!) will opine differently. The latter varieties were popular in Darwin’s time — the (Muffed) Old English version was mated with other breeds (Malay?) to produce the Modern English form as cockfighting “sports” became banned in 1849 and breeder attentions shifted to the polar opposite of producing showy, fancy birds instead. And thus the bufante, feathered-hair-adorned 1980s pop-rock group was created, to sing about mating or moulting or melting with people or something terribly disgusting and probably having nothing at all to do with chickens,  cake, or cockfighting, or other more seemly pursuits.

So, we have come to the end of my photos of Darwin’s chicken leg bones and such. If you’ve learned something here about chicken breeds, patellae, cake, or Darwin, that’s simply frabjous. Enough of those poncey pigeons, already! I’m crying fo… no, I won’t use that pun. Nevermind. Not even remotely cake-related. Let’s give Darwin’s chickens their just desserts, is the point– and a much better pun, too. Darwin’s chickens are an important part of Darwiniana, and an interesting evolutionary study in and of themselves. I’ve certainly become impressed during my researching for this blog post by the diverse, fascinating biology of chicken breeds. My copy of the “Complete Encyclopedia of Chickens” will be getting some more thorough reading shortly.

Today, however, I am off to return to the NHM-Tring and peruse their other, non-chickeny Galliformes and Anseriformes, with a detour to the mythical hoatzin. But… but… there may be a cake detour involved, too. I shall report back in due course. Off I go!

No, hopefully not that cake.

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Come do a heavily freezer-based PhD studentship with me!

Posted in Shiverin' Sesamoids!, tagged , , , , , , on October 30, 2012| 9 Comments »

A short(ish) post, but to me an important one. As I’ve mentioned here before, and still mean to write a detailed post on, I’m on a 1-year Royal Society Leverhulme Trust senior research fellowship (pause to breathe… long phrase there!) to study the mechanics and evolution of the kneecap (patella) in birds. Knees are very cool, and the patella is one of the coolest parts of the knee. My fellowship is aimed at returning to my roots, i.e. my PhD research on theropod dinosaur hindlimb evolution (anatomical and functional), to focus in great detail on just the patella (this, not this).

The patella is a mysterious structure: a sesamoid bone like I’ve argued elephant predigits are, and probably the best known sesamoid, but still quite enigmatic– especially in non-humans and most particularly in non-mammals. Why did it evolve three different times, at least? What mechanical/developmental environment encourages it to form? Why don’t some species have them? Does the presence of a patella tell us anything about posture, gait, or anything else? Why did no giant dinosaurs evolve patellae?

Anyway, I now have a related PhD studentship that I need a great EU/UK-based student to apply for, and I’m casting a wide net. It’s a very, very freezer-based PhD: imagine cutting up the knees of the frozen zoo of critters that I’ve shown on this blog already, to your heart’s content! And studying fossils, and doing histology (cool imaging techniques with RVC faculty Michael Doube and Andy Pitsillides, along with bone uber-guru Alan Boyde), and conducting experiments with real animals, and computer modelling both experimental and fossil data… this PhD has it all.

Here are the details. If you know anyone in the EU/UK looking for a good PhD that seems to fit the bill very well, send them my way please!

We now return you to your regularly scheduled frozen organisms… and there is a fun post coming tomorrow!

The knee of an emu from my freezer, showing the many muscles and other tissues that connect to or surround the patella. It’s complicated, and that makes for fun science!

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