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Posts Tagged ‘dissection’

I’ve described our “Walking the Cat Back” Leverhulme Trust-funded project with Dr. Anjali Goswami and colleagues before, but today we really got stuck into it. We’re dissecting a 46kg male Snow Leopard (Panthera uncia) as the first “data point” (actually several hundred data points, but anyway, first individual) in our study of how limb and back muscles change with size in felids. No April Fools’ pranks here; real science-as-it-happens.

Stomach-Churning Rating: 7/10 for skinned leopard and globs of fat. Much worse in person, hence the downgrading from what could be a higher score. Don’t click the photos to emkitten them if you don’t want to see the details.

This leopard is the same one that Veterinary Forensics blogged about. It died in a UK cat conservation/recovery centre. Today is simply a short post, but it is the first in what will surely be a continued series of posts on felid postcranial anatomy and musculoskeletal biomechanics by our felid research team, with bits of natural history and evolution thrown in when we can manage. As befits one of my curt “Anatomy Vignette” posts, pictures will tell the story.

Skinned and mostly de-fatted snow leopard, with fat piled up on the lower left hand corner near the hind feet. Here we are identifying and then removing and measuring the individual muscles. Project postdoc Andrew Cuff is hard at work on the forelimb while I'm mucking around with the hindlimb.

Skinned and mostly de-fatted snow leopard, with fat piled up on the lower left hand corner near the hind feet. Here we are identifying and then removing and measuring the individual muscles. Project postdoc Andrew Cuff is hard at work on the forelimb while I’m mucking around with the hindlimb. The fat here is about 3kg subcutaneous fat, so around 6.5% of body mass. And as the cat has been around for a while, that fat has gone a bit rancid and that is not nice. Not nice at all, no… Usually smells do not bother me, but this took some adjustment. Fortunately, the muscles are still OK, and work is coming along well.

UCL PhD student Marcela Randau,, carving up our cat's limb muscles. As usual in comparative biomechanics, we measure the "architecture"- parameters of the muscle that relate in a somewhat straightforward fashion to function.

UCL PhD student Marcela Randau, carving up our cat’s limb muscles. As usual in comparative biomechanics, we measure the “architecture”- parameters of the muscle that relate in a somewhat straightforward fashion to function. This muscular architecture includes things like muscle mass, the lengths of the fibers (fascicles) that make up the muscles, and the angle of the fascicles to the muscle’s line of action. These parameters correlate reasonably well with the force and power that the muscle can develop, and its working range of length change. Other posts here have discussed this more, but by measuring the architecture of many muscles in many felids of different sizes, we can determine how felids large and small adapt their anatomy to support their bodies and move their limbs. This will help to solve some lingering mysteries about the odd ways that cats move and how their movement changes with body size.

This research is being driven forward mainly by Andrew and Marcela, shown above, so I wanted to introduce them and our odoriferous fat cat. Upcoming dissections: 1-2 more snow leopards, tiger, various lions, ocelot, black-footed cat, leopard, and a bunch of moggies, and whatever else comes our way. All were EU zoo/park mortalities (there are a LOT of big cats out there!).

EDIT: Had to add a photo of the CLAWS! Whoa dude.

CLAWS

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(John: here’s a guest post from my former PhD student, soon to be 100% legit PhD, Dr., and all that jazz, Julia Molnar!)

This is my first guest post, but I have been avidly following what’s in John’s freezer (and the blog too) for quite a while. I joined the lab in 2009 and left a month ago on the bittersweet occasion of surviving my PhD viva (oral exam/defense), so I’d like to take a moment here to thank John and the Structure & Motion Lab for a great 4 years!

Moving on to freezer-related matters; specifically, a bunch of frozen crocodile spines. It was late 2011, and the reason for the spines in John’s freezer was that John, Stephanie Pierce, and I were trying to find out more about crocodile locomotion. This was anticipated to become my first major, first-author research publication (but see my Palaeontologia Electronica paper on a related subject), and I was about to find out that these things seldom go as planned; for example, the article would not be published for more than three years (the research took a long time!). Before telling the story of how it lurched and stumbled toward eventual publication, I’ll give you some background on the project.

Stomach-Churning Rating: 3/10; x-ray of dead bits and nothing much worse.

A stumbly sort-of-bounding crocodile. They can do better.

First of all, why crocodiles? For one thing, they’re large, semi-terrestrial animals, but they use more sprawling postures than typical mammals. Along with alligators and gharials, they are the only living representatives of Crocodylomorpha, a 200+ million year-old lineage that includes wolf-like terrestrial carnivores, fish-like giants with flippers and a tail fin, even armored armadillo-like burrowers. Finally, crocodiles are interesting in their own right because they use a wide variety of gaits, including bounding and galloping, which are otherwise known only in mammals.

Nile croc

Nile crocodile skeletal anatomy

OK, so why spines? Understanding how the vertebral column works is crucial to understanding locomotion and body support on land, and inter-vertebral joint stiffness (how much the joints of the backbone resist forces that would move them in certain directions) in particular has been linked to trunk movements in other animals. For this reason, vertebral morphology is often used to infer functional information about extinct animals, including dinosaurs. However, vertebral form-function relationships have seldom been experimentally tested, and tests on non-mammals are particularly scarce. So we thought the crocodile spines might be able to tell us more about the relationship between vertebral morphology, mechanics, and locomotion in a broader sample of vertebrate animals. If crocodile spine morphology could be used to predict joint stiffness, then morphological measurements of extinct crocodile relatives would have some more empirical heft to them. Several skeletal features seem to play roles such as levers to mechanically stiffen crocodile spines (click to emcroc’en):

Croc vertebra-01

Anatomy of a crocodile vertebra

We decided to use a very simple technique that could be replicated in any lab to measure passive stiffness in crocodile cadavers. We dissected out individual joints were and loaded with known weights. From the movement of the vertebrae and the distance from the joint, we calculated how much force takes to move the joint a certain number of degrees (i.e. stiffness).

Julia w vertebra (480x640)

Me with crocodile vertebra and G-clamp

Xray

X-ray of two crocodile vertebrae loaded with a metric weight to calculate their joint’s stiffness

Afterwards, we boiled the joints to remove the soft tissues – the smell was indescribable! We took 14 measurements from each vertebra. All of these measurements had been associated with stiffness or range of motion in other studies, so we thought they might be correlated with stiffness in crocodiles also.

morphometrics

Some of the vertebral measurements that were related to stiffness

Despite my efforts to keep it simple, the process of data collection and analysis was anything but. I recall and exchange with Stephanie Pierce that went something like this:

Stephanie: “How’s it going?”

Me: “Well, the data are messy, I’m not seeing the trends I expected, and everything’s taking twice as long as it was supposed to.”

Stephanie: “Yes, that sounds like science.”

That was the biggest lesson for me: going into the project, I had been unprepared for the amount of bumbling around and re-thinking of methods when the results were coming up implausible or surprising. In this case there were a couple of cool surprises: for one thing, crocodiles turn out to have a very different pattern of inter-vertebral joint stiffness than typical mammals: while mammals have stiff thoracic joints and mobile lumbar joints, crocodiles have stiffer lumbar joints. Many mammals use large lumbar movements during bounding and galloping, so crocodiles must use different axial mechanics than mammals, even during similar gaits. While that’s not shocking (they did evolve their galloping and bounding gaits, and associated anatomy, totally independently), it is neat that this result came out so clearly. Another unexpected result was that, although several of our vertebral measurements were correlated with stiffness, some of the best predictors of stiffness in mammals from previous studies were not correlated with stiffness in crocodiles. The study tells a cautionary tale about making assumptions about extinct animals using data from only a subset of their living relatives or intuitive ideas about form and function.

Finally, the experience of doing the experiments and writing the paper got me interested in other aspects of crocodilian functional anatomy. For instance, how does joint stiffness interact with other factors, such as muscle activity and properties of the ribs, skin, and armor in living crocodiles? Previous studies by Frey and Salisbury had commented on this, but the influence of those factors is less tractable to experiment on or model than just naked backbones with passively stiff joints. In the future, I’d like to study vertebral movements during locomotion in crocodiles – especially during bounding and galloping – to find out how these patterns of stiffness relate to movement. In the meantime, our study shows that, to a degree, crocodile backbone dimensions do give some clues about joint stiffness and locomotor function.

To find out more, read the paper! It was just featured in Inside JEB.

Julia Molnar, Stephanie Pierce, John Hutchinson (2014). An experimental and morphometric test of the relationship between vertebral morphology and joint stiffness in Nile crocodiles (Crocodylus niloticus). The Journal of Experimental Biology 217, 757-768 link here and journal’s “Inside JEB” story

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I Can’t Remember Freezermas…
Can’t Tell Dissection from a CT.
Deep down Inside I Feel to Freeze.
These Wonderful Scenes of Anatomy!
Now That the Week Is Through with Me,
I’m Waking up; Ratites I see
And There’s Not Much Left of These:
Nothing remains but bones now

(digested from Metallica’s “One“, in …And Justice For All, the pummeling, slickly produced, huge-sounding, Jason Newsted-bass-playing leviathan of a thematic album (1988). It was all downhill for Metallica after this one, but it was a good year for rock! The song is about a soldier who had traumatic injuries and was left paralyzed, “locked-in” to his own mind. Themes/footage from “Johnny Got His Gun” (1939 book/1971 movie) are interspersed. Did you see this track coming? If so, you’re just as demented as I am; congrats!)

And so another year ends; we’re at the final post of Freezermas 2014: The Concept Album. We had 7 tracks involving leitmotifs of ostriches and cats and 2 vs. 4 legs, and CTs and x-rays, and epic dissections, and disturbing pathologies, and some twisted lyrics that mangled classic albums. There are so many more concept albums I could have touched on- great ones by Rush, Yes, Savatage, Helstar, Mastodon… many more. But I’ll give you a chance to sit in the DJ’s seat in this post!

Stomach-Churning Rating: 6/10. Some internal organs.

Today’s one mystery dissection photo is of two things, and the Mystery Anatomy challenge is to identify both (the 2-part brown thing and the 1-part whitish thing). They are from our friend the ostrich.

Your task is to weave your answer into the lyrics of a song from any concept album (2 lines or more)- you must identify the song, artist and album with your answer so we can figure out the tune. Any genre is OK as long as it is clearly a concept album (music, that is). You have freedom. Use it wisely! As always, bonus points for extra cleverness.

Whazzat?

We’ll let Maytagtallica sing us out:

♫Hold my breath as I wait for points
Oh Please John, blog more?♫

no

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Freezermas continues! Today we have a treat for you. Lots of detailed anatomy! This post comes from my team’s dissections of an ostrich last week (~3-7 February 2014), which I’ve been tweeting about as part of a larger project called the Open Ostrich.

However, before I go further, it’s as important as ever to note this:

Stomach-Churning Rating: 9/10: bloody pictures of a dissection of a large ostrich follow. Head to toes, it gets messy. Just be glad it wasn’t rotten; I was glad. Not Safe For Lunch!

If the introductory picture below gets the butterflies a-fluttering in your tummy, turn back now! It gets messier. There are tamer pics in my earlier Naked Ostriches post (still, a rating of 6/10 or so for stomach-churning-ness there).

All photo credits  (used with permission) on this post go to palaeoartist Bob Nicholls (please check out his website!), who got to attend and get hands-on experience in extant dinosaur anatomy with my team and Writtle College lecturer Nieky VanVeggel (more from Nieky soon)!

Research Fellow Jeff Rankin, myself and technician/MRes student Kyle Chadwick get to work.

Research Fellow Jeff Rankin, myself and technician/MRes student Kyle Chadwick get to work, removing a wing.

This is a male ostrich, 71.3 kg in body mass, that had gone lame in one foot last summer and, for welfare reasons, we had to put down for a local farmer, then we got the body to study. We took advantage of a bad situation; the animal was better off being humanely put down.

The number for today is 6; six posts left in Freezermas. But I had no idea I’d have a hard time finding a song involving 6, from a concept album. Yet 6 three times over is Slayer’s numerus operandi, and so… The concept album for today is Slayer’s  1986 thematic opus “Reign in Blood” (a pivotal album for speed/death metal). The most appropriate track here is the plodding, pounding, brooding, then savagely furious “Postmortem“, which leads (literally and figuratively, in thunderous fashion) to the madness of the title track, after Tom Araya barks the final verse:

“The waves of blood are rushing near, pounding at the walls of lies

Turning off my sanity, reaching back into my mind

Non-rising body from the grave showing new reality

What I am, what I want, I’m only after death”

I’m not going to try to reword those morbid lyrics into something humorous and fitting the ostrich theme of this post. I’ll stick with a serious tone for now. I like to take these opportunities to provoke thought about the duality of a situation like this. It’s grim stuff; dark and bloody and saturated with our own inner fears of mortality and our disgust at what normally is politely concealed behind the integumentary system’s viscoelastic walls of keratin and collagen.

But it’s also profoundly beautiful stuff– anatomy, even in a gory state like this, has a mesmerizing impact: how intricately the varied parts fit together with each other and with their roles in their environment, or even the richness of hues and multifarous patterns that pervade the dissected form, or the surprising variations within an individual that tell you stories about its life, health or growth. Every dissection is a new journey for an anatomist.

OK I’ve given you enough time to gird yourself; into the Open Ostrich we go! The remainder is a photo-blog exploration of ostrich gross anatomy, from our detailed postmortem.

(more…)

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Hey, a short post here to say go check this new blog out! I love it. The first main post-introductory post is a dissection of a snow leopard, documenting a real vet case attempting to figure out why it died. The “Veterinary Forensics blog” is going cool places, and it is a kindred spirit to this blog. You might, as I do sometimes when walking into a veterinary pathology/postmortem facility, see surprising and rare stuff– like in this photo of urban foxes:

troop of foxes

 

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Jason Anderson, vertebrate paleontologist and anatomist at the University of Calgary (Canada), shared these two intriguing photos with me, and agreed for me to share them with you. Yay, thanks Jason! Good timing for a badly needed Mystery Dissection post:

What are they (species ID) *AND* from what region of the body?

(they are the same region, same specimen, same animal)

RULE: Your answer must be in the form of a winter holiday song (at least four lines)!

If you’ve been following some of my recent tweets, I’ve been tweeting about the “joys” of increased academic paperwork around holiday-time; e.g. this one:

As always, you can score extra points for creativity.

Remember: the scoreboard is here.

Difficulty: Integumentary

Stomach-Churning Rating: 6/10; if beauty is only skin deep, then ugly is, too?

Here they are…

(more…)

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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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