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Posts Tagged ‘biomechanics’

SupraHoloNet Transmission

Year 277 ABY, Fourth Imperial Age

Hoth System (location classified)

From: Dr. Zhonav Diphyryzas, Imperial Corps for Yesterday’s Misplaced Information; Knowledge Harvesters Unit; New Imperial Science Department

To: Dr. John of the Freezers, Unaligned World Contact #1314, Terran system

Subject: Functional Anatomy of Tatooine Megafauna

 

Dear Terran Science-Invigilator Dr. Freezers,

I write to you with the detailed correspondence I promised for your “blog carnival, whatever that is, and in honour of our Fourth Empire’s glorious leader Empress Syrrhosyx—may her inestimably wise and orderly rulership soon grace your distant world as it has our not-so-far-away galaxy. I hope that my Galactic translator continues to function properly with your crude technology. Our Empire’s embrace would grant your culture midi-chlorian-powered devices that would make our dialogue far simpler via intermental transmission, with minimal apparent side effects for you. You need not worry about the apocryphal stories that your people told about our first Imperial Age. That Skywalker kid was a terrorist, pure and simple. However, our inside sources reveal that the “documentary” in progress by the Terran named Jjabrams includes a rather accurate portrayal of the perfidious giant muromorph race from planet Dis’snai. “Baby steps”, as you say.

Our communications continue to be crippled by the mynock infestation that has plagued my orbital facility, and moreso by your own barbarian apparati. Thus the resolution of my images included here is a pale reflection of what our holo-imaging can achieve. But your readers can click the images to enhance their magnitude.

As the subject indicates, the transmission concerns my recent visit to the desert world of Tatooine, stimulated by investigations I conducted in the Corellian Science Museum. In that museum I found rare skeletal remains of the little-studied, reportedly extinct arthroreptile the Krayt Dragon (Tyrannodraconis tatooinensis by your archaic nomenclature). I’ll revisit this further below, because a subsequent discovery changed everything for me. I just wanted to whet your appetite, and this image of museum specimens of krayt dragons may do so:

Two fragmentary skeletons of small Krayt Dragons, from the Corellian Science Museum. (Image source here)

Two fragmentary skeletons of small Krayt Dragons, from the Corellian Science Museum. (Image source here) Note their short necks and quadrupedal limbs.

With growing fascination for the large land vertebratomorphs that are so startlingly diverse on Tatooine, I secured Imperial funding for an expedition to Tatooine, to survey the exotic megafauna and search for fossils of Tyrannodraconis that might further illuminate their evolution. My ensuing report summarizes my trilogy of investigations and discoveries from this “holiday in the suns”:

 

Stormtrooper on a Dewback in the Eastern Dune Sea (image source here).

Stormtrooper on a Dewback in the Eastern Dune Sea (image source here). Note how gracile the limbs are below the elbows/knees.

Investigation 1. Dissection of a Dewback, Mos Eisley

My ample funding (I’m sure you’re jealous) secured and stocked a laboratory for me in the colourful Mos Eisley spaceport, which has seen unprecedented commercial influx in recent years and now largely serves as an adventure park for hyperspace tourists (funded in part by the muromorphs of planet Dis’snai). With coliseum seating for a gathered host of some 1.6 million curiously slavering punters and drunken local yokels, I completed a full dissection of a fresh adult dewback (Iguanomorphus homoplasticus) specimen, illustrated below at its climax: exposure of the great fat body of the tail and the large caudofemoral muscle in the left thigh.  (curse this infernal Jawa 37C-H4 sketching droid’s malfunctions!)

Jawa 37C-H4 sketching droid illustration: My dissection of a common dewback, showing the caudofemoral muscle and tendon, tail fat body, and fibrous pads used while resting on the sand.

Jawa 37C-H4 sketching droid illustration: My dissection of a common dewback, showing (ventral view) the caudofemoral muscle and tendon, tail fat body (obscured by the nearby muscle), and fibrous pads used while resting on the sand.

My main observations support those of prior scholars, even from the Rebel Alliance era (bucking the trend of having to correct all their mistakes!): dewbacks have earned their moniker well by the characteristic water-condensing tissues on their dorsal surfaces. Microdroid explorations of these tissues, which lie within a dimpled midline ridge, house a high density of capillaries in a countercurrent network that surrounds a large number of specialised pores, or stomata, which smooth muscular rings contract to pull open when humidity, temperature and shade are best suited to cooling the surrounding air (via air currents encouraged by the stomata, and by local cooling via the capillary rete).

Previous scholars overlooked this mechanism, which conducts excessive warmth to the heat-emanative fat bodies in the bulky tail and the neck hump (my dissections nicely revealed these; similar tissues are concentrated in the foot pads and sternal pad). The mechanism also allows the body to be up to 20% cooler than the ambient air; an analogous adaptation to that seen in the banthas (below). My peers also failed to realize that the social nature of the dewback is key to its water conservation: while the stomatal rete can draw in some condensed water, it is far more effectively ingested by licking the backs of fellow dewbacks. Lone dewbacks thus are more prone to dehydration. The night-time group-huddling habits of dewbacks to conserve heat that they would otherwise too easily shed in the cool night air is yet another testament to the benefits of their sociality.

As ectotherms, dewbacks are slaves to the hot-cool cycles of the Tatooine wastes, but their sociality liberates them. Further escape comes from their large size (>800 kilograms of Terran mass units), which renders them mostly homeothermic, but never endothermic like some of your otherwise unimpressive Terran reptiles of past or present.

A laser-histology trek by microdroids showed the “scaled” hide around the rest of the body to be composed of siliceous material embedded in the thickly fibrous connective tissue of the skin, forming stereotyped arrowhead-shaped “siliceoderms”, as I term them, shown below.

Curious microstructure of the small "siliceoderms" from dewback skin that I have described-- single 'derm on the left, multiple 'derms surrounding a stomata on the right.

Curious microstructure of the small “siliceoderms” from dewback skin that I have described– single ‘derm on the left, multiple ‘derms surrounding a stoma on the right. To see these structures, one must view the “scales” at high magnification, ideally with microdroids.

I surmise that: (1) these siliceoderms are formed of fused Tatooine sand grains; (2) the grains become embedded into the soft, pliable skin as dewbacks grow, giving them insulation and physical protection; (3) young dewbacks display a previously mysterious behaviour of “sand-rolling” that encourages this embedding during the maturation of a dewback; and (4) the high strength and stiffness of this composite skin not only armours dewbacks but also pressurizes them, ensuring that blood can circulate through their large bodies without backflow or clotting issues, particularly in their gracile lower limbs, which are themselves passively supported by their skin tissues.

With your interest in animal locomotion, you may be curious about tales of how dewbacks can outrun landspeeders, especially in poor weather or terrain conditions. The skin-stiffening agents noted above surely play an important role in this. Indeed, much like your terrestrial varanid lizards, dewbacks do not follow the usual trend of straightening their limbs to support their body more effectively at larger body sizes (improving “effective mechanical advantage” as your field terms it), but they do draw them more closely under the body rather than remain sprawling. I revisit the matter of limb posture toward the end of my transmission.

Furthermore, the huge caudofemoral muscle shown above is able to transmit force from the tail to the thigh, and then its thick tendon transmits the force down the limb to the feet, acting as one strong limb extensor that powers and supports locomotion. No Terran animal does it so well. Banish any thoughts of how the dewback’s wrists and ankles seem implausibly thin– they are pressurized cylinders of dense tendon and bone, more like a Terran horse’s distal limbs than any lizard’s, and linked to far larger tail-to-thigh muscles. The expansive foot pads and reversed first toe (hallux; as in your Terran birds but with no association to arboreality) likewise give dewbacks a stable base of support and spread out their weight over the treacherous desert sands, reducing the work otherwise lost to deforming the sand’s surface and also keeping pressures on their feet at safe levels. Thus dewbacks have many features that explain their reputation for bursts of fast speed (~14 Terran meters/second or 50 kph/30 mph).

Yet whilst during the daytime and over short distances dewbacks can outpace banthas or humanoids on foot, their ectothermic nature causes them to accumulate fatigue too quickly, and thus they must rest. So sans cybernetic enhancements, dewbacks will never be winning any podraces. Nonetheless, I am sure you are awed by how Tatooine’s native reptiliforms, the dewbacks, exceed any living Terran reptile in their size and extreme adaptations to aridity. I have not even described the variations seen in feral, grizzled, cannibal or mountain dewback species, which can surpass the common desert dewback’s. Toward the end of my transmission I will show you animals that exceed even the greatest dinosaurs in sheer glory and ferocity.

Unlike the durable Tauntauns of my home system’s ice planet Hoth, however, dewbacks are ill-suited to cold climates because they are adapted to shed heat, not gain it. But the insulation of the next animal shows a more versatile performance…

 

Convincing image of a Bantha being ridden by a Sand-Person, from your world's fake documentary "Star Wars Episode IV: A New Hope", from Lucasfilm/Twentieth Century Fox.

Convincing image of a Bantha being ridden by a Tusken Raider/Sand-Person, from your world’s Rebel propaganda film “Star Wars Episode IV: A New Hope”, by Lucasfilm/Twentieth Century Fox.

Investigation 2. Field Dissection of a Bantha Bull

My anatomical study of a large male bantha (Megalingua feteoclunis) was hastened by not only the merciless heat but also by the imminent arrival of a horde of ravenous womp rats. Some quick incisions with my relict lightsaber sped my work. I focused my attention on three issues of scholarly interest: its marvellous tongue and glossopharyngeal adaptations (how does such a tall animal eat in a world that is far below it?), its hirsute integumentary system (what lies under that thick fur and how do banthas cope with the heat while wearing many wookies worth of wooly warmth?) and its peculiar, pillar-like limbs. The spiralling horns that add rings as the bantha grows, the nuchal ligament that supports the heavy head and neck, and the convoluted, multi-partitioned digestive tract that wrenches every last bit of nutrition from the lichens and other flora hidden beneath Tatooine sands are better understood. And with this bull I had no opportunity to study where the famous blue bantha milk comes from, but I have heard stories and no Terran mammal-esque udders are involved, let me tell you that much…

Anatomy of the oral apparatus of the Bantha, which I correct in my report although it is largely right (but how, Terran?). (source)

Anatomy of the oral apparatus of the Bantha, which I correct in my report although it is largely right (but how, Terran authors Terryl Whitlatch and Bob Carrau?). (source)

I don’t know how your Terran science-invigilators managed to get accurate information on bantha tongue anatomy (above) but I have to credit them, they almost got it right. With your can-do attitudes combined with your bungling mistakes, you’d make good Fourth Rebel Alliance members, but don’t get any new hopes. However, as the illustration below shows (and I had to leave the guts in the picture for their sheer impressiveness!), the tongue-projection mechanism extends not around the rear of the skull (occiput) and into the eyes or sinuses, but far back along the giant, spar-like breastbone (sternum) to the hips (pelvis, or propubis).

That mechanism’s powerful projection can extend the tongue as far as 3 Terran meters (10 feet). The tongue is expelled by stretching and then releasing (slowly for precise control, or quickly for a catapult action) a fibrous sac that surrounds the base of the tongue, and this sac then recoils elastically when released to withdraw the tongue. I’ve studied your Terran elephant and chameleon and it combines aspects of both of these, with the tongue having several layers of fine muscle fibres as in the former animal, and the “power amplifier” catch mechanism of the latter, thus providing a superior combination of control and speed. All of these are rightly called muscular hydrostats, but the bantha’s is the best.  You might mention your Terran pangolin as a counter-example, but does that little creature have the spiracle-bearing, ultrasensitive chemosensory tongue and majestic size of the bantha? No. I rest my case.

Jawa 37C-H4 sketching droid illustration: My dissection of a bantha, showing the tongue attachments (note the distal bifurcation), digestive tract and foot structure. The colour variations in the digestive tract seem to be produced by commensal arthroreptiles.

Jawa 37C-H4 sketching droid illustration: My dissection of a bantha, showing the tongue attachments (note the distal bifurcation), digestive tract and foot structure. The colour variations in the digestive tract seem to be produced by commensal arthroreptiles.

A naïve Terran like yourself might wonder why, of all things, a giant desert mammal such as the bantha would evolve to be clothed in thick fur. Here you would reveal your feeble way of grasping about the diversity of pangalactic Nature. First of all, banthas are not mammals as you know them; a Terran word like pseudomammal would suffice. They lack the diagnostic traits of mammary glands, true hair, and inner ear bones that diagnose the Mammalia of your homeworld, but evolution at a giant size in a hot, dry clime has chastened them to become at least superficially similar to a Terran mammal such as an elephant or mammoth. One might be so naïve, even, to think that a bantha is merely a proboscidean in hairy disguise, but drive such thoughts from your rickety cerebral-implant-deprived mind.

Behold, the true nature of bantha fur, as I have seen with microdroid holo-imaging: it is a second, external circulatory system of sorts. Simply put, the hairs have a thermo-conductive submolecular structure that deflects heat (and even, to a degree, the energy of a blaster) and traps cooler air near the body with an intricate network of cross-linking of barbed fibers more like a Terran bird’s feathers than mammalian hair. In this cooler locale, tracts of spongy skin tissue collect condensed water and direct it to absorbent epithelial beds on the chin and lips, belly, and toes, where the bantha imbibes it, or simply sheds it off to carry further heat away. Thus here we have a fascinating case of convergent evolution with the reptiliform dewbacks, but surpassing even that animal’s adaptation and evolving what you would likely call an air-conditioning system. Banthas cool themselves by circulating a slick of cool water around their body inside a heat-resistant fluffy outer mesh. Whether their horn tissues or tails contribute to this system is yet to be investigated.

Lastly, I have conducted holo-viewings of the biomechanics of bantha gaits from numerous remote studies of wild and Sand People-ridden animals, in light of my own dissections of this bull. What strikes me is the phenomenal convergence with giant quadrupeds on your homeworld: like sauropods, elephants and other species, banthas have evolved “graviportal” or weight-bearing adaptations: (1) limbs that are proportionately longest above the elbow and knee, not distally elongated as in “cursorial” animals; (2) heavy, robust bones that lack much of a marrow space; (3) short, thickly padded feet ending in bulky claws or hooves (three toes in the case of banthas); (4) an emphasis on lateral sequence (left hind-left front-right hind-right front) footfalls when walking, extended to a slightly bouncing, rolling “amble” at faster speeds; (5) strongly vertical limbs when walking, using the limbs more like pillars to support the weight more effectively; and (6) slow maximal speeds, limited to ~7 Terran meters/second (24 kph/15mph) at best.

At around 4000 kg of typical body mass, banthas overlap with the masses of your planet’s erstwhile giants that have such features. I did not uncover any “predigits” supporting the feet of banthas as you had in elephants; rather, their “heels” involve dense fibro-elastic cartilage, which works analogously to give shock-absorbing and resilient properties to the feet. This suite of graviportal features reinforces an idea that is now recognized pan-galactically: At huge sizes, land animals must act relatively more constrained by gravity, becoming forced to adapt more aspects of their biology to resist its pull, lest they strain muscles, break bones, snap tendons, or fall and injure themselves. Thus the convergent evolution of banthas and elephants is no surprise. But is there another way to be an imposing giant? Perhaps…

 

Investigation 3. On some remains of the “extinct” Krayt Dragon

Ever since I left my home system, thoughts kept tumbling through my mind like rocks in an asteroid field, concerning the krayt dragon bones I had viewed in the museum on Corellia. With the krayt (Tyrannodraconis sp.) lineage reported extinct since at least the year 22 ABY, following much publicity of its awesome nature, its menace seemed now but a phantom. Consequently I could only fantasize of deeper study. That is, until a rumour came to me while resupplying in the well-preserved city of Bestine: not far off on the edge of the Jundland Wastes, a stormtrooper patrol had taken down a strange, enormous, multi-legged arthroreptile that had gone after their dewback mounts. A quick skyhopper flight and I was there, giddy with the adrenaline of impending discovery.

Another Terran artist renders a compelling illustration, of a Greater Krayt Dragon in life. Where indeed do they get their information from? Bothan spies, I suspect. (Source)

Another Terran artist (one of Terryl Whitlatch and Bob Carrau) renders a compelling illustration, of a Greater Krayt Dragon in life. Where indeed do they get their information from? Bothan spies, I suspect. (Source)

It was a magnificent carcass. Sandworms and scurriers were already attempting to scavenge it, but with little luck and easily driven off with a few shots from my carbine. No stormtroopers remained (alive, anyway), so I didn’t get any details of the fracas that led to this well-timed demise, but the blast points on its body were too precise for sandpeople, and characteristic dewback tracks were everywhere. Even my antique lightsaber seemed poorly up to the task of dissecting this titan: it was over 30 meters (100 feet) long and surely 100 tons of Terran mass if not more; on the scale of your sauropods, but so vastly different in other ways. Right away, from its tracks I could see it had a peculiar mode of movement in life: it had slid up to some rocky cover in these badlands, dragging its belly and bulk along with ten limbs that were slender in comparison to its body, but still each as big as a large bantha’s. I took a deep breath and cut into what was the first Greater Krayt Dragon seen in some 255 years.

Jawa 37C-H4 sketching droid illustration: My dissection of the Greater Krayt Dragon, to extract the Dragon Pearl. The stormtrooper shown forgot the tale that Krayts take 1 hour to die, and so got too close too soon.

Jawa 37C-H4 sketching droid illustration: My dissection of the Greater Krayt Dragon, to extract the Dragon Pearl. The stormtrooper shown forgot the tale that Krayts take 1 hour to die, and so got too close too soon.

If the bantha dissection was a rush job, this one was a sprint. Pockets of gas were forming and erupting while I sliced my way toward the bones and other organs of most interest, with the forces of decomposition slowly winning a race against my science. Oh, if only I’d had a Jawa sandcrawler to repurpose as a mobile freezer! And the sandworms and scurriers were still lurking about, with far nastier things surely soon to be drawn by the carnage out in these remote wastes. Those two days blurred exhaustion and inquiry and disgust and elation into a mire in my mind more pernicious than any on Dagobah. I’m no longer sure of what I saw– you’re probably wondering if I found the fabled krayt dragon pearl in the gizzard, and yes, there was one but I lost it somehow. Same with the venom sacs. Maybe I sipped from one of those; that would explain a lot. I made a sketch that I reproduce here, but then in a crazed, diaphonic state of dehydration and euphoria and frustration I am pretty sure I cut my sketching droid to pieces too, so this is all that remains to bolster my frazzled memories.

Now that I’ve recovered and ruminated, I have come to some conclusions. First, I am left doubting all the little we know about krayt dragons. It is said that they existed in canyon, normal and greater species, and the immense variation of curved horns, clawed limbs and flanged tails lent this taxonomy much credibility in the past. But, call it chronic heatstroke or inspiration as you may, what if all krayt “species” are just stages of a long and repeatedly metamorphic developmental sequence? As my graph below shows, and this is admittedly pieced together from what few museum specimens and documents I have since marshalled to test my hypothesis, krayt traits change uniformly with their body size. As they get bigger, krayt dragons get more multi-legged and longer-necked, diverging from the form of their relatives (in the evolutionary sense of your sciences, sister group or outgroup) from Ruutan, the Kell dragons. The genus Tyrannodraconis, more so than the Kell, betrays its arthroreptile ancestry with their spines, exoskeletal plates, and tendency for polypedality. Their sternum also elongates to support their chest as they change from lumbering, bantha-chasing quadrupeds to slithering, sarlacc-snatching octa- or decapedal behemoths.

Although based on little concrete data, my analysis of known Krayt and related specimens suggests that they change continuously during ontogeny, although leg number may shift more suddenly (I predict this happens during their first metamorphosis at sexual maturity). Strong allometric scaling of neck and total length is evident- if the two lengths scaled as mass^0.33 they would be maintaining shape across the proposed growth series. But they don't.

Although based on little concrete data, my analysis of known Krayt and related specimens suggests that they change continuously during ontogeny, although leg number may shift more suddenly (I predict this happens during their first metamorphosis at sexual maturity). Strong allometric scaling of neck and total length is evident- if the two lengths scaled as body mass0.33 they would be maintaining shape across the proposed growth series. But they don’t.

I return to the best-documented krayt dragon remains: those that even Terrans have seen in the Rebel propaganda film you call “Episode IV”. Dr. Freezers, even your fellow blog-invigilators at SV-POW! discussed it. Witness the large size and long neck of the typical Krayt; whether horns existed or not in that form from the film is uncertain, and I note that these could even be a sexually dimorphic feature, but this is beside the point. Remnants of the body and limbs were never found. But this specimen fits well with my idea that all krayts are one species, or two at most—and how many top predatory megafaunal species could coexist on a desolate arid planet like Tatooine anyway?

What still strikes me is the phenotypic variation in krayts: some large or small varieties have from two to four toes, and different scythe-like horns on their tail tips. This leads me to heap speculation atop my precarious pile of hypotheses: what if krayts are simply phenotypically labile, varying their traits almost stochastically between individuals due to relatively flexible ontogenetic programming, but still following strong overall trends as size increase, like those I have plotted above? Those stronger trends might be more tightly regulated by homeobox-like genes similar to those that have shaped so much of your Terran metazoan diversity, influencing features along the body axis like those I have mentioned (neck, limbs) across growth? I like this idea too much for it to be true, I admit. But if one krayt dragon existed just a short time ago, it is not simply fodder for the cryptoxenozoologists. And so, sooner or later, someone will answer my scientific salvo. I predict that burrows where the krayt dragons metamorphose between life stages, growing new legs and longer bodies, will be found in due time.

However, I have a stronger inference that I present to you as part of our common interest. On Terra and Tatooine alike, larger animals tend to adopt more straight-legged limb poses to improve their leverage, as I outlined with the dewbacks above. I plot existing data for Terran animals with my best estimates (for dewbacks and banthas, quite reliable; for krayts, my guesses) for this “effective mechanical advantage” below. What this shows is that dewbacks and Banthas both fall below the “normal” curve for Terran land mammals, as I explain:

In the case of dewbacks, this decrease of limb leverage seems offset by passive support from their pressurized scaly legs and enlarged whole-limb extensor muscles of their hindlegs, so they are overall about as well adapted to bursts of speed as large mammals from your world, such as buffalo or large antelope, even if their endurance suffers (a tradeoff, perhaps, for their reptile-like adaptations to desert life).

In the case of banthas, they do no better or worse than elephants; all are slow due to their size and “graviportal” focus of adaptations. Like elephants, but unlike dewbacks, banthas do not “invest” more body mass into supportive leg muscle, and so they are slower than they might otherwise be.

Effective mechanical advantage of the limbs, with Terran data for mammals (red+blue) (source 1 and source 2), and my new data for Tatooine megafauna. Past a moderate size, EMA either declines or remains constant. Once the limbs are fairly straight (near the size of a Terran horse), EMA cannot be much improved.

Effective mechanical advantage (EMA) of the limbs, with Terran data for mammals (red+blue) (source 1 and source 2), and my new data for Tatooine megafauna (green). Past a moderate size, EMA either declines or remains constant. Once the limbs are fairly straight (near the size of a Terran horse, or Tatooine eopie; vertical dashed line), EMA cannot be much improved.

But the krayts (young or smaller species aside) suffer more from their size than other Tatooine megafauna, as they do not increase their limbs’ mechanical advantage any more than the others do, and so they must become slower as they grow. This explains, however, why their ecology shifts from being a mobile predator when smaller (feeding on dewback, then bantha-sized prey) to being more of an ambush predator or specialist on slow/immobile prey like sarlaccs as they attain titanic sizes. Their limbs, despite becoming more numerous, must become less able to support them as size increases, as in other Terran and Tatooine megafauna, and thus they are destined to benefit from giant size (in many ways, including near-invulnerability and capacity to take the largest prey) at a cost of athleticism (but with prey like sarlaccs, who needs it?). In the greater, or fully mature, krayt dragons, I suggest that the limbs each become less supportive and more of a stabilizer to prevent their slug-like bulk from rolling over, or a set of “oars” to help them navigate through sandy environments like the Dune Seas. They support their weight not so much with limbs and levers, but with a larger, cuirass-like breastbone system, rings of muscles and fibrous tissue, and their whole elongate body.

The ultimate implications of my biomechanical research are summarized below—I am sure you will agree with my reasoning.

Maximal speed vs. body mass data from (black) Terran animals (source), and (green) Tatooine megafauna (plus non-native Kell dragons for comparison). As size increases past ~100 kg mass, speed inevitably declines.

Maximal speed vs. body mass data from (black) Terran animals (source), and (green) Tatooine megafauna (plus non-native Kell dragons for comparison). As size increases past ~100 kg mass (when EMA in the other graph above is already maximal), speed inevitably declines.

As for those that have said that Greater Krayt Dragons and such are thereby confined to a life as scavengers and nothing more, I would welcome them to explore the Jundland Wastes locales armoured by all the security that this foolish notion provides. I, for one, would enjoy viewing such a visit, but only remotely via a probe droid’s holo-feed.

One of your Terran artists (jeddbub on deviantart) produced a provocative imagining of a Greater Krayt Dragon facing a Jedi. I'd wager for the former.

One of your Terran artists (jeddibub on deviantart) produced a provocative imagining of a Greater Krayt Dragon facing a Jedi. I’d wager for the former.

I submit this report in honour of Empress Syrrhosyx and the Fourth Empire– may you find the contents enlightening and may her rule grace your benighted homeworld before you, too, have nothing left of your megafauna but stories of dragons.

I welcome your comments, and perhaps some of your lauded “freezerinos” would care to comment below—but they must behave themselves, lest I find cause to deposit them in carbonite for hyperspace shipping to a lonely suffering on a lonely planet!

I shall shortly return this “blog” to your control, when the mood strikes me. That is the deal for this correspondence. Pray I don’t alter it any further.

Enjoy your little blog carnival, Terrans…

Pangalactically,

- Dr. Zhonav Diphyryzas

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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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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 salamander

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So in my last post I promised to put up the videos of my cat biomechanics footage online (cut scene from “The Secret Life of the Cat” documentary). Here I deliver on that promise.

Note that all this footage was filmed at 250 frames/second, so it is 10 times faster than conventional UK/EU (PAL format) video and thus it plays 10x slower if replayed at PAL format speeds. Hence it is often called “slo-mo”/slow motion video. However, most experts would call it high speed video due to the high frame rate that gives us higher temporal resolution, ideal for studying fast movements.

It was cold that day; indeed the Colchester Zoo area where we filmed the tiger videos below had been snowed in earlier; so the posting of these videos on my freezer-based blog is DEFINITELY apropos.

First, the cat (named Ricochet, not Rocket, I now recall; I’m sure you’re all ineffably outraged at this mistake in my prior post) that we filmed to show how a standard; if rather shy; cat walks:

Second, here I am goofing off. High speed video is so fun! OK actually I was testing the video camera to ensure it worked; we only got one chance with each of 2 tigers. As you can imagine it’s not easy to get a tiger back in its indoor enclosure when it’s nice and sunny outside! So my gear needed to work, and it did, despite the cameraman’s bum being in the shot here:

Third, a tiger whom we filmed at Colchester Zoo. It nonchalantly strolled out of its indoor enclosure upon release. No drama. It was a bit unnerved by our presence but took its time.

Finally, this is the video that we were really hoping for with the tiger; a dramatic turn and gallop out of the “tiger chute” into its main enclosure:

Pretty nice! And thanks to the magic of blogging, you get to see it, rather than having it banished forever to the purgatorial cutting room floor!

Here are some parting shots of the male tiger happily checking out his snowy paddock upon release, and then…

Tiger outdoors

I turned around and he was checking me out; I was just on the other side of the fence. That was a fun surprise! Some close-up time with a curious tiger.2013-03-12 12.38.13

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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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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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This post will walk through the basic steps we take to do some of the major, ongoing research in my team. It comes from our lengthy project aiming to determine how elephant legs work at the level of individual muscle/tendon/bone organs. We need fancy computer simulations because anatomy, mechanics, physiology, neural control etc. are all very complex and not only impossible to completely measure in a living, moving animal but also extremely unethical and unjustified in the case of a rare, fragile animal like an Asian elephant. We want to do such complex things to test hypotheses about how animals work. For example, we want to estimate how fast an elephant could run if it wanted to, or why they cannot (or will not) jump or gallop like smaller mammals do— even as baby elephants (~100 kg or 220 lbs), which is an ancillary question we’re tackling. That’s cool basic science, and that’s enough for me. But the applications once such models and simulations are established are manifold– human clinical research now routinely employs such approaches to help treat “crouch gait” in patients with cerebral palsy, plan corrective surgeries, aid in rehabilitation strategies, and even potentially optimize athletic performance. Non-human research is pretty far behind this kind of confident application, because there are too damn many interesting non-humans out there to study and not many people using these approaches to study them (but it’s catching on).

Breaking up the monotony of the text with a baby elephant we met during our research in Thailand (Chiang Mai, here) in 2001. It was just a few days old and VERY cuddly and playful (chewing on everything!) but it’s mother did not want us playing with it so we only gave a quick hello.

I use the term model to refer to a simple abstraction of reality (such as an anatomically realistic computer graphic of a limb), and a simulation as a more complex process that is more open-ended and generally uses a model to ask a question (such as what level of extreme athletic behaviour a modelled limb could support). We use models and simulations to test how all the structures of the limb work together to produce movement. This also reciprocally gives us insight into the question, as I like to say it, of why is there anatomy? What is anatomy for? Why does it vary so much within so many groups and not so much in others? This can more easily be addressed by focusing on the consequences of a given anatomy rather than the more tricky question of why it evolved.

These approaches also can answer the frightening question of “Does anatomy really matter?” Sometimes it does not. And those “sometimes” can be impossible to predict- although sometimes they can be easy to predict, too. I think we are not at a point in the maturity of biomechanics/functional morphology to usually know a priori when either is the case.  Many factors in addition to anatomy determine function, behaviour, or performance; that’s why; and biomechanics aims to unravel those relationships. A lot of anatomists, palaeontologists, etc. assume that form can be reliably used to predict function, but plenty of studies have shown already (and if you peer deeply into the details, it comes from first principles) that one cannot be sure without either measuring what anatomy is doing in a particular behaviour or estimating that function in a computer model or simulation.

Anyway, I’ve covered my perspective on this in a paper which you can read if you want to go into deep philosophical details of the science (and read me blabbering on more about this particular hobby horse of mine?). This post will proceed mostly with pretty images and simple explanations, although I welcome comments and queries at the end. As part of this post, I’ll try to give an idea of the timespans involved in doing the research. Some steps are quick and easy; others can take dauntingly long — especially to do well, without building a digital house of cards.

I’ll start, as my posts often do, with a deceased animal, and in this case it will again be an Asian elephant. Incidentally it is the same animal from the “Inside Nature’s Giants” series (see previous post).

Above: the hindlimb viewed from the rear, showing the medial (inside) region of the thigh skinned down to the superficial musculature. The hip is toward the left of the screen, and the knee is to the far right (whitish rounded area), with the shank (still bearing most of its grey hide) heading to the bottom right corner of the picture. Muscles pictured include ST (semitendinosus) and SM (semimembranosus); major hamstring muscles; as well as the thin, sheet-like gracilis, the straplike sartorius, and the massive adductors toward the top of the image.

When collecting data from dissections for functional analysis including computer models and simulations, we dissect the muscles one by one as we identify and photograph/sketch them, then remove them and do a suite of measurements to characterize how their form relates to some basic functional parameters. From the mass (weight) of the muscle and the length and angulation (pennation) of its fibres (bundled as fascicles) we can estimate what is called the physiological cross-sectional area (PCSA) of each muscle, which is known to strongly correlate with the force the muscle can produce. Different muscles have different PCSAs; for example check out these pictures of a long-fibred, lower-PCSA muscle and a short-fibred, highly pennate and high PCSA muscle:

Above: the long muscle fibres (bands running from left to right, somewhat diagonally from the bottom left corner toward the top right) of a hip adductor muscle in our specimen. The adductors are fairly simple muscles that run from the underside of the pelvis to the inside of the thigh (femur).

Above: the tensor fasciae latae (TFL; pretty sure of ID but going from memory) hip muscle of our specimen, cut open to show the short, angled fibres (each leading at around a 45 degree angle to attach onto a thick central internal tendon). The TFL is just out of view at the top of the screen in the whole leg anatomy picture above; it is on the front outer, upper margin of the hip/thigh and runs down to the outer side of the knee, invested with thick sheets of connective tissue (fascia).

The maximal isometric force (Fmax) of a muscle is computed as the PCSA times the muscle stress (force/unit area), which is fairly conservative in vertebrates. A square meter of PCSA can produce around 200-300 kilonewtons of force, or about 60,000 cheeseburger-weights (the standard unit of force on this blog). That’s a lot of quarter pounders! And an elephant has pretty close to that many cheeseburgers worth of leg muscle (around 150 kg mass, very close to a square meter of PCSA; total Fmax would be around 80,000 cheese-burger weights!). That much muscle is important because an Asian elephant like this one weighed 3550 kg or about 9000 cheeseburger-weights. So if all the muscles in one elephant hindlimb could push in one direction at once, in theory they could hold about 9 elephants aloft. However, as the picture above shows, they do not all act in the same direction. Furthermore, there are many other factors involved in determining how hard a leg can push, such as the leverage of the muscle forces versus the actions of gravity and inertia (mechanical advantage). All those factors, again, are why we need computer models to address the complexity. But the end result is that elephants cannot support 9 times their body weight on one hind leg.

Enough talk about cheeseburgers and enough possibly savory pictures of giant steak-like leg muscles. I don’t want to be blamed for hunger-induced health problems in my beloved blog-readership, dear Freezerinos! The above steps take about a week to complete for 2 legs of a big elephant, rushing against decomposition to try to get the best quality data we can. On to the digital stuff- let’s turn the geekitude dial up to 11 with some videos of computer modelling.

Our next step, often featured on this blog because I do this so often, is to take CT (and/or MRI) scans of the specimen that we wisely did before we cut it to bits, and use those to make a computer model. That’s the easy step; a scan nowaways takes me less than an hour to complete, including moving the specimen back and forth between the freezer and imaging centre. MRI scans can take quite a bit longer. Here is a CT scan of a similar hindlimb (right leg for the toes up to the knee, from a juvenile elephant; the above leg was too big for our scanner!). See what you can identify here:

And then here is a resulting computer model of the same animal (just knee down to toes), showing how we took each CT slice of even the muscles and turned them into fully or partially 3D digital organs, in our case using commercial software that makes this procedure (a step called segmentation) very easy:

The segmentation step for bones is usually incredibly simple; it can take anywhere from an hour to a day or so, depending on anatomical complexity and image quality. For muscles, this is harder because the images are often more hazy and muscles tend to interweave with each other, segue into tiny tendons, take sudden turns through bones or other narrow spaces, or even fuse with other muscles. So when we do this kind of musculoskeletal modelling, it gets pretty laborious, and can take weeks or months to finish.

Ahh, but once you’re done with the basic anatomy, the real fun begins! We take the 3D images of bones, muscles, etc. and import them into our biomechanics software. We use two packages: one commericial item called SIMM (Software for Integrative Musculoskeletal Modeling) for making models, and a nice freebie called OpenSim for doing simulations (although actually we’re finding SIMM is often better at doing both modelling and simulation for more unusual animals). Quite a bit more anatomical work is required to get the joints to move properly, then position the muscles in accurate or at least realistic 3D paths (depending on segmented image quality), then check the muscles to ensure they move properly throughout the joints’ ranges of motion, then import all the PCSA and Fmax and other data we need from dissections, then do a lot more debugging of the model… this takes months, at least.

But the greatest joy and pain comes in getting the biomechanics done with the models and simulations. You can get quite simple data out of the models alone; such as the leverages (moment arms) of individual muscles and how these change with limb joint position, across a gait cycle, etc… That’s pretty interesting to us, and can just take a few days to crank out from a finished model. Yet the ultimate goal is to do either a tracking simulation, in which we make the model try to follow forces and motions that we measured in experiments from the same or a similar animal (standard, harmless gait analyses), or a theoretical simulation, in which we set the model a task and some rules (‘optimization criteria’) and then set it to run (for hours, days or weeks) to solve that task while following the rules. In both cases, the simulations estimate the muscle activation timings (on/off and intensity) and forces, as well as the kinematics (motions) and kinetics (forces) of the limbs. Then we check the results, play around with the inputs (unknown parameters) as part of a sensitivity analysis, and re-run the analyses again, and again, and again… Here is a draft of a tracking simulation we’ve run for our elephant’s hindlimb:

Above: again, a right hindlimb of an Asian elephant. This test of our tracking simulation is replicating real experimental data (from motion capture and force platform analysis) of an elephant running at near its top speed; over 4 meters/second (>10 mph/16kph). The red lines are the individual muscles, and the green arrow is the ground reaction force, equal and opposite to the force that the limb applies to the ground. In a fast elephant that force can exceed the elephant’s body weight, so the muscles need to crank out kilo-cheeseburger-units of force!

And that’s about as far as I’ll get today. My team’s previous research (explore links for some fun videos) has shown that elephants can run about 7 meters/second (~15mph; 24kph) and that they have pretty poor mechanical advantage when they do run, so their muscles must have to work pretty hard (about 6 times more cheeseburger units in a fast run vs. a slower walk). So how do they do it? And what prevents them from going faster? What would happen if they jumped? What limits speed more; muscles, tendons or bones? Stay tuned. I’m still not sure how much longer this final step of the research will take… (presumably will precede the heat death of the universe by a long shot) But overall, the whole process when everything works nicely can take a year or so to do, proceeding from whole limbs to a simulated limbs.

As a final teaser, here is work we’ve done on using a different kind of model, called finite element analysis (FEA), to estimate how many cheeseburgers it would take to break an elephant’s femur (thigh bone), for example. How “overbuilt” are bones vs. muscles or tendons? This is still a poorly resolved question in biology. We’ve established some rigorous methodology for doing this, now we just need to see what answers it gives us…

(the colour shows the strain (deformation) in the bone in a simple bending experiment; “hot” colours are higher strain. The visualization of the strain is greatly exaggerated; in the real results they are barely visible, as bone only bends a tiny amount before fracturing)

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