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Night Stalker Rex Part II: Tyrant Tummy Tucks & Where the Rubber Meets the Road

October 21, 2016:

by Duane Nash

As Khalil Beiting pointed out in my last post T. rex is actually not the only known barrel chested terrestrial theropod. Allosaurus, though certainly not displaying the thickness of T. rex, has a pleasantly plump countenance. And certainly all other tyrannosaurids display a thickened torso to varying degrees. In the case of Allosaurus a highly agile, cursorial nature need not be selected for - giant sauropod carcasses, sauropodlets, and stegosaurids are not winning any foot races. Having a little extra in your back pocket might come in handy for Allosaurus when wrestling teenage sauropods and intimidating/fighting over carcasses with rival mega-avepods. In the case of other barrel chested tyrannosaurids I believe this increasing girth - culminating in T. rex of course - speaks to a general trend of highly sensory adapted, nocturnal, stealthy, territorial, quick killing, and calculating predators.

Of course when I speak of "fat" tyrannosaurus or other theropods I am not implying that they are fat the way a super weaner elephant seal pup is. Obviously they probably carried some fat depending on the season and condition but this fat would be concentrated at the base of the tail, thigh, abdomen and hip near the center of gravity (kind of like a chicken). When I speak of "fat" T. rex & tyrannosaurids I mean that they are coming at you with the thickness. A professional football linebacker or a sumo wrestler are both athletes, are both powerful in any sense of the word, are both athletically gifted in any sense of the word, and they both are carrying not a little, but a lot of fat. But these "girthy" athletes are probably in better shape than the average reader of this blog and one would hesitate to call them "fat" in the negative connotation of the word if they were within arms reach of you. It is a bit paradoxical that such large athletes are rarely described as "athletic" even though they perform amazing feats of power and strength. The term "athletic" seems to be reserved for only the svelte, lithe, trim, and quick athletes in the pantheon of "attractive" olympic body worship culture.

It is this bias I speak of - "what constitutes athletic?" - and how this concept intertwines with being slim, of low body fat percentage, and being of a culturally established level of physical beauty and attractiveness. It is this bias, I assert, that creeps into and underpins our thought processes when imagining what constitutes athletic and attractive creatures of deep time and how they should look.

It is my contention that we want slim attractive theropods - especially tyrannosaurids - because this matches what we want to see in our own vaunted athletes. Slim equals beauty, success, athleticism, and adaptive superiority. Fat equals ugly, inferior, sickly, tired, slow, and headed towards the evolutionary dustbin. The notion of fat dinosaurs, especially fat theropods, also strikes a dissonant chord within us because this was the predominant past visage of dinosaurs prior to the dinosaur renaissance. And we all know that the past researchers of dinosaurs (pre-renaissance) got everything wrong, right?

Above is the old - and now overhauled - predatory pose of Daspletosaurus dubbed affectionately "Gorgeous George" over some dumb duckbill at the Field Museum of Chicago (special kudos to DinoGuy2 from the dinotoyblog forum for jotting my memory of it). Although I never saw it in person I do remember this image vividly from my childhood. What I want to talk about is not the outdated vertical mount, or the tail dragging, or the pronated hands, or the dubious taxonomic status of this specimen. Go read this excellent write up The Glorious Journey of Gorgeous George if you want to learn more about the history of this mount. What I want to draw attention to is the gastralia in this mount that denotes a very thick and round countenance.

Gastralia are rarely included in mounts, even to this day, and I can't overstate the caveat that skeletal mounts sometimes get it wrong. On the other hand can anyone prove to me that the gastralia as depicted here did indeed get it wrong? As noted in the linked history of this mount the gastralia is not of the original bone. But it looks to be a pretty seemless transition of the gastralia from the pubic bone to the furcula. Based on articulated specimens of other theropods with intact gastralia this should be what to expect.

What is interesting, and maybe it is just perspective playing tricks here, is that when we look at the refurbished mount of Daspletosaurus at the Field Museum, Gorgeous George looks like he has lost a few pounds.

It appears that Gorgeous George in his new dynamic posture has received a bit of a tummy tuck. Where did this tummy tuck come from?

Well if you go back and read Predatory Dinosaurs of the World Gregory S. Paul advocated hollowed out bellies for theropods:

"...theropods probably looked lean, sleek, and a little bony, like big dogs and cats. "Plump" theropod drawings are certainly wrong." (Pp. 105)

"Predators gorge at a carcass, then fast until they are hungry again. The stomach is highly distensible so it can hold big meals. In accordance with this the abdominal "ribs" or more correctly gastralia, of predatory dinosaurs were poorly ossifiied, multijointed, and very flexible. So hungry theropods on the hunt should be drawn with hollow cat- or dog-like bellies. In some of the big mounted skeletons, the abdominal ribs are mounted to form a distended belly, which would be true only after feeding on a kill. A satiated theropod mush have waddled away from its meal!" (pp. 106)

His skeletals follow suit. Go peruse his theropod skeletals, especially of any large bodied forms, and you will note he gives a distinctive tummy tuck to the gastralia just after the pubic bone.* But is there any evidence for such a tummy tuck in theropods? Would the gastralia of a hungry theropod necessarily have formed such a hollow cavity or would a theropod belt - line been a bit more ample? I have not found any preserved specimens and I welcome any evidence supporting such a tummy tuck. Crocs don't seem to have it. I can't discern such a tuck in any of the remarkably complete specimens of theropods... you can connect the dots or the gastralia as you want BUT there might just be a bit of a modern day bias in trimming up theropod skeletals/mounts in some cases. Perhaps the ol' skool look had a little bit more truthiness to it than we might initially presume... I have not noticed the tummy tuck in Scott Hartman's skeletals but I do think his flesh outlines are too svelte.

*I am not suggesting that GSP ignored or misinterpreted data merely that his depiction of tummy tucked gastralia is consistent with his assertion of hollow bellied, svelte theropods.

Things seem a little equivocal on the exact neutral placement of gastralia but there is some work done go here. Instead of gastralia allowing a "tummy tuck" look as GSP asserts Classens advocates a more concave look for theropod gastralia:

"In ornithomimids preserved in situ the ventral outline of the abdominal wall as indicated by the gastralia is usually concave. Although this may be a taphonomic artifact, midventral shortening of the gastralial system would result in ventral movement of the abdominal wall (fig 16 A-C below). The ventral movement of the body wall during protraction would result in an increase in trunk volume"

Also form Classens 2005 it does appear that in crocs there is strong musculature linking the pubic bone to the gastralia seeminly negating the possibility that such a tummy tuck would be apparent in life. Instead the gastralia likely moved as one functional unit and might not "pinch in" to denote an empty stomach. Indeed if an empty stomach would cause the "tummy tuck" look to appear we should see lots of evidence of this look in crocs since they are ectotherms and often have empty stomachs. But do we see this "tummy tuck" in living crocs? Nope.

As you can see adding the tummy tuck has a profound effect on how the rest of the gastralia line up, dramatically altering the profile of the animal. Classens cites a paper by Carrier & Fisher that during gastralial retraction the abdominal cavity could expand 14% in Allosaurus !!

Obviously the above image has some glaring issues - but maybe the rotund girthiness offers a lot more truthiness in it than we might be comfortable in conceding?

Where does the truth lie with regards to gastralia placement? Maybe a bit in between the Gorgeous George look and the GSP tummy tuck look? Or is that just a needless compromise? Personally I suspect past "chubster" depictions might offer a shade more truth than the more recent svelte, trim depictions. Perhaps we prefer our theropods svelte, trim, and "athletic" looking just like we prefer our modern day "athletes" to look with respect to olympic body spartan hero kult skinny worship?

Think about balance for a second. Having the most rounded, heavy part of your body towards the center of gravity makes absolute sense for a horizontal obligate biped, especially one with a big head. Functionally theropods would be more stable in that configuration.

Did I just make all theropods - not just tyrannosaurids - "fatter" or phatter if you prefer? Yeah I said it, every svelte looking, skinny, tummy tucked theropod is OBSOLETE!! ;')

Weird enough for you?

Whiskers, of course it had whiskers. A big fat tail base because of the caudemofemoralis and fat storage, of course. Prominent pterygoideus flare just like in big crocs - why not for the strongest terrestrial biter ever? Obscene tufts of thickened skin around the head, neck, and forequarters - biting into the neck of T. rex would be like biting into a flat big rig truck tire. But probably the first thing that catches your eye is dem big honking toes and feet, enough to give any pedicurist nightmares...

The feet of course are why this post is subtitled "where the rubber meets the road" because it is the feet that take much of the impact of the stresses and strains of a biped the size of a small whale. They would need cushioning - gel soles if you will - and lots of it. More so than is pretty much always depicted. In other words pretty much every image of large theropod feet is - OBSOLETE!!! ;')

Because the feet of Tyrannosaurus and other - quite literally - mega-avepods have to react to the stresses incurred by high weights we should think about the ol' square cube law. Since volume increases faster than surface area large theropods should have relatively bigger, derpier, and more rotund toe and foot pads than their smaller brethren. Trackways confirm this.

Richard T. McCrea, Lisa G. Buckley, James O. Farlow, Martin G. Lockley, Philip J. Currie, Neffra A. Matthews, S. George Pemberton -http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0103613

In situ tyrannosaurid Bellatoripes fredlundi Trackway A images. a) Print #2 of Trackway A (in situ) - PRPRC 2011.11.001 (right); b) Trackway A (in situ) view to the east of prints #1–3. Note the thick layer of kaolinite in the freshly excavated area in front of print #3.
There is also loads of examples of large theropod footprints getting confused with large ornithopod footprints and vice versa. Almost like there is some sort of biomechanical constraint imposing limits on the pedal morphology of giant bipeds? Hint, hint there likely is...

Also of note is the reported gigantic abelisaur footprint of recent news that features a positively gigantic foot pad. I have heard some chatter it might be from a sauropod back foot but when giant biped get their foot on it just may have looked like that...

Not only are giant theropod feet bigger, wider, and more plump than generally depicted, the claw itself was likely fairly elevated off the substrate in neutral position with only the tip contacting the ground and perhaps only when it pushed off. Think more like giant dog paws. YW Lee was kind enough to share this purported photo displaying massive toe pads on the feet of Concavenator. I honestly don't know if I am breaking some embargo here or if this should be taken down (let me know if so), but sheesh that padding is incredible.

Anyways make of these pics what you will, perhaps I severely underestimated the amount of toe padding in my illustration?!?

In any case there are good examples from present theropods that have toe pads to suggest that as bipedal terrestrial theropods get bigger the padding on their feet get relatively bigger to compensate for the exponential expansion of volume (i.e. weight).

Compare the foot padding on a turkey to an ostrich:

For paleoartists wanting to draw large theropod feet with a bit more truthiness: draw them bigger, plumper, more elevated claws, more uglier, and just plain derpier than you see in all other depictions (including any and all "world renowned" professional paleoartists). It is quite interesting why big ol' toes and toe pads have not got a "footing" so to speak (bad pun is always intended) in theropod paleoart. I have discussed the patently obvious issue of ignoring abundant large toe pads in dromaeosaurids before - which calls into question a tight grasp needed for the RPR model of dromaeosaur predation. We have had evidence suggesting as such for some time via these footprints. But in my estimation only a paltry foot pad is given and never do you see the claws actually raised off of the ground.

Big, gnarly, ugly toes and feet are simply not as attractive and sexy as the slender, refined, and petite toes and feet of modern theropod paleoart. We keep wanting to export our cultural baggage with us in our excursions into deep time.

So back to stalking technique and what big foot pads, chubby toes, and gel shoes meant for T. rex and other large theropods. What these attributes imply is that one of the most iconic scenes from Jurassic Park - the cup of water rippling at the approach of T. rex - is truly and utterly false. Not only that, such a noisy approach is diametrically opposed to the stealth mode that these animals operated in.

T. rex and other giant avepods would have been disarmingly quiet when walking around. Their huge and fleshy toes and foot pads smothering and muffling the sound of any snapping vegetation or substrate that might betray their presence. In heightened stealth mode - when they were actually stalking - they would have moved with the precision and care of a gigantic heron. Students of natural history should immediately think of the commonly observed silence that elephants can move with. An uncanny ability to slip into stealth mode is often attributed to these animals by hunters/poachers/naturalists as they can at will slip into the brush and disappear noiselessly.

Elephants are also useful in providing an example of unequivocally gigantic, stealthy, and strategic (plant) predators that make successful and repeated nocturnal raids on the subsistence farms of hyper vigilant but nocturnally ill - equipped hominins.

When T. rex and other tyrannosaurids were not out performing stealth raid operations at night what were they doing during the day? Probably a lot of lounging around on their big fat bellies, preferably in a morass of cooling mud or body of water like the self satisfied tyrants they were. Probably looking quite ridiculous while doing so. And yes they could lie down just as I depicted below. (Pp 199 Ch. 11 Rex, Sit: Digital Modeling of Tyrannosaurus Rex at Rest Stevens, Larson, Will & Anderson Tyrannosaurus Rex: The Tyrant King).

Cuz bad asses do what they wanna do and they don't care what you think about 'em or how ridiculous they look doing it.


The Glorious Journey of Gorgeous George. Extinct Monsters

Classens, Leon P.A.M. (2004) Dinosaur Gastralia: Origin, Morphology, and Function. Journal of Vertebrate Paleontology 24(1) 89-106: March 2004 online

Paul, Gregory S. Predatory Dinosaurs of the World. 1988 New York Academy of Sciences. Sime & Shuster




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