Friday, April 15, 2016

Not Your Daddy's Tyrannosaurus rex...

You may have already heard the chatterings, mumblings, and rumors spread hither and thither. In the smoky backroom chatboards, comments sections, forums, and discussion threads a growing disquiet over a certain very real - but also mytho-cultural - beast. To those attuned to the dinosaur blogosphere internet meta-brain this notion should be none too radical but to those uninitiated the notion is simple and revelatory at the same time: we might just be getting Tyrannosaurus rex totally wrong as goes appearance, especially in the face. T. rex might look just plain silly, or weird, or altogether more surreal than what we have built it up to look like.



Tyrannosaurus rex - as both a scientific and cultural phenomena - is imbued with both values as goes it's appearance. And humans - as culturally adapted critters - try as we might can not decouple the two as stringently as we might hope in reconstructing this beast.

This post is going to be necessarily both a cultural and scientific deconstruction of Tyrannosaurus rex facial appearance focusing on two main aspects. As such we must wear both a cultural and scientific hat here in an attempt to de-clutter and re-imagine a creature undeniably real but also imbued to an obscene degree by cultural baggage, gender notions, and aesthetics. This treatment will also hold implications for many other extinct theropods to greater or lesser degrees. Where you fall down in the end as goes appearance - will be a blend of science, aesthetics, and culture - which is as how it has always been with these guys (i.e. extinct animal restoration).

The beginning (and really the end as well we shall see) of T. rex facial reconstruction must really start at ground zero - the skull. Just take a second to breath it all in... it really is structurally and aesthetically a work of art and powerfully built symmetry.

AMNH 5027, A.E. Anderson Public Domain

Now as appealing as this bony synthesis of power and grace is we must concede that the bony appearance of an animal's skeletons is often times not a direct reflection of an animal's outer appearance. In T. rex the skull's beautiful, symmetric, and aesthetically pleasing appearance may have a lot more to do with being influenced by a uniquely and profoundly strong set of muscles than it being a true reading of it's life appearance. T. rex has  evolved to deliver crushing bites and sustain stresses in multiple force vectors. It is built to give and take a licking and keep on ticking.

But just take a second to bathe in the below photos...


Red Tegu photos credit from Helen Zhu.
The above x-rays (borrowed from Helen Zhu's research page) should give you moment to pause and reflect upon how much soft tissue can surround and obscure even a reptiles skull (diapsids generally being impoverished in facial muscles compared to mammals). It should be noted that huge jowls of the red tegu are a male feature and are mainly for show although the huge pterygoideus muscles certainly help with cracking snails and shellfish - a common part of the animal's diet.


As the above youtuber puts it these prominent muscles in the tegu form some very voluptuous "neck boobs" on the side of the jaw. Crocodiles also feature said neck boobs that form the dominant jaw closing group of muscles in their particular jaw apparatus (they don't put a lot of muscles on the top of the head for concealment reasons).

Now to what extent and how much T. rex, and other tyrant lizards - or even theropods in general had prominent pterygoideus muscles is equivocal and loaded with uncertainty as is the muscular reconstruction of any extinct animal. But as one of the largest and in fact the strongest biting terrestrial vertebrate T. rex likely had some rather prominent "neck boobs", at least more so than is almost always depicted.

Here are some pics on how the pterygoideus muscles may have attached in T. rex and Majungasaurus:

Pterygoideus group in purple (from Bates & Falkingham, 2012)
Pterygoideus muscles = mPTv from C.M Holliday 2009

credit Ira Block/ model Brain Cooley
Again this post is not so much about the bite force and the technical side of theropod / T. rex biting but appearance and the cultural conceits there of. So whether or not T. rex had red tegu sized "neck boobs" or maybe something like a croc or somewhat less than that - there is a lot of room for variation in how much "neck boob" you want to put on your T. rex as well as other theropods. But do we see this variation in T. rex paleoart? I can say almost universally nope, no we don't. Go peruse T. rex art and you will see that the pterygoideus is petite at best and sometimes not even there.

One avenue of looking into how much muscle T. rex was packing there is to compare the size of this muscle in juvenile versus adult crocodilians. As is seen in these dissections of immature crocs the size of the pterygoideus is fairly modest in relation to the animal's whole head. This changes with adulthood when we the grotesquely flared pterygoideus of large crocs.

If we peruse this nice color schematic of the jaw closing muscles of the American alligator (Alligator mississippiensis) it is obviously that it is a youngster (big eyes) and it does not have quite the degree of pterygoideus flare or "neck boob" as the boomer sized adults have. From Holliday et al 2013 Plos One A 3D Interactive Model and Atlas of the Jaw Closing Musculature of Alligator mississippiensis)

credit Holliday et al 2013 pterygoideus in orange/red

Note prominent jaw muscle "neck boobs" CC2.0 credit fvanrenterghem
Now compare the muscles in a large croc to a baby croc:

Getty Images
Is this ontogenetic change due to a shift from small prey to large prey? I don't know if that is completely the answer... in fact I am not sure that adult crocs prey on animals any larger relative to their own size than baby crocs. I suspect it has a lot more to do with the ol' square cube law. As crocs get bigger their volume increases disproportionate to their surface area. Muscles have volume but they are also influenced a lot by surface area. Big crocs have to move a lot more mass (i.e. from having more volume) relative to small crocs and grow muscles disproportionately larger than small crocs to basically do the same job - bite and subdue prey. There is probably a paper or two in there somewhere but I don't know if it has been written.

Following from this maybe... just maybe... T. rex had to grow some quite impressive jaw closing pterygoideus muscles to do it's job amply - after all it was certainly no light weight.

Again my main point in all of this is not to convince you one way or the other if T. rex had red tegu sized neck boobs or something more moderate. Chances are it had something prominent there and given it's size and proclivity for a particularly strong, tenacious, and evenly distributed bite the pterygoideus would and should be apparent in life.

But do restorations give this muscle enough flare, weight, and voluptuous girth? I would say no and the  reason I think it is underrepresented I suggest is cultural.

We have all been smitten, bedazzled, and suffered a bit of a man-crush on T. rex's hypermasculine and all too handsome jawline.

You heard me right, the jaw line of T. rex features a jaw line that any A-list Hollywood actor would kill for. The human male jawline is a perhaps seldom mentioned but very distinctive and sought after trait in male sex symbols and is also ubiquitous across... hypermasculine male superheroes.


Pixaby


credit Elaine Thompson AP
We are drawn to Tyrannosaurus rex - possibly on a subconscious level - because the skull encapsulates many of the male attributes we find desirable in our own species both sexually and for our leaders, warriors, and mythical superheroes.


And I did not even mention the strong chin of T. rex which adds a whole other layer to the hypermasculine attributes we are drawn to in the T. rex skull.

John Gurches now iconic T. rex. Note prominent chin and jawline well displayed. Archetypal hero stance

But what if the strong jawline of T. rex - seemingly chiseled out of tooth, scale, and hypermasculine hero worship - was cloaked by layers of feather, flaps of skin, or as suggested earlier in the post by particularly voluptuous "neck boobs" and jowels giving the animal a decidedly softer, rounder and perhaps feminized appearance? Things could change a lot as goes appearance. The skull of T. rex is optimized for muscular performance, not to appeal to the cultural and sexual biases of extant hominins.

Astute readers should note that this cultural and anatomical analysis of T. rex appearance has implications for how other theropods are restored to greater or lesser extents it is just easier to make the point with big ol' sexy rexy.

For the next part of my analysis I want to talk about a soft tissue that regular readers of the dino-blogosphere should be well aware of and which is quite possibly one of the most contentious issues in theropod soft tissue restoration: lips. Yep, I am going into lips.

Instead of making a long and lengthy review of this issue I am going to outsource some of the background as the issue has of course been gone over extensively by Jaime Headden - Making Lip of It, Support For a Lipless, Cheekless Dinosaur World, Cheeky Commentary on Ornithischians & others

To summarize my views going in and add some arguments that probably need reiteration:

Theropods most likely had lips. I also think that these lips (contra most depictions including my own) would have mostly or even completely covered the teeth. While the notion of a croc like skin sheathing the head of theropods has been argued, probably most vociferously by Tracy Ford, what I find lacking is that fully exposed teeth and oral cavity would put a lot of burden on the animal in terms of water loss via exhalation. Here it is worth noting that terrestrial predators keep a pretty tight seal on the mouth. Aquatic animals, not so much - sharks and crocs come to mind but there are many more examples of exposed snaggle toothed aquatic animals. There definitely seems to be a bit of bias for aquatic animals having more exposed oral regions than terrestrial.

One of the critiques for lower lips in theropods is that the preserved skulls for many theropods suggest that the upper teeth would penetrate into the lower lips and gums of said animals cutting such features to shreds. Check these pics out. However one of the best rebuttals to this argument was done by Tyler Keillor in the chapter Jane in the Flesh: The State of Life-Reconstruction in Paleoart from the excellent book Tyrannosaurid Paleobiology. Let me quote Keillor directly as I don't know if this argument gets enough exposure:

What's my name? extreme jaw closure credit James St. John CC2.0

On Jaw Closure (pp 160-161):

"...fossilized theropod skulls have been found with the jaws tightly closed. While some artists have used this as the living animal's closed-mouth pose, I offer another interpretation. The jaws that are tightly clenched may show a postmortem deformation, akin to the "death curve" seen in the axial columns of many vertebrates under certain conditions. As tissues desiccated and shrank in the dead animal, the massive jaw closing muscles may have shortened and pulled the jaw tightly closed, more so than it would have been in life. Punctures in the palate of Sue occurred after death, when the jaw's dentary teeth were closed further than they had been in life (Brochu 2003). In skulls that are preserved right-side up and resting on their jaws, overlying sediment compaction after burial could further crush the jaws closed in dorsoventral compression (Bakker et al. 1988)"

I would actually go a little further than Bakker and suggest that irregardless of whether the skull is preserved right side up compression from multiple angles could compress the jaw shut. Why? Because the earth shifts and moves all the time not just from top to bottom.

Furthermore Keillor draws attention to a rather simple and seldom mentioned critique of the "extreme close mouthed" interpretation which is bone on bone contact with no room for soft tissue. When a skull was put in this pose (extreme close mouthed) Keillor noted "contact between the quadrate and angular, the jugal and extopterygoid come close to touching the surangular, and the dentary teeth contact the palatal bones and medial maxillae (pp 162)".

Keillor also decides that in the situation of tyrannosaur lips he must look beyond the extant phylogenetic bracket of modern birds and crocs due to their unique specializations (beaked and aquatic)  not offering the ideal evolutionary context for a toothed terrestrial predator. And here I agree the EPB feels a little lacking. Keillor expands the bracket to consider large terrestrial predatory lizards i.e. the komodo dragon as the ideal model for looking at the type of "lippy" tissue present and the ideal neutral position of jaw closure. Essentially this lizard lip type arrangement allows a tight seal when closed - to enhance "sniffing" presumably - as well as protect the oral cavity and teeth from dehydration and abrasion. Yeah it is kind of a "just so" argument but keeping your cutlery sheathed and moist probably has some fairly obvious benefits to it in drying terrestrial environs full of abrasives.

Probably one of the best representative views of the lizard lips hypothesis is that done by the promising game Saurian. Picture below borrowed from said development team:

credit Saurian development team
You should note that when the mouth is open the upper teeth have nice little "pockets" to fit into between the dentary and outer lower lip. When the jaw is shut the lips seal things up nice and flush to create a tight seal that inhibits moisture loss and enhance the ability to suck up smells via the nose.

That the upper teeth went below and lateral to the dentary is corroborated by the path the nutrient foramen follow on the dentary.

Below one of my favorite skeletal mounts of T. rex because it eschews the overdone Rex vs Triceratops battle. You can see quite clearly how the nutrient foramen on the upper jaw come right to the edge of the alveolar margin on the upper jaw (maxillae). But if you trace the path of the nutrient foramen on the bottom jaw (dentary) you will notice that while the nutrient foramen come up against the edge of the teeth in the anterior and posterior they take a noticeable dip towards the middle of the jaw - which corresponds directly with where the longest teeth from the upper jaw would be presumably in closure.

Houston Museum of Natural History. credit Daderot CC. Edmontonia & Wyrex

note how nutrient foramen take a dip along bottom margin of jaw corresponding to longest upper teeth
So all is hunky dory right? T. rex - and probably most predatory theropods - had lizard lips fairly similar to monitor lizards like komodo dragons right?

Not so fast Mr. Lizard Lips...

To prime you for my argument please take a good long hard look at another readily available wiki pic of ol' sexy rexy that is taken from the front. If you look into its orbits and squint just a bit you will see it....

credit ScottRobertAnselmo CC3.0 "Sue"
There are some (blasphemy!!) very mammalian things going on here...  those endearing forward facing eyes looking right into your soul... then there is the VERY prominent nasal region (smell being a noted mammalian sense)... that pinched in upper snout which allows the binocular vision... which itself creates a sort of "muzzle"... which terminates in some heterodont dentition with vaguely "incisiform" front teeth for nipping and the tallest but still very stout and almost caniform teeth midway back on the upper jaws... and that flared back of the skull creating a vaguely cheeky countenance. Not only are we attracted to ol' sexy rexy for it's ruggedly handsome jawline but, well, to put it frankly it is harkening up some distinctively mammal type sentiments in us that remind us vaguely of the mammal things we are ourselves and which we allow most intimately in our homes and lives.

Cave Bear. wiki commons
Furthermore when we look at terrestrial predators that share these same attributes of heterodont dentition, binocular vision, a dominant olfactory sensory apparatus - they don't have lizard lips, they have loose, draping, jowel like lips. Yes I am looking at canids, ursids, hyaenids, and even felids to an extent. And yes I took the liberty of extending the bracket further than reptiles to include these predators that might offer more utility than a lizard. Because really what we are talking about is simply growing more skin and all kinds of animals grow all types of skin so again here I don't think the EPB offers much utility. I can see why people are more comfortable with the lizard lips hypothesis for T. rex it might feel safer than what I am offering. But let's break that somewhat arbitrary rule and see where it takes us...



To clarify I should stipulate that I am not suggesting we consider muscular mammal style lips in T. rex and other theropods but basically loose and hangy jowls of flesh (think condor cheeks but not continuous across mouth).

What is lacking in the lips debate is really any type of analysis comparing the adaptive benefits of tight sealing lizard type lips versus the more open hanging mammalian style lips. That debate has not occurred because, well to put it bluntly, mammal type "bulldog" like lips in T. rex and other theropods has been shut down by not being talked about at all really. These are the assertions that essentially shut down the topic I hear and feel free to illuminate me if there are more rigorous reasons not to consider bulldog lips in the comments section btw.

"Too far outside the phylogenetic bracket" 

- Well when we infer lizard lips we are already outside the phylogenetic bracket... so.... and it is a bit telling that many seem to have no problem inferring fleshy mammalian (albeit non-muscular) cheeks in ornithischians but how do dare you consider fleshy, hangy lips in a theropod!!

Or my favorite: "I find them unlikely"

- Like that is all you have to say on bulldog style lips to not consider them? No support at all for not considering, just saying "unlikely"...

I suspect that there is more to it than this and people don't want to consider bulldog style lips because well... aesthetically and culturally it is not what we might like or even feel comfortable with on theropods and especially ol' sexy rexy. Because as I have been saying all along these are as much cultural creations as they are objective scientific animals. Both academics and fans of theropods and T. rex have ignored the idea of hangy, floppy lips in these animals because... for the most part they just seem to laugh and ridicule the idea away.

So as opposed to trying to decipher the type and extent of "lip" in these animals via skeletal traces which I think is a proposal loaded with potential pitfalls - for example how do you account for the amount of stem cells that might just grow loads of skin and tissue (?) - I am going to take another line of inference. I will be exploring lizard lips versus jowl style hanging bulldog lips in terms of relative adaptive benefit. This is admittedly not going to seal the deal either way because there is some subjectivity involved as well as the fact that animals don't always evolve into "optimal" or "perfect" organisms. However I do think comparing the relative benefits of either style of lip in lieu of really being able to eliminate either possibility is a valid form of inquiry. Again it might not seal the deal but it may open up some minds to possibilities...

The Smell Situation

There is one important distinction between lizards and theropods/mammals. Lizards primarily scent the world via their Jacobson's organ - the vomeronasal organ. In all lizards and snakes this organ is present and in reptiles that scent their prey the distinctive fork tongue is the tool that is used to gather sensory input from the environment and put into contact with the vomeronasal organ. Lizards and snakes - because of this system of sensory input don't need loose lips to let information from the environment into their oral cavity because their forked tongue does all the work for them. For lizards and snakes having loose lips to let chemical cues into the oral region is redundant and an unnecessary potential source of water loss. It is true that certain mammals have this organ but in general it is substantially reduced compared to reptiles. I can find no reference to this organ in birds and crocs and it is likely absent or extremely reduced in dinosaurs.

However, as anyone who has had or watched a baby explore its environment via its mouth can attest,  having a relatively open and exploratory labial region may carry significant adaptive advantage. Animals can taste things and loose lips that can be pressed into various substrates can help pick up and adhere odors that can then be picked up by the nose or tasted. Having loose jowl type lips in this scenario of helping to scent or taste things would hold substantial adaptive advantage over the tight sealing lizard lips associated with reptiles that explore the world via their fork tongue.

The bloodhound dog breed - a specialized scenting breed of dog - has low hanging ears that trail along the ground, loads of wrinkles on the face, dewlaps, and very prominent jowls. All of these features have been suggested to stir up, trap, store, and distribute sensory cues for the nose.

Bloodhound. credit Superfantastic CC2.0
It is not unreasonable to argue such adaptive benefits to various theropods - especially T. rex - in scenting and tracking food, rivals, mates etc etc. The open jowls and additional sticky substrate exposed to the environment  would help trap and collect scents in close proximity to the nose. Certainly a lot more potential adaptive benefits in these regards than thin closed lizard lips.

Hellhound Rex by Duane Nash

Tactile Input, Prey Handling & Delicate Nipping

Another benefit of having more open "bulldog" style lips versus closed lizard type lips is the potentially higher amount of sensory data collection points available to "feel out" things. This ability comes in handy in terms of how to react and fine tune grip/bite strength/position when engaged with struggling prey. Having lips that can sense and anticipate muscular twitches of struggling prey is a great advantage to have as it allows the predator to fine tune its own biting and avoid suffering undue injury. Lizard lips, exposing much less sensory surface area than bulldog type lips, offer less data collection points to make these rapid adjustments. Again, adaptive advantage goes to the bulldog lips.

I know that there is something about cats I should be saying here I read somewhere. That when biting struggling prey the sensitive lips and whiskers are able to detect and collect information on the prey. Ok found something I can give to you from The Other Saber-tooths: Scimitar tooth Cats of the Western Hemisphere:

from pp.26:

"large scale movement of the prey relative to the predator can be constrained by powerful forearms, but fine scale adjustments in upper canine placement require tactile input from whiskers, lips, and nerves in the periodontal ligament and pulp cavity." 

Granted T. rex was probably not making the precise bite adjustments of a felid but still could be of use.

The "incisiform" front dentition which allows delicate scraping of meat off of bones is also potentially aided by exposed and extensive lippage. Having a bit of a blind spot here and lacking sensory tactile front paws T. rex could feel out where the trace bits of meat are on a bone and better position its incisors for delicate nipping. Thin and not too supple lizard lips would be less efficient in these regards. Or whiskers...

Take home point: precise biting/nipping with heterodont dentition is associated with loose lips in extant animals and not lizard lips.

Teeth Baring




Although humans have bastardized this traditionally violent signal of aggression into something called a smile the ability to bare your teeth in a visible threat display is a potent and well understood universal across the animal kingdom. The lizard lip model might allow the teeth to show a little bit and maybe not at all in some theropods but in the bulldog lip model the upper teeth are potentially totally obscured ( I doubt that they had facial muscles to enact a sneer) but the bottom teeth and gums would be totally exposed when the theropod opened its mouth just slightly, creating a startling and disturbing visage of exposed gums and teeth. Once again, adaptive advantage goes to the bulldog lips.



Water Loss

Now you would thing that the tight fitting lizard lips would hold a substantial advantage over the more loose and draping habit of bulldog lips there might be more than meets the eye. Mucous could be particularly viscous inhibiting loss. The gap between the lower two mandibles forms a natural trough so that saliva would not be spilling out at a high rate anyways. And camels. Yes camels. If there was ever any animal that should be outfitted for water conversation among mammalia it is camels. Yet camels are noted for having particularly loose and jowly lips. And also, not coincidentally I suspect, camels are noted for a particularly good sense of smell. So whatever evolutionary disadvantages are incumbent upon having a loose set of lips in the dry desert they are not profound enough for camels to evolve a tight set of lips - or at least tighter fitting than the pics below attest.

credit AP


Tight Seal For Sniffing

Sort of a toss up. Reptiles with tight fitting lizard lips should get a pretty tight seal that will enhance sniffing. You would think that the more loose and drapey lips of mammal sniffers would be inferior but it does not seem to stymy them much as they seem to be doing just fine in terms of olfactory prowess. I don't see why such an arrangement in theropods would not work as well for sniffing.

Probably a mention of an extensive secondary palate in T. rex is worth mentioning here...

On a related note I did some research viewing of how bears - the penultimate scenters - actually do their sniffing. What I found was surprising and interesting and I don't know if it has been explored further. What I noticed is that sometimes when a bear is intently sniffing it will repeatedly open and close its mouth. Is it trying to taste the air? Or is it trying to suck air in closer to the nose by opening and closing it's mouth creating a vacuum. Check it out:


Check out the same sniff then open and close mouth behavior in this video as well:


And this brown bear does it too:


Anyways if the bears in these videos are trying to draw air into and closer to the nose I can easily imagine a T. rex doing a similar sort of behavior. Or maybe this behavior has something to do with a (reduced) Jacobson's organ?

Another interesting bear fact I learned in making this is that the lips of bears - apart from all other carnivorans - do not attach directly to the gums. Presumably this is to allow fine tune manipulation of small objects - such as plucking a single berry off a bush. Interesting to think how omnivory and the quest for high quality food items might engender "prehensile" appendages (I am looking at you ankylosaur tongues).



Anyways,

There is no terrestrial predatory tetrapod alive today that shares the suite of characteristics that T. rex has and which also has tightly sealing lizard lips. Asides from the vagaries of what can be gleaned from being one bracket closer on the subjective extant phylogenetic bracket in choosing the Komodo dragon as the best analog I would suggest that we look at the complete adaptive package of T. rex /tyrannosaurids and find the best and most comparable extant analog. Tyrannosaurus rex and other tyrannosaurids line up more closely with mammalian predators in terms of  adaptive features including; a dominant nasal olfactory apparatus; heterodont dentition with precise "nipping" incisiform like front teeth; forward facing eyes; high metabolism; and an extensive secondary palate. I suggest that we have been more than a little hoodwinked by a serrated toothed, poisonous, scaly faced, fork tongued, and lizard lipped trickster in the Komodo dragon that fails compared to mammalian carnivorans in terms of nearly every metric listed when comparing tyrannosaurid facial anatomy, especially in terms of extraoral tissue (i.e. "lips"). 

Let the saliva spray!!

HorridRexDarkerSepia by Duane Nash


credit Carli Davidson


As I alluded to earlier in the post although I concentrated on T. rex this inquiry into lips may have implications for many theropods to varying degrees. Certainly I would hedge my bets towards more of the jowly type of lips in olfactory dominant tyrannosaurids and dromaeosaurids. There is room for nuance in many of the other lineages of theropods though; with variation ranging from more of the lizard type arrangement in some theropods up to this more jowly visage with all the various factors I mentioned in this post coming in to play: how important is scent? tactile prey handling or precision biting important? threat display important?

I also did not mention feathers in this post as this issue is taken up very well in this youtube video:


Feathers can be on top of skin, scales can be on top of skin but feathers and scales can not exist on top of one another.

And I am under no illusion that this post will overnight cause a whole scale reevaluation and overhaul in how we depict theropods. I fully expect most to adhere to the lizard's lip paradigm as that is what classic phylogenetic bracketing dictates. But in the end I find the lizard lips adaptation adaptively inferior to the bulldog lip adaptation. Ironically I have old images that still show lizard style lipped theropods which I still plan on using too... funny thing is I really wanted to concentrate on theropods other than T. rex but this is where my questions took me!!

Cheers!!




"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Wednesday, March 9, 2016

Spinosaurus Unauthorized III: Run, Spino, Run!! & An Anatomical Incongruity

Faster Spino!! Run-Run-Run!! by Duane Nash click image for larger view
I am not completely averse to Spinosaurus bounding around on two legs. You will note I did depict the spinosaurs here as ontogenetically immature and their bipedalism really just a mad dash towards the relative safety of the water as two Rugops have their eyes set on baby spino dinner. Because abelisaurids always seem to roam paleoart as duets - ever notice that? Cenomanian North Africa was not so much a large herbivore based ecology but a fish and fish eater based ecology. And Spinosaurus, especially the juveniles, potentially formed a large part of the prey base for the carcharodontosaurids and abelisaurids that - possibly to some extent - were temporally and environmentally coincident.

As the close-up here attests I put the little spino in a semi-contorted posture with the head and torso pulled back to bring the center of gravity closer to the hips. With each forward lunge the body is in danger of toppling forward as the larger individual in the mid-foreground is getting perilously close to doing so. But by pulling the torso and head back with each footfall at a rapid clip I can picture this locomotion working for the youngins. To help with balance the arms are splayed laterally like a tight-rope walkers balance pole.


I still maintain belly sliding takes care of that pesky center of gravity question and also allows them to negotiate the muddy/intertidal terrain they lived in. But the bipedal heritage of Spinosaurus can not be denied and I find it very probable that - like young/small crocodiles today - smaller spinos had much more liberty in terms of locomotory options on land than the more ponderous, gargantuan adults.



To take you into my minds' eye I think that they would somewhat resemble the quick bipedal sprint of basilisks (Jesus Christ lizards) and frilled lizards.



However some, or even many, of you reading this are not convinced of Ibrahim et al's proportions for Spinosaurus nor are you convinced that a novel adaptation such as some form of quadrupedalism or as I proposed belly sliding need be invoked for this animal(s). Consensus has been agnostic or equicocal concerning Ibrahim et al's proportions for Spinosaurus. Which leaves us in a funny place because renderings and depictions of Spinosaurus continue to come about and for the most part the professional paleoartists have gone into a sort of compromised position of depicting Spinosaurus having somewhat shorter legs than other theropods but still being a good ol' biped. The recent artwork depictions of Spinosaurus by Julius Csotonyi , Mark Witton, and Sergey Krasovsky all hedge their bets towards a longer in body, shorter legged, but still fundamentally bipedal Spinosaurus. I call this compromised sort of depiction of Spinosaurus the true "chimera" in all of this for reasons I will elaborate later.

To what extent was Spinosaurus bipedal? Most would say "we need more data", I say we have enough already to dismiss Spinosaurus as a less than ideal biped on land.  An anatomical incongruity has been rather summarily dismissed or just glossed over in discussions which I will highlight later. 

To me everything circles back to one fundamental question we should ask when settling on the interpretation of an animal: does this animal make sense as an evolutionarily successful animal in it's environment? Can it, in a reasonable manner do things like forage, move, mate, evade predators and in general get along in none too friendly environment full of obstacles, competitors, and predators? This notion that some animals from the fossil records are "in the process of adapting" or "an unfinished product" is bogus to me. Not only does such a sentiment smack of neo-Lamarckism but it also begs the question: where are all the unfinished products in today's biota? Is a mudskipper a less than perfect transitional species on its way to becoming terrestrial? No it's an animal doing just fine in the environment it lives in. Are gliding animals inferior to flying ones or are they better viewed as just good enough for where and how they live?

The jack of all trades, master of none interpretation of Spinosaurus as mixed forger of land and water is not congruent with the wealth of anatomical attributes pointing towards a primarily aquatic existence. The reluctance to give up obligate or classical theropodian terrestrial bipedalism - as evinced by the artistic depictions I mentioned earlier - is at odds with Spinosaurus' peculiar pelvic anatomy. There is a layer of evidence - sitting in plain sight as is so often the case - that speaks against "classic" theropod bipedalism. This anatomical incongruous - especially when viewed in light of the animal's likely habitat of complex, intertidal estuarine fluvial systems - essentially creates a vanishingly small window of opportunity for the bipedal loyalists to maintain Spinosaurus as just another good ol' bipedal theropod. 



You may or may not recall that paleo-super hunk and Papa John spokesman Paul Sereno starred in a very well done promotional video that coincided with the infamous Spinosaurus Science publication. In this video Paul offers some really great and captivating sound bites and a little background on this most fabled of dinosaurs. For our purposes here he makes special emphasis on the femur of FSAC-KK-11888:

On lacking a marrow cavity: "It didn't have a marrow cavity. We had never seen this in any predatory dinosaur. they all have good marrow cavities. And that resembles animals that are actually spending a lot of time in the water. They want to be a little heavier than the water so they don't float all the time and they can control their swimming movements."



On the proportion of the thigh bone (femur) vs shin bone (tibia): "This thigh bone is shorter than the shinbone by several inches.... In animals that are sitting on top of the water and using their limb to paddle that thigh bone becomes short and stocky."



On the caudemofemoralis attachment "On that thigh bone we noticed that the attachment for the muscle that moves it back is huge. So what were looking at is an animal that has adapted it's hindlimb largely for paddling in water."

A couple of things here. While it's old hat that Spinosaurus lacked a marrow cavity I want to point out an inconsistency in Paul's thinking. In one instance he asserts that such animal's want to be a "little heavier than the water so that they don't float all the time" and to "control their swimming movements"This makes sense and I mostly agree with what he is saying here. But then later on Paul - when talking about the use of the hind limb and it's expanded musculature to paddle through the water contradicts himself saying, "In animals that are sitting on top of the water and using their limb to paddle that thigh bone becomes short and stocky".

Did you catch that? We can't have it both ways - Spinosaurus is either a floater or sinker. It's either heavier than the water (a sinker) or lighter than the water (a floater). In order for Spinosaurus to be a floating paddler like a duck or seagull we would not expect such dense bones. Spinosaurus is therefore - as I have been arguing for a while now - a sinker and when dense bones are combined with a dense dermis, which is not unparalleled,  it is more tenable to interpret Spinosaurus as an animal that sinks right down to the bottom. Which is where the true nature of Spinosaurus' unique and powerful pelvic anatomy come to fruition as an underwater walker.

Before I go into how and why Spinosaurus was such a superbly and beautifully adapted underwater walker one final nail in the coffin of this notion of Spinosaurus as floating paddler. Surface area. One of the most important concepts in paleo - functional analysis is the square-cube law.  As an animal increases in size the volume (read bulk) increases at a much higher rate than the surface area. Therefore a structure that is dependent on surface area to do it's job efficiently - such as a paddle - must hold pat and increase at a concurrent rate as size increases. In other words a 5 ton duck should have relatively larger paddles than a 2 lb duck. Like crazy huge paddles. Spinosaurs is a big, heavy and long animal. Even the most rudimentary, intuitive spitball analysis looking at it's paddling arsenal shows that it does not really have the type and spread of foot paddle needed to even move at the relative speed of a duck on the top of the water - much less the type of speed needed for a predator that, you know, had to go out and catch stuff. Just check out the huge rear foot paddles on a true rear foot paddler in the beaver pictured below.

 Beaver on bank lower Kern River. credit Ryanx7. CC3.0

Within the same line of reasoning it is easy to dismiss Spinosaurus, indeed all spinosaurids really, as wading, stalking heron type predators - they just did not have the foot spread to support such a lifestyle. Indeed when you extrapolate the amount of spread in heron feet - which often weigh just one or two kilograms - and assume the same level of spread in giant bipeds of several metric tons - you come up with an improbable amount of foot spread needed to achieve a wading/soft substrate stalking lifestyle. Now I am not saying that in the history of spinosaurid existence a spinosaurid never waded out and caught a fish like a heron does - just that these animals make more sense placed in the water with the fish rather than stalking and catching them from above heron style. Not to mention the lack of binocular vision, relatively straight neck, and tactical face suggesting immersion in the water.

For argument's sake let us dispense the center of gravity work, all those bits and pieces that probably belong to Sigillmassasaurus, and just look at FSAC-KK-11888 as a single entity - which it most certainly was as there is no duplication of material and the bones are ontogenetically congruent (i.e. come from an animal of same age). What we have in FSAC-KK-11888 is a simple case of deduction. If we can exclude rear paddle swimming on the grounds that the foot lacks adequate surface area, then we are left with Spinosaurus being either a powerful biped underwater or on land as indicated by the robust muscular attachment so noted by Sereno & Ibrahim et al. It was using that powerful leg for something after all. 

Now recall Paul Sereno's emphasis on the grossly enlarged muscular attachment on the femur for the caudemofemoralis - the muscle that pulled the leg back and which he assumed was pivotal in the paddling stroke. As I alluded to earlier there is an anatomical incongruous - two things that do not fit together - that stood out to me from Ibrahim et al., an observation that was plainly laid out for everyone to see but which, again, is seemingly glossed over in just about every online discussion both professional and lay regarding FSAC-KK-11888.

From Ibrahim et al.:

"The pelvic girdle and hind limb are considerably reduced in Spinosaurus. The surface area of the iliac blade is approximately one-half that in most theropods, and the supracetabular crest that supports the hind limb is low."

This is a crucial point that the bipedal loyalists have seemingly glossed over. The musculature and skeletal framework that are exactly crucial for standing bipedally (on terra firma) are diminished in Spinosaurus. Not only are the legs proportionately smaller in FSAC-KK-11888 (the proposed neotype) but the legs are relatively diminished in their capacity to support and maintain bipedality.

From Ibrahim et al.:

"The femur in Spinosaurus has an unusually robust attachment for the caudofemoral musculature, which is anchored along nearly one-third of the femoral shaft, suggesting powerful posterior flexion of the hind limb. The articulation at the knee joint for vertical limb support, in contrast, is reduced. The distal condyles of the femur are narrow, and the cnemial crest of the tibia is only moderately expanded."

What we have here in FSAC-KK-11888 is an incongruity that needs explaining. On one hand the femur and musculature attached give us a signal for massive power in the horizontal plane. Discordant with this observation is the relatively weak and diminished musculature and skeletal structure for the vertical plane that would be needed to support a biped of this size. How to explain this seeming contradiction?

Let's revisit my contention earlier than an animal should work reasonably well in it's environment. If we put Spinosaurus in the large, complex mangrove/deltaic/intertidal habitat that is most likely for it and infer bipedalism we should expect the opposite pattern of limb development. That is, far from being diminished in size, the skeletal and muscular framework for bipedalism should be hypertrophied (larger & stronger). The reason is that pushing yourself through water, mud, thick sand, tangles of mangrove vegetation as a biped is hard work. So if Spinosaurus was indeed doing this as an obligate biped we should see greatly expanded musculature for bipedalism in terms of vertical support, which we don't.  I cite the remarkable robusticity and upper muscular development for the swamp lions of Botswana's Okavango delta. These impressive lions - the females of which are as big as male lions elsewhere - have expanded chest and shoulder musculature that assist in not only their main prey - Cape buffalo - but also in swimming, wading, and pushing through their swampy, flooded habitat. There is even some suggestion of a separate subspecies emerging.


So using simple deduction if we can eliminate paddling as a way to explain Spinosaurus' pelvic anatomy on the grounds that it simply did not have too great of a surface area for foot paddling and if we can eliminate terrestrial walking/wading on the grounds that the exact structures needed for such an adaptation are diminished in Spinosaurus - the exact opposite of what should occur in such a large biped in a swamp - then we are left with underwater walking or "punting".

Underwater walking is consistent with the dense bones, diminished size of pelvic area, and greatly expanded caudemofemoral attachment. Neither obligate bipedalism nor paddling addresses the unique and seemingly incongruous features in Spinosaurus. Furthermore the lack of vertical support at the knee joint as noted in the Ibrahim's et al. paper speaks against both bipedalism and quadrupedalism and is another line of evidence in support of belly sliding. Even if Spinosaurus were to have evolved some form of quadrupedalism there is no reason for such an adaptation to cause a decrease in the ability of the hindlimbs to hold weight.



Finally those puny legs - a seeming weakness - are actually superior to long legs for an underwater walker. In one of the few research papers that actually attempted to quantify and bring some discourse to the manner in which hippo run underwater it was found that short, quick steps or "punts" actually outpace the longer "gliding" paces in speed when measured in controlled observations of hippos walking underwater.

Comparing hippo locomotion underwater to humans moving in a "microgravity" environment (i.e. outer space) Coughlin & Fish wrote in their abstract:

"Ground contact time decreased with increasing horizontal velocity,"

Which translates to as the hippo moved faster underwater the amount of time that the foot hit the ground decreased.

"vertical displacement during the unsupported intervals increased with an increase in ground contact time,"

"vertical displacement" refers to how high the hippo rises off the bottom of the tank in their observations. Since longer ground contact time is associated with slower relative speed when the hippo is moving relatively slowly its foot contacts the ground longer and it rises higher in the water column (i.e. gliding phases).

"and time between consecutive footfalls decreased with an increase in horizontal velocity."

which is pretty straightforward - as the hippo increased in velocity footfalls became more frequent (but still relatively short in duration).



Spinosaurus likely had the same pattern of locomotion underwater. Slow speeds with increased foot contact time and longer gliding phases (how beautiful to imagine btw). Higher speeds had decreased foot contact time and shorter unsupported intervals. Some might poo-poo this line of reasoning "you can't compare a bipedal dinosaur to a quadrupedal mammal blah, blah" but much recent work has highlighted congruity in all forms of tetrapod locomotion - especially remarkable convergence in aquatic locomotion in tetrapods. Furthermore you can test it out yourself as a biped. Go to a pool or body of water up to your chest and run. You will quickly see that short, quick steps with little gliding phase outpaces longer paces with lengthier gliding phases. As the authors note in the paper: "Under conditions of microgravity, humans switch from a walk to a run at slower speeds. (Kram et al, 1997)"

And don't for a second dismiss underwater walking or "punting" as a less efficient or even speedy way of moving through water than swimming. Check out the speed and alacrity in which the hippos in this  clip move. Although you can not see them as the people are in a boat - you can surmise from the wake and relative speed of the boat that the animals are moving along underwater at quite a pace.



The short and powerful legs of Spinosaurus are therefore beneficial to walking underwater at speed since short and quick paces outperform long paces for underwater walking.

In the discussion from the hippo/microgravity paper the authors also highlight the importance of the animal in question being denser than the water,

"Effective bottom walking requires a body that is denser than water when submerged."

As I argued in my first post in this series on Spino there is reason to make Spinosaurus denser than the water via dense bones and an extensive and dense epidermis not without parrallel to manatees, hippos, and possibly tapirs.

When we put Spinosaurus in it's proper environmental context which is completely underwater - not some bastardized giant heron nor an improbable jack of all trades switch-hitter of surf and turf - now a real functional use for the sail emerges. As I discussed in my last post the sail would not sit above water anyways as the display marker so many have championed, nor would it add any sort of propulsive power either. But what it would do, I suggest, is act as stabilizer - a dorsal keel - that helped prevent Spinosaurus from rolling when twisting and turning underwater. As much as I have championed the hippo as a useful model for Spinosaurus underwater movement, they differ in one fundamental aspect. Hippos do not have to move with much agility underwater because their primary food - grass - does not grow there nor would it swim away from them if it did. Spinosaurus as an underwater hunter of aquatic prey that did not want to get caught - needs relatively more agility underwater than a hippo. Additionally, because Spinosaurus moves as an underwater bipedal walker not a quadruped, if Spinosaurus changes course rapidly underwater and it's body starts rolling it has no way to correct itself with forelimbs (like a hippo). Now caught in an underwater body roll a Spinosaurus' hind limbs would lose contact with the substrate and it would lose it's main propulsive power since pushing off the substrate is required in underwater punting. A sail helps with this dilemma so that as Spinosaurus twists and turns underwater to either sides the sail pushes back against the water and helps prevent rolling.



Ha, ha I made Spino almost comically "fat" but really no more ponderous that a hippo. You will note that I actually depicted another, more subtle, use for the sail in the top pic. That due to it's swayback morophology the sail may have hydro dynamically made movement underwater more efficient. As the animal moves from right to left, as shown by the large arrow - water flows up and over the sail but forms little micro-eddies over each rise and fall of the sail. The effect is that a slipstream develops that allows Spinosaurus to recoup some of the energy dispensed moving through the water. If you think about the way competitive bicyclists use slipstreams or even the "shake and bake" tactic used in competitive race car events this is not far from what I am suggesting. In the biological realm birds flying in formation or even migrating lobsters moving in line take advantage of the energy saving features of slipstreams. Spinosaurus may have done the same with it's sail underwater in addition to it's movement stabilizing attributes and not altogether dismissing possible uses for bluff/intimidation/social signalling, thermodynamics, prey corral, buoyancy control, and mineral storage.

Oh yeah I almost forgot. What animal also has big flat unguals and partially webbed toes? Take a wild guess...



Ibrahim et al 2014


Also it is worth repeating how "barrel chested" Spinosaurus really is. This is an important point and another nick against trying to retrieve any meaningful terrestrial bipedality. The front of this animal was heavy. Furthermore it compares very well with the skeletal framework of - you guessed it - a hippo. Drape on some muscle, meat, and a thick skin and you will have a very voluptuous - and long - animal. The likes of which is going to be very maladapted for bipedal movement on land and even worse off trying to walk through thick tidal muds, sands, and tangles of swamp vegetation.



link Youtube Hippo 3d skeleton

In the water it was a superbly adapted underwater bipedal walker or "punter" - very graceful, powerful and daunting in that environment. On land, not so much. Smaller juveniles could have enjoyed more liberty in moving around terrestrially, perhaps even going into quick bipedal sprints. As I have maintained since before the actual publication of the Ibrahim material it was a belly sliding mud surfer, looking like an amalgamation of a giant saltwater croc, a penguin, and a loon.  But that was ok for what it had to do in life. It conceded terrestrial ability for aquatic proficiency. And that is not radical or revolutionary or even unique - every tetrapod lineage that transitions back into the aquatic realm concedes some or even all amount of terrestrial capability. Otters, beavers, crocodiles, pinnipeds, loons, penguins they all can move around on land but are much less proficient on land than their related terrestrial brethren.

CC 2.0 credit Mike Bowler. Spinosaurus & Onchoprostis

Well for now that about does it for all I want to say on Spinosaurus (although things always change). I am quite confident that my take on Spinosaurus - a belly sliding, underwater punting, primarily aquatic/piscivorous beast of tidal waterways - will prove to have much truthiness to it.

And in closing I leave you with a depiction of an adult Spinosaurus closing off a tidal outlet and using it's length, size and sail to corral aquatic animals trying to exit with the outgoing tide. The experienced adult has enmeshed itself between two thickets of the mangrove fern Weishchelia reticulata and completely dammed off the outflow channel from a tidal mudflat that fish came up through to feed during high tide. Contrary to the vast majority of Spinosaurus/ Kem-Kem paleoart which feature towering cypress canopy relatively low and shrubby cheirolepidiacean conifers and Weischelia should dominate the flora. Some of the fish - Lepidotes - even swim out of the water to escape the hungry maw of the Spinosaurus while other fish such as the sawshark and various sarcopterygians attempt to vault over the striking theropod to get to the deeper safer water on the other side. I would suggest that this form of fishing - not too dissimilar to what modern crocs do - would be a very efficient and likely manner of fishing for Spinosaurus especially amongst the older, larger, and more experienced Spinos that knew how to take advantage of such tidal choke points. A chunk has also been taken out of the Spino's sail. Also take note of the pterosaurs and dromaeosaurids attracted to the commotion and easy feed provided by the spino.

Tidal Harbinger Negative Brown by Duane Nash click image for larger view
Tidal Harbinger Shocked Pink by Duane Nash click image for larger view





I have actually amassed quite a lot of posts on Spinosaurus going back nearly to the start of this blog. Going back and reading these may be of interest to see the evolution of my ideas - including ideas I have since abandoned.

Spinosaurus Unauthorized II: Spino Identity Crisis & Island Hopping Hippos from November 2, 2015 in which I go into Sigillmassasaurus and what this animal means and does not mean for the "new" Spinosaurus and highlight a pivotal point generally overlooked in discussion of the veracity of FSAC-KK-11888. More on hippos and what island hopping hippos tell us and don't tell us about swimming ability and lack there of.

Spinosaurus Unauthorized I: Hippos Are Not Really Fat and Can't Swim from October 12, 2015. I return to the spino debacle and begin building my case that Spinosaurus works most effectively as an underwater walker/punter. In order to do so I have to spend a lot of time on hippos and a whole lot of effort arguing that hippos can not actually swim. I also argue that Spinosaurus sported a very thick and heavy dermis that assisted as ballast control along with the thick bones similar to manatees, hippos, tapirs, and walrus.

Time For the Giant Heron Spinosaurid Analogy to Bite the Dust Part 2: Getting More Than Just Your Feet Wet from November 7, 2014 in which I elaborate on why the heron/spinosaur comparison is very much less than ideal and not at all the best of all candidate analogs. Also why depictions of spinosaurids  standing on the edge of riverbanks hoping for big fist to blunder on by is patently ridiculous.

Time For the Giant Heron Spinosaurid Analogy to Bite the Dust Part I from November 2, 2014. In which Thomas Holtz says I make a straw man argument.

"Last Man Standing... el Ultimo Hombre": As the Dust Settles on the Spinosaurus Bombshell from September 14, 2014. Well the dust is still settling and well, sometimes you have to push the issue to get people to take notice.

Adding Some Context to the Middle Eastern Attack Today. from September 11, 2014. Do you see what I did there? Very meta.

Surf OR Turf: Can a Terrestrial/Aquatic Switch Hitter Really Exist? from August 31, 2014. Skeptical of the notion that Spinosaurus ala JP3 could function equally proficiently in the water or land.

Did Bakker Get Spinosaurus Right After All? from August 16, 2014 in which - upon seeing the leaked Nat Geo photos of the new Spino reconstruction - first mused that Bakker got Spinosaurus right in the animal being very aquatic and where I first argue the belly sliding hypothesis. I am now equivocal on how much the forelimbs - if at all - assisted in belly sliding or a "combat crawl" type of movement or some combination there of. In either case the post is one of my most popular and still gets lots of links and hits never mind the fact that I feel how Spino moved terrestrially is among the least interesting aspects of the animal.

Planet Predator II: Kem Kem from September 7, 2012 in which I muse on the ecology of the Kem Kem & Cenomanian North Africa and Spinosaurus' place in the ecosystem as prey, competitor, and provider of fish dinners for other kleptoparasitic theropods.



References

Coughlin, Brittany & Frank, E.  Hippopotamus underwater locomotion: reduced gravity movements for a massive mammal. (2009) Journal of Mammalogy 90(3) 675-679


N. Ibrahim, P. Sereno, C. Dal Sasso, S. Maganuco, M. Fabbri, D.M. Martill, S. Zouhri, N. Myhrvold, D.A. Iurino (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science 26 September 11, 2014

"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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