Monday, May 9, 2016

Yeah I Said It... Every Sabertooth Image Ever - OBSOLETE

As I anticipated, reaction to my Hellhound rex bulldog lipped Tyrannosaurus rex argument was mixed. Some liked it, some were equivocal, and some were vehemently against it. You should know by now I have more than a little flair for the dramatic and don't think for a minute I have played my full hand when it comes to extreme "lippage" in theropods... That being said I took - for me at least - a very cautious, muted and tentative tone in that post. Not being naive and knowing full well that the backlash yet to come and the strong culturally entrenched reaction against extreme "lippage" in theropods going right to the heart of our cherished and idealized view of these animals... the struggle is real.

So in this post I am going to eschew that waffling, tentative tone and go right in for the kill shot. Yup names will be named. Things will get messy. Feelings might get hurt. Reputations might get questioned. Including my own but that's ok I am willing to play the villain.

But...

I did go through some real searching in how I wanted to approach this post. I mean the good and bad thing about blogging is you can see where and how traffic gets shuffled to your site which means that you get to read the things people say about you - and it does affect you deeply. In various form I have been called overly speculative, aggressive, a bit of a bully, not to be taken seriously, and sort of a mean and angry guy. And I get it why people say these things about me. I have always indulged in what I consider plausible speculative possibilities. I fully admit that I have a bit of chip on my shoulder that has a lot to do with not getting recognition and blogging not being recognized as a form of science communication on par with the "peer reviewed word" but I think that is changing. I have no problem calling out the "luminaries" of the field when they leave out data, make less than ideal suggestions, and use the weight of their name as a bully pulpit. At the same time I am fully confident that if you spent any amount of real time in the flesh with me you would come away with a perhaps very different or at least more nuanced impression of me than the above characterizations. I have also seen it written that I am too passionate and excited about my own ideas. "Too passionate and excited"... think about that for a second.... I've said it before and I'll say it again there is a little too much tone policing in paleo these days when passion and excitement are discouraged. If you have not noticed science is in a war and is failing to create the excitement, fun, enlightenment, fullfillment, and yes mysticism that other forms of belief are giving people for better or worse.

Never the less it is a hard thing to tell someone that a significant chunk of their life's work is obsolete and you have to be just a little bit of a bully to do so.

To quote the great "Nature Boy" Ric Flair: "To be the man you gotta beat the man!! Whoo!"




To really s - p - e - l - l it out for you I am make the allusion to "professional wrestling" to evince the level of venom, anger, and aggression in my heart - none at all really. It is all a bit of a bluff theatrical arrangement. Of course tone has a way of getting misconstrued in writing. And no, I am not on cocaine.

That being said I am really going out to pick a fight on this one and you better believe I am coming in swinging, guns blazing, and with the gusto!!


La Brea Tar Pits. Charles R. Knight public domain

There is a bit of a problem in sabertooth paleontology. An echo chamber has evolved where one man and one man only seems to dominate the narrative over this eco-morphological grouping of animals. And that man is Mauricio Anton whose books, papers, artwork, and blogging have cast a heavy influence on our view of these animals. Truth be told he deserves the recognition and there is good reason for this respect. His artwork is captivating and in a class of its own. His books are well written, engaging, and straddle the difficult line between being overly technical and approachable. However when the artistic and scientific leanings of only one man become the main voice heard or recognized that is never a good thing in any social or scientific activity. Biases can and do slip through. Unconscious memes passed on.


Charles R. Knight. Public Domain

In the case of this one aspect of sabertooth predators that I will be addressing the cultural transmission of this meme has gone on and on for some time now, Anton as the de-facto principal conveyor of sabretooth aspect and imagery merely inherited it from Knight and paleoartists/paleontologists of the past. It is not really his creation. However Anton "is the man" in sabertooth paleobiology and paleo-art. Heavy lies that throne and any reappraisal of sabretooth anatomy and imagery can not eschew mention of his influence. There really is no way to avoid going through him.


Enough beating around the bush, it's time for Mr. Sabertooth Tiger to get some self respect, stop walking around all exposed, have some decency AND COVER UP THOSE DAMN DAGGERS!!

Yup, sabertooth predators its time to grow up and cover yourself properly with nice big luscious lips sheathing your cherished daggers. You know, like is the case for EVERY EXTANT MAMMALIAN TERRESTRIAL CARNIVORAN. Is that phylogenetic bracketing enough for you? Truth be told phylogenetic bracketing should never be looked at as the ultimate truth, just a rough road-map. It is always better to take a pluralistic approach imbuing the EPB with a heavy dose of adaptationism - Stephen Jay Gould be damned. That is the approach I took with my last post on a heavily lipped T. rex and it is the method I will take here. One caveat of the adaptationism approach is that the feature you are looking at should be one that has a strong influence on survivorship and hence sexual success. So yeah, I think a feature intimately influencing, protecting, lubricating, and assisting in killing via those precious daggers counts in that regard in a very robust way.

"But what about elephants, walrus, and other tusked mammals? Their teeth are exposed all the time."


Pacific Walrus. Cape Pierce Public Domain

You know, I have to admit to throwing up a little in the back of my mouth whenever I hear this argument trumpeted out again and again. First of all it is moving further and further away from the extant phylogenetic bracket. We already have tons of living extant carnivorans to infer from, all of them cover their teeth completely or mostly. Even the clouded leopard the cat >most< often compared or likened to sabertoothed predators covers its teeth with a nice set of lips. Secondly, tusks don't even compare in form or function to saber toothed canines. Tusks are robust, coarse choppers for plowing into trees, roots, gouging into sediments, and >most importantly< fighting with and intimidating rivals. That they are always exposed has a lot to do sexo-social signalling. Sabertooth canines do none of these activities, are often serrated, and are intrinsic to survivorship. Tusks are always out and on display because a better strategy for always getting into costly and risky fights is to bluff your way to the top by always having your weaponry out, exposed, and in full view. Sabertooth daggers were not sexo-social displays and/or fighting tools, an argument Anton (among others) has summarily dismissed. Finally tusks keep growing in many animals that have them. Sabertooth predators had no such luxury. Comparing sabertooth daggers to tusks is like comparing a surgeons scalpel to a machete - a machete that keeps growing back. As you can tell I don't take this argument very seriously. In fact I would call it special pleading.

clouded leopard. credit Vearl Brown CC2.0


clouded leopard skull

We already have numerous and unequivocal osteological evidence of direct evolutionary pressure on sabertooth predators to sheath and protect their cutlery.

Rubidgea. credit Ghedoghedo CC3.0

Thylacosmilus atrox. credit Claire Houck AMNH. CC2.0

Machaeroides eothen. credit Ghedoghedo. CC


Pogonodon platycopis. Edward Drinker Cope public domain

Eusmilus. wiki commons

Hometherium crenatidens fabrini. Public Domain

Above you see examples of the bony correlate in all six of the respective sabertooth predator radiations; gorgonospid synapsids; thylacosmilidaen metatherians; machaeroidinean creodonts; nimravidaen carnivorans; barbourofelidaen carnivorans; and felidaen carnivorans.

It is in the form of the mandibular flange. In some examples it is quite profound, in others it is a little incipient. However it occurs in all radiations of sabertooth predators giving us a strong example of convergent evolution. But to expect evolutionary pressures to exert an influence on just the mandibular, inferior section of the tooth and not expect protection from above - where blows are most likely to come from? Evolution are you drunk? Should we really expect evolutionary pressures to exert an influence on protecting just the bottom aspect of the dagger and not the top? Really, you think so? When you blink does your eyelid only cover half of your eyeball? Does a turtle carapace only protect half of the turtle? Does your cranium only cover half of your brain? Sounds like a very half-assed protective strategy to me.

Instead I would argue a much more robust inference is that ALL sabertooth predators protected their cutlery from above and below. Some species show evidence of the inferior protection via the mandibular flange which itself was sheathed in a very rugged and durable layer of "skin" a lot like the darker area of the jowls you see in your own pet dog. The upper protection would come from a fleshy expansion of the upper lip region - just as you see in any felid or carnivoran today - except larger. As sabertooth predators evolved larger and longer daggers so to did the soft anatomy that protected and assisted them evolve in tandem. Pull up the upper lips to expose teeth and bite. Let lips go loose when teeth are not in use. That a Smilodon with big droopy facial lips seems shocking now is only an artifact of the cultural shock of multiple decades of toothed exposed iconography.

Such protection would not be 100% but I would hedge my inference in favor of protection rather than not. If a feature can evolve that can assist in the struggle for survival, then it should be there.

"How dare you compare sabertooth lips to the lips of artificially selected dogs and cats? Stop it."



Nope, not stopping. The reason I posit this distinctive bulldog looking Smilodon is that artificially bred mammalian carnivorans aptly demonstrate that there is a lot of plasticity in the facial region of these animals. That humans bred them this way for looks, for better scenting abilities, for whatever... I don't really care. All that these domestic breeds show me is that giving the evolutionary context and pressures (i.e. fleshy lips to protect large dentition) there is the genetic potential in mammals that such a look >could< evolve in a wild extinct sabertoothed animal. That the bulldog look comes about is, well, try drawing a sabertooth yourself and the only prerequisite is that the teeth are mostly or completely covered by lips and it is hard to avoid the bulldog look.

Extensive Lips & Fleshy Oral Tissues Allows Enhanced Proprioception of Sabertooth Head & Daggers in Relation to Prey. We Have Direct Osteological Evidence Of This Too.

As tool using, reduced canine having primates I think we often fail to appreciate the risks incumbent upon biting down into something that does not want to get bitten into. I mean, it is a pretty simple thought but revelatory at the same time. You are literally ramming your most vulnerable external body part into another organism latching onto and often holding onto them. Let me restate that again: your most vulnerable body part is in direct line of fire for whatever you are attempting to latch onto. Remember you have to do this again and again to make a living so to speak ecologically. All of these pitfalls would be especially true for sabertooth predators which seem to show a penchant for not only large, strong and retaliatory prey but direct and relatively prolonged contact (i.e. not a bite and flee predator but a tackle, subdue, and bite predator) in which their vulnerable daggers are put into jeopardy. If there is ANY advantage you can potentially and reasonably evolve that helps you to make a killing safer, quicker, and more efficiently then that evolution will likely occur and the inference is a robust one.

Large fleshy lips and oral tissue not only provide a better means of protection from struggling prey (although not 100%) but they also provide a larger and more extensive tactile surface area to position the teeth for efficient and safe biting.

Let me just quote Anton directly here from his book Sabretooth (pp 178-79 Sabretooths as Living Predators):

"One consistent feature of most sabertoothed carnivores is the relatively large size of the infraorbital foramen... (discussion of potential muscular insertion, rodents, Barbourfelis)... there are other structures that pass through infraorbital in all mammals - specifically, the infraorbital nerve, veins, and arteries. The infraorbital nerve is a branch of the maxillary nerve, and it provides sensory nerve endings to the whiskers. Once the nerve crosses the canal, it begins to branch; and when it reaches the roots of the whiskers, it forms a true "nerve pad," creating a characteristic swelling on the sides of the muzzles of many mammals. Thus, one tempting explanation for the large diameter of the opening in sabertooths would be the presence of very well developed, especially sensitive whiskers with rich innervation."

While Anton later tempers his stance mentioning issues of direct proportionality he does mention that " the relationship between the development of the foramina and the function of the infraorbital nerve is widely accepted among zoologists."

I would go further and posit that the reason the infraorbital foramen is relatively larger in sabertooths than other predators is that not only was the "nerve pad" more sensitive - it was also absolutely larger than the nerve pad in extant felids. Why such a large and sensitive nerve pad would be needed in these predators is fairly obvious in terms of making precise and safe incisions into struggling and retaliatory prey that could easily snap off or damage your cutlery.

Anton pp 179:

"... the killing bite of sabertooths must have been quite precise in order to avoid accidents involving lateral torsion or hitting a bone in the prey, which could cause the sabretooth to break a canine. Since the target area of the bite would be outside the predator's visual field, the tactile information provided by the whiskers would be especially useful for the precise control of the biting motions. Modern cats are able to move their whiskers thanks to well developed piloerector muscles, and during the killing bite the whiskers are usually directed forward, enveloping the bitten area in a sensitive net of hairs (Leyhausen, 1979). Given the additional risks imposed by fragile sabers, improved perception would be a useful trait for the sabretooths."

I like and agree with everything Anton says here. I just differ from him in inferring an absolutely larger "nervepad" that would ultimately be more adaptive than the smaller nerve pad he prefers that only partially cover the daggers as depicted in his and all others' paleoart. I can already picture some people saying "well what if the whiskers were just longer?" nah, always better to have the tactile ability and protection. That is the more adaptive and reasonable inference not whiskers creeping down like daddy-long legs.


credit Nick Farnhill. CC2.0

As you can see in the above pic of a cheetah throat clamping Thompson's gazelle - in which the canines clamp shut the windpipe and kill by suffocation - the sensitive nerve pad is deeply enmeshed in this activity. Indeed as the bite occurs in a blind spot for the cat it is the nerve pad, especially via the whiskers, that most accurately dictates to the predator where and how the clamp should be applied. Let's think about this for a second. Many modern large felids clamp the windpipe shut with their relatively stout and blunt canines. That is a pretty refined and delicate approach and the utility of having the sensitive muzzle and whiskers enmeshed in close proximity to the bite area is self evident. However when we contrast this method with how sabertoothed predators - especially the "dirk toothed" cats likely killed - they were looking to inflict massive trauma to the general fleshy region of the neck (but also possibly abdomen). Whether the killing stroke severed arteries or the windpipe or both not really important as the end result is the same - death. So if you think about it the killing method of such sabertooth predators is  less precise than many modern felids -  as long as they get their bite in the general non-bony area of the neck (or abdomen) they good. SO WHY WOULD THE INFRAORBITAL FORAMEN BE RELATIVELY LARGER IN SABERTOOTHS? The logical conclusion is that the "nerve pad" was not relatively more sensitive per surface area than modern felids, it was in fact absolutely larger than modern felids and likely equally innervated and fed with adequate blood supply. This soft tissue adaptation would cover up those precious daggers and provide the tactile support to place the daggers in the right spot to make a killing stroke without risking torsional twisting of prey or bone chipping.

Additionally when we consider how this biting action would look and function in a sabertooth with the traditionally depicted modest sized nerve pad a real dilemma occurs. Due to the large size of the daggers - especially extreme in genera like Smilodon - the sensitive nerve pad would be scrunched up and pushed away from the bite area and not very useful for "feeling out" the best place to position a bite when the mouth was open. Indeed it would be the large teeth "feeling things out" - exactly the problem sabertoothed predators want to avoid!!


Ki Andersson, David Norman, Lars Werdelin - http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0024971


You can easily see what I am talking about using this kinematic illustration above. The sensitive nerve pad would be nowhere near the bite area in traditionally depicted sabertoothed predators. But if we infer a large upper lip and nerve pad that completely or nearly completely sheathed the upper teeth even when the mouth is opened then you have a much more efficient and safer ability to "feel out" where and when to engage the teeth with prey. In this manner the teeth are protected and sheathed until the final split second before impact and the upper lip is pulled back to reveal the daggers. The tough and elastic lip need not even be pulled back that far because as the daggers are plunged into prey the body of the prey itself would simply push back against the lip sliding them back further. Large upper lips provide the most safe, efficient, and osteologically corroborated method of biting possible.

"If only we had evidence for sabertooth appearance via cave-art or other ancient depictions" ... well maybe we do.

Yup it is time we revisit the potential Rosseta Stone of sabertooth life appearance: the paleolithic statuette from Isturitz.


Now I want to make it clear - this is an artistic representation by Mauricio Anton based upon the rendering of Czech paleontologist Vratislav Mazak who himself saw representations of the original statuette in 1970. Long story short nobody actually has the statuette as it has been lost since at least the early part of the 20th century. As the statuette has been lost and been redrawn at least two times, maybe even three times as Mazak himself is said to have only seen "representations" of it, the logical conclusion is that there is a lot of ambiguity in this piece. Furthermore as the original piece can not be directly observed i.e. it can not be "tested" by others it should be in fact stricken from scientific discourse. I mean, am I wrong? Is that not the argument put forth why "private fossil specimens" can not be part of the recognized science as they can not be first hand analyzed, observed, and tested by all parties... am I missing something here? Never the less the Isturitz statuette representation has made it through peer review and is part of the "recognized" scientific literature despite the inability to test it (peer review fail #1).

In his paper reconstructing the musculature and facial anatomy of Homotherium latidens (Anton, et al. 2009) steer away from Mazak's interpretation of the Isturitz statuette representing a late surviving Pleistocene Homotherium and instead side with the original interpretation of cave lion. In Facing Homotherium Brian Switek summarizes their argument succinctly:


It should be noted that this analysis dovetails into the facial reconstruction that Anton et al perform on Homotherium in the same paper.


 Compared to:



And a cave lion representation:

Replica Chauvet Cave Lions, France

While Anton et al. do provide some compelling arguments concerning body proportion and the lack of a sloped back in the model as Homotherium would have in life (sort of like a spotted hyena) these gross anatomical inferences can be explained by the lack of forefeet in the statuette which may influence how the posture is meant to be; the possibility the figure represents a dead or lying felid; and simple errors on the part of the artist.

On the chin argument I find it less than compelling that the strong chin and large lower jaw represents the tuft of hair on a lion. It just looks too prominent and large in my eyes and is more consistent with the mandibular flange of Homotherium. There is no abrupt transition from the chin to the neck line as should be expected if the chin was simply a tuft of hair. Furthermore the manner in which Anton et al reconstruct the jaw in Homotherium is inconsistent with how we or most animals actually hold the jaw in neutral pose. They pose it in "extreme" jaw closure as if the animal would be walking around clenching its teeth shut - similar to the argument put forth on extreme jaw closure in tyrannosaurids and other theropods debunked in my last post. I suspect most animals (including you as you read this unless you are like really mad right now ;')  have their jaws just slightly agape in the neutral pose. This would dissuade the need for the teeth to fit into pockets of flesh in the lower jaw as suggested by Mazak and argued against by Anton et al. (sort of like male baboons) but instead the whole upper canine would simply be sheathed by the upper lip/nerve pad. When the jaw was fully closed it would simply lie against the thick tough, elastic, and lubricated skin of the lower jaw. Just like a clouded leopard which, by the way looks to have canines at least as big or bigger as Homotherium relative to its head size.

There is a bit of a tendency in paleo for people to see beautifully rendered muscular and skeletal reconstructions  of extinct animals and take them a little too literally. When in reality there is a lot of guesswork and biases at play in even the most "rigorously" reconstructed extinct animal no matter how aesthetically appealing. In the paper Anton et al. provide a list of references for how they reconstruct the soft tissue for Homotherium latidens:

"For soft tissue reconstruction we followed the methodology outlined in our previous works (Anton, 2003; Anton & Galobart, 1999; Anton & Sanchez, 2004; Anton et al., 1998; Turner & Anton, 1998)." 

Notice any pattern there? If a guy with the last name of Anton is the lead author of the paper and the source methodology for reconstructing soft tissue is also culled from a guy with the same last name it is not unreasonable to suspect a certain unanalyzed bias to seep through? Could there be a bit of an echo chamber here?

Anton et al., also cite the extant phylogenetic bracket as defined by Witmer as a means to infer soft tissue. But what this method lacks is putting soft tissue through the lens of adaptationism.

Anton et al. also assert that if the canines are long enough they should be seen passing past the upper lip. As evidence for this assertion they cite one example of a canine peeking past the upper lip in a dead lioness they dissected.




Now, you need not be a statistician to realize that when N=1 that is not a very large pool of a sample size to draw meaningful data from. Additionally, you need not be a mortician to realize that when stuff dies things change. Muscles grow tighter drawing back soft tissues. Mouths clench shut potentially. Anton et al. did not account for this or even mention these obvious pitfalls on drawing anatomical conclusions from a cadaver of one sample size (peer review fail #2 ). Better to look at live animals. And when you look at live carnivorans - especially felids - the upper canines are completely or mostly sheathed by the upper lip and the mouth is not clenched shut but slightly agape. Go ahead and peruse google images of large felids and see where the bias lies in terms of canines exposed or not. I double dog dare you.

Other facial features that the Chauvet lions display that are not concordant with the Isturitz statue are that the ears of the cave lion are rounded while the statuette's ears are very distinctively pointed. The spotted pelage and what appears to be a countershaded line along the torso in the statuette also do not match well with the striped pelage that has been suggested for cave lions from ancient cave art. This is a notable omission and Anton et al. deserve to be called out for not mentioning these anatomical incongruity. ( Peer review fail #3 & #4)

One of the more interesting ideas put forth is that the figurine represents a cub due to the big eyes. However I am not sure if those eyes are just stylized and if such a bold chin would be consistent with a cub lion. This idea might explain the spotted pelage as cub lions have spots and then lose them; on the other hand the cubs of striped tigers are not born spotted they are always striped.

And finally the tail. Homotherium has a bobtail while cave lions do not. Is the tail broken off in the statuette? I don't know, we can't go back and analyze which is why it probably should not have got into the scientific literature in the first place!!

Finally it is interesting that - if cave lions had manes like modern lions - a female lion would be chosen for the statuette, and not a male. I mean if you look at iconographic imagery of lions made by humans the male lion predominates in representation. It is larger, has a striking mane, is more powerful and the symbology to "warlike" civilizations is obvious; but perhaps the female lion was actually the preferred symbolic analogy used by paleolithic cultures and they in fact had a different set of cultural values than modern humans...

As you can see we are clearly in the subjective zone on this one. Switek says it takes a lot of special pleading to infer that the statuette represents Homotherium but I say it takes just as much, if not more, special pleading to infer it as a cave lion.

Look the statuette can be argued about until the cows come home - which I will abstain from doing so in the comments section so don't even try and tempt me... But it is a compelling and interesting story.

On a bigger level  this whole discourse is a great lesson in how bias can go unseen and get propagated seemingly without question.

If you go back and read the selection I culled from the Switek article he states his bias right up front:
"... and there is no reason to believe that the canines would have been covered by lips in life."

Let me just refresh you on the talking points on why large lips covering teeth should not only be the belief but the null hypothesis that should be disproven in extinct mammalian carnivorans; all modern terrestrial mammalian carnivornans sheath most or all of their teeth in lips and flesh (EPB); an extensive and proportionate "nerve pad" inferred from large infraorbital foramen located proximate to canine entry assists in vulnerable and precise tooth entry; protection of teeth, especially canines, from breakage and grit; osteological evidence of mandibular flange in sabertoothed predators infers complimentary protection from above.

It may appear that I am picking on Brian here but really he is just a fill-in for many of our biases favoring tooth exposed extinct predators, including until recently myself. Darren Naish seemed to have been favorable to the Isturitz statuette representing a late surviving Homotherium when he discussed it way back in 2006. However after Anton argued otherwise Darren seems to have changed his mind in 2010. However if you look through the comments section in that post you will see that longtime Tet Zoo commentator Jerzy makes many of the same arguments (except I don't think the canine teeth need fit into pockets like in male baboons as suggested by Mazak as well) I am making and calls out several omissions from the Anton paper:



Evidence of Morphological Features Evolving in Tandem With Increasing Canine Length In Sabretooth Predators

As cultural creations as much or even more so than scientific ones it is always useful to brace yourself for the shock and cognitive dissonance of a cherished and loved extinct animal taking on a radical, bizarre new look. We see this startling and immediate transformation but I don't think that we always appreciate that an organism is the product of evolutionary pressures and compromises occurring to it and molding it over millions of years. From our perspective large lips smothering a Smilodon's face appear to evolve over night but in reality the large lips and large teeth would be evolving in tandem as each feature influenced and reinforced the other in a feedback loop. It is only the shock and awe of seeing this change so sudden and profound that we rebel against it.

My contention that increasing lips evolved in tandem with increasing canine size is bolstered by a study showing the exact same correlation of increasing forequarter and forearm strength in sabertoothed predators occurring in concert with increasing canine length. Powerful Arms Saved Sabretoothed Killers' Fearsome Fangs, Study Shows


Julie Meachen-Samuels:

"I found that they had very thick humerus cortical bone, much thicker than any non sabertoothed cat living or extinct... I hypothesized that this extreme cortical thickness was correlated with the extremely long sabers. The robust limbs allowed Smilodon to restrain its prey so that it would be able to make a killing bite without damage to its saber teeth... These traits evolved as not only a suite of characters but as a viable distinctive prey killing strategy several times independently. This combination probably evolved several times because the predators that could best protect and preserve their teeth during prey killing survived longer and could have more offspring, thereby making this combination of long teeth and strong forelimbs a winning combination."

So should I connect the dots? Canines start growing a bit longer, lips evolve in tandem to sheath, protect, lubricate, and provide optimal tactile sensory usage. Forelimbs and forequarters get more robust to further the safety and efficiency of the kill. Canines grow a little longer still as do the lips and forequarters. The animals that can best protect their teeth and live longer reproduce the most even if it is just by incremental percentages. Repeat, repeat, repeat until you get something that looks like this:

Duane Nash. EatYourKittenSmilodon

The thing is you can still haz ur scary Smilodon even with the lips covering the fangs. It is often times what you don't see that scares you the most. If anything the big, jangly jowels add a surreal and disturbing touch. And it is all too easy to imagine that upper lip being pulled back to reveal that staggering dental load just glistening with lubricating juices and ill intent.

So just one more time to hammer down the talking points:

Facial tissue completely or mostly sheathing the upper canines as is corroborated by ALL extant terrestrial mammalian carnivorans and is the best null hypothesis; exposed and constantly growing tusked mammals use their non-serrated tusks for coarse hacking, chopping, digging, combat and display and are an inferior analog to sabertooth canines and need not be considered as they fail in comparison along nearly every metric; the clouded leopard which has long canines comparable to many sabertoothed predators covers its canines completely; all five radiations of sabertooth predators display osteological evidence of protective sheathing on the lingual inferior aspect of the canine via a mandibular flange - a logical evolutionary inference is that protection for the superior labial aspect of the canine was also selected for in the presence of a large fleshy upper lip; the presence of this large fleshy upper lip is corroborated osteologically by the relatively large infraorbital foramen found in all sabertooth predators; this large infraorbital foramen supplies the blood and nerve supply to an extremely large and sensitive "nerve pad"; the extremely innervated nerve pad provides tactile support to make precise and crucial placement of canine entry for bite; such tactile support would be diminished in sabertooths depicted with modest sized upper lip region as this area would be scrunched away from the bite area when the mouth is opened and it would be the vulnerable canines that would "feel out" where to bite; large lips and supporting nerve pad evolved in lock step with increasingly large canines and forequarter strength for maximum safety and efficiency in these highly precise yet vulnerable predators.



And I did not even mention the benefits of; having your serrations free of grit & abrasives; accruing scent particles on a larger "environmental swab"; lubrication for cleaner cutting; and preventing excess moisture loss.



Or you can keep your feebly lipped, tooth exposed, non-tactile, maladaptive, vulnerable, culturally enshrined, and just plain weird looking sabertooth predator. But I say you are holding onto a dream... Yup puny lipped advocates it is you and not I that need be on the defensive on this one. Your creature is the myth - not mine. Script. Flipped.

"It is the responsibility of the scientific paleo-illustrator to make sure that his images rigorously transmit the knowledge that the paleontologists have gathered from specific extinct species."

-Mauricio Anton

*Clarification. I can already see some people misconstruing what I am suggesting with the notion that the upper canines fit into "pockets" formed by the lower lip and the mandible as suggested by Mazik. I don't think this was the case as at all. The upper canines simply rested against a more extensive lower lip region that was very durable and tough tissue - again not unlike the tough, elastic usually dark lips of domestic breeds of dogs that have had this feature artificially enhanced. Also don't confuse what I am suggesting with the debunked notion of G.J. Miller who suggested a quasi- "bulldog" look but for other reasons than what I am suggesting. Miller thought that the lip was retracted backwards to allow proper carnassial use due to the canine length. However this premise is faulty because such a lip would cut right into the masseter muscle and it is not needed anyways as modern felids are able to use their carnassial teeth without opening their mouth all the way.

References

Andersson K, Norman D, Werdelin L (2011) Sabretoothed Carnivores and the Killing of Large Prey. PLoS ONE 6(10): e24971. doi:10.1371/journal.pone.0024971

Anton, M. 2013. Sabretooth. Indiana University Press

Anton, M., Salesa, M.J., Turner, A., Galobart, A., Pastor, J.F. 2009. Soft tissue reconstruction of Homotherium latidens (Mammalia, Carnivora, Felidae). Implications for the possibility in paleo-art. GEOBIOS 42 (2009) 541-551

Cohen, Jenny 2012. Powerful Arms Saved Saber - Toothed Killer's Fearsome Fangs, Study Shows. January 4, 2012.

Meachen-Samuels, J.A. 2012. Morphological convergence of the prey killing arsenal of sabertooth predators. Paleobiology 38(1): 1-14

Naish, Darren. 2006. The late survival of Homotherium confirmed, and the Piltdown cats. Tetrapod Zoology. Thursday, March 9 2006

Naish. 2010. Tetrapod Zoology Book One is Here At Last. Tetrapod Zoology. October 7, 2010

Switek, Brian. 2010 Facing Homotherium. WIRED. November 18, 2010


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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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

Support me on Patreon.
Like antediluvian salad on facebook. Visit my other blog southlandbeaver.blogspot
Watch me on Deviantart @NashD1Subscribe to my youtube channel Duane Nash.























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