Wednesday, May 24, 2017

Lips Before Beaks Part II: Croc Faced Killers & Fleshy Lipped Genetic Monsters

I just can't get away from fleshy lipped theropods...

Recently I went out for a hike in the local Santa Monica mountains. Spurred on by the recent heavy winter rains in California I was expecting a bouquet of abundant wild-flowers. The flowers were there of course and it was breathtaking. However as the strange has an unusual affinity for me (and I for it) what got my attention as soon as I opened my truck door at La Jolla canyon was not the flowers, but a dead hatchling theropod on the ground. Not sure what species - probably a larger corvid due to size - but as I peered closer I noted a strange bundle of flesh at the crease of the mouth.




Some genetic aberration? The avian version of a cleft palate? Or perhaps a link to a more primal ancient pedigree of lipped theropodian monster faces? There is a saying in evolutionary theory: ontogeny recapitulates phylogeny. Is this a case of that? I looked at lots of pics of hatchling birds online and can't find any with that degree of bunched up oral tissue at the commissure.  Whatever your thoughts on what this might represent - probably is some genetic defect - you have to admit the weirdness of it all… a dead beaked bird with a fleshy extension of the oral margin directly reminiscent of the very same depictions I have been advocating.

The picture below is a screen shot from a youtube post by C.M. Kosemen detailing his thoughts on the chickenosaurus. The pic is actually taken from a book titled Incredible Life: A Handbook of Biological Mysteries by William Corliss, purportedly a rare treasure trove of arcane biological curiosities described by Kosemen as " the Necronomicom of biological weirdness". According to Kosemen the book documents a chicken from 1878 born without a beak and having strange "mammalian like head features". The oral tissue surrounding the mouth described as a quasi gummy but tough tissue.


Thanks for commenter Casielles for bringing this pic to my attention and noting how much it resembles some of my lippy theropod designs.

Wherever you fall on the chickenosaurus debate, the Dr. Moreau in me is still curious about what sort of oral tissue would come about on a chicken reverse engineered and stripped of its more derived facial attributes into something well… not quite a dinosaur... but not a typical beaked bird either. Could we garner a glimpse at the primordial oral margin of theropods prior to the evolution of beaks?

The photo below is credited to Bhart-Anjan Bhullar and shows how through suppression of certain proteins the premaxillary bone of a chicken (labelled experimental) can be suppressed giving arise to a more basal configuration.


While the fusion and expansion of the two premaxillary bones into the "beak" is certainly interesting,   all of this does beg the question: if beaks can be reverse engineered into snouts can we also reverse engineer the oral tissue that lines the mouth of birds into what once was?

Bhullar et al. (2015) isolated specific proteins that stimulate the development of beaks (i.e. the premaxillary bone) in modern birds. Although I can find no pictures of the creature that they came up with - from what I gather the birds were not allowed to hatch - they were reportedly able to control these proteins and in doing so reportedly come up with a chicken closer to the ancestral state in terms of facial bones and lack of beak. What they said - and what caught my interest - is that this manipulated chicken skull looked superficially normal from the outside but something obscured a clear look at where the beak should have been. What was obscuring the beak area, you ask? A flap of skin was. Was this flap of skin a reversion to a more primordial "lip" condition? I don't know. What is interesting in this study is that another unexpected osteological change occurred - the palatine bones reverted to a more ancestral condition. Manipulation of one aspect - the beak - can have unexpected correlates in another osteological condition and I'm asking maybe even supporting soft tissue components as well…

credit Bhullar. Showcases loss of beak creates ancestral palatine condition

Take what you will from these studies, they of course have been met with loads of skepticism. But I do have to wonder if they hint at a pathway to a closer approximation of soft tissue oral margins in theropods.


Croc Faced Killers

Croc-Faced Lungfish Fighting Mud Frolicking Spinosaurus by Duane Nash

Of course for those keeping abreast of things it is all about crocodile faced theropods right now. Yep, rugged,  tooth exposed, thin lipped, croc faced killers. And let's give credit where credit is due: Tracy L. Ford has been sounding off on this look for years before the Carr paper hit. You know some might think I am against the notion of croc faced theropods - quite the contrary actually.  I do want to go on record saying that the croc faced idea and lack of lips notion in theropods is a good one and a very important concept and likely prevalent in a great many theropods - just not for all of the theropods that this look is normally attributed to.

A necessary prequel to the ideas I will be elaborating on is my last post Behind Your Bony Mask of Face. In this post I made the argument that the texture of the skull of crocodiles has more to do with ecology than it does skin integument, that in fact a similar skull texture is found on many amphibious and aquatic stealth predators - some that have tightly adhering skin and some that do not. What tyrannosaurids like Daspletosaurus horneri and indeed most carnivorous theropods have is indeed a rough and textured skull that, I suggested, helps anchor a particularly tough and textured epidermis. This dermis - possibly even somewhat keratinized and/or cornfield - is not necessarily covered in scales.

Is there a test of this notion of mine? Can we locate an animal - preferably somewhat close ecologically, behaviorally and phylogenetically to tyrannosaurids - that shares such a rugose and textured skull BUT that does not have a scaled facial epidermis?

By golly, yes there is and it comes in the form of a lineage of theropods that are extinct, were arch hunter-scavengers, did have nasty biting abilities, most certainly face bit, were not aquatic, and were most certainly not scaled in the facial region. The answer is phorusrhachoid terror birds.


Phorusrhacos longissimus Royal Ontario Museum, credit Captmondo CC3.0
Phorusrhacos from here


AMNH 5027 public domain

What I am suggesting is that the facial osteological correlate of these animals is not so much a phylogenetic signal, but an ecological one. Large carnivorous derived theropods (i.e. phorusrhacoids) having a textured skull convergent with their ecological antecedents in large carnivorous extinct theropods. A necessary caveat of this is that, as I mentioned, those theropods that most converged closely with crocodilians ecologically likely had a croc - like oral margin and skin texture. These theropods would most notably include spinosaurids. Other small game theropods especially of the "kink - snouted" gestalt may have been similar or split the difference: lack of extra-oral tissue towards the front of the jaw but retaining some "lip" towards the rear of the jaw. Noasaurids which were always scrounging into the dirt after fossorial prey may have diminished lips as well. Many smallish coelurosaurs, dromies, troodontids, and compsognathids that were small prey scroungers may have followed this pattern of diminishing, receding lips and a more croc-like exposed oral countenance.

Toothed Birds, Pseudo-toothed Birds and Small Game Foraging To Lose Lips 

Sinosaurus credit Duane Nash
Sinosaurus has always been a favorite of mine. It looks basically like a more beefed up version of Dilophosaurus. But while Dilophosaurus' more slender teeth and jaws denote a theropod very much engaged with a prey base of smallish stuff and quite possibly dedicated piscivory - Sinosaurus looks like an animals unsatisfied with small fry and aiming at bigger game. However it still has that odd kinked snout in the front which suggests that it could optimally pluck at small game or perhaps evolved from something of a more Dilophosaurus gestalt, but ultimately was more turf than surf in its diet. To reflect this dichotomy of kinked snouted theropods I diminshed the extra-oral "lip" towards the anterior kink of the jaw but retained more fleshy, salivating meat curtains towards the rear.

Sinosaurus credit Ghedoghedo
Returning to Dilophosaurus we are presented with a conundrum similar to saber-toothed predators and extra-oral margins. It has slender, but very long teeth. Actually this is a case where the teeth from the upper jaw penetrate below the level of the neuromuscular foramen of the lower jaw - and actually might dip below the lower jaw itself. Unless of course the teeth in this lower pic by Jaime Headden are actually protruding too much ( I suspect they are). This creates a very dastardly situation for lower lips and looking at Dilophosaurus it might in fact be a true croc-faced killer!!

Jaime A. Headden (User:Qilong) - http://qilong.deviantart.com/art/The-Dilophosaurus-Yawn-252396964

Again with Dilophosaurus it is simple to formulate an ecological reason for it dispensing with lips. Because it shows tendencies towards small game, large lips in the anterior of the jaw would provide a cumbersome block to intricate poking and plucking of small critters whether in the water, in burrows, or whatever. Better to dispense with such lips, evolve a keratinized and/or cornified oral epidermis epidermis and retain sensitivity from the neurovascular foramina. Note how this parallels the argument in my last piece in this series where I suggested that the evolution of beaks and loss of teeth were coincident with an increasing emphasis of omnivorous/herbivorous diets. Where as the constant pecking, plucking, and cropping of seeds, fruitifications, foliage, insects would encourage a beak type oral margin to replace non-muscular fleshy "meat curtain" type oral margins in  theropods: in croc-faced killer theropods the lips would likely recede for the same basic reasons. In these small game hunting theropods the constant abrasion against substrate, the drag imposed on lips in water, the delicate plucking of small game would encourage a loss of extra-oral tissue. Like theropods that evolved beaks, theropods that moved towards specializing in small game, burrowing animals, "piscivory" would lose lips but they would not lose their teeth.

A constant argument I put forth for large lippy extra-oral tissue in large game theropods is that this tissue provides an extensive "neural net" that allows real time sensing of the movement of large prey in the jaw and corresponding bite adjustments. For theropods foraging for smaller prey in the water such a "neural net" is not needed. Water itself provides the medium for sensing prey movement and as the lips would hinder small game plucking, encourage drag, and are altogether redundant they would soon diminish and take on a "croc-like" oral gestalt. The sensitivity remains however, it is just the lips that recede.



It is also possible a very tough gummy type tissue covered up a lot of the tooth in Dilophosaurus. Such gummy tissue would of course be a lot more rugose and resistant to drying than typical gingiva but still anchor and strengthen the teeth.

Teeth, or better yet pseudo-teeth are important for both extinct and extant proper aves and near birds like the often toothed enantiornithines. There are many examples of the evolutionary utility of teeth, choannal papillae, and pseudo teeth in these animals showing us that not only are such projections useful and whenever possible retained BUT more importantly, I would argue, that there is no universal a piori directive, guidance, or eventuality of an edentulous "beak" in theropods. These examples also fundamentally address the importance of ecological consideration when thinking about extra -
oral margins and "toothiness".

Pelagonis mauretanicus crédit Didier Descouens CC4.0
I have to start off with the most obvious choice: the giant pteranodontid mimics, the pelagornithids. Their non-serrated toothlike extensions of the skull bone and rhampotheca just beg for us to consider the ecological utility of teeth in such marine, soaring predators. They also compel us to wonder if toothless pterodontids were not quite so "toothless" and that maybe they evolved a soft tissue choannal  papillae pseudotoooth and/or sharp tongue tooth replacement of their own. If birds were not winnowed down to the toothless beaked species through the K/T extinction one has to wonder if legit toothed birds would not dominate the oceans, like they did in the Mesozoic?

Pseudo teeth penguin credit: http://i.imgur.com/o3vze.jpg
Pseudo-teeth on penguins are a thing. Remember, penguins stem from a fairly early branch of avians and possibly even arose in the Cretaceous (although I doubt it due to competition from hespernornithids) but there are no truly toothed penguins that we know about from the fossil record. This reinforces the idea that only edentulous beaked avians made it through the K/T and had to reinvent teeth when they occupied niches where teeth come in handy.

To bolster this pattern simply look towards the dominant fish eating birds around in the Cretaceous: hespernornithiformes and ichthyornids both have toothed jaws. They had basically lipless keratinized beaks - as should occur given their predilection for aquatic prey. Yet they retained teeth. And there is no reason to suspect that they would lose their teeth if the K/T event did not occur.

 Hespernornis regalis YPM 1206 credit Heilmann 1926

It is worth mentioning that in the above species it has partially lost teeth in the upper jaw, replaced by sockets that the lower teeth slot into. Ichthyornis shows a similar pattern: tooth loss partially in the upper jaw but a continuous row of teeth in the lower jaw. One has to wonder if and why we should expect complete tooth loss in these groups given the propensity for truly toothless birds to evolve pseudo-teeth.

Ichthyornis public domain credit O.C. Marsh
I would be remiss not to put a word in for enantornithines, the true champions of tooth retention in birdy types. They count in their number a fair bit of smallish, predatory type toothed opportunists and specialists. They also, as should be expected, probably had extremely reduced and receding lips to better pluck and peck at small game. But alas they did not make it through the K/T as successfully as true avians perhaps because they did not fully commit to seeds and the ubiquitous "pecking" foraging method so emblematic of modern birds?

credit Stephanie Abramowizc
Indeed, far from showing a tendency to lose or diminish teeth many enantiornithines were going full hog with toothiness. Sulcavis geeorum had some pretty gnarly, crazy teeth seemingly well adapted for chewing up tough crustaceans and insects.

Sulcavis geeorum credit Stephanie Abromowicz

Jingmai O'Connor:

"While other birds were losing their teeth, enantiornithines were evolving new morphologies and dental specializations. We still don't know why enantiornithines were so successful in the Cretaceous but then died out - maybe differences in diet played a part."

So where does this leave us? Admittedly this piece is a little all over the place, and readers might be dumbfounded in how quickly I switch from say a critter like Sinosaurus to Pelagornithis. But there are some general themes and trends that stand out.

- The transition of toothed birds to toothless bird is not a direct line nor is it necessarily inevitable. The prevalence of pseudo-teeth in many modern birds (especially piscivorous) that correspond to toothed Cretaceous analogs should give us moment to pause. Perhaps the Cretaceous toothed ichthyornids and hesperornithiformes with their basal retention of teeth were not the inferior models compared to modern penguins and "gull" type seabirds but actually the optimal model due to their teeth which should outperform the pseudo-teeth of modern birds.

- Enantiornithines provide us with an alternative universe where toothy birds are not only common but the most successful "norm". We might be partially conditioned to think of modern derived toothless birds as the optimal model for what a bird should be, but what if this is not the case? Enantiormithines seemed to dominate toothless birds in the Cretaceous. Did the K/T boundary provide the ecological filter that allowed toothless seed eating birds to get through but prohibiting the more toothed - and carnivorous - enantiornithines from getting through as has been suggested in a recent paper?

- In both the toothed fish eating birds and the carnivorous enantiornithines I would put forth a condition of highly reduced lips - perhaps just a trailing edge of tissue at the commissure. This is also similar - albeit without a beak - to the near lipless condition I would expect in small game hunting, fossorial foraging, and piscivorous theropods. The realities of aquatic foraging, constant abrasion, and intricate plucking of small game would create a less than ideal situation for any substantial, non-muscular extra-oral tissue in these animals. This provides an alternative pathway to losing lips to what I discussed in my Lips Before Beaks part I where herbivory would diminish lips and create beaks in theropods.

In all the above examples I am actually explicitly arguing for an exposed toothed, primarily lipless, and even croc-like oral margin. Wait a second here… wasn't I the guy who argued for lippy sabertooth cats,  beneficial activity of saliva on tooth health and what not? Have I done an about face?

Let's just say that my thoughts have… evolved and become a bit more nuanced. Two things can be simultaneously true and seemingly at odds but still coexist. Sheathed teeth under the auspices of calcium and phosphorous buffered salivary broth I still believe is a great thing to have… just not mandatory in all cases. Pterosaurs, crocs, plesiosaurs they all break that "rule" and a good many theropods probably did too… just not all of them. I would still consider most largish big game, serrated toothed macro predatory theropods to maintain - and even re-evolve - large "meat curtain" type lips. This would include most largish tetanuran type theropods, allos, carchs, predatory ceratosaurus, tyrannosauroids, dromies, megaraptors - generally most serrated toothed zyphodont theropods.

You will note I left out abelisaurids, I think something neat was going on with them which I will save for another post. Yep, some have been asking for it and I finally have enough new ideas to make a post on abelisaurids. Trust me, they will be weird AF when I'm done with them. Weirder than they already are.

And finally I leave you with Austroraptor. It was a South American unenlagine potentially flightless spinosaurid mimic.  Remember spinosaurids themselves are crocodile mimics and share with them a skull texture (spinosaur skull texture is more similar to crocs than tyrannosaur skull texture is to crocs imo) and likely a lipless oral margin. Guess what the skull texture of Austroraptor looks a bit like?




Austroraptor cabezii by Duane Nash

Austroraptor is that unique beast that potentially tells us a lot. Because it was a maniraptoran and quite possibly secondarily flightless it may indeed hail from fully feathered ancestors. If it lost feathers on the face it may have indeed followed the trend of modern naked faced birds and eschewed feathers and scales on the face. After converging with spinosaurids (which converged with crocodiles) it evolved a highly, rugose, textured, and pitted skull. Not because it had a scaly face but because such a skull texture allows - as I suggested in Behind Your Bony Mask of Face - better tactile and neurosensory capability as a sensitive snouted aquatic predator. Hence the convergence of skull features as I highlighted in such disparate groups as temnospondyl metoposaurs, phytosaurs, snapping turtles, crocodilians, various fish, and others. These textured skulls in aquatic predators I hypothesize allow more surface area to "catch" vibrational frequency in the water medium like a gnarled, old used catchers mitt.





Refs

Bhullar, B.-A. S., Morris, Z. S., Sefton, E. M., Tok, A., Tokita, M., Namkoong, B., Camacho, J., Burnham, D. A. and Abzhanov, A. (2015), A molecular mechanism for the origin of a key evolutionary innovation, the bird beak and palate, revealed by an integrative approach to major transitions in vertebrate history. Evolution, 69: 1665–1677. doi:10.1111/evo.12684

Carr, T. D. et al. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Sci. Rep. 7, 44942; doi: 10.1038/srep44942 (2017).online
Ford, T. L., 2015, Tactile faced Theropods: Journal of 
Vertebrate Paleontology, SVP 75th annual meeting, Meeting Program & Abstracts, 
p. 125.


O’Connor, J., Zhang, Y., Chiappe, L., Meng, Q., Quanguo, L., Di, L. 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specializationJournal of Vertebrate Paleontology. 33, 1: 1-12

Weeks O, Bhullar B-AS, Abzhanov A. 2013. Molecular characterization of dentadevelopment in a toothed archosaur, the American alligator Alligator mississippiensis. Evolution and Development 15(6): 393-405. 

"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.
























Wednesday, April 12, 2017

Sinking Ornithoscelidians: Sitting Ducks, Water Chevrotains & Ceratopsid Death Beds

River Bottom Running Ankylosaurus created for this blog piece by Robin Liesens

Dinosaurs back in the water and it feels sooo good… There are probably fewer narratives, memes, and dialogues as storied as the on and off again love affair between dinosaurs and the water in both scientific and popular forums. From pre-renaissance snorkeling duckbills and bottom walking brontosaurs to fanciful water world assertions that all dinosaurs were aquatic to bona-fide actual aquatic dinosaurs such as Spinosaurus the concept of dinosaurs in the water is one that is not soon to leave us. Dinosaurs sloshing, mucking, wallowing, foraging, and hiding in the water is an evocative suggestion because such depictions are not without analogue in many modern terrestrial tetrapods and large mammals in particular.

It is a contention of mine and this piece that just because an animal is not explicitly aquatic does not negate the potential for water to still shape and inform significant aspects of its biology and anatomy.

credit Burian

The opening depiction of a bottom running Ankylosaurus, kindly provided by Robin Liesens (Dontknowwhattodraw94), represents what I view as a logical culmination of the ornithischian body plan with relation to water. Ankylosaurus was quite possibly a sinker not a floater. An evolutionary arms race in ornithischians that gave this branch of dinosaurs especially thick, dense skin to protect from both theropods and intraspecific combat; an osteoderm studded skin; lack of skeletal pneumaticity; thick bones.  What this creates is the distinct possibility that ankylosaurids and perhaps other "dense" ornithischians - especially among thyreophorans and marginocephalians - did not actually float in the water as humans, birds, and most terrestrial mammals do but would sink right to the bottom like hippos, tapirs, and water chevrotains.

Bottom punting animals have a rich history here at antediluvian salad: bottom punting Spinosaurus is the ultimate conclusion I reached regarding the most likely aquatic propulsion for that animal. A necessary caveat of a good bottom punter that utilizes body density (as opposed to changing/shifting lung volume like aquatic turtles & crocodiles) is that actual swimming ability decreases as punting ability - and therefore body density - increases. This creates the paradoxical situation in hippos where they can not actually swim - hippos can not cross deep bodies of water because they sink like a stone. The same situation may have occurred in several ornithischians with thick dermis - not necessarily because they were semi-aquatic like hippos - but because they had embarked on a social and defensive strategy of thick skin, armor, and dense non-pneumatic skeletons. Body density and therefore punting ability and the inferred possible loss of actual swimming ability is an interesting side effect of their particular defensive anatomical pedigree.

All of this discussion should be couched in the recent elucidation (not withstanding a rebuttal) of a revelatory linkage of theropods and ornithischians into ornithoscelida (Baron, 2017). One of the most interesting questions that this linkage of neo-theropods and ornithischians raises is "why would ornithischians have lost the highly pneumatic (and presumably air sac filled) skeletons that most likely was ancestral to both ornithischians and theropods?"

Several commentators on the Tetrapod  Zoology post on ornithoscelidia approach this question and suggest that the ability to bottom feed on aquatic vegetations is a potential reason. I agree, but I would embellish this reasoning with a more dire and immediate consequence: ornithoscelidians did not want to be sitting ducks.

Sitting Duck: A person or thing with no protection against an attack or other source of danger.

Theropods we know were full of air - it is no stretch to imagine that, when immersed in water, they would have floated like a buoy. Maybe not sitting so high in the water as modern ducks but possibly with much of the head, neck, and even some of the back out of the water. This buoyancy would have made theropods excellent patrollers, explorers, and navigators of aquatic environments. It also may have helped in dispersal situations and survivorship of catastrophic aquatic inundations such as tsunamis and the relatively frequent storms surges, tidal inundations, and hurricanes that we should expect in hot house climates.

The floatability in water made diving a little bit difficult but not impossible: for theropods wanting to get under the water they simply point their nose in the direction that they want to go in and enact rear propulsion from the legs and tail. One of my favorite observation recorded of opportunistic hunter/scavenger theropods is of giant petrels (not known for diving abilities) repeated going underwater to scavenge a dead wedded seal.

creditJohn Van Den Hoff & Kim Newberry 2006

This digression also allows me to finally get rid of a piece of art I did quite a while back. Some opportunistic Coelophysis diving to scavenge a dicynodont at the bottom of some recent flood waters. Take note of the opportunistic pterodactyloids buzzing in for dislodged scraps.

Diving For Coins Coelophysis by Duane Nash

What is good for the goose is not necessarily good for the gander. While sitting high in the water may have been a benefit for wide ranging, opportunistic theropods sitting high up in the water for prey animals like ornithischians may have been fatal. And when we look at the earliest ornithischians they were not gigantic, heavily armed, or especially refined cursors. Their niche may have best been approximated by large rodents, small forest dwelling deer and antelope, and water chevrotains (Hyemosuchus aquaticus). It is water chevrotains I want to pay special attention to as here is a small herbivore that utilizes the water to good effect to literally vanish from predators. In the clip below the predator happens to be a modern predatory theropod , the crowned eagle. Also wonderfully narrated by Mr. Honey Badger himself:



Water chevrotains are noted for a thick, dense padding of skin along the rump and around the neck. Skin is actually the largest organ in the body and plays a little heralded but profound role in buoyancy as I discussed in bottom punting Spinosaurus. Readers should note that two other bottom punting specialists - tapirs and hippos - have thick skin and sink to the bottom.

It is quite possible that the earliest ornithischians quickly and resolutely diminished their system of air sacs and pneumatic condition - that in conjunction with thick and sometimes armored skin - allowed them to sit lower in the water. Analogous to water chevrotains and other small mammals that utilize the aquatic medium for concealment these earliest ornithischians set in motion a trend of aquatic concealment that - to greater or lesser degrees - likely persisted throughout their tenure with ornithopods like Thescelosaurus. There is no way to tell at this point where various ornithischians sat in the water - if they achieved true negative density like water chevrotains or if they just sat with more of their body submerged and that was good enough. But the point remains that such animals would have benefited cryptically by sitting lower in the water and dispensing with air sacs.

credit Duane Nash Thescelosaurus hiding underwater from topside threat
But if we assume that the baseline condition for ornithischians was to sit low in the water, when we add density in the form of scutes, osteoderms, thick skeletons, and heavy skulls then we have the likely potential for true bottom-punting, negative buoyancy situations to develop. Among both marginocephalians and thyreophornas we see many likely candidates that may have trended towards  negative buoyancy in these animals.

Water Sports by Duane Nash

For the most part I think bottom punting would have served these animals just fine. They still likely moved with grace and efficiency through bodies of water - they just did not swim in the strictest sense of the word. Moving through relatively shallow streams, rivers, ponds, sloughs, estuaries less than 5 meters deep or so not a problem and waters of this depth would have been what these animals came across in their day to day existence.  Indeed a ceratopsid could easily have been prone to flee into the water when chased by a theropod. The theropod in grave danger from a bottom punting ceratopsid as it floats vulnerable at the surface, its belly exposed to horn thrusts.

However in deeper waters that they could not get up to the surface in that they found themselves in trouble. I am specifically alluding to the ubiquity of ankylosaurid skeletons recovered from oceanic sediments - were these animals taken by sudden intrusions of sea water that put them in waters too deep to kick off the bottom to the surface in? And then you have the infamous ceratopsid mass bone beds, most notably from Centrosaurus that most likely document tremendous inundations of the ocean onto land. Researchers have struggled to explain why Centrosaurus - and pretty much nothing else but Centrosaurus - succumbed to these inundations. The wikipedia web page on the Hilda mega-bonebed summarizes a lot of the work on this topic.

The ubiquity of ceratopsids in these death assemblages is potentially explained by a negative buoyancy for these animals. All the theropods and hadrosaurs in the environment would float away. Ceratopsids were doomed in deep water.

Is there any independent evidence pointing us in the direction of thick skin in ceratopsids? By golly yes there is. Before the world fell in the love with the preternaturally adorable Psittacosaurus soft tissue restoration there was some other work on Psittacosaurus dermis (Lingham-Solia, 2008). What was revealed in the study is that the Psittacosaurus revealed a cross section cut out that had a remarkable density of 40 collagen layers and a skin thickness of .8 inches - which does not sound like a lot but is pretty astonishing for such a small animal. Unfortunately the author behind this work used these multiple layers of collagen to argue that not only was Psittacosaurus not "feathered" - which it wasn't of course - but that the feather impressions recorded on theropods are actually layers of collagen peeling off. The study was pirated by B.A.N.D.I.T. notions and what could have been a perfectly interesting document on exceptional skin thickness got turned into something that it shouldn't have. But let's not throw the baby out with the bath water here. The paper still shows a startling level of skin thickness - among the highest recorded in any vertebrate.



Again, let me hammer that point home, "multiple layers of collagenous fibres in excess of 25, among the highest recorded in vertebrates". There was an arms race in the Mesozoic, or more like it there was a skin race. Prey species attempted to evolve the thickest most durable hide they could to thwart those pesky theropods who more than kept pace in evolving forms more adept at sawing or crushing through thick and armored hides.

There has been some research into this topic of ceratopsid swimming and buoyancy (Henderson, 2014). The work concluded that ceratopsids sat in the water with their heads submerged. On the other hand hadrosaurids were much better natural swimmers with their head above water, hence the lack of hadrosaurids succumbing to such oceanic intrusions. This study points us in the right direction but it left out two things; 1) It did not account or even mention skin - a particularly dense skin may have sunk ceratopsids right to the bottom; 2) Pretty much any large tetrapod that lives in and around bodies of water has at least some capacity to move through bodies of water. Ceratopsids living on coastal Laramidia - especially bordering the western interior sea - would have have come across water all the time - lagoons, estuaries, swamps, tidal channels, rivers. It is absolutely non-sensical that an animal that comes across bodies of water daily has no way to efficiently move through them. Long time readers know that this is a constant theme I iterate on this blog: animals have to make sense. They have to reasonably move through their environment; eat; protect themselves; mate. When you conduct research that points you in the other direction - towards a maladaptive animal ill-equipped to deal with day to day encounters (such as bodies of water) - there is probably something wrong with your scenario. Such an animal, so maladapted to it's environment, would be selected for extinction and not leave a fossil record. Whenever you see a paleontologist utter the phrase "failed evolutionary experiments" run away quickly.

Now some have taken the mantra "most every tetrapod can swim" a little too literally:  I would add the caveat: "most every tetrapod can swim and/or bottom punt". Sinking ceratopsids right to the bottom would at least allow for movement through >most< bodies of water. For a large animal that can bottom punt it can still go through potentially fairly deep bodies of water, at least most bodies of water it will encounter on a daily basis. The problem is when it encounters bodies of water too deep to kick off of the bottom of to reach the surface. Large deep rivers, lakes, and extensions of the ocean can act as barriers to such animals. Or a catastrophic inundation of the ocean. That would be a big problem for negatively buoyant animals.

Bottom punting ceratopsids offers a potential explanation for why these animals were selectively killed while no other dinosaurs suffered comparable losses during large oceanic intrusions. It is not that ceratopsids could not move through water - they could quite well as a bottom punter - it is that in deep water they sank like a stone. It must have been horrific for them when the sea took over the land.

And this speculation is where it gets really cool. Because once you have a geographic barrier thwarting travel - in this case deep water - then you have a potential cause for speciation events. And we all know how wild with diversity ceratopsids on Laramidia got...



Papers

Baron MG, Norman DB, Barret PM (2017) A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature March 23, 2017

Henderson, D. 2014. Duck Soup: The floating fates of hadrosaurs and ceratopsians at Dinosaur Provincial Park, in Eberth, D. and Evans, D. (eds). Hadrosaurs. Bloomington: Indiana University Press. pp. 459-466

Lingham-Soliar, Theagarten. 2008. A unique cross-section through the skin of the dinosaur Psittacosaurus from China showing a complex fibre architecture. RSC Proceedings of Biological Sciences 2008 April 7. 275(1636) 775-780. online

Van Den Hoff, J & Newberry, K. 2006. Southern giant petrels diving on Macronectus giganteus diving on submerged carrion. Marine Ornithology 34: 61-64. online


"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.

Wednesday, April 5, 2017

Behind Your Bony Mask of Face

We all know what this post is about.

Below I will present a few small screen grabs cut out of larger pics of skulls. Let's just say that the representative animals are quite diverse phylogenetically. But despite the disparate vertebrae groups there are some striking similarities - and differences - in the bony texture. Before I reveal what animals are represented I would like readers to simply focus on the textures and patterns at hand, without any phylogenetic prejudices in mind.

One of these things is not like the other…

A.


B.



C.




D.



E.



F.



G.



H.



I. 



J.



K.





Again, without any phylogenetic prejudices creeping into your decision making, what similarities and differences do you observe? Which examples are more textured, which are less? There is a story to tell in all of this I will suggest and after the players are revealed I am going to offer that it is more behavioral - more adaptationist (there is that dirty word again) - than strictly phylogenetic.
.
.
.
.
.
.
.
.
.

A. Belongs to a stinkin' fur ball, the lowland Paca. Amazing is it not? These zygmotatic plates have something to do with the sound propagation of this cheeky little guy. Not only is this animal a bit of an outlier for its mammalian pedigree but it is also an outlier for its terrestrial inclinations.

Lowland Paca. Cuniculus Paca credit Paolo W. Viscari Specimen of the Week
B. One of several fishes I will be highlighting. This is the fanged blenny - Meicanthus grammisteus - which injects an opioid peptide into its prey to sedate them. Incidentally I came across a link to this fish on Facebook on the same day as the Carr paper was dominating my fb news feeds. Credit Brian Fry.


C. Some gnarly looking catfish I "borrowed" off of Flickr. Thanks credit and © to Lonmelo.


D. Another fish, the North American bowfin. Coincidentally another predatory ambush predator of murky aquatic haunts… are you sensing a pattern yet?

North American Bowfin credit
E. American Crocodile. Exceptionally large and rugose skull.

American Crocodile. Credit Daderot Public Domain
F. Another aquatic tactile predator - Suchomimus tenerensis !! credit James St. John.


G. Another nippy creature of murky habits: Amphiuma tridactylum found on Tet Zoo originally from flickr site Boneman 81.


H. Ho hum, another swamp monster Metoposaurus credit Jeyradan, public domain.


I. Daspletosaurus horneri. Does it really compare that favorably to the other examples? I'm not seeing it. There is a general rugose nature to it, but hardly as intricate bone texture as the other examples…


J. The alligator snapping turtle. Seriously what is up with highly textured facial bone among stealth aquatic predators? Credit, pic allows zoom in functions.


K. Yet another textured skulled aquatic predator, the phytosaur Pseudopalatus mccauleyi. Petrified National Park credit Park Ranger. uploaded FunkMonk



Did I hit you over the head enough with rugose skulled swamp monsters?

The recent paper on the Two Medicine Formation tyrannosaur and associated facial integument inferences (Carr et al., 2017) makes the case that crocodile facial integument is the best inference for tyrannosaur facial integument. Also worth mentioning is that this is the argument that Tracy L. Ford (Ford, 2015) has long been making for quite some time (though Carr et al. did not deem fit to mention him). While the media has certainly ran with the story, at least in the online paleo community reaction to this inference has been highly skeptical. I don't want to recount the variable criticisms to Carr et al's inferences as many have done that already. However what  should not be lost on our observations is that several of these textured skulls above come from animals that do not have tightly adhering skin texture such as the various amphibians. Or even have scales at all.

There is potentially a story to tell here...

Let me make another analogy to fantasy creatures. For me one of the most entertaining aspects of fantasy creature creation is to unpack the various - and often times disparate - elements from contemporary or extinct creatures that are spliced together to create a fictional animal. For me one of the most successful creature splices of recent years is the Bashee and Great leonopteryx from Avatar. Darren Naish does an excellent unpacking of the various inspirations and spliced bits of microraptor, bird, pterosaur, bat, fish, and sports car design that went into the creation of these animals.


It is the liberty in splicing all of these disparate animals together that creature creators do to make a strange but believable fictional animal  that paleontology needs to take more inspiration from.

I think the Carr paper is valuable because it draws attention to crocodile skull texture. Yes it is true that tyrannosaurid skulls show some gross similarity to crocodile skulls in sharing a rugose texture and if you had to draw a rough comparison as to what animal best matches large tyrannosaur skull texture crocs are a good analogy. But crocs evince this rugosity all over the skull, tyrannosaurids have many smooth parts with the rugose sections being localized across more of the rostral sections. Of the animals presented above I would posit the Daspletosaurus skull as being the most different texturally from the others. People are naturally drawn to to comparing tyrannosaurids to crocodiles because they are related and predatory. However most theropods (except spinosaurids) are quite distinct from crocodiles ecologically. And that is the gist of what I am suggesting, we are potentially witnessing bone texture as an ecological signal - not as a phylogenetic/anatomical one. Instead of asking; what other archosaur skull looks most like a tyrannosaur skull? we should be asking; why does a crocodile skull look so similar texturally to a temnospondyl, catfish, snapping turle etc etc. skull? 

When we see a diverse array of animals exhibit a remarkable similarity in facial bone texture as well as a remarkable congruence of ecological niche - ambush predator of murky, aquatic haunts - we have to seriously question if this bone texture is really a phylogenetic-anatomical message or an ecological one. There is more than a reasonable and persistent trend of highly pitted, rugose, and textured skulls among aquatic and amphibious stealth/ambush predators. The question is why?

My hypothesis is that such skulls in aquatic predators - highly textured with increased surface area but still maintaining streamlining - work as enhanced sound/vibrational interceptors. Like an old, well used catching mit these rugose skulls are better able to intercept, transmit, and "grab" acoustical/vibrational frequencies in a visually limiting aquatic environment. Vibration may travel through tissues in different ways and bone might offer an added layer of frequency interception that - when combined with other tactile organs  (nerve endings, pressure domes, "whiskers" etc. etc. ) allows for a more comprehensive reading of the environment.

So why do tyrannosaurs - and many theropods - have such rugose skulls? Well in the case of spinosaurids (and maybe other theropods that exploited aquatic environments predominantly) it is possible they converged on a highly textured design for the same reason that other aquatic predators potentially did - it enhanced sensitivity. For most other other theropod skulls - including tyrannosaurids -  I would like to advance an argument from material science: that there is a relationship between bonding strength and surface roughness. In this case the two materials are skin and bone and a rugose bone texture allows for skin to better anchor on the skull - growing into all of the nooks and crannies with increased surface area - in light of a particularly traumatic bite prone existence. That this bone texture is most prominent on the parts of the "snout" most devoid of overlaying musculature and exposed to bites we should expect this rugose nature to be most prominent there. Which it is. Unlike a crocodile skull which displays rugose formations across almost all of the skull - in line with the potential use of such rugose formations to discern water borne vibrations.




Crocodylus porosus credit 
There is potential analogy to the textured skull of theropods acting as a structural adhesive to skin argument: hippo skulls. Animals which have tremendous lips and a very battle prone, bite weary existence. They don't have smooth bone where the lips and skin anchor - they have textured, rugose bone .

credit stock vault author Bjorgvin Gudmundsson

And for the record I do agree with Carr et al. (and Tracy L. Ford btw) that tyrannosaurids (& other theropods) did have exquisitely sensitive, tactile faces. But it was through large lips that grew out from the neurovascular foramina that these nerve endings felt and sensed their world - both the real time struggles of their prey and the touch of a mate or hatchling. It is patently obvious that the pattern of foramina on the dentary (bottom jaw) are arranged in such a way that the upper teeth will not cut into the labial tissue that grows out from them. Note that this is not the pattern we see the foramina take in the crocodile dentary - where they emerge right up next to the teeth.

I also agree that they were probably more romantic and tender than we might typically imagine.

Sources

Carr, T. D. et al. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Sci. Rep. 7, 44942; doi: 10.1038/srep44942 (2017).online
Ford, T. L., 2015, Tactile faced Theropods: Journal of 
Vertebrate Paleontology, SVP 75th annual meeting, Meeting Program & Abstracts, 
p. 125.



"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.








Related Posts Plugin for WordPress, Blogger...