Sunday, August 2, 2015

Death Comes Ripping - Bone Saw Theropods



When researching this post I did imagine how google queries for "bone saw" might raise the suspicion of internet watchdogs. But since this is a post on theropod teeth and not how to dispose of human bodies my alibi is in place bwah haha...

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Now you know if I can squeeze an appropriate song I like into a post I will do it - especially a Misfits song. Today's song is the Misfit's "Death Comes Ripping" and I included a more rare, but still very feral, version by Samhain to boot!!





What you are looking at below is something that likely caused a lot of pain in it's time but also potentially saved some lives. It is an amputation bone saw circa 1950. Despite it's antiquity this
  

amputation saw features some nice design features that would have facilitated as clean and straight an, ahem, amputation as possible. What I am referring to, and what I highlight in the pic below, are the recessed hollowed out portions between every eight or so serrations.


Also take note of the circular bulb that they end in. This feature is also found in modern day circular wood saws and are called expansion slot base holes. Their description via carbide processors



Expansion slots strengthen and lengthen the life of the cutting serration.What happens is that as the cutting tips experience stress and pressure the expansion slots allow excessive forces to distribute throughout the body of the saw. And if you are woodworker trying to make a straight cut or a Civil War doctor field dressing a wounded soldier by amputating their musket bullet demolished tibia the expansion slots allow you to make straighter, cleaner, and more efficient cuts. 

A recent paper Developmental and evolutionary novelty in the serrated teeth of theropods (Brink et. al.) July 2015 Scientific Reports link shows that this cutting innovation did not first arise on the Civil War battlefield or in the Lowes hardware section but was endemic to the most successful radiation of large bodied terrestrial predators ever - the theropods.

Danielle Dufault (c) used w/permission
What Kirstin Brink did - which I can imagine is painstakingly difficult - is to take thin sections of the serrations on various theropod teeth. Now, it is not big news to most that theropod teeth have serrations - ziphodont dentition - and it has even been known that close analysis of the space between serrations reveals a distinctive gap. Referred to in this paper as "deep interdental folds" they were previously interpreted as a feature that occurred epigenetically (i.e. during the working life of the tooth) to mitigate stresses imposed on the tooth but Brink's work reveals different. Analysis of teeth not yet erupted found  that these interdental folds were already in place before the tooth experienced usage. The deep folds were also found on both the mesial and distal side of the tooth. Altogether a strong argument that this feature is nested deep within theropods and arguably assisted in their trajectory as apex predators across the globe for an unparalleled amount of time.



"We proposed a developmental hypothesis that these are structures created when the tooth is first forming," Brink said. "It actually helps to deepen the serration within the tooth and strengthen the serration and tooth overall."

Theropod teeth were bolstered with respect to other predators like monitor lizards and sharks by not only these folds but by a layer of dentine. The "planned obsolescence" of shark/monitor teeth is in line with the short life span of their teeth as compared to large theropods - months as opposed to years. By simply the addition of the interdental folds theropods not only had relatively superior cutlery in their jaws but maintained a distinct adaptive advantage over other ziphodont predators that must constantly replace teeth. With a more thrifty tooth replacement strategy all that valuable calcium and phosphorous that would go to tooth replacement could be used for other things - like growing a bigger skeleton or laying more eggs.

"What is so fascinating to me is that all animal teeth are made from the same building blocks, but the way the blocks fit together to form the structure of the tooth greatly affects how the animal processes food. The hidden complexity of the tooth structure in theropods suggests that they were more efficient at handling prey than previously thought, likely contributing to their success." Brink (link) via Sci-news. 

Several lineages of theropods lacked or had modified deep interdental folds and Brink does not shy away from suggesting that the hypercarnivorous adaptations of theropods with such oral cutlery expanded their niche to include true bone consumption (i.e. not just in tyrannosaurids).
From the paper:


Now "bone crushing" is an interesting topic in theropod diet. Personally, in light of this new tooth data, I would prefer the term bone slicing to describe theropods likely presumed style of cutting into bone (remember the bone saw). But the amount of bone consumption and direct utilization of bones by theropods is equivocal and controversial. Tyrannosaurids, especially T-rex, are well accepted as bone crunchers/consumers based on their robust skulls and likely preserved coprolites loaded with minced bone matter (Chin, 1998). But generally paleontologists have shied away from suggesting direct bone consumption in other more blade toothed theropods. See Chure 1996.


And what should attract your attention is the allosaur pubic foot with a chunk cleaved clean off. This is from one single bite and it should be stated that the pubic foot is, with the possible exception of the sacrum, the most massive bone in the theropod body. Whether this was intention or incidental this substantial damage to a robust bone by a Jurassic theropod discredits the notion that only late Cretaceous advanced tyrannosaurids were capable of bone breaking/consumption.
Morrison theropod tooth marks on bone likely targeting meat

However a more recent survey of theropod bone interactions paints a more nuanced portrait of bone consumption by theropods (Hone, 2009).


Theropods were eating loads of bone they suggest - but it was primarily in the form of small/immature dinosaurs consumed in entirety and the bone largely digested. While I agree with the premise that loads of baby dinos were getting gobbled up I do not necessarily concur that adult or near adults were not also predated or at least that the concentration on babies here is a tad overstated (but that is another post). Both the Churee and Hone papers specifically mention a higher degree of bone utilization in Cenozoic mammalian faunas... BUT in K-selected mammalian communities a larger proportion of the standing meat crop would be locked up in adult bodies. Therefore a higher frequency of bone exploitation should be expected in mammalian communities - exactly what we see. But this observation does not mean theropods did not exploit bone to some extent... AND that Allosaurus pubic bone pictured above was bitten clean through though...

What leaps out at me in the above list is the obvious dominance of North American dinosaurs esp. Allosaurus/Tyrannosaurus. These are some of the most well sampled formations around. Basically a lot of bone/theropod interaction might be getting overlooked.

Additionally, if you look at the above review of theropod/bone interactions coprolites are excluded for whatever reason. There is the famous Tyrannosaurus turd that Karen Chin - she of dino-coprolite fame - documented but what gets less attention is her work on a large putative theropod coprolite with numerous bone fragments titled Exploited twice: Bored Bone in a Theropod Coprolite From the Jurassic Morrison Formation of Utah, U.S.A. 2007 SEPM-Special Bulletin. (contact Chin or myself for pdf I don't think this one is on the interwebz)



This is a really cool paper because it shows insects - Chin suggest Dermestid beetles - boring into the bone in a large theropod fecal mass, likely for safety. Not only is that interesting ecologically for it's documentation of complex insect/dinosaur interactions but it can not be determined who got to the bone first. That is, did the theropod consume bone already infiltrated with insects borings (and therefore likely old bone) or did the insect exploit bone in the theropod feces for shelter (shelter is assumed because of shallow borings)?Now Chin does at one point lean towards it being more likely that the theropod exploited the bone after the insects drilled into them - which therefore implies the bone was likely a bit old. But she hedges her bets the other way - that the insect bored into the bone after the theropod defecated it.



What's also interesting is that, unlike what Hone above suggested with small dinosaur bones becoming largely absorbed upon digestion, these fecal masses were clearly full of obvious cortical bone among smaller bits. 



We have to assume three possibilities; this theropod ate small dinos and the bone was not fully digested; it bit chunks of meat off a carcass and incidental bone was ingested; or this theropod targeted bone purposefully. It should also be noted that Chin in this paper recorded another theropod coprolite of similar bone composition and size nearby:


Of the possible culprits (Allosaurus, Ceratosaurus, Torvosaurus) none of these theropods are similar to tyrannosaurids in skull/dentition. Maybe you don't have to be especially robust in jaw to consume bone just have the right bone saw dentition that easily slices up parcels of bone small enough to be swallowed whole.


And I think here is where we really need to look at our semantics and the biases implied. When we say "bone crunching" what immediately springs to mind is the spotted hyena (Crocuta crocuta). But that is the mammal solution to consuming bones because they can chew a bit and have heterodont teeth/molars. Theropod mouths were like scissors. Shouldn't we expect a uniquely theropodian solution to bone consumption? Turns out we might already have a good candidate that hints at how theropods consumed bones via a modern day bone eating theropod, the Lammergeier/bearded vulture (Gypaetus barbatus).

A bone/marrow eating specialist the bearded vulture/lammergeier/ wiki
This is a true bone specialist, more so than even spotted hyenas, with bones/bone marrow accounting for most of it's diet . It cracks open surprisingly large bones in its own jaws but principally drops bones from height when flying on rocky substrates and then eats all the shattered pieces swallowed whole. Take note that if you were a paleontologist of the future there would be no tell tale sign of bone use by bearded vultures because unlike hyenas they do not chew and crack bones. They swallow it all.



And this for me is part of the solution to the conundrum of why dinosaur bones are impoverished compared to mammal bones in being modified by predators. Mesozoic theropods were not dropping the bones from great height - but the bones that they were eating they were swallowing in large pieces (and crapping out the fecal masses full of chunks of bone everywhere). The way they were breaking down the bones was by surgically biting them into smaller, manageable sizes that were then swallowed whole. And they did the bone cutting with their uniquely strong and robust serrated dentition which was full in effect for even Coelophysis (Brink, 2015).

And then there is the strong possibility that dinosaurs, like modern birds, differ from mammals in the extent and distribution of red-blood cell making marrow locales. With dinos having highly pneumatized skeletons - especially sauropod vertebrae - the dietary cost/benefit of consuming these parts of the skeleton may have been too low. In dinosaurs there likely wasn't much marrow midshaft like in mammals but concentrated at the epiphyseal ends of bones like birds. From ornithology avian/circulatory system:



Maybe that chunk of pubic bone bit off the allosaur in Chures's paper was intentional and that was a localized area of bone marrow? Following from that thought it is possible that some of the red-blood production in dinosaurs took place outside of the bone and was outsourced to organs analogous or equivalent to the Bursa of Fabricus in modern aves - which is located in the cloaca of modern birds. Interestingly this get's me thinking again about that Allosaurus pubic bone cleaved off in the above paper by Chure, 1996. Maybe this organ was consistently targeted in dino carcass utilization.

And finally if the idea of optimal foraging strategy is invoked - in this case where a consumer of a substantial carcass concentrates their efforts on the spots with prime nutrition - large bones in dinosaurs might rank substantially low on a scale of nutrient value to other parts. So after the nutrient dense organs are consumed - liver, intestines, lungs, kidneys, heart, and reproductive organelles and then the fat deposits, and then onto the muscle... and finally perhaps after several days or weeks of feasting on a particularly large sauropod or saurolophine, now maybe the theropods is starting to look at the bones... But because of the hot, tropical climate much of the protein and fat within the bones has started to leach and bubble out of the bones - robbing them of the relatively little nutritive value that they had. And now that theropod - after feasting on the large carcass for several days or weeks already - now that theropod starts to really consider if the bones are even worth the effort? Might it be wasting more energy and time trying to wrest the relatively small amount of nutrients out of these bones and tie up its digestion with them? It's not so unusual - polar bears often only eat the fat of the seals they hunt and eschew the muscle meat. I can direct you to this very interesting link where they look at the carcass utilization by a pack of wolves on Isle Royal.


differential carcass utilization in same pack of wolves 
On optimal foraging strategy with regards to large carcass utilization in Isle Royal wolves:

"The idea is that when prey are relatively scarce it pays, obviously, to eat all that you can kill. However, when prey are relatively easy to catch, it pays to eat only the good parts (or perhaps leave behind the least choice parts). It may take more effort than it is worth to chew and digest the last bits of low quality scraps that remain after most of the carcass has already been eaten."

What is a bit of a paradox is the realization of robust tyrannosaurids sometimes being dainty eaters delicately stripping the bone off of carcasses - though they had the arsenal to eat the whole bone - and other theropods less orally equipped to consume substantial amounts of bone doing just that - such as the above Morrison coprolites - probably Allosaurus, Ceratosaurus, or Torvosaurus - (Chin, 2007), the cleaved Allosaurus pubic bone (Chure, 1996), and dromaeosaurs swallowing azdharchid bones (Hone, 2012). Clearly a more nuanced portrait of theropod bone utilization is called for. By invoking optimal foraging strategy, where marrow occurs in bird bones, and theropod tooth design I have outlined my meta-analysis of what was most likely going on with theropod bone use and the strange, sometimes seemingly discordant signal we receive from the fossil record sits more well with me.

Mammals show a stronger signal than dinosaurs for bone consumption due to an interplay of the following factors:

a) Differential exploitation of adult animals in respective communities, with mammal predators more biased towards adult carcasses in k-strategist communities (few young which mature quickly) versus theropods concentrating on growing and immature dinosaurs in these r-selected communities (many young which mature slower). Therefore much of the biomass is locked up in adult bodies in mammal communities and would therefore have been under relatively more frequent predator utilization both alive and dead. And being larger these mammal modified bones would benefit from preservational bias favoring their input into the fossil record, Generally in line with Hone, 2012 (although I think the notion of baby killing specialists is a bit overstated).

b) Relative cost/benefit of exploiting bone in respective communities. Mammals are well known for rich, fatty bone marrow in shaft of long bones. From what we know of bird marrow distribution their marrow is more patchily distributed. Certain dinosaur bones - especially pneumatized - may have generally been ignored unless dire environmental conditions encouraged utilization. Even tyrannosaurids - which unequivocally had the arsenal to crunch large bones - were sometimes delicate feeders and did not willy-nilly smash and eat all parts of a carcass. Bone may have often been a last resource and often ignored when there was other preferable pieces available to harvest. And in especially large carcasses by the time theropods got to the bone much of the good stuff (fats, proteins) may have leaked away making the bones further undesirable.

c) Mammals and theropods differ in their capacities to swallow large parcels of food. Theropods showing several distinct advantages in bolting large pieces of food such as large mouth and gape, expandable gular region, and ability to slightly "bow" out lower mandible in some lineages. This would allow both whole small dinosaurs/infants and large bones to be swallowed whole. Is supported by the observation of large chunks of bone in dinosaur coprolites (the more nutritious fats/proteins already sequestered in digestion), comparison to modern bone specialist avian theropods (bearded vultures), and preservation of large azhdarchid pterosaur bones in a dromaeosaur (Hone, 2012).

d) With the exception of possibly large tyrannosaurids there was probably little "bone crunching" in theropods directly analogous to hyenas. Instead, when bone was exploited, it was simply sawed off - via their advanced cutlery - and swallowed whole. Compared to mammals this methodology would leave little trace on the skeleton - since the evidence is swallowed whole - as opposed to mammals where bones are thoroughly chewed and crushed up but not always entirely consumed. But again, as discussed above in b, dinosaur bone was likely a relatively inferior food resource than mammal bone and therefore did not rank as high relatively in dinosaur carcass utilization. So mammal usage of bone is likely relatively higher. And this is consistent with the pattern of bone utilization seen in the respective dinosaur/mammalian communities and also large chunks of bone in theropod feces.

e) Never the less theropods, even non-tyrannosaurids, had the ability to saw off bone from large carcasses. This is supported by the cleaved off chunk from the allosaur pubic boot (Chure, 1998), the bone riddled coprolites dating to the Jurassic Morrison (Chin, 2008), and the work of Brink et. al. (2015) documenting novel features in theropod serrations suggestive of a relatively more robust and efficient cutting arsenal in theropods than generally appreciated.

And finally a long standing, but to our eyes crptic, tradition of bone consumption in theropods throughout the whole of the Mesozoic just makes more sense. I am a firm follower of the dictum that "nature abhors a vacuum" and it is simply incongruous that theropods would >only< start targeting large bones with the advent of large tyrannosaurids in the late Cretaceous.

Carcharodontosaurus credit Franko Fonseca. wiki

Riffing on this topic I decided to depict some theropod carnage highlighting some theropod bone sawing action. And yes dino carnage is a little over done but I feel like I have a special knack for it and when I do it I give it the Grand Guignol treatment. But not with a tyrannosaur - but with Carcharodontosaurus, Mr. Shark tooth himself. I think carcharodontosaurids get a little overshadowed by the tyrant lizards. It is a shame because they were nasty, brutish thugs and I would not be surprised if they had devised one of the most crippling bites around. What I am intrigued by in this family are those dorsal spines on the back. I wonder if they had a specialized musculature that rocked those massive heads back and forth like a saw (future post)? And then their shark like teeth are pretty impressive too. You don't have to read too many shark attack incidents to come across bone/limbs/torsos getting completely sawn off by sharks (not crushed!! It is an obvious homage to Robert Nicholl's 2x Death piece which recently spawned it's own scientific paper, Now I discussed why I think that paper had some flaws (no where in their analysis to they account for leg/caudal musculature assisting in the lift) but it still an iconic image. I just want to change it with respect to what happens when carch jaw meets titanosaur flesh. Sorry sauropod fans this is not one you might like... but sometimes you gots to remember where the food chain ends.

And if you think reading this was as enjoyable as that 3$ cup of starbucks you got today consider supporting me on Patreon.

Double Death credit (c) Robert Nicholls
2x click image for larger view.





Cheers!!

papers

Brink, K.S.  et. al. (2015)  Developmental and evolutionary novelty in the serrated teeth of theropod dinosaurs.
Scientific Reports 5, article no. 12338, July 2015

Chin, K. et. al. (1998) A king-sized theropod coprolite Nature, 393

Chin, K. et. al. (2008) Exploited twice: bored bone in a theropod coprolite from the Jurassic Morrison formation of Utah, U.S.A. Sediment-Organism Interactions: A Multifaceted Ichnology SEPM special publications No. 88

Chure, Daniel J. et. al.(1996) Prey bone utilization by predatory dinosaurs in the Late Jurassic of North America, with comments on prey bone use by dinosaurs throughout the Mesozoic. December 1996, GAIA

Hone, D.W.E. et. al. (2012) Pterosaurs as a food source for small dromaeosaurs. Paleogeography, Paleoclimatology, Paleoecology

Hone, D., & Rauhut (2009) Feeding Behavior and bone utilization by theropod dinosaurs Lethaia DOI



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Wednesday, July 29, 2015

Jurassic World Stole Indominus Rex From Ray Harryhausen

From Ray Harryhausen's "Evolution" 1938-40. Notice the hands of course!!





Still better than Jurassic World btw.


Saturday, July 25, 2015

Plesiosaur Machinations XI: Imitation Crab Meat Conveyor Belt and the Filter Feeding Plesiosaur

Fist of all Patreon, support me please!! You know this blog per month is worth at least as much as a cup of coffee from Starbucks. You want more of it? Give 'til it hurts...

All right for this post - and this is the one I hinted to a while back with allusions to imitation crab meat - I want to discuss a seldom mentioned idea for the neck. Now I don't know who first suggested this idea, I do know I first came across it on Adam Smith's post for "Why did elasmosaurids have such a long neck?" The suggestion, which at first notion might appear a little ludicrous, is that the hyper long neck of elasmosaurids (and maybe other plesiosaurs) could serve as a (Patreon) food storage device.

credit Adam Smith from plesiosauria.com
And, as Adam Smith points out, there is some parallel to this in the tortured oesophogeal loops of the leatherback sea turtle. You see, although the leatherback does not have a long neck it has an extended oesophagus that does not make a straight shot to the stomach but instead loops around to the back side of the stomach. This allows for extended storage space of the leatherbacks main grub - jellies, siphonophores, and other gelatinous critters. This prey base, although episodically abundant, is mainly water and relatively low quality for such a large, active, pelagic cruiser. So when the turtles reach their feeding grounds they stuff themselves to the gills, so to speak, in order to acquire enough calories to fuel their metabolism, fat reserves, egg production, and migrations. This allows a non-stop conveyor belt of jellies to be devoured which the oesophagus, along with their cuddly backward pointing papillae, keep the foodstuffs moving along.

Leatherback papillae. wiki commons
Leatherback eating pyrosome credit Brian Skorm
Now with the black hole that is plesiosaur/elasmosaur diet it is quite possible that some plesiosaurs ate jellies and other soft bodied prey - and hey maybe even had those nightmarish papillae lining their oesophagus isn't that a thought? But even if there were no jellyfish munching plesiosaurs the ability to sequester and store prey and calories when conditions are right is a pretty good tactic. Especially in the boom/bust cycle of oceanic food chains.

As I have stated before I think the biggest dietary signal we get regarding plesiosaur (long necked) is opportunistic - and with dietary items ranging from marine reptiles, pterosaurs, shellfish, scavenging, and crustaceans  - that is a pretty defensible stance. Additionally I am of the bias that, on a whole, the predatory reptile brain is a lot less picky when it comes to diet than many derived mammal or even bird predators. Reptiles think but two thoughts; 1) Can I overpower it? and if so 2) Can I get it in my belly?

But what about choking? It's one thing for the leatherback sea turtle to stuff itself full of squishy stuff, but if plesiosaurs are eating shelled stuff, vertebrates, etc etc., can't that stuff block the windpipe?

True, but one solution would be for plesiosaurs to have an elastic glottis that connects to the trachea and just as snakes can breathe through it while swallowing large prey so could a plesiosaur snatch a breathe with a throat stuffed full of food. As an added cool point a pliable glottis would allow plesiosaurs to "hiss" as snakes do with theirs.

Glottis of boa swallowing. credit reptile-parrots.com
Of course this is all very speculative if you have not figured that out already, we are talking soft tissue after all. But my point is that this idea of the oesophagus as food storage tool is not a non-starter. There is some analogy to it in the form of the leatherback oesophagus, the choking hazard can be solved as snakes have done with a pliable glottis, and it makes sense to harvest as many calories as possible when the feeding is good. And finally it's just really cool to imagine plesiosaurs with their necks crammed with all sorts of weird seafood on it's way down to the gastric mill and then stomach.  Styxosaurus after a gluttonous feeding bout stuffed to the throat full of strips of rotten scavenged mosasaur, swarms of belemnites and ammonites, assorted fish and chondrycthians, crabs, shellfish, colonial crinoids, and molluscs. All of it mashed together in the gastrolith and reaching the stomach like some rancid Mesozoic version of imitation crab meat - the hot dog of the sea!! If this was the case then damn their breathe sure must have stank!!

Anyways, the point was to have fun with this idea. There is no reason I can think of to discount the neck as a food storage device and some arguments to be made for it. I guess it's up to you...

But for the second part of this post I want to discuss the "trap guild"plesiosaur characterized by having fine, homodont, interlocking toothed dentition, and provide an augmentation to the already established idea that this guild strained food from the water column/substrate. That is the neck itself played an active role in prey harvest beyond stealthy approach. What I am suggesting is that the oesophagus could, in conjunction with the gular region, expand to accept large volumes of water with prey. And then, shutting the mouth and closing the finely meshed teeth, expel this water back out through the shut mouth. The fine, needle like teeth of this morpho-ecological guild retaining any organisms that were taken in with the water.  


Aristonectes lunge feeding on krill. Duane Nash
And a diagram illustrating this technique:


I) Suitable prey is detected

II) Jaws are opened to receive prey and water. Powerful and rapid flipper thrusts propel the animal toward food patch. Engulfment of water forces open gular pouch and oesophagus.

III) Gular pouch and oesophagus further expand as the animal continues forceful swimming.

IV) Mouth is shut upon maximum volume achieved. Forceful swimming diminishes.

V) With mouth firmly shut contraction of oesophagus and gular pouch force water out while prey is retained behind finely, meshed teeth. Prey is swallowed after water is voided.

This scenario does invoke a classic question in paleo-marine reptile ecology. Why no baleen whale/giant filter feeding equivalents among marine reptiles? I have pondered this a lot. We now have evidence of a previously largely cryptic Mesozoic lineage of filter feeding fish. And ammonites might have taken up this niche. We will revisit this idea later...

Here I want to make an important distinction between two general strategies often times put under the banner of filter feeding. First of all is the more passive filter feeding - best exemplified by the giant Bowhead whale and basking shark. These animals, jaws agape, slowly cruise after and eat abundant microscopic organisms, copepods, etc, etc, which they are constantly filtering through their baleen and gill rakers respectively.

Basking Shark feeding. wiki. credit Conscious
Now I want to contrast this method with the more aggressive method of targeting discrete clumps or shoals of abundant small prey and literally taking "bites" out of these massive blocks of small prey. This is the method used by rorquals - the lunge feeding tactic - which has famously become referred to as the "largest biomechanical event on earth". I don't want to get bogged down too much with rorquals - they were the subject of a Tet Zoo classic back in the day so go freshen up your knowledge there - the point I want to get to is that in both of these interpretations of filter feeding - passive and active lunge feeding - what is common to both of them is the ability to engulf a large volume of water. And in both the whales and sharks the solution to taking in such a large volume of water is to have a large mouth and, in the case of the rorquals, extensible throat pleats/buccal pouch to accept ridiculous volumes of water.

Humpback feeding on yoy pollock. Alaska. wiki. credit NOAA
Now this seeming prerequisite towards filtering prey out of the water - required for both active and passive methods - presents a bit of a stumbling block for any hope of plesiosauromorphs to explore this lifestyle. They are, by definition, relatively small in the cranium. However this conundrum is resolved by relegating the head to merely acting as the point of entrance for water/prey and not the storage area - having the gular region and oesophagus accepting the volume of water/prey makes this lifestyle feasible. This would require an extensible and somewhat muscular gular and oesophogeal region, analogous to the extensible buccal region of rorquals, both to accept a large volume of water and then push out the water when the "bite" is complete. Again, this is conjectural but a reasonable inference given the other anomalous attributes of some of the "trap guild" plesiosaurs I will get to later.

Let us explore this feeding method with the genus (and probably family) of derived elasmosaur, Aristonectes. These animals are very peculiar indeed and don't get the attention they deserve compared to other plesiosaurs and marine reptiles. My reasoning for this is that they are not big fanged and nasty looking. And that they come from the southern hemisphere while the vast majority of paleontologists /hobbyists/fans come from the northern hemisphere. There is that. And they are also relatively new to science. Let's do a quick primer on what we know.


Above are some views of Aristonectes parvidens Holotype MLP-40-XI-14-6 Chubut Province Patagonia, Argentina Cabrea 1941. Although plesiosaurs are often described as having needle-like teeth this is not always the case but here that description rings true. Also note that the angle where the upper jaw and lower jaw meet is pushed way back. That will give these animals an especially wide gape, useful for maximizing amount of water taken in during feeding. If we look at a view of the lower mandible from a ventral view we can get a scope on how relatively wide the jaw is - I liken it to the shape of a toilet bowl. Image from Adam Smith plesiosauria.com and credit Gasparini et. al. 2003.


Same specimen as above but this ventral view really exposes the relative width of the jaw. If, as these animals are sometimes suggested to be, they were specialists on soft bodied squid why not grow the jaw longer to resist water resistance and expand reach when snapping shut? And I am not suggesting that they could not hunt squid - far from it I always assume opportunistic foraging unless shown compelling reasons otherwise - but I don't see how this design is optimized for that lifestyle.

Aristonectes. Chaterjee & Small 1989
Aristonectes. Chatterjee & Small 1989

Now, with these anachronisms in mind (small, pin like interlocking teeth combined with broad jaws) let us move on to the rest of the skeleton in these guys and see what other clues they might reveal.


Abstract for above diagram:



Ok, so the phylogenetic part is interesting and suggests Aristonectines are derived elasmosaurs but now onto the morphology: "It is a large plesiosaurian with a relatively large skull with numerous homodont teeth, a moderately long and laterally compressed neck, and relatively narrow trunk, with slender and elongate forelimbs."

Now again, some anachronisms with the head and neck. If you were a small game specialists of squid, small fish why evolve a relatively large skull but retain pins and needles for teeth? And then why a laterally compressed neck? The laterally compressed neck is inferred from the relatively diminished transverse processes of this particular plesiosaur - which also highlights the fact that most plesiosaur necks are not restored muscular/thick enough as well. Better reframed this way: Why diminish the lateral musculature of your neck if you are specialized for darting after small prey? Wouldn't you want ample musculature for capturing such a prey base? However if you are adapted primarily to swim straight into vast shoals of food a diminished lateral neck musculature is not a problem.

Also why, in the illustration above, do the transverse processes along the neck trend towards the anterior of the animal?

Crytoclidus. credit Adam Smith plesiosauria.com


Note how in Cryptoclidus (below), another member of the "trap guild" although only distantly related, we see the transverse processes as basically horizontal to the vertebrae or trending posterior...? It's interesting and perhaps speaks towards some reorganization of the neck musculature in aristonectines perhaps due to its feeding specialization.

The name Aristonectes literally translates into "best swimmer" and there are some features suggestive of that description being apt. Note the description of above aristonectines having a relatively narrow trunk. Now, as I have discussed before, a lot of illustrations of plesiosaurs are too gaunt and feature the shrink-wrapped look, but here with aristonectines we see this group was relatively less round shaped than other plesiosaurs. In fact with this elongated look I am reminded of another clan of lunge feeders - rorquals - which are relatively sleek and streamlined (especially compared to passive filter feeders like Bowheads). The narrow trunk, slender and elongate forelimbs may have been adaptations in aristonectines, that allowed for efficient transit to and after highly dispersed but concentrated feeding patches.

Minke Whale Orange county coast CA. credit & (c) Shane Keena
And it would make sense for aristonectines to be among the most fast and seaworthy of plesiosaurs. Their food was not only highly dispersed and, bereft of the toothy snaggle-toothed grin of other elasmosaurs, they were relatively defenseless. With their "double-penguin" underwater flight, laterally compressed necks, relatively slender torsos they must have been a sight to behold and among the most majestic and graceful of marine reptiles in motion, like rorquals are today.


Again what I am describing is none too dissimilar from what may be described as general consensus that Aristonectes was more or less analogous to something like a crabeater seal - which uses specially derived cusped teeth to filter krill from its Antarctic waters. What is new in my interpretation and which has never been suggested before to my knowledge is that the gular region/oesophagus expanded to hold the water/food prior to being pushed back through the teeth.

Crabeater Seal. wiki
And now back to the long running question of filter feeding marine reptiles. While the crabeater seal, hailing from class synapsida, is bequeathed with a nice compliment of facial muscles reptiles are noticeably impoverished in that regards. Sucking, gulping, sieving, expelling - all of these actions require loads of facial muscles and nerves. And this lack of facial musculature in reptiles has been a bit of a problem in imagining filter feeding marine reptiles as a possible lifestyle choice.


A little thought experiment. What is the simplest, most parsimonious (fewest steps needed) way to turn a base model elasmosaur - imagine something like Thalassomedon - and turn it into an efficient filter feeders? It would prove very cumbersome and, in my opinion, outside the bounds of Darwinian evolution, to invoke the evolution of complex facial musculature, innervation, and so on to create a mode of filter feeding exactly the way mammals do it. Instead simply arranging the oesophagus and gular area into a food storage area - and co-opting the musculature already there to assist in pushing water back out through the sieving teeth is the simplest way to achieve this adaptation. No need to make the buccal area highly complex with large mobile tongue, muscles/nerves etc etc - simply through using what is already there to best fit - exaptation - you got yourself a pretty nice lunge feeding filter feeder equivalent to rorquals for all intents and purposes.

Kaiwhekea credit Cruickshank & Fordyce from Plesiosauria.com

Ok, but what about the other trap guild specialists? Cryptoclidus is probably the best known.  It had a more rounded profile, relatively larger teeth, and seems more of a generalist overall than aristonectines. It did have a wide "toilet bowl" mouth and the teeth did intermesh so it could have possibly strained food from the water or sediment but overall seems less dedicated to this lifestyle than aristonectines. My thoughts are the same for Kimmerosaurus. Kaiwhekea (above) is a strange bird. I hesitate at putting it at the level of dedication comparable to Aristonectes for this lifestyle. The teeth certainly fit the bill but what trips me up is the relatively high head. If it was feeding like Aristonectes I would expect a pretty similar low, long, and wide head. Maybe sieving infaunal prey was more its style? I have discussed Tatenectes before but dietary remains (hybodont shark) and pachyostosis in this plesiosaur (heavy, dense bones) seem to preclude it from being a true pelagic lunge feeder/filter feeder but infaunal sifting may have been important. It should be noted that the technique I described could also be applied to infaunal sifting, simply take in a large volume of sediment into gular region/oesophagus and flush through the teeth - retaining prey.


And finally, just for fun, if you have came along with me so far in aristonectines being further along than generally appreciated in the filter feeding sweepstakes let's play a little revisionist history - speculative evolutionarily speaking. If the K/T extinction event never occurred, or if aristonectines slipped through it, it is not without reason to assume that they would have further followed this lifestyle and occupied the eco-morphospace used by modern rorquals. And so we might have had 100-200 ton krill feeding aristonectines in the ocean!!



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