Monday, August 10, 2015

Allosaurus - More of a Vulture Than a Falcon

 Allosaurus credit Shizoform CC generic
You could be forgiven for dismissing Allosaurus as a bit "vanilla"as far as theropods go. On average it was not very large. Teeth and skull fairly moderately sized. It had some nice head crest ornamentations but overall no spectacular display structures ala a big sail, crest, or other kaiju like feature. It has been known for a long time from dozens of specimens so no big mystery to speak of as goes general morphology. But what makes it interesting is the faunal dominance of this theropod compared to the other theropods - large and small - of the Morrison formation. Despite it's seemingly meager attributes in terms of skull and tooth size compared to the larger toothed/skulled Torvosaurus and Ceratosaurus, Allosaurus held sway numerically by a large margin and it's difficult to ascribe this dominance to mere collection bias.



For those who, despite these seemingly "vanilla" attributes for Allosaurus, intuitively felt that there was much more to this animal than meets the eye - your hunches might be more true than you even imagined.

In this post I aim to present a startling new theory on Allosaurus feeding technique that resolves these anatomical and ecological incongruities and offers utility in looking at other ziphodont theropod predators - to a greater or lesser extent - in terms of feeding adaptation. I will also in the process describe a unique and as yet undescribed feeding adaptation in several lineages of flesh rendering birds.

As background readers should be well versed in the paper by Bakker, 1998. Brontosaur Killers: Late Jurassic Allosaurids as Sabre-Tooth Cat Analogues. GAIA, December, 1998. Pp 145-158 available online here. and the more recent, but largely congruent study Snively, Cotton, Ridgely & Witmer 2013 Multibody Dynamics Model of Head and Neck Function in Allosaurus (Dinosauria, Theropoda). Paleontologica Electronica May 2013 online here.

In fairness it should also be mentioned that the finite element analysis of Allosaurus by Rayfield et al. supported a "slash and tear" attack (2002) while Frazzeta & Kardong come out against the "chop and slash" hatchet attack. While I lean towards the neck driven attack in Allosaurus this style is not a prerequisite for what I am going to outline. My theory will focus on the step between the initial bite/hack/purchase and the head pulling away with a bite of food. Mine is the intermediary step.

Charles R. Knight. wiki public domain
I must address the obvious trolling attempt I perpetrated by naming this post "Allosaurus - More of a Vulture Than a Falcon". This post is not suggesting that Allosaurus is an obligate scavenger. But I do want to highlight the negative knee jerk reaction that I - and probably many feel - at the mere suggestion of Allosaurus, Tyrannosaurus, and other charismatic theropods as mere scavengers. Although there is good enough reason to doubt the ecological feasibility of massive, terrestrial obligate scavengers it is also worthwhile to look at more of the cultural and emotional connotations ascribed to scavenging - especially contrasted against highly predaceous animals. Words like "lowly", "inferior", "weak" and "cowardly" immediately spring to mind. However a purview of the behaviors of the most iconic of modern scavengers - New and Old World vultures - reveals very different. These are often highly combative animals - both between themselves and other species. Andean condors have been documented harassing cougars off their kills, causing them to hunt 50% more than North American cougars. And those brawny, proud eagles and other "respectable" predatorial birds of prey are routinely routed from kills/scavenging opportunities by battle ready vultures such as in the youtube clip below.


What also should get your attention is the intricate social hierarchies between not just species of scavenging birds but between individuals of the same species. Note the lappet-faced vulture (Torgos tracheliotos) moving in and dominating the impala just before the leopard seizes it. Also note that many vultures are more concerned with fighting and establishing dominance amongst themselves rather than, you know, actually getting to the rapidly dwindling carcass. Establishing who is who in the pecking order seems to be very important to these animals. Of course looking at the intricate feeding guilds, carcass location tactics, and niche partitioning in these extant flesh rendering theropods are other fascinating avenues of discussion beyond the scope of this post. My main point being vultures are intelligent, social, and intensely competitive. Inferior and cowardly they are not.

I really love this video too. Pay special attention to the shifting eyes of the vultures as they sense the jackal moving off. And then just the mosh pit of activity as they rush in. And pay special attention to the lappet-faced vulture and how it struts it's stuff and just establishes dominion over that carcass.



And now on to the feeding adaptations of vultures (both old & new world). What I am about to introduce - and what forms the crux of a large part of my argument - is that vultures have a peculiar and, to my knowledge, as yet undescribed (anecdotally or in the scientific literature) feeding mechanism. And it is this feeding mechanism - which as I will show you is and has been in plain sight all along - that separates vultures from other birds of prey with regards to efficiency in harvesting large carcasses. And pinpoints them as more useful analogues to Allosaurus, and many other ziphodont theropods, in feeding mechanics. And, again I believe it has likely been the social stigma of "lowly scavenging carrion birds that has kept this feeding method invisible to us while it has always been in plain site.

Let's start with a youtube video - plenty more to come - that I think most succinctly captures the vulture feeding mechanism. I have seen the whole video before, it was I believe a show from the Discovery channel looking at the evolution over time of a large carcass (btw it was not a bison but I think a hippo or some other large African mammal). Be advised that the action happens very fast - you will find yourself probably watching some of these videos several time.



On the velocity of action:
"Look at the speed - it looks like it's insanely speeded up but it isn't is it? It's for real"

On the vulture feeding technique:
"Fast nibbly action rather than this sort of hooking in and pulling huge hunks out as would an eagle"

That "fast nibbly action" is what we will be looking at for a bit. And, as the vulture researcher posits, this style of feeding is different than the typical "hooking in and pulling" action of eagles, hawks, falcons and other more predatorial birds of prey. You can go check out other birds of prey and see the difference but I have a video below of some nice close ups of bald eagles feeding on discarded fish that - especially played after the above vulture video - highlights the differences.


Ok so what if all those "fast nibbly parts" are just the vulture swallowing little bits? This idea is negated by the fact that in the vulture videos they tilt their heads back to make an obvious swallowing motion when they are doing it.

It should also be stated that vultures plainly use the "hook and pull technique" like a falcon or eagle. But what should not go unnoticed is that the "fast nibbly part" almost always occurs right before the "hook and pull" part. It is almost as if the vulture is softening or chewing up the meat to better facilitate breakage when the "hook and pull" part comes. Maybe go watch the video above again "Jackal Vs. Vulture" and go to 1:40 where the Lappet-faced vulture starts feeding and you can see that it follows the pattern of "fast nibbly part" before "hook and pull".

And this feeding technique is not just found in old world vultures (Accipitridae) as depicted above but also it is characteristic of New World vultures - which represent a different lineage family (Cathartidae). Whatever is going on here is so efficient it evolved twice. You will see a convergence in feeding below in this video depicting California condors (Gymnogyps californianus) feeding on a deer carcass.


This technique is also evident in black vultures (Coragyps atratus) which starts at 5:30 although the host seems like an interesting fella too.




And here is another with loads of clear shots of the "fast nibbly parts".


And wait, if that's not enough to convince you of the utility of this feeding method in birds that render flesh off of large animals, giant petrels, both the northern/southern (Macronectes giganteus & halli family Procellariidae) use this same feeding method. You can see it to good effect in the video below of giant petrels as well as neat display and fighting behavior. So we have a remarkable case of convergence in that the most dominant large carcass rendering of the New and Old World, and southern/Antarctic oceans all have a similar style of eating.


However the giant petrels take this "fast nibbly part" a step past what vultures routinely do with dead bodies and use it on live animals. Below is the video that can give you nightmares - you have been warned. But if you sit through it (and I have several times) you will see that before the petrel literally scalps the chinstrap penguin it gives it several "fast nibbly parts" that likely helped facilitate the "hook in and pull" part pulling off a plug of skin and meat.


And, based on this video below of albatross feeding on whale blubber, it looks like other tubenosed birds utilize this feeding technique as well.



All right so what is going on here with these "fast-nibbly parts"?  Let's look inside the mouth. On the roof of the mouth of birds they have something called "choanal papillae" which can take various forms but you might better know it as pseudo teeth. You can see them quite obviously in the penguin below.

penguin with choanal papillae. via Discovery
In the penguin above the papillae are quite apparent. But in vultures and giant petrels the choanal papillae are more subtle and form several minutely serrated ridges on the roof of the mouth. At first this might seem counterintuitive but it is explained by the fact that in the penguin it is using it's papillae to help grasp single small  prey items but vultures and petrels are using their papillae in a different manner as I will explain in a second. But let's look at some images.


Above is a frequently memed image of a king vulture and you can see the fine layers of choanal papillae on the roof of the mouth. But below is an even more telling picture of a turkey vulture that suggests a method as to how this whole operation works.



What you should note is that not only are there small serrated papillae lining the roof of the mouth, but the tongue too. Credit Williston Conservation Bird Trust Blog.


Now this is all common knowledge that vulture mouths have serrated/barbed tongues and papillae lined throats. But during the "fast nibbly parts" - a term I will replace from here on out as choanal grinding - I have outlined a hypothesis that best explains what is going on.

After a parcel of meat or skin is clenched in the beak the tongue rapidly retracts and grinds the food item against the choanal papillae. This action, combined with the rapid movements of the whole neck further enacting different force vectors, serves to mince and grind the meat down ultimately diminishing it's structural integrity. And then, after the tissue has been been broken down a bit, comes the classic "hook in and pull" routine which dislodges the parcel of food which is then swallowed.

Again, to the best of my knowledge this has never been suggested or explained as such. I could be wrong and there is an open comments section below.

So if we look at this "choanal grinding" it is happening almost imperceptibly fast and it provides an elegant explanation for why birds that routinely render carcasses larger than themselves all share this characteristic feeding behavior while the tug and pull "raptors" such as hawks, eagles, and falcons - which more commonly feed on items smaller than themselves - do not. Further testing could include ultra slow motion film of these birds feeding and/or in some type of controlled setting.

But while searching for images of vulture tongues - surprisingly there is an extreme paucity of such imagery on the net - I came across a bit of independent confirmation of my hypothesis. What I came across was an image, via the Vulture Conservation Foundation,  of a Griffon with tongue protruding from the neck observed in France!! Evidently, probably from some anthropogenic cause, this griffon got a hole in the neck from which the tongue just kind of lopped out. But wait, it gets bettor (or worse).

credit Francesco Panuello via vulture conservation
Evidently this is not the only time such a macabre disfigurement had been observed. Another - perhaps the same - bird was photographed and documented in a short paper
Vulture News 64 July 2013. An Eurasian Griffon Gyps fulvus disadvantaged for feeding. Written by Alvaro Camina and Luis Miguel Guerroro, this time seen in northern Spain. And here it gets really interesting:

"The bird had a perforation just on the throat that left the tongue outside the skin, and the tongue moved forward and backward while the bird was eating."

Now this is astounding. The tongue in this bird - which remember is not even in the oral cavity where food is being processed - still flicked forward and backward when it was feeding. This suggests that the tongue rapidly moving back and forth is involuntary and intrinsic to their feeding adaptation!! Drop the mic.

Interestingly of the picture provided in the paper of this vulture feeding it is quite clearly in "hook and pull" mode on a rather small morsel of pig.

All right, so I am gonna say that makes a pretty strong case for choanal grinding for what I have to work with now.

Time to segue back into the Allosaurus question. In light of that last bit, I am going to go with birds that actually render the flesh of large tetrapods - New & Old World Vultures, Giant Petrels - as a superior model than falcons, eagles, hawks that typically on average eat animals equal to or smaller than themselves (don't light up the comments with eagles attacking deer/wolves, I mean on average). Am I suggesting that Allosaurus and other theropods had gnarly choanal papillae and serrated tongues? No, quite the contrary in fact because they had a superior set of cutlery already in place - their rows of serrated teeth.

As I mentioned at the start of the post it will prove useful to be familiar with both the Bakker, 1998 paper and Snively et al., 2013. Bakker, through comparative anatomy and Snively et al. through multibody dynamics finite element analysis converge on a similar anatomical adaptation in these animals. Allosaurus had an exceptionally powerful and flexible neck which was especially augmented for rapid dorsoventral movements. The rigorous analysis of Snively bolstered Bakker's theory of rapid neck strikes, coupled with widely gaping jaws to enact "brontophagy".

Rayfield et al. 2001



Additionally Snively et al. suggest that this astounding musculature that facilitated such forceful hammer blows was then used when feeding to  pull the head back forcefully - like falcons and other birds of prey "hook in and pull"-  the flesh. And I have no problem with both the hammer saw blow from Bakker or the falcon hook in and pull technique. What I am suggesting is that a step is missing between both the initial strike and the pull back. And that step is the allosaurian equivalent to the just discussed choanal grinding in extant carcass rendering birds. But instead of barbed tongues and choanal  papillae doing the cutting it was serrated teeth.

After biting into a large food item (alive or dead) then the theropod bonesaw would come into play. Rapid and forceful back and forth pumpings of the neck in the dorsoventral plane - as suggested by the work of Bakker, Snively et al., and Rayfield - then allowed a uniquely devastating and vicious sawing to commence. Now the tissue in the mouth will be - partially by it's own inertia - be sawed back and forth over both the fore and aft serrated margins of the teeth when the pumpings occur. This action - most effective with a large individual piece or a plug from a large carcass to allow more resistant inertia- will effectively negate the use of strong jaw closing muscles - which Allosaurus was relatively impoverished in - and outsource the driving musculature to the neck. A rather weak bite is actually more efficient because that will better allow the meat to slide back and forth over the teeth sawing into it. And because both sides of the serrated tooth are equally in use the cutting edge of the teeth will be better preserved.

Based on a number of factors this bonesaw shimmy as I will call it from here on out was utilized with a variety of techniques.  What is probable is that the pumping bonesaw shimmy worked best on big hunks of meat and smaller bits were swallowed or fed on with the "hook in and pull technique".  As in the vultures and petrels (you probably want to watch some more videos at this point), this action was occurring almost imperceptibly fast and were interspersed with various other actions, letting go to readjust, pulling back. Probably not as fast as in the birds because Allosaurus is bigger - relative muscle strength diminished with size etc etc - but still looked freakishly sped up. As in the "fast nibbly parts" the jaw is - for the briefest millisecond - opening up to allow the parcel of food to be moved in the mouth and scraped against the tongue/papillae as can be seen in this photo right here in a lappet-faced vulture. Seeing a mob of Allosaurus chowing down on a Camarasaurus  carcass (or eating it alive) must have looked diabolically horrific on a disturbing scale. Take that Petrel Vs Penguin video and crank it up to 11.

credit Kevmin fossil C. carcharias Miocene Atacma desert Chile. C.C.

Let me prime your mind a bit with some youtube clips of serrated toothed sharks feeding on whale carcasses. You will notice that as the sharks shake their heads side to side to saw off a hunk of blubber this action allows both sides of the serrated tooth to work over the tissue just as in the scenario I painted above.





Again, these rapid dorsocentral bonesaw shimmies would take advantage of both the fore and aft serrated cutting edges on the Allosaurus tooth for maximum sawing efficiency at minimal damage to tooth. Since strong bite force is not required crown breakage is curtailed and because serrations on both sides of the tooth are utilized the stress is spread out evenly across the teeth and serrations.

Allosaurus SDNHM public domain
Seen holistically as a mechanical unit from this perspective the seeming anachronisms of the Allosaurus skull fall into place as not disadvantages but benefits. The light, pneumatic skull is the optimal design to allow rapid movements of the head as necessitated in this model. The stout - but relatively short teeth - are now optimized to work as series of serrations acting in concert to shred and saw. If some of the teeth were substantially tall this would likely diminish the sawing efficiency as long teeth would cause tissue to get hung up on them during these movements. The mobility, strength, and strong dorsoventral movement capacity of the neck all line up in this scenario. The relatively deep but narrow skull make sense. The depth of the skull allows the skull to absorb the forces unleashed in this action. But the lateral narrowness of the skull is what really completes the saw or blade parallel. You want the line of action of the teeth to line up with the skeletal framework of the skull for maximum transfer of power and stability. Likewise you do not want a knife that bends in the blade as that will diminish efficiency.

As I alluded to in my previous post Death Comes Ripping the recent work by Brink et al. suggests a uniquely efficient and strong tooth in ziphodont theropods which may have expanded their niche into true bone utilization. But not via crushing as I argue (with the exception of tyrannosaurids) we must disabuse ourselves of the hyena paradigm of bone consumption. Instead the bonesaw shimmy worked to effectively slice not only meat but cartilage and bone.


Here is a bit of rough sketch to give you a visual. Again, you have to imagine this happening at a very rapid pace - interspersed with the jaws opening a bit occasionally to allow movement of the bone.


Now we get back to the ecological conundrum of Allosaurus' dominance in the Morrison theropod predatory guild. It was uniquely equipped among it's contemporaries for bone slicing. Ceratosaurus had very long, narrow blade like teeth and a relatively straight neck not augmented for this type of feeding action. Although Torvosaurus was probably capable of some bone consumption it's massive bulk limited it ecologically speaking to a more specialist niche. Torvosaurus might well have been the lappet-faced vulture of the Morrison. Rare - but dominant - and it's big skull and teeth, large powerful and lithe body may have better allowed it the ability to open up and dismember exceptionally large sauropod carcasses - which allowed smaller theropods like Allosaurus better access. As I have been preaching for awhile we do not always have to look at dinosaur coexistence through the lens of competition but also through commensal/facultative relationships. So Allosaurs could exploit all parts of  a large carcass efficiently. This expanded niche, with a potential mobbing behavior, and moderate size that allowed flexibility in food choice gave Allosaurus the edge.

So where is the hard evidence of Allosaurus accessing all these bones? The Morrison is so well trodden by collectors we should have bones sliced by Allosaurus lying around everywhere. Well, it turns out we already have the evidence. For whatever reasons, it never really made the news.

Now in my last post I discussed the Chure et al (1996) paper Prey bone utilization by predatory dinosaurs in the late Jurassic of North America in which the tip of an Allosaurus pubic bone was basically cleaved right off. The pubic bone - especially the foot - is not an insignificant bone to cut through. Especially if this was just incidental contact as the author's suggest. Now we don't know who was the perp - the authors suggest Ceratosaurus or Torvosaurus - but this piece of evidence should not go overlooked because we know at least some type of theropod cleaved off that piece of bone. Given the numerical dominance of Allosaurus in the Morrison chances are it was Allosaurus.



An additional layer of evidence for bone utilization by some type of theropod in the Morrison, also detailed in my last post, is provided in Karen Chin's seldom discussed paper Exploited twice: bored bone in a theropod coprolite from the Jurassic formation of Utah (2008). Chin mention not one but two likely theropod coprolites full of chunks and shards of bone (the Morrison lacked large crocodilians) one of which shows substantial amount of insect borings of the bone enmeshed within the coprolite. What is extremely interesting is that Chin can not resolve whether the insect bored into the bone first - which would suggest that the theropod in question consumed a largely defleshed bone - or if the insect bored into the bone after the theropod passed it. Chin interprets the bone as incidental bone taken in with carcass consumption, which given the generally dismissive view of bone consumption in theropods seems like the most parsimonious conclusion to make. But I would beg to differ. Allosaurus has teeth in the front of it's mouth that are D-shaped in cross section so, like tyrannosaurids, it could if it wanted to carefully pick meat off a skeleton without much incidental bone contact. If this was indeed an Allosaurus coprolite (statistically speaking that is the most likely culprit) and if Allosaurus was bone slicing using the technique as described we should expect several characteristic of the bone preserved in coprolite. These predictions are that we should see lots of small splinters/shards of bone from the sawing action together with larger chucks of bone swallowed whole. And, indeed, when we look at the coprolite - in real life view and microscopically - from Chin's study that is the pattern we see. Prediction met.



Wait there is more. Sometimes a paper - or maybe just a small bulletin - is published that falls through the cracks because it is made by people not specialized is said discipline or just is so obscure that no one more heavily invested in the issues at hand takes notice. I have found such a piece.

Although as far as I know the authors are paleontologists they are not dinosaur guys so they may have been unaware of the significance of this specimen. I tried to contact them as well but the lead author Dwayne Stone is deceased and I can't find an active email for the second author Edward Crisp although I think he is still active. It was published as an abstract at the 2000 GSA summit of Reno, Nevada. It's on the web here and I transcribed it below (screen shot did not fit here).

A LARGE MEAT-EATING DINOSAUR COPROLITE FROM THE JURASSIC MORRISON FORMATION OF UTAH

Author(s): STONE, Dwayne D., Dept. of Geology, Marietta College, Marietta, OH 45750; CRISP, Edward L., Geology Dept., West Virginia University at Parkersburg, Parkersburg, WV 26101, ecrisp@alpha.wvup.wvnet.edu; BISHOP, John R., Rt. 2 Box 137, Ravenswood, WV 26164


Keywords: Coprolite, Jurassic, Morrison Formation, Allosaurus
A theropod dinosaur coprolite has been excavated in Emery County, Utah from a red-brown mudstone of the Upper Jurassic Brushy Basin Member of the Morrison Formation. The coprolite is nearly complete and is divisible into two parts, the main mass and a dribbling zone. The well-indurated main mass, which tapers at both ends, is 1.52 m in length, 0.457 m in maximum width, and 10.2 cm thick. The 1.52 m long dribbling zone consists of small isolated coprolites that curve towards the end of the dribbles. The coprolite geometry is interpreted to indicate that the main mass was defecated first, then the animal walked forward to release smaller amounts of feces. The coprolite consists of dark gray bone fragments, ranging from pebble to sand size, in a red-brown matrix. Bone fragments represent about 50% of the mass and have broken, jagged ends, possibly indicating breakage by the biting action of a carnivore. XRD analysis of the bone fragments and matrix reveal that both are primarily composed of carbonate fluorapatite. The large size of the coprolite and its geometry and stratigraphic location indicate that it represents fecal droppings from a large Allosaurus. Further support for this hypothesis is the fact that a broken distal end of an Allosaurus tooth was found within the coprolite, indicating that during mastication a tooth was broken and ingested. The carnivore did not grab a portion of flesh and bone from a prey animal and then swallow it whole. Instead the eater masticated its meal and broke the bones into smaller portions. This is the largest and oldest theropod dinosaur coprolite known. Work is continuing on a second theropod coprolite higher in the section at this location and pieces of theropod coprolites from two additional localities have been identified. Morrison Formation theropod coprolites are no longer considered to be absent or scarce and future searching should reveal additional large specimens.


Ok so first things first this theropod turd blows that Tyrannosaurus turd out of the water in terms of size. This one is over 1.5 meters long and (sorry king) the turd documented in Chin's paper (1998) was a paltry .46 meters. So on the Couric scale of crap size Tyrannosaurus needs to take a seat cuz this Morrison theropod has got it beat. Not only was this poop larger - the pooper had a more fibrous diet as well - with about 50% bone mass while Chin estimates about 30-50% bone mass in the T-rex coprolite. And then it get's even better:
(from abstract)

"The coprolite consists of dark gray bone fragments, ranging from pebble to sand size, in a red-brown matrix. Bone fragments represent about 50% of the mass and have broken, jagged ends, possibly indicating breakage by the biting action of a carnivore."

Again, as in the Chin (2008) paper, the prediction is met to have a mix of small bone chips - further embellished by the notation of "broken, jagged ends: i.e. the bone was not swallowed whole but was indeed processed.

And finally the clincher:

"The large size of the coprolite and its geometry and stratigraphic location indicate that it represents fecal droppings from a large Allosaurus. Further support for this hypothesis is the fact that a broken distal end of an Allosaurus tooth was found within the coprolite, indicating that during mastication a tooth was broken and ingested."

What is the quote, dogma can blind us to the truth? Sorry tyranno-enthusiasts they got some new competition for bone consumption in the Mesozoic. And - besides my other arguments - it just makes more sense ecologically for bone consumption to have evolved in theropoda before the tyrannosaurids. Nature abhors a vacuum.

Although this post dealt specifically with Allosaurus - there is the most data on it for starters - there is much room to investigate how alternative "bonesaw" cutting techniques evolved in different theropod clades. Allosaurus was uniquely equipped for powerful dorso-ventral neck movements but that does not preclude other relatively long necked, ziphodont theropods - certain dromaeosaurids, coelophysids off the top of my head - from engaging in a similar technique. Other lesser known Jurassic allosaurids/carnosaurs may have evolved similar mechanisms to saw. Abelisaurs and tyrannosaurs likely fell more towards the grab and pull spectrum and were doing something a little more power crunch based as opposed to slicing and dicing. There is lots to explore.

Tsaagan Giant Petrel Style credit Markus Buhler. Bestiarius on deviantart
And one group in particular - carcharodontosaurids - I will cover in a future post where I will discuss a largely analogous but unique method of food processing for them that, instead of being driven largely by neck muscles, sawing actions was achieved via epaxial musculature.

And now - because I think I threw a lot of stuff at you and people will need time to digest that a bit. No doubt this theory will change and evolve over time as it is refined. But for now to put you in my mind's eye, I want to go into a little speculative story telling. A Morrison tail of life, death, and cutlery in action...

Mobile Sauropod Body Processing Units of the Morrison

If the old bull Camarasaurus grandis had the emotional intelligence to develop feelings of gratitude, it would feel especially thankful to the 10 meter Torvosaurus tanneri bearing down on it's neck with jaws and claws granting it a relatively quick death. This was a far cry from the several days and nights of torturous harassment by a mob of 9 adult Allosaurus fragilis not to mention the several other dozen allosaurs arranged in assorted size classes tagging along. It was the old bull's 27th year and it suffered several broken foot bones jostling with other males. And now, during the height of the dry season migration to the floodplain seepage wetland, the ever present and ever vigilant allosaurs were quick to locate and capitalize on this hobbled sauropod. The allosaurs concentrated on biting at the cloacal region, caudemofemoralis muscle, and back of the lower legs. While the Camarasaurus had backed into dense vegetation to thwart such attacks before - exposed on the dry vernal ponds and under the pressure to get to water it had suffered debilitating blows. Attacks came almost non-stop from the hatchet head strikes followed by rapid fire bonesaw raking - the disgusting bonesaw shimmy - severing muscles and partially disembowling the 20 ton animal. But even with this trauma the Camarasaurus did not die. Sauropods in general were hard to kill having abundant air sacs throughout their skeleton able to keep the ATP machinery firing past the point where a mammal would be able to survive. But the allosaurs were persistent. They sensed the sauropods strength flagging and the foot and tail strikes no longer packed the punch they did earlier. So when the Torvosaurus arrived it was able to relatively easily dispatch the giant as it was being eaten alive.

Torvosaurus and Allosaurus have a complicated relationship. The adults of both species routinely kill and eat each other's young. But the adults are largely copesetic. Adult and near adult torvosaurs usually "adopt" their own mob of allosaurs. The allosaurs do the leg work of finding, harassing, and weakening prey. The torvosaurus usually comes in to do the coup de grace for large prey items that have been weakened by the allosaurs. But the allosaurs benefit by the torvosaurs presence at the carcass. Their absolutely larger size, stronger jaws, and bigger teeth allow more efficient dismembering of the carcass than the allosaurs are capable of. Using the torque in their large, flexible bodies and tails the torvosaurs rip femurs from hip sockets like macabre wrestlers. But torvosaurs are fiercely possessive of their mob of allosaurs and will not tolerate other torvosaurs trying to move in. So, paradoxically the adults of both species tend to tolerate each other - and often feed together on large carcasses less than a meter apart. This does not imply that they do not eat each other if wounded or deceased.

Once the feast begins it is a blur of activity. Although the torvosaur is easily twice the weight of the allosaur they both feed side by side but use different methods. The torvosaur more dependent on it's large tooth studded jaws and strong body to leverage large pieces swallowed whole. It moves slowly and deliberately. The torvosaur shows a strange penchant for swallowing tough, gristly mats of skin and ligament while the allosaurs concentrate on the flesh. But the allosaurs appear to be moving at 2x the speed. Their necks darting about at all angles followed by almost imperceptibly fast sawing motions of the head carving up meat, skin, sinew, and bone. While not challenging the torvosaur the allosaurs are constantly battling amongst themselves in a never ending quest for dominance and establishment of pecking order. 

Ceratosaurus wikicredit Richie D.
And then come in several large 7 meter Ceratosaurus nasicornis. They approach from the scrub conifer thicket from which they have been following the action. They like to operate in tight places. Once the torvosaurus has it's fill and the larger allosaurus start to look sated the ceratosaurs make their move. They appear as monsters out of revelations. The horned head, oversized teeth, armor and frill plated skin and loud bellowing croaks allow them to punch above their size through sheer spectacle of appearance. They waste no time in establishing their provenance on the carcass - deep inside the torso. Tough muscle, sinew and bone they look past as they go after the deep internal organs. Pushing into the cavity they seek out the liver, heart, lungs, and kidneys. The allosaurs generally avoid going into the cavity when ceratosaurs are in there - they prefer more room to manoeuver their long necks around in.

And finally after the adult allosaurs, torvosaurus, and ceratosaurus have fed move in the hordes of various age classes of allosaur. They loosely follow, but segregate themselves from the adult allosaur mob. You see, even though the allosaurs are intensely social, they are also intensely 
cannibalistic. Working away at the pelvis, delving into the torso, clambering up and climbing up through the carcass to get at choice spots - all parts of the body are explored. Unexpectedly a 4 meter long juvenile torvosaurus joins the hordes of youngster allosaurs. Perhaps this torvosaur is attempting to adopt his own mob of allosaurs? In any case the juvenile torvosaurus is trying to attract as little attention to itself as possible. It does not want to raise the ire of the other adult torvosaurus in the vicinity as they are fiercely defensive of their allosaurus mob and will kill any encroachers. 

Juvenile Allosaurus and one juvenile Torvosaurus feast on Camarasaurus. credit Duane Nash
Other theropod predators of the Morrison exploit the carcass over the next couple of days. A pursuit hunter of salt pans and open scrub flats, Tanycolagreus topwilsoni - an early tyrannosauroide - makes stealthy meals of the carcass under cover of night. A cavalcade of small terrestrial crocodiles and pterosaurs are also a constant presence at the carcass. Also emerging form the nearby scrub thickets at night are small Ornitholestes hermanii to pick at the carcass between feeding bouts of the larger theropods.

Tanycolagreus topwilsoni restored skull cast credit Daderot. wiki 
After about a week all that remains are some of the ribs, larger limb bones, vertebrae, pelvis and bits of skull. With all of the meat, skin, and viscera consumed some of the larger allosaurs move onto the bones that offer the most marrow. This includes the ends of the limb bones, sections of the pelvis and pubic boot. Otherwise the vertebrae, ribs, and skull do not interest the allosaurs enough to saw into - being largely pneumatic and lacking marrow. The bones that are worthwhile consuming are sawed into smaller pieces and swallowed. Large bones are regurgitated up after the remaining fats and proteins have been extracted in the stomach but the smaller shavings and chunks pass right through into the excrement.

Finally after all the flesh, skin, fat, and marrow rich bones have been harvested and the theropods departed, a colony of specialized bone consuming termites sets up shop on the site of the remaining bones to complete the wholesale recycling of the sauropod into the ecosystem.



Cheers!!

References

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

Bakker, 1998. Brontosaur Killers: Late Jurassic Allosaurids as Sabre-Tooth Cat Analogues. GAIA, December, 1998. Pp 145-158.

Camina, Alvaro & Guerroro, Luis Miguel 2013 . An Eurasian Griffon Gyps fulvus disadvantaged for feeding. Vulture News 64 July 2013

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


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


Stone, Dwayne D., Crisp, Edward L., Bishop, John R. (2000). A large meat-eating dinosaur coprolite from the Jurassic Morrison formation of Utah. Abs No. 50526. 2000 GSA Annual Meeting - Reno, Nevada

Snively, Cotton, Ridgely & Witmer 2013 Multibody Dynamics Model of Head and Neck Function in Allosaurus (Dinosauria, Theropoda). Paleontologica Electronica May 2013




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27 comments:

Anonymous said...

Ni mention if Saurophaganax anywhere?

Duane Nash said...

Yeah I wanted to stick to the Morrison theropods with better remains and fairly straightened out taxonomy. I guess you can say I didn't mention Edmarka Rex or Epanterias as well...

khalil beiting said...

Well this is an astonishing article. This kind of has to do with the carcass story, but what do you think Marshosaurus' niche/prey was? Also, since you mentioned Epanterias and Edmarka, do you think they are both valid, or are they just giant variants/morphs of Torvosaurus and Allosaurus respectively? Also, what do you think Saurophaganax's niche was (I'm assuming the role of "uber Sauropod slayer"). Now, one last question (sorry for all of the questions), do you think that I could "copy" your (amazing) carcass story for my spec evo project? I'd like to recreate/draw this scene in my Mesozoic Feild Guide (if I stop procrastinating of course ^^). Thanks and sorry for all of the questions.

Duane Nash said...

Thanks and excellent questions. I am agnostic as goes Epanterias, Edmarka etc etc. They might just be large morphs of Allosaurus/Torvosaurus. And that question would be better addressed to the people who work first hand with the bones, have access to the specimens, and so on - which I do not. So I am going to decline to offer a staunch opinion either way because I don't have access to the specimens and I don't try to portray myself as a "taxonomy " guy any ways. I provide insight, ideas, and theories that might lead to future more rigorous testing. But my gut tells me that as the sauropods were getting bigger and bigger so were the theropods - whether or not this translated into bigger morphs or new species I don't know. And to tell you the truth ecologically it does not matter that much if those exceptional large theropods were different species/local variants/large morphs. The sauropods got bigger and so did the theropods.

In theropod niche partitioning I tend to think that unless there is extreme reasons to infer a speciality in diet I tend to go with most carnivorous theropods having a lot of overlap in diet actually - complete with generous amounts of intraguild predation and cannibalism. For Marshosaurus I have not really looked at it too closely but the skull reconstructions suggests a pretty typical mesopredator - baby sauropods, young of other theropods, scavenging - probably fits the bill. My suspicion is that niche segregation occurred more on the landscape level than strong dietary differences. For instance maybe one species likes open plains, another closed canopy forest, another wetlands. This is how best you can achieve high diversity with lots of dietary overlap.

In my speculative essay I implied a little partitioning between Ceratosaurus, Torvosaurus, and Allosaurus based on differential exploitation of large sauropod carcasses because I feel that this is where competition between the three is greatest. Torvosaurus is the best at breaking apart limbs, gaining access to large carcasses and it focuses on gnarly cartilage, skin, smaller bones, muscle. Ceratosauruss likes to poke deep inside carcasses after soft internal organs. And allosaurus exploits a ll aspects of the carcass, including the bones. And this wide feeding niche and inferred "mob" type sociality gives Allosaurus numerical dominance.

khalil beiting said...

Why thank you for the feedback. Like you, I can't look at the bones and everything so I've basically no clue on what is valid and what isn't. Also, is it true that Saurophaganax and/or Epanteris is only known from the upper morrison? If they're both only from the upper, than there's a slightly higher chance they might actually be valid. Them being a new species/genus/sub species/morph is another major question, but since neither of us actually have material to base off of, than I guess we just have to twiddle our thumbs and hope for a paper on either one of them.

When it comes to mesopredators, intraguild predation, niche partitioning, etc., do you think you will do an article sometime in the future that talks/discusses them? You could even do a series like what you're doing with Plesiosaurs and Theropods, but I'd completely understand if you were busy. I'm only 16, so I have a lot of learning and research to do, so I jsut wanted to know if you would ever go in-depth with it.

Oh, and could I re make your carcass scene for my spec evo project? I must mention though, this spec evo project of mine isn't really about an alternate time line like many other spec evo projects, but rather just about the ordinary Mesozoic. It has all of the animals we already have the fossils of, along with many species that aren't known, but that are possible (if not likely) due to our understanding of Archosaur evolution. I will also explore fossil sites with very little dinosaur fossils, therby making up new (likely and/or plausible) species, along with restoring already known animals in ways that are reflective of how modern day animals are all unique and/or strange (i.e. flamboyantly plumed giant Theropods, feathered Sauropods, Ankylosaur/ceratopsian omnivory, Hadrosaur inflatable nose/throat sacs, etc...you know what I'm getting at here ;)). I will also even make up new fossil formations that aren't known, like offshore islands, Appalachia in general, etc. So basically, I was wondering if in my feild guide, I could recreate a scene like what you wrote, except completely drawn in several slides that show the gradual proccess of the complete consumption of the carcass and how all of the Theropods biomechanically work. When (or if) I do this, I will upload it on DeviantArt, and if you allow me, I will give in the description a link to your blog, and the amazing article you did on Allosaurus biomechanics (along with any future reference you make on Theropod biomechanics).

One last question, but do you already know what Theropod species/group you will do next?

Duane Nash said...

Yes you can use my art it is all on deviant art and Creative Commons so use it and abuse it. Just specify what ideas are mine - and which are yours in your speculative project.

I don't want to give too much away for my next post... just know that I have not played all my cards on this post and that several theropod lineages (possibly not all Mesozoic) are gonna get a little bit of a reboot here.

khalil beiting said...

Thanks, but just to let you know, I wasn't going to actually use your artwork. I was going to just make a scene similiar to the scene you vividly imagined. I was thinking of adding a few other animals, some speculative behaviour, maybe one or two speculative evolution species, etc. I'll definitely post a link to your work.

Oh, and I can't wait for your next article ^^. You know, you are my favourite researcher in plaeontology. You make such excellent articles, with large amounts of evidence to back you up, all the while writing it in a way that's very intuitive and makes the reader really feel engrosed in your theories. The latter is something very lacking when it comes to the average formal paper, because those papers are usually boring and incredibly monotonous. They explain everything in a way that only a robot could truely understand. You on the other hand do a perfect job at informing and persuading by your drawings/guides, links to other modern day analogues that give a better understanding, etc. *Sigh* I wish other scientists were as good as you. Keep up the good work ^^.

Duane Nash said...

Thanks so much for the kind words khalil beiting. Much of what you mentioned formed my impetus for this blog/my work. I was getting discouraged that "dinosaurus with laser beams coming out of their eyes" seems to be more of a trending topic in paleontology on facebook than my post here but some things take time to sink in and I am ok with a slow burn rather than an explosive fire. I have got enough encouraging words and interest here to keep me going - and so far no damning critiques - and your comment really made my day.

khalil beiting said...

No problem ^^. You truely are an intelligent person, so I just had to tell you in case you thought otherwise ^^. Keep up the good work, especially on your new Theropod posts. I can't wait to see what you have in store next *cough* Phorusrhacoids *cough* ;).

Sean McCabe said...

Perhaps Epanterias or Saurophaganax morphs were like the lappet faced vultures in those first videos; they could walk up to a carcass being fed on by several allosaurs, and establish that he's in charge.

Duane Nash said...

Exactly Sean!! In fact I directly suggest that Torvosaurus could have been the lappet-faced vulture of the Morrison, opening and dismembering large carcasses for other animals, in the paragraph after my diagram of bone slicing Allosaurus. Dominating small carcasses yeah, but if we are talking about a 20-50 ton carcass it can't monopolize all of it - especially against the much quicker and numerous Allosaurus.

BrianL said...

I must admit I am quite amazed by your post and, though that's not the best route to take, I hope you are (mostly) right about what you propose. It so happened that yesterday, I visited Artis zoo in Amsterdam where I got to have a look at the Griffon Vultures being fed. I have seen vultures eating before, but given the contents of your post I decided to use the opportunity to give them an extra good look and indeed, I could see the nibbling and hook-and-pull actions taking place, even if the vultures were fed dead rats rather than a big carcass. Of course, dominance was much in play too and for bonus points, the zookeeper mentioned to the watching crowd that despite all the squabbling taking place, young vultures are generally allowed to eat by the adults (presumably meaning their parents, mostly). Not too sure about that last thing, but certainly an aspect worth considering.
By the way, Griffon Vultures in Spain are also on record as having killed weakened calves and sheep by mass attacking them. This is taken as extreme behaviour due to lack of carcasses in recent years, but is nevertheless interesting behaviour that may or may not give insights to *Allosaurus*'s feeding methods. Certainly a mass attack on a live animal by vultures would be a very sordid and grisly affair.
A last thing worth pointing out, though you undoubtedly know this already, Lappet-faced vultures are also capable hunters of live prey in their own right, even if they mostly scavenge.

Duane Nash said...

Yes thank you Brian L for your insightful and strangely prophetic comment. Yes, I too was worried about getting taken in by the whole "coolness factor" of it all - but hey, sometimes nature really is that cool. Nice to hear about your independent observations of vulture feeding. It happens so fast that I think that choanal grinding has been overlooked. And on prey capture by vultures this is a topic I want to go into more in my next post so stay tuned.

On young vultures feeding at carcasses/various sized species feeding at once. I think a couple of factors are at play. The size of the carcass certainly dictates how many can feed at once. Smaller species/youngsters would certainly be more agile than older brutes. SInce theropods had more laterally facing eyes than mammalian carnivores this could allow them to feed and keep an eye on neighboring theropods. That being said there are loads of instances of even large mammalian carnivores or crocs/lions feeding side by side because the bounty of meat is so great fighting is just not worth it.

Robert Haan said...

Interesting point of view, and one which has a legitimate backing of credibility to it. i especially like your take on the social aspect of allosaur behaviour, and i think you've highlighted this in your first few plesiosaur posts, just because an animal isn't hardwired to cohesive teamwork and complex coordination, doesn't exclude the possibility of some form, perhaps the most basic of cooperation between individuals towards a common goal. Too often we tend to shoehorn a particular animal into only fitting into a particular niche . I hope viewpoints like yours will be more common in the coming times .

Duane Nash said...

Indeed I want to elaborate more on social behavior in future posts. I actually think selfishness = as opposed to any kind of "mammalian" type empathy or emotional attachment was the glue that held these guys together. Basically if I run in cahoots with others of about my size we will have more feeding opportunities. I watch what my cohorts do and react in turn to what they see. Andrea Cau has been speaking of a similar nature for theropods for quite a while too so not a completely novel interpretation but one I tend to espouse.

Robert Haan said...

Exactly ! It doesn't take a great intellect to figure out that if I do things a certain way and it yields a greater turnover then I'd best stick with that method of doing things, if Allosaurus was reaping a greater benefit from hunting together then it'd make sense that they'd be willing to tolerate one another, regardless of whether there being any form of emotional sentience within them.

Jaime A. Headden said...

I like your idea, Duane. However, my concern is that I do not think the oral papillae are durable enough to perform the behavior that you ascribe. Without knowing precisely what is being done here, we can assume a role for the tongue and oral papillae for some manner of prehension. When it comes to the much, much larger oral and esophageal papillae in penguins, sea turtles, and various other pelagic animals without teeth, we can assume that these assist in preventing slippage. Thus, they aid in prehension. But that in other birds seem smaller. Feeding behaviors differ. Ducks, geese, and flamingos use their lingual papillae and scrape inside their mouths, so lingual "ramming" back and forth might serve a process of managing small bits of food, or rendering, but never it seems very large bits. That's the function of the book and pull, after all. Of standing on the prey item and lifting up. As much as choanal grinding seems to make sense given the observed behavior, I am loathe to give it more concern without in vivo study of this behavior. As it is, we might rather expect these papillae to be advantaged when there are many of them, yet in these birds there are fewer. This suggests a smaller role in tongue assisted prehension than, say, penguins.

Jaime A. Headden said...

I like your idea, Duane. However, my concern is that I do not think the oral papillae are durable enough to perform the behavior that you ascribe. Without knowing precisely what is being done here, we can assume a role for the tongue and oral papillae for some manner of prehension. When it comes to the much, much larger oral and esophageal papillae in penguins, sea turtles, and various other pelagic animals without teeth, we can assume that these assist in preventing slippage. Thus, they aid in prehension. But that in other birds seem smaller. Feeding behaviors differ. Ducks, geese, and flamingos use their lingual papillae and scrape inside their mouths, so lingual "ramming" back and forth might serve a process of managing small bits of food, or rendering, but never it seems very large bits. That's the function of the book and pull, after all. Of standing on the prey item and lifting up. As much as choanal grinding seems to make sense given the observed behavior, I am loathe to give it more concern without in vivo study of this behavior. As it is, we might rather expect these papillae to be advantaged when there are many of them, yet in these birds there are fewer. This suggests a smaller role in tongue assisted prehension than, say, penguins.

Duane Nash said...

Thanks for commenting Jaime, I know you said that you had trouble getting into the comments here so thanks for lending your thoughts. Well we might be at an impasse as it comes to both of our - what essentially boils down to - opinions on the strength of the papillae until further study. As I mentioned there is no studies on food processing as I have laid out here with vultures/petrels. All the work I can find on vultures is essentially having to do with carcass location/niche partitioning/conservation and this avenue of food processing is understudied. Be that as it may as you mentioned the much larger papillae in penguins serve to grasp the much smaller papillae in vultures serve to rasp. And if you watch closely the feeding behavior the choanal grinding as I have dubbed it occurs before the hook and pull. What I argue is that this friction augmented by the tongue and neck movements serves to weaken and disrupt the integrity of the meat. And here the small serrations would work better than larger papillae that the meat would get hung up on - keep in mind this all working very fast. After which - when the meat is softened up a bit - the leveraging hook and pull technique comes into play. And it is quite demonstrable that these carcass rendering birds differ substantially in their feeding mechanism than eagles/hawks/falcons so something is going on different here that much is for sure. I am open to other ideas but this seems the most logical. And did you not take note of the paper and pictures I referenced of the griffon vulture with a hole in its neck? Even though with the tongue lopping out of the neck it was still observed to ram back and forth when it was feeding. Therefore this behavior is so hardwired the bird is jamming its tongue back and forth even when it can't assist in food processing! This demonstrably discounts your suggestion that the tongue plays a smaller role in tongue assisted prehension than say penguins (which I admittedly know nothing about so feel free to illuminate me on how they are using their tongue) and is about as in vivo as we got right now. The theory as I laid out here best fits the observations.

And no thoughts on the bonesaw shimmy? Yes it was inspired by watching the vultures but the two ideas can be looked at independently i.e. one is not dependent on the other.

HoveringAboveMyself said...

Really interesting read and hypothesis, sadly I do not think I'm knowledgeable to comment much on it so I'm going to stick to what I know.

Even ignoring the fragmentary relatives, grown adults of Allosaurus and Torvosaurus are actually similar in size. Specimens of Allosaurus like AMNH 680 and AMNH 290 approached 10m, with femora about 1 meter long (inferred for AMNH 290). In the side of Torvosaurus, the Dry Mesa material comes in two sizes, a "subadult" and 2 "adults" of similar size, we also have "Brontoraptor" which is similar in size to the small Dry Mesa specimen, using Hartman's skeletal as a guide the small ones would be about 8m long and the large ones would end up shy of 10m and based on "Brontoraptor" their femora would also be about 1m long. Edmarka rex isn't actually much larger than this, only about ~5%.

Duane Nash said...

Thanks for commenting HoveringAboveMyself

If you are referring to the disparity in size between the Torvosaurus and the Allosaurus in the pic that is because the allos are all small immature 1-3 years old while the torvo is only about 1/2 grown itself. Fair enough with the max size for both species matching up... I was always under the impression A. fragilis was generally a bit modest in size. But maybe the population curve was skewed towards subadults and full grown 10m+ adults were rare?...

HoveringAboveMyself said...

I was referring more to the story you wrote (Mobile Sauropod Body Processing Units of the Morrison). Yeah the population curves seems to be skewed towards subadults, in fact it seems we don't have a single fully grown Allosaurus, Bybee et al. (2006) found no external fundamental system in even the largest specimens they examined (including AMNH 680 and AMNH 290).

Duane Nash said...

Interesting off the top of my head I recall recent chat that Ceratosaurus grew a lot larger than generally portrayed... A system perhaps dominated by loads of subadults, maybe a live fast die young ecoystem. A new ecology paper came out today pointing towards ecosystems with loads of adult herbivores have counterintuitively less predators than a system with less herbivores (but more young). If there was a lot of intraguild predation going on, rare adult sauropods pumping out tons of baby sauropodlets this could substantiate a predator heavy ecosystem.

predator Prey study may reveal surprising new law of nature

Darius Nau said...

I think komodo dragons are perhaps the best extant analogue.

Not only do they share the most similar tooth morphology of all extant animals, they also tend to engage in the same macropredaceous and even brontophagous activity. When feeding they rock their heads or entire bodies back and forth to power a drawing motion of their teeth, analogous in function to what you described here.
They even have that tendency to eviscerate their prey in this manner and start feeding while it’s still alive.

Here are some examples:
https://www.youtube.com/watch?v=41tgpV1Z1Ug
https://www.youtube.com/watch?v=XPBiLXp5Uj8
https://www.youtube.com/watch?v=JIv-ASfimX0
https://www.youtube.com/watch?v=aQ1vbKm7BnE
https://www.youtube.com/watch?v=S5Syko2Yo4w

Where they differ is that their skulls are broader and flatter.
Accordingly their feeding motion has more of a lateral, curved component (as does that of sharks), and less of the initial slash/strike motion (probably served to give the tooth rows an initial push and drive them deep into the flesh) Allosaurus is adapted for.

Duane Nash said...

Thanks for comment Darius Nau

While I think komodo dragons are useful analogues for some theropods - esp carcharadontosaurids which lack long flexible necks - I prefer the action of vultures/giant petrels for many other theropods.

If you compare a komodo dragon to say a dromaeosaurid like let's say Tsaagan (which I believe might fit the bonesaw shimmy model well) yes they do converge on serrated teeth but the komodo falls down in almost every other anatomical correlate to the theropod. Komodos don't have long muscular flexible necks; they are not bipedal; they don't strike downwards; and, as you mentioned, their skulls are broader. However in birds that feed on the bodies of large carcasses like new/old world vultures these modern avians converge on these anatomical correlates with the theropod. They only thing that the birds lack are the large/reinforced serrated teeth so that the damage that they can incur - esp. against live prey - is >much less< but I think that the general feeding/biting action had a lot of commonality. So much that I would consider vultures the best analogue among extant animals for several (but not all) carnivorous theropod lineages. And this is not so radical when you consider that vultures/giant petrels are derived theropods after all.

lkwalters said...

Hello again,

Although at first, I thought your argument for a bone-saw-shimmy was perfectly plausible, I've done some thinking recently that's made me question some aspects of it.

I think the first question to ask is: how well would theropod teeth stand up to such frequent use on bone with a sawing action? They're quite a bit more thick and blunt in nearly all cases compared to shark teeth, which I think would mean that they're not nearly as effective in the proposed sawing motion. I also wonder about the tooth crowns breaking from such a motion. I know that the denticles are unique in structure and last considerably longer than komodo dragon teeth (Brink et al, 2015). But, again, I don't know how they would stand up to the "bone saw shimmy". Bone is extraordinarily tough, after all, and if theropods were already adept at sawing bones, then why would we see Tyrannosaurids evolving a bone *crushing* bite, when the bones could already be sawed so easily? Hmmm....

I also think the large coprolite could be explained by one, possibly two things: The first could be that the Allosaurus had already swallowed the prey (and prey parts) whole during feeding, and the resulting breakup of the bone is due to the digestive process. Bone eating vultures such as the Lammergeier have extremely acidic stomachs to help them digest bone, and they don't have a crop. (See: http://www.reed.edu/biology/courses/BIO342/2012_syllabus/2012_WEBSITES/IvyH.BeardedVultures.2012/mechanism.html ) Therefore, Allosaurus and other bone-consuming theropods almost certainly would have had a similar adaptation in place.

Secondly, there's the fact that some gastroliths have been found associated with large theropod remains. See: http://dml.cmnh.org/1999Apr/msg00504.html Lourinhanosaurus was probably ecologically similar to Allosaurus, and I can't think of a reason that large theropods would have gastroliths other than to help their stomachs grind up bones! After all, these theropods probably weren't using it for buoyancy, and I don't think they would have possessed crops that needed cleaning out, either. (I've read that kestrels and some other small falcons will consume grit to rid their crops of a greasy lining from the insects they eat.)

I also think the observed score marks on the bones could have simply been made by sheer bite force. Although Allosaurus isn't typically imagined as a bone-crusher, I'm sure that its jaws could produce enough force to bite through certain parts of bone. Perhaps its massive neck muscles could have also helped drive the tooth row into the bone and cause the marks we see?

I'd also like to know if there's pictures of any bones that have been sawed by sharks, or vultures, etc. I'm curious as to what the marks look like and how they compare.

-L. Walters

P.S. I still think the sawing motion certainly seems plausible, but perhaps it was used more against tough flesh and skin rather than bone...

Duane Nash said...

On tooth durability and theropod teeth being more " thick and blunt compared to shark teeth". Are you sure of this? Carnivorous theropod teeth (exception being tyrannosaurid teeth) are characterized as being laterally compressed i.e. not thick and blunt Yes the tooth crowns could very likely get worn and broken. In fact there are loads of theropod teeth showing this exact attribute. As I mentioned several times in the post bone may not have been that high on the list of preferred food stuffs because dino bone may have altogether been more pneumatic and less marrow filled than mammal bone. "bone is extraordinarily tough" yes but when fresh still very wet and easily cut into. And the teeth got replaced eventually.

Think about it this way: a theropod depending on the meal at hand has to make some value judgments on the friction and wear put on its teeth versus the benefits accrued from the meal. Young and small dinosaurs obviously had less meat and smaller bones than adult dinosaurs. So they were likely sliced and diced and eaten completely since the theropod did not have to cut through such thick/mature bone and it was hungrier anyways. But when we look at the bonanza of food that a 20,30,40 ton carcass provides, now we can be picky. When I have tons of high quality food to go through why gunk up my insides with relatively poor quality bone when I have all this meat, entrails, fat etc to eat up. Plus I can save my teeth from excess wear. This matches the fossil record too, especially for sauropods. Preserved adult and subadult sauropods but the young ones have been disappeared.

On acidic stomachs in theropods. All the data we have suggest bone passed through theropod digestive systems relatively unscathed. All the shards and broken off splints of bone in theropods have sharp edges not the type you would expect from an acidic wash of the type you are implying. If theropods had the highly acidic stomachs compared to crocs we should see a pasty coprolite of dissolved bone not the jagged sharp bits we are seeing. In fact in a future post I will go more into the consistent occurrence of shards of bone in theropod poop. Shards of bone is a prediction that is met with the bonesaw hypothesis and I highly doubt it was gastroliths. For starters if gastroliths were so common in theropods we should find more of them especially the Cleveland-llloyd allosaur deposits.

"used more against tough flesh and skin rather than bone..." I think you are thinking too narrowly. Dinosaur skin was often riddled with osteoderms. So if you are doing the bonesaw shimmy through dinosaurs skin you are in fact biting through bone. And if it is likely that theropods were eating tons of baby dinosaurs I doubt that they were - or even had the capacity - to delicately slice through and carefully avoid the bones in all those wee little dinosaurs. The laterally compressed, industrial strength teeth were powered by a laterally compressed head on the end of long and muscular neck which was the main source of power - or to put it better friction. The whole operation was based on speed and friction not really power as in the crushing power of a hyena bite. Which I am troubled with "bone-crusher" being the de-facto assumption as you seem to posit as well as everyone else. Ironic that in modern industrial animal processing it is speed and friction that processes animal carcasses not crushing power. Let go of the hyena mindset.

I don't have or have seen any bone saw traces from sharks and vultures don't have the dental equipment. The main point of vulture part was to show the inspiration for the idea.

Good questions and critiques, you keep me on my toes but I have uncovered other layers of evidence (future post) that have only bolstered my hypothesis.

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