Sunday, August 23, 2015

Teratorn Blood Festival

Deep in the Peruvian Andes lives an astonishing tradition. In isolated villages throughout the area natives enact a symbolic clashing of civilizations. An Andean condor (Vultur gryphus), is captured, fed and groomed for several weeks, and finally latched onto the back of a bull in an arena.

credit Mollie Bloudoff. NPR
This visually startling tradition kicks off the annual Yawar, or blood festival. In the eyes of the native Peruvians the bird represents native Incan resistance, or even an Incan god, triumphant over the imperializing Spanish forces represented by the bull. Injury or death of the bird is seen as a portent of bad luck for the coming year.

credit Mollie Bloudoff. NPR
Now here is where a rather lengthy discussion pertaining to obvious issues of cruelty to animals and conservation ramifications for a dwindling population of these birds could be inserted. Countered in turn by charges of cultural relativism and the hypocrisy of western industrialized nations own dietary dependence on mechanized, polluting, CO2 enriching, factory farmed cruelty ridden meat crops.

BUT THERE WILL BE NO SUCH SENTIMENTAL BLOVIATIONS IN THE GRANDE GUIGNOL THEROPODA!!

Instead, for a more meta-analysis that should resonate with this audience, let the bull represent the merauding advances of synapsid mammalia and the condor represent the hallowed heritage of archosaurian theropod dominance.

lappet-faced vulture fends off mother Thompson gazelle while cohort
attacks fawn. credit Roy Mangersnes

The following, very tenable, paleo-fiction should best be enjoyed with the following Alice In Chains song "It Ain't Like That" cranked loud for maximum deathly ambience. Plus it has the line "vultures cry when flesh is ripping". And the singer died of a heroin overdose to lay rotting in his own house for several days before being discovered, there's that too.



Less than 15 minutes into its earthly existence the newborn Bison antiquus calf was already at deaths door. Despite its mother's valiant defenses the repeated bites, yanks, and shreddings of a dozen Terratornis merriami had at first yielded blood, then flesh, and finally breaching of the body cavity via trauma sustained to the anal region. Death was neither quick nor painless upon the calf but it was none the less assured.


Bison antiquus was the most common - and most aggressive - large herbivore of the La Brea plains and foothills. The young mother of this calf - it was her first calving - had in its life already faced down and survived encounters with dire wolves, smilodons, lions, and short faced bears. She was 2700 lbs of hoofed combative weaponry. But she had underestimated the predatory tactics of these birds.

While she had noticed the teratorns before - they always seem to be a dominating presence at any large carcass - in her finite thought processing machinery she had never considered these birds on par with the other four limbed terrestrial carnivores that she had dealt with. This was a grave mistake - because although the birds posed no threat to her - terratorns are responsible for more new born calf depredations among La Brean hoofed herbivores than all mammalian carnivores combined. The  other grave mistake of the mother was in choosing to give birth in the open sagebrush plains. Other, no doubt terratorn savvy, more experienced cows opted to calve in dense cottonwood/willow riparian thickets. In these closed quarters the big birds with their 12 foot (4 meter) wingspans could not manoeuvre.

And this flock of terratorns - the Bombardiers - anticipate at least some of the young bison making this mistake and every calving season gather in this same locale in anticipation of them. While other terratorns work in smaller flocks harassing deer, peccaries, and antelope for their newborns this flock has grown specialized - some might say even developing an incipient culture - in preying on bison calves. Some of the Bombardiers are over 50 years old and have been refining their hunting tactic for this long. The long life span and observant nature of these birds gives them an exquisite knowledge base concerning the habits of all the other fauna on the La Brean plains. They know when and where the mammalian predators move. How to follow turkey vultures that could locate a carcass in dense foliage with their sense of smell. When to move to the coast to feast on seabird colonies, marine mammal carcasses, and pinniped mortality events. When and where each herbivore species gives birth. Time and knowledge is on their side.

When the first terratorn struck it did not do so from the sky but it approached from the ground. And its object of intent was not the calf but the mother - nipping her on the tail just hard enough to send a shudder of pain through the mother's psyche. The cows next response at this unexpected intrusion was confusion, bewilderment, and ultimately anger. The bird had counted on this response. The mammalian brain was hardwired for emotion. The terratorns' brain was unencumbered with such emotional sentience. Instead the computational hardware of the bird brain had a much faster processing CPU. Information was gathered, processed, and acted on accordingly based on a constantly shifting positive/negative benefit scale. 

And so as the cow reacted to the increasing rage at the thought of this "mere bird" plucking at its tail it failed to notice the eleven other terratorns in the sky and on the ground who had been watching in anticipation for the mother to leave its calf unattended. And as she obliged their wishes by charging after the first terratorn - which mockingly sauntered off not by flying away but by nimbly running away - they fell upon the calf.



The birds went for the softest parts first - under the limbs, the neck, the anal region. No one bite was fatal. And the action was fast and almost imperceptible. While the large hooked jaw was the most obvious feature of the bird and the first to suggest how it killed the true damage occurred inside the bill. After the hook of the beak had seized a plug of tissue then the cutting technique commenced. Rapid fire movements of the stiff and serrated tongue would grind and pulverize the flesh against the minute rows of serrated papillae on the roof of the mouth. Augmented by rapid oscillation of the neck musculature the whole operation was incumbent not upon bite strength - which the bird lacked - but speed and friction - which the bird had in abundance.


Andean Condor still from youtube clip. Note the stiff/muscular yellow tongue that - when feeding - pumps back & forth shredding meat against the choanal papillae. 




In above gif note the large/stiff tongue starting to move back & forth in the male condor as it anticipates a feed. Another similar and independent observation of more rapid tongue movement in a griffon vulture with a hole in its neck from which its tongue lopped out was observed in Spain (Camina & Guerrero. 2013) and France. The morphology of the tongue - convergent in New & Old World vultures, and several tubenosed marine birds - notably giant petrels - is referred to as canaliculate. This style of tongue follows the contour of the lower jaw, with a canal or trough in the medial section, and serrated edges on both lateral edges.

By the time the mother bison realized that its newborn was being set upon by numerous teratorns she had been drawn away from her calf by over 60 feet (20 meters). Blood had already been spilled on the chapparal. Now confused, bewildered, and even more angry at these developments she rushed back in defense. However the teratorns, now emboldened by the taste of blood on their beaks,  redouble their efforts. They harry the cow from all angles. Several swoop from above at opposite angles, while others dart around on the ground like macabre turkeys plucking at her back legs and tails with their serrated tongues/papillae. And again they raise her ire to the point where she charges furiously at birds but in doing so leaving her calf open to repeated attacks.



The more experienced terratorns have several tactics that prove especially infuriating to the cow. One of these used during ground operations is to feign running away and when the cow draws near and prepares to gore the bird the bird deftly leaps off the ground and kicks its talons off the face and horns of the bison. And in doing so uses the momentum of the charging cow and their high wing loading to quickly become airborne.


The repeated strikes at the cow from ground and air and her fruitless charges have worked to fatigue her after 10 minutes. While her girth, power, and weight worked to her advantage against land bound mammalian carnivores they are proving a liability against the birds. They are always one step ahead of her. Meanwhile the body cavity of her calf has been breached and the birds are now essentially eating it alive. Her counterattacks have become increasingly half hearted and now the birds, sensing her loss of resolve, don't even bother to lift off when she charges and feed with impunity right in front of her. Smarting from the eventuality of the situation, her increasing fatigue, the blood on her own face, and the realization that she herself is now vulnerable to predator attack due to her fatigued state she concedes her calf to the birds.

And over the next several weeks the Bombardier flock continues to feed on bison calves - and even does battle successfully with a giant camel for its newborn. Several birds become so gloated that they can't fly and roost in some local oak trees until they digest their load of mammal flesh...

So that's my take on Teratornis merriami. It should come as no surprise to you that I don't really take seriously suggestions that it was some type of piscivore (really? terrestrial socal is not too much of a fishy place now or then - especially in tar pits where the great T. merriami is often pulled from). Or that it was some type of small prey land stalking specialist... eating rabbits (seriously sometimes paleontologists, in the pursuit of "conservative" interpretations actually jump the shark into less than tenable realms)? Nope this was a bird that was intimately tied to and dependent upon the large megafauna it co-evolved with and eventually became extinct with.

And while I am not the first to suggest such aggressive predatory tactics in teratornithids I am certainly the first to frame it in this fashion with an emphasis on calf predation/group tactics/choanal grinding.

Now I did this little bit of - extremely plausible - speculative paleofiction on T. merriami cuz, you know, I'm a California guy. You can make up what you will with what was going on with Argentavis magnificens...



L to R. T. merriami, CA Condor, Golden Eagle. credit Travis. CC2.0


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Tuesday, August 18, 2015

Convergence in Form and Function Across 230 Million Years of Theropod Evolution



Jack Horner can dispense with his mad scientist franken-chickenosaurus machinations. We already have plenty of fine and dandy carcass processing theropods in all corners of the world - land and sea - right now, thank you. In my last post, Allosaurus - More of a Vulture Than a Falcon, I described a remarkable convergence in several lineages of carcass rendering birds that use a macabre feeding technique I have dubbed "choanal grinding". This feeding method in turn inspired a theorized feeding technique in Allosaurus that I outlined and referred to as the "bonesaw shimmy" - the shimmy being a dance based upon rapid alternate movements of the shoulder, outlawed due to it's overtly sexual nature in the 1920's . This "bonesaw shimmy" in turn may yield implications for other theropods to varying degrees I suggested.

In this post I want to expose a known anatomical characteristic linking past and present carcass rendering theropods (forgive me for using the term theropod loosely as such, for me it implies both extant aves and Mesozoic theropods/paraves/true avialians unless otherwise specified) . This characteristic - which is so painfully obvious it has hid in plain sight - has the potential to offer much utility in inferring likely feeding behavior and technique in both Mesozoic and Cenozoic theropods.

But as I am one with a little bit of a penchant for theatrics, I do not want to introduce that overlooked anatomical characteristic just yet but instead let us first spend some time with the bearded vulture aka the Lammergeier (Gypaetus barbatus).

Lammergeir. credit unknown but too cool not to share
Is there really any bird more classically dinosaurian than the Lammergeir? Everybody coo coos about the cassowary but for my money, if you want a direct portal to theropodian antiquity look no further than the bearded vulture. Not only is it strikingly colored, eats bones/marrow with gusto, is pretty darn large but it is also - along with a suite of other "carrion birds" - more predatorial than generally appreciated. I have to encourage you to watch the following youtube clips. They really give you perspective on the size, intelligence, awareness, impact and general gravitas of these impressive birds. The trainer seems like a cool dude too but I have to subtract some points for use of the John Mayer music.



Impressive, no? And for some nice footage of bearded vultures at a feeding station. If you squint your eyes a bit, not too hard to imagine dromaeosaurids or unenlagines in the clip below.


If you are still smitten with the regal beauty of these birds here is a nice close up video (the first pic of this post is a screen grab from it).


Now maybe you have never spent that much time up close and personal with these birds until now. They are astonishing - and that strong dinosaurian vibe you get off their appearance is not a mistake. Whether or not you keyed into the anatomical congruence that unites 230 million years of carcass rendering theropods yet is ok - you probably subconsciously sense it.

What I am referring to - the uniting anatomical peculiarity - is the supraorbital ridge or brow ridge if you will present in this and many other carcass rendering birds and Mesozoic theropods. Relatively obscured in the lammergeier due to feathers it is more noticeable in the lappet-faced vulture below giving it that distinctive "evil" glare. Not coincidentally (as I will discuss) the lappet-faced vulture is a large vulture with a penchant for the particularly tough and gristly parts of carcasses as well as a noted predator.

lappet-faced vulture.ccsharealike2.0. credit KCZoofan
If we look at another unrelated large carcass rendering bird - my hometown hero, the Californian condor (Gymnogyps californianus) - we can see a relatively thick ridge along the top of the skull and thickening supraorbital ridge.

CA condor skull. credit Kai Schreiber. CCsharealike2.0
Additionally, in another lineage of carcass rendering birds - giant petrels - we see a strong rugose brow above the eye and flange anterior to the eye.

Southern Giant Petrel skull. credit OVAM. CCbylicense
note the "eagle eye" brow ridge. CC3.0 credit Graham Curran
Now this supraorbital ridge and thickening bone at the top of the skull I have noted in these birds - keep in mind these are all fairly disparate lineages of bird - shows convergence. Of course this "eagle eye" countenance is of course most noted in eagles. But if we look at their skulls something a little bit different is going on.

eagle skull. credit Kai Schreiber. CCsharealike2.0
Eagles have a distinctive flange or process of bone forming the ridge while in the above examples the ridge is more solidly built into the skull. As I discussed on my last post eagles and other raptorial birds of prey are inferior harvesters of large carcasses compared to vultures/petrels. Furthermore they are often shoved aside at feeding opportunities by "carrion birds". So for these reasons and because the more "raptorial" birds of prey kill with their talons and not their heads/beaks I am going to treat them as a bit of an outlier as goes the evolutionary narrative that you might already be guessing at.

The tops of Mesozoic theropod heads are also adorned with an array of crests, eye ridges, lacrimal horns, knobbly protuberances and often times fairly thick bone deposits. In fact you can take a fairly base model crest such as you see on Coelophysis or Allosaurus and the vast majority of predatory theropod heads are but slight deviations.

Coelophysis bauri

credit Witmer's Lab
Now these crests. ridges, rugosities, brow horns, bosses, and lacrimal horns that line the top of the skull  have to varying degrees been interpreted as display structures, built in sun visors, or head butting devices (again the bone in these structures is often very thick). However none of these ideas have been adequately tested nor has anyone suggested a reason why, for over 130 million years, theropods were so damn conservative in their choice of headgear?!? I mean that is a long time for any piece of apparel to stay in fashion. And if they were head butting devices, presumably used to avoid lethal biting, these animals sure didn't display much restraint in terms of face biting evinced by the numerous lines of evidence suggestive of such biting incidents.

Mapusasaurus roseae showing the thick lacrimal/nasal crests along top of skull. credit Kabachi CC2.0

Instead I am going to offer an alternative explanation: These structures - although potentially co-opted for display, combat, sun shielding - had their impetus not for any one of these reasons but were generated for biomechanical reasons.

The biomechanical origin for these structures lays in absorbing stresses and strains from strenuous feeding activities.

Again, let me get a little nuanced here because I think nuance is sometimes lacking in these types of discussions and people get hemmed into either/or debates. For sure, in critters like Dilophosaurus or Monolophosaurus these structures are custom built as display structures. But what I am suggesting is that if a structure is in fact a display structure - it is usually obvious. And in the vast majority of theropods the head gear is a lot more conservative and primarily serves a mechanical function.

If we look at the theropod head it is a compromise between strength and lightness of build. The head had to be strong enough to interact and sustain integrity through  vigorous encounters with prey/rivals. But it also had to be as light as possible to facilitate the rapid neck driven feeding mechanisms that were fairly ubiquitous across the group. The lacrimal horns, ridges, rugosities etc etc. serve as "energy dumps" where the stress and strains encountered across the mouth are transferred up and away and "dumped" into the thick deposits of bone and pneumatic cavities at the top of the skull. A study of stress and strain distribution in the skull of Allosaurus pretty much spells it all out.


Note how in the above visual (from Rayfield et al. looking at forces in the skull of Allosaurus) that compressive forces marked "yellow" are being concentrated towards the lacrimal, nasal, frontal bones up those struts of bone away from the tooth row. Most telling is the pic on the bottom right where the course of the compressive forces appears to be literally tracing the crest line on the top of the skull of the allosaurus. In fact if you take a second to look at the architecture of a theropod skull holistically - it appears biomechanically designed to move stress/strain away from the tooth row towards the top of the head. This makes sense for a predator that needs to bite stuff and does not want to suffer mechanical failure of its teeth/jaw. Excessive forces can be shunted away towards thick crests/nasal bosses/brow ridges etc etc. Not only that but it minimizes the deposition of heavy thick bone throughout the whole skull - which would add cumbersome weight - and maximizes the animal's ability to move its head quickly and efficiently.

credit Scott Robert AnselmoCC3.0. Trex

And you can see this thickening of the top of skull to full effect in the pic here of T-rex. A mechanical design begetting thick theropod crests. If we accept the maxim that form follows function the mechanical advantages of such a design elegantly explain the long tenure of the design.

Why has no one has approached the issue of why certain theropods have converged on such thick lacrimal/nasal/orbital ridges before is a good question. Maybe we just are taken in by the cool factor of it - they do add a bit of style and flair to their look. But, as I always tell my traffic school students, things have a way of hiding in plain sight.

Ok, so if my hypothesis has merit - that these structures serve as "dumps" for excessive forces incurred during vigorous feeding bouts - then a good test would be to see if said structures are diminished or absent in theropods that feed on small prey, fish, or have explored a more omnivorous or herbivorous lifestyle.

Ornitholestes hermanni. Osborn 1903. AMNH 619, holotype from Carpenter et al. 2005
Ornitholestes hermanni the famed "bird robber" of the Morrison. Yeah they have a nasal horn (update false no horn there)  - as I said earlier most likely such obvious features are display related - but if you look up on top things are pretty thin. And with it's reduced serrations, modest sized head, and gracile build this critter is assuredly a small game hunter. Prediction met.

Masiakasaurus knopfleri
Another theropod interpreted as a small game hunter Masiakasaurus knopfleri (more on this guy in a later post btw). While the top of the skull looks a little thickened there is but only the incipient hint of a crest and no big, thick supraorbital/lacrimal crest to speak of - at least not on the order of true ziphodont theropods. Prediction met.

Suchomimus.creditAStrangerin theAlps.CC2.0

Suchomimus tenerensis. Usually interpreted as a fish eater, although an opportunistic small/medium game predator is likely given the dino/pterosaur consumption shown in close relatives. And don't be fooled by the notion of "mere fish eater" either. Some of these fish on the menu were huge with heavy, ganoid scales. So in spinosaurs we see a single crest with some pretty thick looking bone as well as some nice ridges around the eyes. So although not as heavily crenulated/crested as carcharodontosaurids. allosaurids, tyrannosaurids and other large game hunting theropods there is still some amount of crest/ridge action consistent with the stresses likely incurred from a diet of small/medium game and large armored fish. Prediction met.

What is interesting is what we see in terms of headgear on several other medium-largish theropods that have also been suggested as occasional to frequent consumers of fishy - aquatic type prey. The species I am referring to are Dilophosaurus wetherelli - which Kirkland has been advocating as a fish eater for years - and Ceratosaurus nascicornis of which Bakker, more controversially, has been interpreting as a fish (esp. lungfish) predator for a while now.

credit Jaime A. Headden aka Qilong. CC3.0
Those frills are described as especially thin and fragile - a far cry from the gnarly thick crests of big game hunting ziphodont theropods. The lacrimal crest is relatively diminished. Given those relatively thin teeth, kinked snout, and generally gracile build a predominantly piscivorous - with potential inclusion of medium game/scavenging - adaptation is looking more and more promising. Prediction met.

Ceratosaurus. credit Tremaster. CC2.0
But Ceratosaurus clearly is relatively more robust in terms of headgear than Dilophosaurus, especially those lacrimal horns. So I am not ready to call it a dedicated piscivore - although it certainly could have opportunistically exploited lungfish, aquatic prey etc etc.

And what about dromaeosauridae? Well they run the gamut. But the pattern seems to hold up. Regardless of how big they are, dromaeosaurids with reduced serrations/adaptations for small game are  relatively impoverished in terms of strong head gear while dromaeosaurids with serrated teeth/deep skulls/homodont dentition aka "classic ziphodont" styled animals have relatively robust headgear. I am going to concentrate on two extremes.

One of my favorite dromaeosaurids is the South American unenlagine Austroraptor cabazi (Novas, 2008). The long low snout, conical dentition lacking serrations, and general build have inspired comparisons to spinosaurids - which became extinct at that point as far as we know in South America. So despite it's size Austroraptor appears to have been another small/medium game specialist with adaptations that speak to this. And if this is the case according to my theory it should fall short in terms of robust head gear comparatively speaking. Although it has a bit of rugosity on the top of the skull and some supraorbital/crest action it definitely falls short compared to true ziphodont theropods. Prediction met.

Austroraptor cabazi credit  Esv. CC3.0
And now as the contrast let's look at one of the smallest of all theropods Bambiraptor feinbergi *update potentially baby Sauronitholestes (Burnham et al., 2000). Despite it's cutie pie name and diminutive stature I am going to suggest Bambiraptor has a lot more in common morpho-ecologically with Allosaurus fragilis than it does with Sinornithoides youngi.


Bambiraptor feinbergi or baby Sauronitholestes?. credit Thesupermat. CC3.0

Dispense with your notions of what the size of the animal implies - this animal was punching above its weight. Check out the deep skull.  And those teeth, if you look at them closely they are not conical small game teeth but stout, serrated chompers. This little bastard must have been the bane of dinosaur nesting colonies. At this size (size matters) we might not expect the crest to be as sturdy as in larger ziphodont theropods but there is a nascent double crest arising along with a thickening lacrimal area anterior to the orbit - very analogous to the suggestion of a crest in the birds that I started this post with.

If we look at a ziphodont dromaeosaur that is a little bigger, such as Deinonychus, we should expect to see a relatively more sturdy development of head gear. Prediction met.

Deinonychus. credit onfirshwhois. CC3.0
Going further in our test if robust head gear was adaptive for ziphodont theropods then we should expect that theropods which made the transition to a more herbivorous/omnivorous adaptation should have diminished headgear.

Erlikosaurus andrewsii lacks a double or even single crest along the top of the jaw but it does have a bit of lacrimal bone thickening evident along the margin of the orbit. All in all though this animal does not have the same extent of thick crests/supraorbital ridges in ziphodont theropods. Prediction met.


I am not going to go into oviraptorids, avimids, or orhithomimids because their skulls have diverged substantially from the basic theropod design while therizinosaurids still maintain the same basic shape as other carnivorous theropods. But feel free to check out their skulls, they are lacking or diminished in robust headgear compared to ziphodont theropods.

But now I want to follow another line of inquiry this time into Cenozoic theropods .... errr birds .... errr what is the difference again? What I want to look at is extinct carcass rendering birds of the Cenozoic. If this hypothesis has merit we should see increasing robusticity at the top of these skulls in the form of solid crests, supraorbital ridges, lacrimal thickening, thick brows etc. etc. Luckily enough we have two great test groups - teratornids and phorusrhacids.

And what do you know, when we take even a cursory look at terror bird skulls the prediction is met.

Titanis walleri. credit Amanda. CC2.0
Andalgalornis CT scan. credit Witmer labs CC2.5
Note the thick ridge of bone (analogous to the crest in Mesozoic theropods) as well as the thick brow over the eye. These structures also served as "dumps" for excessive stress/strain imposed on the skull I am going to suggest.


A number of features pinpoint phorusrhacids as not only hearkening back to Mesozoic theropods in some sort of vague way, but I will argue that in form and function phorusrhacids are actually directly analogous to their Mesozoic brethren - especially Allosaurus. But that is for a future post. Let's just say for now that I doubt these were mere small game hunters...

And now on to the teratornids - a group that I am especially fond of because of their ubiquity at a location not too far from me, the La Brea tar pits.


To no one's shock the skull of Teratornis merriami has a strong ridge of bone right above the eye as showcased in the above picture from the La Brea Tar Pits Blog.

Teratornis merriami credit Ellen. CC2.0
The pic above lets the light catch the supraorbital ridge just right. These would have been astonishingly wicked looking birds. And, as I will argue in a future post, fishing or rabbit hunting was not their modus operandi.

Originally I wanted to include more detailed discussions on these two groups in this post but upon seeing how long this post already is I think it will be more practical to dedicate several future posts to both the terratornids and the phorusrhacids respectively. If you paid attention to my last post where I introduced a novel technique among modern flesh rendering birds it should not be too hard to guess what I will infer for both groups. Additionally, in doing so rectify some of the excessively conservative interpretations that have been dominating thought about how these birds fed.


To further embellish my point, that the reason for the bony protuberances, nasal/lacrimal crests and horns in theropods are not just there to make them look wicked but serve a biomechanical outlet for excessive stress, I want to point out that similar features are present in the skulls of other even more distantly related ziphodont predators.

Baurusuchus salgadoensis - the terrestrial croc of late Cretaceous Brazil was sporting some fashionable brow ridges.


credit Marco Aurelia Esparz CC3.0
Pristichampsus an early Cenozoic terrestrial ziphodont croc had the stunna' shades going for it as well.

credit Robert Bakker
How can I forget the wonderful Postosuchus and the assorted ziphodont rauisuchids/psuedosuchians ? This Triassic radiation of archosaurian predators had some impressive head gear too.

Postosuchus credit Mark Byzewski CC2.0
Batrachotomus kupferzellensis. credit Gedogeheo. CC3.0
Prestosuchus chiniquensis. credit Vince Smith. CC2.0
I can't forget to mention that monitors have some head crest/supraorbital ridging action occurring as well...

Perentie (Varanus giganteus) credit Flyingtoaster CC3.0
Although monitors, especially the Komodo dragon, tend to have relatively wider skulls than the relatively deeper and laterally compressed skulls of theropods so they are not the best comparison.

Is it just a coincidence that multiple lineages of Mesozoic theropods, terrestrial ziphodont crocodiles, pseudosuchians, several lineages of extinct/extant carnivorous birds, and monitor lizards all converged on similar headgear designs? I don't think so. This convergence is due to similar solutions to similar mechanical problems incumbent upon ziphodont skulls in both feeding and grappling with large prey items.

Majungasaurus crenatissimus. credit James St. John. CC2.0

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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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