Tuesday, December 15, 2015

Theropod Table Manners: Did Concavenator Sport A Spiked Arm Gauntlet?

One theme that I keep addressing in this ongoing theropod series is that theropod table manners at large carcasses (i.e. who gets to eat what and when they get to eat it) is a subject of much natural interest but has received relatively little rigorous scientific attention. Instead much research focuses on how prey or landscape is partitioned but what about how large carcasses were partitioned? What I mean by this is that when we look at large carcasses - especially giant sauropods or even some of the bigger saurolophine hadrosaurs - this is a bonanza of resources that just begs to be exploited by the local theropod population. And I mean, the whole local theropod population...

There is a recurring sentiment that I keep coming across in theropod research - that overemphasizes niche partitioning to an extreme. "The young of such and such tyrannosaur species had different jaw mechanics and therefore ate different prey than the adults." Or the other corollary that "multiple coexisting large theropods had some almost benevolent driving force admonishing them to concentrate on different food stuffs to avoid too much competition etc. etc." And this is probably true to a certain extent I have to concede. However too often we assume that extreme partitioning has to occur. Modern examples beg to differ. For example lions and spotted hyenas are both social, live in the exact same habitats, and have significant dietary overlap.

When the shit hits the fan environmentally - when all the small prey has went into torpor, when all the fish have retreated with receding water or aestivated in the mud, when all the young dinos have migrated out of the neighborhood - that is when the true crucible of theropod competitive fires is stoked.  That cauldron I speak of is who gets to eat what, how much, and when at carcass gatherings. This really should come at no surprise when we look at how modern theropods i.e. birds partition carcasses especially in times of environmental stress. Let's forgo the vulture example because it is too obvious and instead pay some credence to the importance of large carcasses to many passerines, corvids, and raptors in areas of extreme winters.

What I want to attract your attention to is a sentence towards the end: "As snow depth increased, jays and great tits increased scavenging. We suggest that carrion use by scavengers is not random, but a complex process mediated by extrinsic factors and by behavioural adaptations of scavengers."

Most readers of this blog are in know well enough to be aware of carcass utilization by such birds but I think it bears a little reinforcement that such usage is often linked to environmental stress - in this case heavy snow. In the Mesozoic it could as well have been a devastating drought. In such circumstances partitioning for theropod dinosaurs as it is often invoked goes out the window and truly weird menageries of scavenging theropod guilds potentially gathered at carcasses. Yes I am even looking at theropods traditionally interpreted as herbivorous, insectivorous, and omnivorous such as ornithomimids, oviraptorids, alvarezaurids and therizinosaurids potentially joining the cue to exploit carcasses in such circumstances.

Chickadee scavenging elk carcass credit Jacob W. Frank

As interesting an aside as the thought of therizinosaurids moving in to scavenge among more traditional predatory theropods is, the take home message I am trying to convey is that such feeding bouts at  carcasses likely shaped theropod social and behavioral ecology. Furthermore it is also entirely possible that some theropods developed intimidation and defense mechanisms to gain leverage at such dinner parties.

Among mammalian carnivores we don't often think of them having defensive mechanisms at hand or combative/intimidation arsenals to dominate carcasses - aside from their teeth and claws - and growling/hissing. Social carnivores can dominate carcasses in relatively cohesive groups but, especially among solitary felids, retreat is the usual option - even when faced with throngs of scavenging birds. Several bears - armed with bulk, a thick skin, and a fat layer - are well provisioned for carcass monopolization and spotted hyenas with size, thick skin, muscular forequarters, strength, and group tactics also come to mind.

However among several extant diapsids better analogies exist that offer lessons in Mesozoic theropod table manners. Crocodiles and komodo dragons have dermal ossifications embedded in their skin which offer utility in rugged feeding encounters. It is also little appreciated that nile crocodiles will swarm en masse to drive off land based predators from carcasses. Which suggests some semblance of, dare we say it, "group social tactics"

Despite the attractiveness of looking towards big toothy lizards and crocs when it comes to how Mesozoic theropods monopolized carcasses we are literally spoiled with analogies among modern theropods that regularly feed on such foodstuffs: giant petrels and vultures. No need to look so far away phylogenetically when we have, you know, actual dinosaurs that do this stuff today. Furthermore not only are carcass feeding vultures and giant petrels better analogies phylogenetically, they are, let's be honest here,  a lot cooler to watch around carcasses than big crocs, monitor lizards, or mammalian mega-predators anyways!!

If there is one word I can use to describe these birds around carcasses it is theatrical. I really love this video of giant petrels gesticulating around a pinniped carcass. Not only does the video have a nice, grainy 1980's VHS gore movie quality to it the birds put on quite a dramatic show. The racket raises some questions - at least for me - about what these skirmishes really mean. There appears to be enough food there for all the birds yet the battles, both mock and actual, never let up. Are these confrontations really about setting up a pecking order when food is actually not so easy to come by? Another observation I want to draw attention to which I will return to later is the use of outstretched wings to maintain a "zone of influence" on the carcass that keeps other birds at bay.

Of course I would be remiss to not pay heed to one of the great Grande Guignol Theropoda performers of all time - the always on point lappet-faced vulture. Such presence. Such gravitas.

Note also in this portrait I am painting of intensely theatrical, gesticulating, and combative carcass skirmishing theropods, the last post I made on face biting theropods plays directly into this one. Grotesquely adorned, carnuncled, and gnarly faced/necked/forequarters would have all come into beautiful display and usage in such barbaric feeding bouts.

With these disturbing thoughts and images swimming inside your head let us revisit the paradoxical situation of the ulnar quill knobs in Convavenator. I refer to the situation as paradoxical because - although the trend of increasing "birdiness" in theropods is certainly a thing (or is it that increasing theropodness in birds is a better way to put it?) Concavenator was truly and squarely a carcharodontosaurid. These "land shark" megapredatorial theropods were not becoming birds nor were there antecedents on the way to or from flightedness. If anything they seem to be going in the opposite direction with smaller and smaller forelimbs and pretty much dedicated to hyper-carnivorous ways with out even the slightest hints of even an omnivore among the ranks. It is weird that quill knobs implying some sort of feather quill in these theropods appears, almost like evolution by proximity?

from Ortega 2010
There has been some skepticism which, as far as I know has been some critiques voiced online by Darren Naish and others (at least according to Wiki) that the irregular placement of these features argues against quill knobs and that they can be ulnar muscle scars. Addressing these contentions is an abstract presented at SVP2015 by Cuesta, Ortega, & Sanz that, well let me just cut and paste the abstract in their own words.

So their work seems to indicate that muscle scars don't best explain the features and that there is more diversity in these features placement in modern birds than generally assumed. Let us for arguments sake assume that their findings are valid and robust that as they put it "indicates the presence of skin appendages in Convavenator, preceding the wing feathers present in Maniraptora".

Note the careful language that they use calling them"skin appendages" instead of feathers and "preceding the wing feathers in Maniraptora".  I think that Cuesta et al. were very intelligent in making these semantic distinctions. What was most likely there - and what is most likely the most basal integument in dinosaurs - is literally a simple, shaft "quill" type feature.

The important word to keep in mind here is "quill" and here I want to revisit the observation I drew your attention to earlier of giant petrels establishing a "zone of influence" with outstretched wings at carcasses. If we imagine sharp and robust "quill" type appendages attached to these notably unusually placed "ulnar knobs" then it is not too hard to imagine their obvious utility at feeding bouts. Like the giant petrels earlier with wings outstretched these posteriolaterally projecting quills would help Concavenator "elbow in at the dinner table" among other theropods.

Concavenator "Mouth For War... Last Fix2" by Duane Nash
Of course such a general theropod gestalt has been portrayed before. Brett Booth has been drawing spiky projections coming off the arms of theropods for some time now. BTW what happened to that artist?

Such devices remind me of the ludicrous spiked arm gauntlets worn by some black metal artists. I do recall going to several punk/metal shows and how studded shoulder spikes and wrist spikes were a definite and dubious threat in the mosh pit and became banned at many venues for their danger!!

Here I wanted to depict three very different predatory theropods Concavenator and a mega-dromaesaurid and baronychine converging on a Pelecanimimus carcass. Normally there is some dietary partitioning between these predators but a drought has forced them into proximity and competition over carcasses. With it's spiked and uncouth countenance the Concavenator is able to monopolize the carcass.

Theropod Table Manners Gone Bad by Duane Nash

It's also worth noting that the outstretched wings of maniraptorine theropods could serve a similar function at carcass disputes - serving to both intimidate and establish a zone of influence at carcasses.



Referencia: Cuesta, E., Ortega, F., Sanz, J. Ulnar bumps of Concavenator: Quill Knobs or Muscular scar? Myological Reconstruction of the forelimb of Concavenator corcovatus (Lower Cretaceous, Las Hoyas, Spain). Abstracts of papers of the 75th Anuual Meeting of the Society of Vertebrate Paleontology: 111-112.

Naish, D. (2010). Concavenator: an incredible allosauroid with a weird sail (or hump)... and proto-feathers?. Tetrapod Zoology, September 9, 2010.

Ortega, F.; Escaso, F.; Sanz, J.L. (2010). "A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain" (PDF)Nature 467 (7312): 203–206. doi:10.1038/nature09181.PMID 20829793.

Selva, N.; Jedrzejewska, B.; Jedrzejewska W.;  Wajrak, A. Factors affecting carcass use by a guild of scavengers in European temperate woodland. Canadian Journal of Zoology December 2005 83(12): 1590-1601 pdf

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Bk Jeong said...

That last image seems like severe overkill.....

khalil beiting said...

Interesting post as always, and it makes sense for carcass monopolizing Theropods to evolve something that enables them to actually stay at said carcass. Since Concavenator has evidence of quill knobs that could possibly act as arm guards, then why haven't other giant Carnivores been found with these knobs? Is it becasue the bones aren't well preserved enough? Also, what's up with the back of that Baryonychine? It looks cool and unique, but what is it and what's it's purpose?

Duane Nash said...

@ Bk Jeong maybe or I could argue that the vast majority of theropod depictions are overly derivative and conservative. The truth probably somewhere in the middle.

@ khalil beiting Good question why such knobs are not on all theropods. There is indeed a lot of skepticism out there that they even represent quill knobs... I kind of took the idea and ran with it. The early Cretaceous was a time for diverse theropod lineages all over the place so perhaps competition was pretty high then as well. On the baronychine I added lots of colored skin flaps to act as protection from combat, act as ballast in the water, and general display.

PHoovy said...

I like how you're focusing a lot in carrion use by theropods and how they established an hierarchy, its the sort of thing that must have been very commom, but somehow isnt that commom to be decipted in paleoart, maybe eating carrion is thought of as an "lesser" or less interesting activity? But in reality it sure isnt, my favorite part is when a jackal and a lappet-faced vulture end up fighting, so you can get some nasty diapsid vs synapsid action going on.

The crocodile vs hyena video also made me wonder about how imposing large adult predatory theropods were during these feeding bouts, im just imagining a horde of crocodyliforms and small/juvenile theropods retrating when such a giant arrives.

Im pretty confident now that those daspletosaurus buried together were not pack hunting, but opportunistically trying to get some carrion and must have likely interacted with each other, trying to estabilish dominance and stuff.

Anyways, just to end this comment, you always manage to bring new views of both, extinct and extant animals and plants for me and i find that really amazing, so keep it going!

Duane Nash said...

Thanks PHoovy I am glad I stimulated some thought.

Yes theropod carcass feeding affairs - whether killed or scavenged - must have been astonishing scenes. It's beyond me why massive feeding scrums - including multiple species and age classes - converging to feed on a giant sauropod or other megaherbivore are not more commonly portrayed in paleoart. Seems everyone is infatuated with skeletal/body profile pics.

Part of the interesting speculation for me regarding asserting feeding rights is that at the end of the day it is always better to bluff your way to dominance as opposed to actually physically fighting. Hence my love of weird and macabre body adornments, spikes, frills, and an emphasis on theatrical gesticulations as so eloquently displayed by lappet-faced vultures and giant petrels.

Bk Jeong said...

I can get quills on the arms, but quills all over the body?

Bk Jeong said...

That said, a cool idea.

YW Lee said...

Like I said in FB, I would not put any idea on the base of "Concavenator quill knob." Most who read SVP poster said that evidence is weak and unsatisfactory.

Duane Nash said...

Well we can differ. I am not sure what poll or survey you are referring to when you say most find the evidence "weak and unsatisfactory". As far as I know the only objections have been online of which this abstract addresses i.e. myological muscle scars. So, as it stands, both from my own observations of pictures and the published articles, quill knobs is the best explanation I have seen for these structures. I would welcome other explanations for these structures but so far I find these arguments lacking.

Christian Halliwell said...

Oh, I forgot to mention, it's vambrace not gauntlet :).

khalil beiting said...

Hey Nash. This has to do with the begining of the post, but do you plan on doing any posts in the future about how herbivorous dinosaurs might have changed their diet due to environmental changes? I'd really love to see much more about niche partitioning (or the lack thereof), changing diets, etc. I know you don't do requests, but I just thought that might be a great topic that you could easily get into (since I know you love carcass rendering animals and the lack of major niche partitioning). I'd especially like to see what you think of the idea of massive, carcass pilfering Ceratopsians. Maybe you could also draw a scene from the Dinosaur Park formation with all of the boar/hippopotamus like Ceratopsians, detritus grazing Ankylosaurs, jay like scavenging Oviraptorsaurs, Ornithomimids and Pachycephalosaurids. And those are just the "herbivores" ;). That's all up to you of course, and I just reminded you so you can get your brain thinking.

Duane Nash said...

Would love to do that but no tiempo right now... and I still have a backlog of posts/ideas/illustrations I have to complete.

khalil beiting said...

I'm happy whenever you post something, so keep up the good work! I look forward to a new year of blood drenched scavenging Theropods, death metal feather gauntlets and bone saw shimmies!

Lam Luong said...

I've read your journal about the bone-sawing method in Allosaurus, and I was thinking about that behavior in Concavenator while reading this one. It had me thinking with such spiky armaments for an aggressive display to "elbow in" on a carcass, coupled with a bone saw method of eating, what would be the implications of Concavenator ecology?

The first thought I had in mind was the red-faced vulture, who muscles in on a carcass and opens it up for other scavengers who can't (and thus would have to wait their turn). That was my idea, but I wanted to ask your opinion on the matter.

Lam Luong said...

I'm sorry, I meant red-headed vulture.

Here's a video showing what I'm trying to discuss:

Anonymous said...

Holy camptosaurs, that last image was the stuff of nightmares, but then again, it isn't far fetched. Now all you have to do is add the serrated tongue and "roof teeth" and then you will get a true beast. Also, I was wondering if T.rex had a weaponized tail, in which the stage 1 feathers found in Yutyrannus evolved to become longer,harder, and sharper, and the animal would then swing its tail whenever a competitor was approaching from behind.

L. Walters said...

I found an update that throws a bit of a wrench in this theory...

Andrea Cau has posted some very convincing evidence showing that the supposed "quill knobs" are on the wrong side of the arm, and are therefore highly unlikely to be such.

Here's the blog post by Cau:

I also translated it to understand it more fully, but the diagrams speak for themselves. The indentation (green arrow) is where the radius articulates. Thus, the "quill knobs" are on the anterolateral surface and not the posterolateral. Therefore, the line of "quill knobs" is a lot closer to the articulation of the radius and ulna, and not on the usual area (posterolateral) where we would expect to see quill knobs.

(You can also see this indentation in Slide #7 quite clearly on this articulated arm of Acrocanthosaurus: http://www.bhigr.com/store/product.php?productid=64 )

I realize the authors have posited another explanation for this: that the quill knobs have an unusual orientation due to this being the case in some extant birds: but Cau brings up two more points against this. The points are spaced irregularly and are also part of a clear cresting of the bone, which is a very strong indication of a muscle attachment scar.

He also mentions that Balaur has a similar scar on its ulna, and this scar doesn't have a relationship to flight feathers.

Of course, this *doesn't* mean that Concavenator absolutely didn't possess feathers. Perhaps it did- we just don't have enough evidence to bracket it at high certainty yet for most theropod clades I think. (But personally, I'm going to err on the side of caution and assume feathers for most theropod clades.) It's also possible it still had quills on its arms- but they would not be attached in the same way as flight feathers and thus, we'd never see evidence on the fossils themselves. (For instance, if they are simply anchored in the skin.)

Duane Nash said...

Indeed... likely rugosities along a muscular ridge/crest.

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