Thursday, November 26, 2015

What Do Face Biting Birds - Including Turkeys - Tell Us About Face Biting Dinosaurs?

Hey theropod freaks, check out my tome Dinosaur Enlightenment: Piercing the Veil on Kaiju Dinosaur in an Ege of Disruption available now at Amazon in ebook and soft cover!! Get your freak on!!
This post will serve as a bit of a primer for a series of upcoming posts on theropod behavior and anatomy in which I introduce some new arguments and argue against some prevailing memes concerning their life appearance. I thought I could put it all in one post but I didn't make it to fedex kinkos before the holiday in time to scan my artwork so you know how that goes.

I wanted to make a Thanksgiving themed post today but I wanted to make it a little different. Instead of the usual "don't forget turkeys have some bad ass relatives" digression I wanted to make the argument that turkeys themselves are bad ass and they might teach us directly about some aspects of Mesozoic theropod behavior and appearance. Namely that male turkeys - in addition to their elaborate plumage & courtship displays - also regularly engage in combative behavior, including face biting behavior (insert discussion on abundant evidence for face-biting in Mesozoic theropods).

Pretty astounding behavior check out the full video here. Such behavior is not limited to wild turkeys as domesticated male turkeys will take on all kinds of foes including roosters as shown in this youtube video below. Now right here one can insert a whole discussion on cock fights, the long history of breeding fighter birds by humans, and the ethical issues raised. But for our purposes it should be noted that such behaviors are not without parallel in the wild fore bearers of these birds.

Or this particularly violent and prolonged battle between a Muscovy duck and some variety of fighting rooster (Asil?). As you can see in the comments someone mentions that this is how dinosaurs fought and I would have to concur.

Now I want to hit you with what this post is really all about. I will do this by pointing out - what is essentially staring at you literally right in the face - is that whether or not we are talking about tom turkeys, fighting cocks, or combative Muscovy ducks is that they all share one feature in common: abundant and garrulous, usually red, facial caruncles and a mainly naked head & neck.

credit The Photographer. Cairina moschata momelanotus. Margarita Island, Venezuela CC
credit Charles Toth youtube clip
What I am saying is that the convergence of a heavily adorned, wattled, dewlapped, caruncled, and combed cervical adornment in these three highly combative modern aves should not be glossed over. Usually interpreted as sexo-social signaling devices - and I am not disputing this adaptation - I think that they offer another, more functional usage. That is that in combat they offer up a convenient - and brightly colored - choice target to get bit upon. Why would a combative animal have such evolutionary pressure to offer up a choice morsel to get bit upon? Because losing a chunk of skin is preferable to losing an eyeball!! Feathers would be less than ideal because once plucked out little defense is left.

To embellish my point let's not forget to mention both old & new world vultures which are often bald headed and heavily caruncled. Except for these birds such features may offer more utility in fights over territory and food as opposed to sexo-social battles as in the other birds mentioned.

Red-headed vulture. credit Shepherd, Dayton OH CC
Andean Condor. credit Flickr Art G. CC
lappet-faced vulture. wiki-commons

Long time readers of this blog should not be surprised that I have been heralding both new and old world vultures as the best modern analogue to generalized, serrated toothed Mesozoic carnivorous theropods for quite some time now. People just need to get over the "scavenging" stigma for these animals - they offer more utility than sharks or monitor lizards in terms of how Mesozoic theropods behaved, moved across, and partitioned the landscape. Not only do sharks and monitor lizards fall down compared to theropods in terms of just about every meaningful gross anatomical/metabolic characteristic but the trait that is usually put forth as the unifying character linking these groups - serrated teeth - as I argued here both old & new world vultures (and giant petrels) have likely evolved an equivalent method of cutting and shredding carcasses: choanal grinding. Furthermore giant petrels, and both new & old world vultures are, you know, actually living derived theropods so there's that but it always seems to be that parsimony goes out the window with these things because TEETH. Get over teeth - modern day derived, soaring theropods are consuming more flesh on the African plains than all those "toothed" mammalian carnivores combined.

So when I stumble upon a youtube video (full video) showing essentially gang-turf warfare between two familial groups of black vultures (Coragyps atratus) and it has got "only" 711 views I got to raise a little ruckus. Not only are black vultures highly opportunistic and bold in their foraging - taking everything from turtle eggs to newborn calves - they also have evolved a kin-based group foraging method, are fairly terrestrial, and - as suggested by the author of this video - engage in territorial combat. Long story short this is the closest we are going to get to watching Mesozoic theropods engaged in combative face biting behavior. So I find it a little ironic that this window into the past is blatantly overlooked by a society supposedly obsessed with dinosaurs, especially face biting tyrannosaurids. Check out towards the end (about 20 second mark) where a chuck of one of the vulture's face gets ripped off and another vulture quickly gobbles it up.

"Now wait a second I thought group foraging was fairly rare in predatory birds and only Harris's Hawk regularly hunted in any sort of group hunting method?" 

Black Vulture wiki commons
Which brings me to my next point. Theropod interpretations both behavioral and appearance wise- especially dromaeosaurid - have been hoodwinked by the "hawk" analogy to a large degree. I presume this is because of the "predatory" nature of classic "raptorial clawed" accipitriformes. What is not in dispute is that hawks, eagles, owls, they do engage in some pretty startling and daring predatory ventures which I think capture the imagination and get us thinking about Mesozoic theropods. However  what should not go unstated is that "raptorial clawed" raptors of all ilks are dominated by a feet first method of predation. The head is almost never involved in the actual killing or subduing of prey except after the claws have sufficiently weakened the prey. This trend is immediately apparent in the startling video here of an eagle going after a very large ruminant and the prolonged battle. Never once does the eagle interface its head with the prey despite the rough and tumble engagement.

This trend of foot first predation with the head essentially not interacting with the prey until after it is killed or incapacitated is in stark contrast to generalized predatory theropods which all - even dromaeosaurids - maintained good sized jaws and serrated teeth. Dromaeosaurids never became >as specialized< in foot dominated predation as eagles, hawks and other raptorial birds of prey. The head remained a useful and probably necessary tool in prey acquisition and dismemberment, not to mention combat both intra & extraspecific.

credit Luis Rey. Maybe he was right all along? Link Deinonychus saga
Therefore, I argue, when restoring theropod heads - especially feathered - look more towards old & new world vultures, turkeys, chickens, muscovy ducks and other face biting highly combative birds than "classic" raptorial birds of prey. Give 'em mainly naked heads and necks, gnarly protuberances, grizzled bumpy ridges, combs, wattles, quills and frills. An apparent nape of thick feathers - like in many vultures and analogous to a lion's mane is quite defensible. In essence, make them less pretty. But please don't make 'em look like ground hawks because such birds don't kill or even really fight with their heads. Exception being theropods that lived in especially cool climates they likely had feathers all over just as cool adapted Lammergeiers have fully feathered heads. If you go look at all the artwork that came out surrounding the new Dakotaraptor it will very quickly become apparent that they are all just variations on the same "ground hawk" riff meme. The head is restored usually after a red-tailed hawk or peregine falcon.

Dakotaraptor Emly Willougby CC4.0

Ask yourself, what do we really have in terms of full body feather preservation for medium-largish generalized dromaeosaurids? Not much really. Microraptor hardly counts as it is small, fairly specialized, and lives in a cool environment anyways. So I say better to look towards the birds that actually do combative stuff with their heads as opposed to hawks and eagles which don't really engage their head in battle much at all...

Gobble, Gobble.

"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Chris DiPiazza said...

The whole fully feathered face of nonavian theropods I think started with Anchiornis, which indeed had lots on there down to the snout tip if I remember correctly. However like you imply there is so much room for variation especially in larger more ground-dwelling kinds. My Dakotaraptor painting, although not gnarly with waddles, is lacking feathers on most of the face.

Iris-Katyayani said...

So basically like this:
Nice to have some more ideas on all the grotesque and painful behaviours found throughout Theropods. This of course can also translate to many other members of Dinosauria, and even into Pterosauria. You should try to draw a scene with Dromaeosaurids (or any other non avian Theropod) with-to put so eloquently-badass fleshy wattles like vultures and turkeys, and/or a strange feather "hood" like with the chickens.

Duane Nash said...

Good comments.
@ Christopher DiPiazza Yes much room for variation and glad you mentioned Anchiornis. We know Liaoning was a pretty chilly place and, like Microraptor, Anchiornis was a small little guy and probably not commonly intensely competing with cohorts and other theropods over large carcasses so it makes sense for them to have fully feathered heads. My contention is with dromaeosaurids of a larger size class and more obvious tendencies towards combative behavior. It is also possible that something like an oviraptor was heavily wattled and full of caruncles too.

@Khalil yes but as you know I am not particularly fond of tyrannosaurids being fully feathered unless they lived in cold climates i.e. Yutyrannus, Nanuqasaurus but I plant to discuss my thoughts on a future post. And I do have some drawings done but could not make it to get them copied due to holidays.

Jay Cooney said...

I thought I'd say how enamored I am with your blog. It's great to see an appropriately speculative take on these animals' functional morphology, and it is fantastic that you produce original artwork to illustrate the proposed behavior. The interpretation of theropods as possessing a brightly colored and naked face opens up the possibility for numerous sociobehavioral functions, and is a hypothesis which certainly deserves further inquiry. Keep up the fantastic work, Mr. Nash, and I hope that this comment may lead to some correspondence between us!

Duane Nash said...

Thanks Jay you can always get in touch w/me on fb or deviantart. Note that there is no artwork I made for for this piece but some coming up in future posts.

Andrew Raymond Stück said...

Your hypothesis definitely makes sense for beaked birds, but would caruncles make that much of a difference when slicing/stabbing teeth are involved?

Elijah Shandseight said...

Even if I find it very intriguing what you're proposing, I want to raise some questions and doubts to see if they're actually plausible.

One thing that I think you've overlooked regarding the first three birds (turkeys, roosters and muskovy ducks) is that they're not predators. As a matter of fact, sexo-social signaling devices - although present in carnivorous genra - are far more frequent in vegetarian (or at least omnivorous) animals because they have very different lifestyles: instead of big league predators they tend to interact more frequently with each other, they're very social animals and this fact leads to the development of visual signs. Speaking about birds you'll see that the great majority of combs and wattles are not seen among raptors but in far less sensational groups.

Talking about attractive nucal skin, to be the most adorned ones are usually the males due to sexual pressure (which doesn't mean that this corresponds to better genes as we used to think; however that's another matter). If what you're saying is true (“in combat they offer up a convenient - and brightly colored - choice target to get bit upon. Why would a combative animal have such evolutionary pressure to offer up a choice morsel to get bit upon?”) then this would mean that the female members should have them too to the same degree (as a matter of fact, they can engage in violent fights too). The reason why they keep targeting those areas is because A – they're sexual and social signs (if I ruin them, I ruin you) and then B - it's exposed skin (as you say, to attack feathered regions is less than ideal) but that doesn't necessarily mean that they are really important for that task. Lots of birds without skin appendages fight in the same way as turkeys and roosters do.
Perhaps I just misinterpreted what you were trying to say, but if the message was: “Don't hit me in the face, hit me in the combs!”, well I'm not totally sure about that.

Predatory species, not being social to this level, don't have the need to develop those structures – they do fight with each other, but I'm sure not with the same rate as galliforms or anseriforms.
Old and New World vultures have developed a wide arrange of wattles and combs because of they're increasing social life and abandoning of most (not all, of course) raptorial behaviours; without the 'predator costraints' (be less visible to both preys and other predators and yadda yadda yadda) they could accentuate their 'visual side'.
You're absolutely right talking about naked faces in predatory species (for example, most accipitriforms don't really have feathered faces – right now I'm thinking about caracaras and secretary birds, but they are not the only ones) but I think that caruncles and wattles should not be integrated by default because they are not equivalent. Some of the points you're trying to make can be however applied to predators of small game, which can be adorned to a very high level due to not always be obliged to the same rules of the so-called 'major predators'. Still it's a very complicate subject and probably I got most of this thing wrong.

Curiously, I find these ideas far more believable for ornithischians and herbivorous theropods; say, I think that a hadrosaurid with dewlaps and crests is more 'realistic' (as much as realistic can paleoart be) than a tyrannosaurid with the same set.

I'm absolutely in favour of adorning dinosaurs with crazy skin ornaments and I'm not against this post (actually, I think it's very clever) but I'm arguing if the extremes of roosters and turkeys can be applied to allosaurs, giant dromaeosaurs and so on - we must always wonder how widespread they really are and among which species these features can be seen.

Duane Nash said...

Excellent points Elijah!! Thanks for commenting I have to go to work right now but will back in the eve to delve further into these issues raised.

Mellivora capensis said...

Compelling argument, but I also think Shandseight's comment makes a few good counterpoints. I'd love to see these ideas fleshed out (no pun intended) to account for phylogeny and potential fossil evidence. For example, are facial caruncles in extant Anseriformes, Galliformes, Cathartiformes, and Accipitriformes homoplastic or homologous? Is enough known from extant birds and fossils to infer ancestral condition for relevant nodes?

I doubt you'd be able to find direct evidence for these structures in the fossil record, but what about indirect evidence? Presence of horny, keratinous beaks has been inferred by the distribution and abundance of nutrient foramina on the premaxillae of ornithischians and some weird synapsids. Perhaps fleshy caruncles, wattles, or dewlaps leave some similar osteological trace.

Finally, what of mergansers? There are social and solitary varieties with serrated, tooth-like modifications of their bills (see Mergus serrator), but varieties with which I am best acquainted are fully piscivorous and often engage in face-biting despite their fully, feathered faces. I recognize this as a single counterexample and that hydrodynamics might outweigh the defensive selection pressure, but I've seen some pretty vicious fights among a few merganser species.

Great post, as always!

Unknown said...

I must say, on the note of dromaeosaurid feather impressions, that unless I am very much mistaken there is a medium-sized dromaeosaur known with full-body feather preservation: Zhenyuanlong.

BK said...

Maybe, but look at giant petrels; a lot of brawling and face-biting, uses head as weapon (especially the chainsaw technique), and they are not bare-headed. Considering sheathbills share the habitat and do have bare heads, this probably doens't have to do with the Antarctic climate.

BK said...

Also, most Old World vultures do have feathering on their heads (Torgos being an oddity).

Duane Nash said...

Nice comments.

@Elijah Shandseight "the great majority of combs and wattles are not seen among raptors but among far less sensational groups" Exactly as I have argued such adornment offer not only socio-sexual signaling cues but are common in face biting birds. As I mentioned several times raptorial clawed raptors (i.e. those that kill with claws) do not regularly engage with prey or conspecifics with the head. But look how common these adornments are in both old & new world vultures who aggressively interact with conspecifics and competitors with the head. Take another look at the black vulture video. It has a highly caruncled/crenulated head and there are no strong colors in its head adornments (i.e. not likely primarily for display) suggesting that defense is the prevailing reason for its skin morphology on its head.

Another question that should be asked are there any heavily frilled/wattled/caruncled birds that don't engage in violent combat face biting?

"the most adorned ones are usually the males" Yes that holds true for say Andean condors but what of black vultures? And lappet faced vultures both male and female look just about identical in terms of fleshy folds on the face

"Don't hit me in the face hit me in the comb" that is not exactly what I was saying, more like I would prefer to lose a chunk of skin that will grow back as opposed to my eye. If you watch the video of the several fights I posted chunks of skin, wattles, frills are regularly getting bit and yanked.

"Lots of birds without skin appendages fight in the same way as turkeys and roosters do" Yes just about any bird will fight each other - but are most birds as highly combative in general as turkeys and roosters? To the point where they have spurs and humans have bred them specifically for this task? I think you can exclude just about any pair bonding bird as being on par with roosters/turkeys/muscovy ducks in terms of dedication to a combative lifestyle. No one is raising fighting pigeons that I know of.

Duane Nash said...

On predator constraints, not sticking out yadayada... Glad you mentioned this because I think we assume too much that the way it is today is the way it was in the Mesozoic. Perhaps for many theropods they did not give a hoot if their prey saw them. If you are living in sauropods dominated habitats not really any need to stalk your prey and sneak up on it as it is primarily young and numerous (sauropodlets) or old, damaged over the hill adults. In both cases they could not outrun a theropod.

My view of many theropods is that competition both intra and extra specific was concentrated at large dinosaur carcasses. Which species could dominate and monopolize the best parts of a carcass? Making a big stink at such confrontations - with sound, theatrical display (including wing mantling), and all sorts of sordid gyrations - spelled evolutionary success for many of these animals. Having a grotesque, intimidating, and sacrificial flesh necklace of wattles, combs, quills, and frills not only helped secure a good meal but protected both the eyes and neck for these animals. Long story short I think there was intense social display and intimidation at say dead sauropod carcasses just as there is among vultures today on the African plains. So I would have to disagree with the notion that Mesozoic theropods were antisocial isolationists. They might not have been loving but they were intensely aware of one another and who dominates who. Watching a lappet faced vulture dominate a carcass should give you a glimpse into my mind's eye.

"We must wonder how widespread these features really are and among which species these features can be seen" True it is a hypothesis but I think the same question should be asked regarding fully feathered theropod heads. We must hold both hypotheses to the same rigor is all I am asking. And, although the "hawk" faced dromaeosaur has become the go to choice such birds do not provide a good model for head biting behavior as they don't really use their beaks much in such ways.

@ Mellivora capensis All good points and I don't think any work has been done concerning these structures, how to look for evidence of them etc etc. Regarding mergansers - sure all and any birds can be combative - but I would not class pair bonding mergansers in the same combative realm as tom turkeys, roosters, or muscovy ducks (none of which btw are pair bonding romantics). They are just in another class. Additionally, as you mentioned, stream lining and probably insulation in the water play a role.

@Christian Haliwell good mention for Zhenyuanlong. Sometimes I go a little overboard and overly dramatic in my statements. In one of my later paragraphs in this post I did concede that in cold/cool climates (Liaoning fitting the bill btw) a feathered head would be likely. I made the comparison to cold adapted Lammeiergier vultures that forage in the high Himalayas and have featherd heads unlike most vultures.

@BK Jeong Giant petrels are out in the cold and sheathbills hardly have bald heads and necks to the extent I am alluding to but have more of a cheeky bald spot. "most Old World vultures do have feathering on their heads" Yes there is going to be some feathering in there but it is much reduced. Don't forget Sarcogyps the red-headed vulture too so I would not call Torgos such an oddity.

BK said...

Andean condors live in some cold areas too, and they still have bald heads. Yet giant petrels, which get as aggressive and intensely competitive, do not have bald heads, despite the fact a) both species are sympatric in Patagonia and b) both are competitive meat-renders that fight often.

IMO, bald heads are an 50/50. Some big-game hunting theropods may have had them, but there is no reason to suspect all of them did even within the same conditions.

Elijah Shandseight said...

“Another question that should be asked are there any heavily frilled/wattled/caruncled birds that don't engage in violent combat face biting?”
I actually don't know. Perhaps marabou storks and some ibises and cranes, jacanas, certain cormorants... I can name some species but I'm not sure if they fight in a 'normal' way or if they engage in a specific combat face biting.
I do wonder about cassowaries though, with their naked heads and their ferocious spirit. - is there any video of two cassowaries fighting with each other?

“what of black vultures? ... And lappet faced vultures both male and female look just about identical in terms of fleshy folds on the face”
In that statement I was referring to galliforms and anseriforms. My bad.

“But are most birds as highly combative in general as turkeys and roosters? To the point where they have spurs and humans have bred them specifically for this task? I think you can exclude just about any pair bonding bird as being on par with roosters/turkeys/muscovy ducks in terms of dedication to a combative lifestyle. No one is raising fighting pigeons that I know of.”
Funny thing: doves, for example, are bastards – many times they would fight their opponent to the death. So do starlings. Pheasants are a curious case, because they can have both flesh appendages but with fully feathered heads, but even the full feathered species fight in similar ways the others do.

The thing is that galliforms, anseriforms and Old and New World vultures have developed wattles and combs because of their social life, something that can't be verified for non-avian theropods. I think that yes, skin appendages were common among theropods but not necessarily between the big league genra, 'the proper killers on a site” (big league not for their size, but for their predatorial lifestyle). Nevertheless, all the 'scavengers' and 'little league' predators could had them to a higher degree. I do however believe that, even between big theropods, a fully feathered head is implausible and that a caracara-like look (or at least, a naked face) was far more common.
One thing that I would still like to know is how widespread are these kind of structures among strictly predatorial species. Aside from vultures (which are predatorial in a very different way), the other birds you've mentioned are still vegetarians/omnivorous – I still can't find a species which is a major predator and has the features you're proposing. It's true that sauropods offer some interesting scenarios, but I don't know how much we can trust them. Let's say that we must keep in mind both a regular scenario (because the present holds the key to the past, no matter what others say) and a (reasonable) speculative scenario. I also think that we're looking at both sides of the same coin: if we're taking into account the face biting behaviour and the monopolization of a carcass, the fleshy version is of course very plausible; but if we look to the ecological role and to who actually killed the animal in the first place and how it might have looked, things can be very different.

Thanks a lot for your answer, this surely is a good talk!

Ps: By the way, sorry for the atrocious way I wrote my previous comment. Gosh. Just awoken+Writing right away is not a good combo. And I'm doing it again right now, so excuse me for all the errors within this comment.

Unknown said...

I might be wrong but aren't there at least some preserved feather covering around the orbital areas of Yutyrannus huali and Zhenyuanlong suni? Afaik the feather covering in those was somehwat intermedaite between raptorial predators and vultures

I think the truth might be somewhere in the middle and likely there was a very big diversity of behaviour between extinct Theropods, maybe Dromeosaurids didn't involve in head bitting as much as advanced Tyrannosaurids (and it's rather evident that they didn't use their jaws for hunting to the same extent as Tyrannosaurids).

Duane Nash said...

Thanks for comments Elijah and babehunter.

@babaehunter Zhenyuanlong was discussed in above comments and I mentioned towards the end of my post that cold adapted theropods (which would include both Yutyrannus and Zhenyuanlong) would likely have more feathered heads.

@Elijah Good comments did not know that about doves I should look more into that... Also, and saving this for my next post, I think there was other "armaments" going on in theropods besides caruncles, wattles etc etc stay tuned!!

Duane Nash said...

BK Jeong Good point. I can be OK with 50/50. However, as I pointed out in my post, if we look at the popular representation of say giant dromaeosaurids, Dakotaraptor being a great example, the representation is overwhelmingly fully feathered and "hawk like" in visage. If my take home message for this post is one thing I think it is that there is merit for both types of representation yet we are only seeing one type out there in reconstructions (JP raptors notwithstanding...).

Unknown said...

@Duane Nash I actually did draw a lappet-faced vulture-like Dromaeosaurus a while back, and started writing about them. However, I cut the episode I had them in a while back, and I haven't had the time to finish the picture. I think if any dromaeosaurids had caruncled skin on their faces as a defense from face-biting, dromaeosaurines would almost certainly be the ones.

Robert Haan said...

Ya know Duane, a thought came over me when i was in the shower this morning ,being the Spino fanboy (that's almost a dirty word now, i am no expert but i do know abit more than the layman) that i am , do you think it plausible that the sail /ridge on Spino's back would have among its other uses played a similiar role to such fleshy face appendages you have suggested in this post ?Here we have a large , prominent feature on the animal's body with minimal blood vessels present in the event of a tussle the sail/ridge would have provided ample area for an adversary/predator to grab hold of/ bite on to , without it damaging the Spino too much in the process. Of course, this does not take into account an animal's preferences of going for the head, neck etc in the event of a squirmish, just a general question i needed to ask.

Duane Nash said...

Hi Robert. Interesting thought but it perhaps risked spinal injury in that scenario. The spines were extensions of the vertebra after all... As I argued in previous posts thick skin - to aide in negative buoyancy - is a definite possibility in spinosaurus and perhaps the whole family. You can see what type of abuse hippo skin gets subjected to from other hippos, lion attacks etc etc

Duane Nash said...

Ironically I do have a spino pic I drew for an upcoming post where I put a healed chunk taken out of the spine on the animal.

Robert Haan said...

Yeah, there was a specimen of the dorsal spines that was shown to have healed after being bitten clean off, i believe it was highlighted on that Planet Dinosaur show a few years back, that was what became the basis for my suggestion actually.

BK said...

Speaking of spinosaurs, is it possible it used the sail to spin it around like a windmill to dismember prey?

L. Walters said...

Hi Duane, I really enjoy reading your posts and find them intriguing and thought-provoking.

I came up with some possible counterpoints to your arguments for facial ornamentation / carnucles, and I'd like to know your thoughts on them.

One, at least one theropod taxon (Majungasaurus), was almost certain to lack heavy facial ornamentation as some have depicted it with. This is due to, what I'm almost positive of despite having only seen the skull in photos and once at a museum, the presence of an armor-like dermis on the face: nearly all of it, in fact!
Why do I think this, you might ask? Take a look at Figure 7 of Hieronymus et al 2009...the osteological signature for it is present on nearly the whole face of Majungasaurus. I believe that the same author also published a study on this and came to the same conclusion (or maybe it was Witmer?), but it wasn't a full, peer reviewed study...rather a summary from a dissertation. Sadly, I can't find this anymore, but if I find it again, I'll share it.

Therefore, I believe more study is needed akin to the Hieronymus et al 2009, but applied to theropods instead of centrosaurines. If certain facial structures are present (such as an armor-like dermis or keratinous sheath), this would preclude the existence of any elaborate, comb like crest or carnucles on those parts of the head.

Two, I think that for certain taxa with large crests (for example: Guanlong, Dilophosaurus, Allosaurus, Yutyrannus, and Cryolophosaurus), the crests alone may have provided enough of a deterrent or protection from facial biting. Allow me to explain...the sheer size and orientation of the crests in these taxa at least, would have provided some protection against the opponent getting a good enough bite on the face to damage the eyes or the back of the skull, unless the opponent attacked from behind...the crests may have also provided a visual "bluff" to prevent the encounter from escalating to facial biting. As far as I know, facial biting evidence is only on tyrannosaurids and Sinraptor dongi. (I also read from Molnar, 2001 on the Wikipedia entry on Theropod paleopathology, that a bite to the skull of a Velociraptor mongoliensis from a conspecific did not show signs of healing, indicating it led to its death.)

It would be especially interesting to see if any facial bites turn up in these large-crested species...if they don't, it may turn out that they simply weren't engaging in it...

(Cont'd in another reply.)

L. Walters said...

Three, I thought of one key difference between birds and theropod dinosaurs: (parrots notwithstanding!): Sheer bite force. Nearly all large theropod dinosaurs must have had bite forces substantially greater than any of the facial- biting birds you mention. And this incredible force meant that bites could have been, and almost certainly were, deadly at what incentive would there be to evolve giant combs that could be bitten off easily, or carnucled skin that offered little protection against the devastating bite force of another T. rex? Extant facial biting avians, with their smaller bite forces, can easily get away with having a big wattle or comb as a "distaction" to more vital targets, because the soft target itself isn't going to be obliterated right away. It will be picked at, damaged, and yet continue to serve its purpose against conspecific bites.

Perhaps jaw width also plays a role...with a wide jaw, there would need to be a very wide surface to deter such massive bites...and quite literally, "getting a thicker skin" might just be the easier evolutionary option!

It's also very, VERY interesting to note the thickened skulls of certain theropod taxa...I'm thinking of Sauroniops here. While head-butting isn't out of the question...given that some theropods were already face-biters (Sinraptor being a metriacanthosaurid, and not all that distant from carcharodontosaurids), the thick skull may have evolved to protect against just that! I personally find it a much more likely scenario, at least...and since the skulls were already thick, they may not have needed much in the way of facial ornamentation.

Sorry for writing a book here...but any good hypothesis needs to stand up to counterpoints. I'm very intrigued by this idea and will almost certainly illustrate taxa with facial ornamentation.


Sincerely, a fan,

L. Walters (http:// lwalterspaleontography. wordpress . com )

Duane Nash said...

Thanks for commenting L. Walters

Good mention on Majungasaurus

On large crests etc etc acting as deterrent I have to admit not entirely sold on that idea - some crests are said to be almost wafer thin. Could they have added a startling visual element of shock & awe to confrontations? yes, very much so. But mechanically I don't think that they would have prevented or absorbed a good bite.

On bite force of theropods making caruncles/wattles of little use. Interesting point and I do admit to thinking along this same line of thought. What I find interesting is that part of the disgust reaction many people have to the frills/caruncles and other garrulous displays of some birds is that they remind us of tumorous or cancerous tissue. In other words tissue that is dividing on a cellular level at a rapid place. In humans tissue that is subject to repeated trauma will sometimes turn cancerous or at the least scar tissue. What I am suggesting is that the frequency and severity of biting might promote such rapid cellular division and actually create such garrulous tissue anyways in theropods. And I would not be so quick to dismiss the bite of certain vultures, they can and do kill with their beaks and many instances of handlers suffering cuts from their serrated tongues/choana. Much more so than the more highly touted eagles/falcons/hawks which rarely engage with their head - and not coincidentally I argue lack such caruncles.

I have to admit to not really being sold on head butting in theropods. I just don't see the need for it to evolve when they have so many other forms of weaponry already in place. I think that the thickened skull roofs/lacrimal/nasal crests absorbed stresses and strains from biting which I outlined on this post

At the end of the day there is every possibility and likelihood for a wide range of head accoutrements. From fully feathered to fully scaled. From bony armored heads to fleshy wattled heads. We can and should allow room for - when actual compelling evidence is lacking - this variety in renderings. Currently I don't think this is the case - for instance >all< dromaeosaurids seem to be depicted as having fully feathered heads when that is not the case in all living birds - especially as I have mentioned frequently numerous birds that engage with their head.

L. Walters said...

Thanks for the reply, Duane!

As far as the crests providing defense: I should have been more specific! I actually did not mean a structural defense- as I am aware that the crests are quite wafer-thin- but actually a defense in terms of their size: in essence, they would provide an alternative target to more vital areas of the skull. If the opponent would get a bite on the crest(s)- it’s better to lose a crest or have it damaged than to have a deadly bite to the back of the skull.
However, at least in large-crested taxa, thus far there have *not* been any reported pathologies associated with either the skull or the crests in regards to biting. While the sample size is still quite small, if we continue to see the trend of no evidence of facial biting, perhaps that means that the crests were effectively serving the “bluff” / size- deterrent I am envisioning.
Again, it is also interesting to note that the taxa I mentioned previously that have evidence of facial bites, simply do not have the elaborate crests of the others.

The idea that the caruncles look the way they do, due to rapid cellular division from being subject to repeated attacks: I can’t say I’m convinced of this, as intriguing as the idea may be. Vultures and galliformes (and other caruncled birds), have these tissues in place long before they become subject to the repeat attacks of a conspecific. I can’t find any literature pertaining to tissue healing as in wattles compared to other parts of the body, and for me personally to believe the claim that healing would be faster and cause the wattles to become even more garrulous, I’d need to see literature supporting this.

As far as vulture bites go: I was not arguing that the bites of vultures are uninjurious or nonfatal to their prey (or the humans who handle them)! Rather, I was saying that there is a key functional difference. The bills of vultures are hooked and narrow, and although they may be quite formidable in their own right and should not be underestimated, they still differ from those of theropods, especially the larger-bodied clades. The wider jaws and immense bite forces of these taxa would make wattles as a defense mechanism quite pointless, as they would be obliterated in one bite, and /or bitten clean through to the underlying tissue and bone, possibly with fatal results…even the bites of “mere” Velociraptor was quite devastating to its conspecifics, considering Molan believes the injuries on the skull of one specimen were the result of a fatal bite to the head!

The fact this specimen died soon after the bite would tell me that, at least in regards to Velociraptor, facial biting was far more injurious than biting wattles or other distractions from vital targets. However, I concur that the hawk, eagle, and owl look is far too common amongst paleoart of Maniraptorans. I chose to illustrate my Velociraptor with a snout reminiscent of a Caracara, but more with thermoregulation and display in mind rather than facial bites.

I did read your post on the form and function in theropod crests and I wholeheartedly agree with it! I just remembered that in regards to Sauroniops as well…but maybe, just maybe, the thickened skull roof could have been co-opted as a defense against intraspecific bites. But unless we find evidence of head-biting in this taxa, it may not have served this purpose at all. Still, something interesting to think about I suppose.


L. Walters said...

There are also a couple of other counterpoints that I think should be addressed in regards to this. Also, I hope you won’t think I’m attacking you. I’m a huge fan of your bone-saw shimmy hypothesis and I definitely hope that paleontologists will study it! I also think your hypothesis about Spinosaurus being somewhat hippo-like has merit. But this particular hypothesis of yours…I think that maybe, just maybe, the vulture and galliform analogy might be being taken a bit too far. However I would appreciate a greater diversity in the appearances of reconstructed theropods, and wattles, thick textured skin, snoods, and etc were almost certain to have been present amongst a number of taxa, given how common they are in extant birds. However, they may have been a bit *rarer* than in modern birds…

One thing to consider is cerebral volume. An excellent study on this was made by Larsson, 2001.
Once you get to avialans the cerebrum becomes quite enlarged, indicating a greater capacity for more complex social behaviors. Therefore even if their ecology is more similar and makes a better analogy for how theropods may have interacted around carcasses…vultures would still fall short since they quite simply are more advanced socially. Although theropods (and particularly Coelurosaurs) may have been more social than traditionally envisioned, they were probably still quite aggressive when it came to interactions with each other. Instead of being as focused on signaling, defense, and intimidation by use of caruncled skin, they may have been making more “primitive” use of body posturing, charging, vocalizing, and attacking the way crocodilians do, given how their brains are closer to crocodilians than birds…

Another thing is consider is that even though theropods were engaging with the head, we cannot underestimate the importance of the forelimbs in interaction.

In the re-examining of the Dilophosaurus type specimen, numerous forelimb pathologies were discovered. The authors even hypothesize that some of these injuries *may* have been inflicted by a conspecific. This shows that (assuming the injuries *weren’t* caused by a prey item…which they still could have been), these dinosaurs were heavily engaging with the forelimbs in addition to only using their jaws.

The highly robust and adapted forelimbs of many theropod species (in particular I’m thinking of basal tyrannosauroids, including megaraptorans, and also allosaurids and carcharodontosaurids such as Acrocanthosaurus) would give them an additional weapon to attack conspecifics with. Extant avians have no choice but to use the head (or spurs on the wings, or ankles), whereas theropods could not only use their heads but also their forelimbs to a greater degree than any extant avian. These almost certainly were used in predation, and therefore it is highly likely they were also used in conspecific combat. And…just as you said with how accipitriformes rarely engage with the head, perhaps species with oversized arms and claws (therizinosaurs and megaraptorans in particular) may have had similarly feathery heads due to how the claws were the main weapon in combat.

We also cannot overlook the importance of crocodilians as an analogy in some respects…the way crocodilians fight with each other, I think, gives a good look into the combat of non-coelurosaurs. Molnar looked at pathologies on Acrocanthosaurus, and there’s a broken and displaced 16th tail vertebra, which could be due to a bite wound. The 13th rib may have also suffered a bite wound, and there’s a scapular pathology on another specimen from a puncture wound. While impossible to determine, it could be from the manual claws of another…
These pathologies match up pretty well with the way extant crocodilians fight, in which they do not *only* attack the heads but also the tails, limbs, and bodies of their opponents.


L. Walters said...

(Last post in the series, promise!)
In short, I think theropods were exhibiting quite the mosaic of characteristics intermediate between crocodilians and birds, with both bird-like behaviors and integuments as well as crocodilian behavior (and in some cases facial integument as shown on Majungasaurus).

IMHO, your idea of facial wattles might be the best for short-armed, long snouted taxa, as well as some Maniraptorans…although it can’t be completed ruled out for the others, and it would bring a great diversity to paleoart. But the ecology and anatomy of each taxon must be carefully considered before adding this character to a particular species, in my humble opinion.


Duane Nash said...

Thanks for your thoughts and comments L. Walters they are a great addition to the post! Yes I don't have anything to really base my argument that a hideous caruncled appearance can arise from face biting. I do think it would be neat if there was some work done on modern birds with such features to see if there is any similarity in cell growth there to tumors/cancer growth etc etc

To spitball a little bit on the croc analogy thingy: lets not underestimate the social skills of those animals too. And if they were not aquatic ambush predators they might have a more decorative countenance. Crocs and monitors can be pretty sophisticate socially and although I see where you are going that theropods were not as sophisticated socially as modern birds something along the croc/monitor lizard level of sociality still leaves a lot to play with.

One final thought, something I have been toying with for a bit. Painting with broad strokes here theropods were often faced with two food sources throughout the Mesozoic: 1) abundant and relatively easily dispatched young dinos 2) the rare windfall of large and sometimes gargantuan carcasses. For both food sources stealth and cryptic adaptations not really at a premium. THis is somewhat supported by the flamboyant display structures of theropods - features that are almost totally lacking in just about every and any successful lineage of large terrestrial predator I can think of. In fact theropods are pretty unique in being the only large terrestrial predators with such display headgear. If they could invest in elaborate headgear why not elaborate skin foldings/caruncles/wattles etc etc.? The attributes that can be given to headgear/crests etc etc can just as easily be applied to skin enfoldings/wattles/caruncles etc etc.

That some theropods have evidence of elaborate headgear such as crests that we have evidence for via bony remains is all the more reason I argue to assume we are missing fleshy display structures on the head. The notion that some theropods decided to go off the deep end with bony display structures on the skull and the rest were just conservative with skin draped over skull just doesn't make a lot of a sense. Why would the evolutionary pressures that that resulted in crested display in theropods not apply to other theropods? Some were flashy and others just mundane.? I cant really buy it.

Anonymous said...

Hi again!

I'm so glad that you think my comments are a great addition to your blog! I really appreciate it.

Yes, I agree that both crocodilians and monitors can display more sociality than would be expected, and also have quite elaborate courtship rituals, in the case of crocodilians...and crocodilians are even able to use tools: sticks on top of themselves to fool birds into using them for nesting materials, and then attacking. I'm sure you knew about that already, though.

I completely agree with you about the abundance of easily dispatched prey (young), and also about how sauropods provided gargantuan carcasses for them to feast upon. Indeed this probably meant that theropods were a lot more colorful and "flamboyant" looking than previously imagined and I like that your post examines that.

As for crests and wattles, etc, being more common than depicted: it's certainly possible, but I don't really think it was universal. Amongst all birds and lizards, some of them really "look" like their skulls, and others are so covered in wattles, feathers, or flaps that you can't tell! Therefore I think this rule applied to the Mesozoic non-avian theropod fauna as well. Certain taxa may have been engaging in predation on prey they needed to hide from: mid-sized predators going after mid-sized prey would be a good example. Some animals are just not ornamented, and there doesn't seem to always be a discernible reason why. For instance some of the Old World vultures have merely a thin covering of "fuzz" on their heads, which wouldn't be expected given their more elaborate looking relatives.

But I agree that this topic needs to be researched further! I keep hoping someone will research the ideas in your blog.

-L. Walters

Beetle Boy said...

You gave me inspiration for my theory on what Tarbosaurus looked like - see my blog for details:
Anyway, just wanted to say thanks!

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