Tuesday, January 5, 2016

The Disservice of Tyrannomania: Taking the Tyrant Lizards Down A Notch

This post, necessarily in my opinion, addresses both a social and scientific melange surrounding that guy and his cohorts - the tyrant lizards. I have been putting off talking about Tyrannosaurus rex and the tyrant lizards in this theropod themed kick I have been on lately because what really is new to say about them? I mean they are probably the most studied group of dinosaurs nay prehistoric critters of any type and we probably know more about not just the anatomy but foraging/biting behavior of these animals than many extant predators such as sperm whales or several giant deep sea teuthids.

To give a bit of a qualifier here I really do love and adore the tyrant lizards. I and probably several of you reading this post would likely not be here if it wasn't for them. I mean that head, the bite force, the whole package is just iconic. However I do think it necessary to take down these animals a peg or two relative to other theropods. Ok, ok maybe not take tyrannosaurids down a peg so much as elevate other theropods. I think that - both culturally and scientifically - tyrant lizards have become too much the yardstick for what it means to be a hyper-carnivorous theropod. It should always bear repeating: these animals are overgrown coelurosaurs largely independent in descent from the other large carnivorous theropods.

People love stories, are drawn to them, and understand the world through stories. When we look at the story of theropod evolution it should not go unnoticed that tyrannosaurids, and most pertinently Tyrannosaurus rex, appear at the end and culmination of the dinosaur saga respectively. I know that will be common knowledge to my readers but just breath that thought in for a second: Tyrannosaurus rex not only was for many years the largest recognized theropod but it was one of the last. The fact that it occurred in the American west only adds to the lore, mystique, and seemingly manifest destiny of this penultimate theropod to lord over all other theropods.

It is, when you really stop and think about it, quite amazing the coincidence of the largest, biggest, baddest, and last hyper-carnivorous theropod occurring at the death knell of the Cretaceous in the eternal frontier of the American west... quite a good story if you unpack it a bit. With these thoughts swimming around in your head it should come as no great stretch to imagine a popular narrative unfolding: Tyrannosaurids and Tyrannosaurus rex represent the apex, the gold standard of theropod evolution, all other theropods were lesser versions of this last and final model.

The take home message being that yeah Allosaurus was all right but it was merely a lesser, imperfect version of Tyrannosaurus rex. Mapusasaurus was cool, but still not a tyrannosaurid. Crylophosaurus, pretty neat but no T. rex. What this is all smacks of is some real neo-Lamarckian thinking. As if, for 140 million years give or take of theropod evolution, theropods finally get it right with the tyrannosaurid model after many botched, failed attempts.

Of course this way of thinking about evolution is inherently wrong. Organisms are not striving to become some ultimate model or have some type of end game in sight. Evolution is blind and groping and just hobbling together with the best fit jerry-rigged from existing parts at the time. Unfortunately I think we - including some paleontologists - lose sight of this picture and play a little bit of Monday morning quarterback with interpretations of past organisms. If failed, botched attempts are such a hallmark of the fossil record then where are they now in our present biota? What animals represent such evolutionary hiccups?

This is of course a cultural unpacking - that is not too great a controversy I am sure we can all find some truth in. But what I believe is that this narrative has spilled over into the scientific realm. What I speak of - the controversial bit I can not dispense with - is the notion that tyrannosaurids in general and Tyrannosaurus rex in particular were far and away more devestating, powerful, and all consuming than other hyper-carnivorous theropods.

Where I think this line of thinking gets the greatest cashet is the notion of bone consumption and dismemberment among tyrannosaurids - a topic of much interest for me. The general gist of tyrannosaurs being elevated over other theropods, by both lay and professionals, is most succinctly summarized as such: "only the great tyrant lizards - especially Tyrannosaurus rex - had jaws robust enough and teeth strong and stout enough to pulverize and consume bone". And the corollary: "Blade toothed theropods (i.e. everybody else besides tyrannosaurids) avoided bone assiduously and were especially careful eaters".

These statements have become a bit of a mantra among both fans of dinosaurs and most professionals. They all tow the party line - tyrannosaurids ate bone but other theropods did not. But the way I read it is different. For some reason theropods waited more than 140 million years to eat bone? Furthermore blade toothed theropods not only had to have been especially careful and dainty eaters to avoid chipping a tooth while biting into the internal bone of dinosaur prey, but had to be careful in biting into the skin of a wide variety of dinosaurs? The reason is that osteoderms - bone growing in and essentially embedded within the skin - is especially widespread among dinosaurs!! Nodosaurs, stegosaurs, ankylosaurs - essentially all thyreophora - had osteoderms. Among sauropods titanosaurids seem to have been especially bony skinned. And osteoderms were especially abundant among the various archosauromorphs that evolved with the first theropods. Blade toothed theropods lived with and evolved with osteoderm bearing animals for pretty much the duration of the Mesozoic. To take this notion seriously - that blade toothed theropods were so careful and selective in biting into their fellow prey species - is patently ludicrous in my opinion and just flies in the face of what it takes to have been at least a somewhat competent predator,  much less the most successful and persistent radiation of terrestrial vertebrae predators ever.

And besides these two arguments is the evidence of deliberate, unequivocal and sometimes alarming bone cutting, chewing, and consumption that can only be attributable to blade toothed theropods.

Tyrannosaurus rex gets all the headlines in terms of bone consumption but if you really investigate all the lines of evidence it falls short compared to blade toothed theropods in two pretty notable categories.

1) The largest and most bone riddled theropod coprolite does not - as often claimed - belong to the tyrant king but actually is the work of a particularly bone hungry Allosaurus way back in the late Jurassic. I talked about this little known tid-bit on my post on Allosaurus feeding mechanics here but it is worth a reprint:

A turd 1.52 meters long!! And 50% of it is of bone fragments - not whole bones but minced shards of bone. Exactly what would be expected to occur in the "bonesaw shimmy" method I postulated. It is worth reiterating that bone passes largely undigested through theropod guts and there is no evidence of gastroliths in Allosaurus. This bone chipping was being done in the mouth, not the work of a bone cruncher but a bone mincer.

T. rex (L) and Allosaurus (R) Two solutions to the same problem, A bone cruncher and a bone saw

So T. rex can not lay claim to the biggest and most bone riddled turd we know of.

2) The "tyrant lizard king" can not even lay claim to the biggest and deepest score marks on bone. The largest and deepest score marks on bone comes from an unknown early Cretaceous theropod that left traces on some giant sauropod caudal vertebrae in Korea:

These deep scores are not the work of T. rex nor are they likely the work of any classic late Cretaceous style "bone crunching" tyrannosaurid. Although a tyrannosauroid can not be ruled out here it is worth noting that early Cretaceous tyrannosauroids had a lot more in common with other blade toothed theropods than the latter bananna toothed killers.  I consider earlier tyrannosauroids as likely candidates for the "bonesaw shimmy". I also am starting to seriously consider that the young of giant tyrannosaurids as well as alioramids as likely candidates for neck driven vibrational feeding.

Alioramis. All the hallmarks of a true chainsaw mouth. credit SteveoC CC3.0
I think the question that we should be asking is not why did blade toothed theropods fail where tyrannosaurids succeeded in bone consumption because a thorough review of multiple lines of evidence suggests that blade toothed theropods evolved a parallel method of bone processing (i.e. chainsaw mouthed, neck driven "bonesaw shimmy" in my opinion) but what made tyrannosaurids so different from the vast majority of carnivorous theropods? That is the question in my mind although I don't really have a precise answer. Some have suggested ornithischian dominated habits stimulated a crushing/pulverizing bite. I am not certain as there were nodosaur and iguanodont dominated formations in the early-middle Cretaceous. Gregory S. Paul often spoke of an arms race between tyrannosaurids and their prey - perhaps part of this arms race involved the increasing dermal thickness of prey species? Additionally the pulverizing bite of tyrannosaurids may have allowed for more quicker and efficient killing than blade toothed theropods and therefore more time to consume prey before competitors and especially conspecifics showed up to challenge for a bite. Likely a combination of these and multiple factors...

Why have tyrannosaurids, and especially T. rex, received all the attention for bone consumption?

Well, in addition to the narrative I have played up so far, I think that there are several not entirely mutually independent reasons.

1) The pull of the recent. Tyrannosaurid bearing formations are younger, well sampled, well studied, and generally get a lot of attention. Western North America in particular. For many of the formations such as Dinosaur Provincial Park or Hell Creek there are so many good remains that meaningful statistical analyses can occur. I don't think you can do the same for let's say middle Jurassic Chinese stegosaurids or early Cretaceous Australian titanosaurids. We just have better representation of tyrannosaurid dominated formations and therefore "see" more evidence of bone utilization.

However, even from my armchair analysis of what I find peppered on the web I keep coming across published and more anecdotal references of bone chips in theropod coprolites or - especially in the Morrison formation - quite dramatic unpublished and published tooth marks on bones. I mean, check out this carvery done on a Camarasaurus ilium. Can you really chalk that up to "incidental contact"? From SV-POW credit Matt Weddel used w/permission.

theropod damage on a Camarasaurus ilium. credit Matt Weddel SV-POW

2) The hyena mindset. Bone crunching not bone slicing or mincing is how we are "prepared" to think about bone utilization since that is what the most famous bone consumers hyenas do. Since we have this mindset in place already we "expect" stout bananna toothed tyrannosaurids to access bone but blade toothed theropods not so much. But when direct and unequivocal evidence of bone utilization in non-tyranosaurid bearing formations is found it seems to be discounted, ignored, explained away, or even sometimes attributed to some unknown crocodile or as yet undiscovered lineage of tyrannosaurid in the late Jurassic or early Cretaceous. Not to, you know, the blade toothed theropods that actually lived there.

What is interesting when we think about the hyena analogy is that hyenas - which we can all agree are bone consumers - do not indiscriminately eat every scrap of bone available to them. In fact this study  on the extinct giant hyena Pachycrocuta makes the point explicit. Marrow rich long bones were highly sought after but other bones left relatively unscathed. Tyrannosaurids likewise did not eat every scrap of bone available to them - in fact there is much evidence of nipped and delicately stripped bones by tyrannosaurids despite their awesome jaws and bone crunching dentition. So just because you can eat bone doesn't mean you eat it all the time, eat other parts preferentially, or just ignore the bone. Some bones in dinosaur carcasses - especially highly pneumatic ones - were likely left alone. The more marrow rich bones in dinosaur carcasses - which no one really knows which ones they are although I suspect the ilium, caudal vertebrae, and some ends of long bones - may have been more heavily exploited.

Let us escape from the paradigm of bone crunching and think about sharks and shark attacks for a bit. Reading about shark attack accounts is both horrifying and terrific. What is amazing about them is that they are rife with accounts of sharks cutting through and sawing through human bone, literally dismembering humans while still alive. Happens all the time. These are sawing animals, not hyena like crunchers. We know from the work of Brinke et al (2015) that theropod teeth were mechanically stronger than other ziphodont predators and likely better rooted and reinforced than shark teeth. In my estimation there's nothing a shark could do that a similar sized blade toothed theropod couldn't do. Sharks shake their body left and right to allow their serrations to work their way through hard objects. Theropods shook their neck and/or body fore and aft to allow their serrations on the front and back end of their teeth (labial & lingual) to work their way through tough objects.

However, for whatever reasons these nuanced conditions that determine when to eat or not eat bone go out the window when we talk about blade toothed theropods. Despite the fact that for many dinosaurs - and especially sauropods - we have a sample size of n=1 so, unlike the abundant hadrosaurids and certatopsids in tyrannosaurid formations, it's sort of hard to make any meaningful claims on the frequency of bone exploitation in large sauropod dominated formations.  However it is also worth mentioning where are all the juvenile, teenage, and subadult sauropods in formations dominated by blade toothed theropods? Not all sauropods would have been whale sized behemoths. In any sauropod population numerically there would have been many more elk, water buffalo, rhino, and elephant sized sauropods than whale sized adults. Where are they all? These would have been sauropods too big to be swallowed whole (the baby killer specialist scenario as postulated by Dave Hone) but large enough to have easily been preserved in the fossil record. So where are they all? If blade toothed theropods were assiduously avoiding bones we should have them or at least their bones... Could it be that blade toothed theropods were in fact "disappearing" entire carcasses Joe Pesci style? ( a future post hint, hint) Let me flip the script here a bit and suggest that blade toothed theropods were eating more bones than tyrannosaurids - in fact they were eliminating entire size classes of sauropods from entering the fossil record. After all it is blade toothed theropods that hold the record for largest bone riddled poop and deepest bone score mark on bone - not the tyrant lizards.

heavily worn Carcharodontosaurus tooth. paleodirect
ditto. note wearing down of tip

"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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khalil beiting said...

Amazing post as always. We seriously need more attention on the massively diverse lineages of non Tyrannosaurid Theropods. Like seriously, just look at how "diverse" Tyrannosaurids are. You basically just have Tyrannosaurs rex kind of forms that just have giant robust jaws with tiny arms, and then you have little dainty forms like Alioramus that have long teeth and long snouts; although they still have about the same body plan. There are some forms in between but that's about it. But look at literally any other Theropod group. Bull horned Abelisaurs, pack hunting uber mega sauropod/stegosaur hunting Carnosaurs, small sized basal Neotheropods that (possibly) used mob/hoard tactics to viscerate large sized prey, near sabertoothed Herrerasaurids and Ceratosaurs, giant crocodile mimic Megalosaurids (although Spinosaurus is WAY too over hyped), giant scythe armed Megaraptorids, nocturnal Troodontids that were essentially ground dwelling owls with the attitude of a pissed of Cassowary and giant and even semi-volant Dromaeosauirds were all stalking and eviscerating the multitude of prey items in their habitats. Well, enough with my long ramble, you get the gist of it. You're doing a great service to the paleontological community by focusing on Theropods that were utterly destroying flesh. I look forward to your next post!

Duane Nash said...

Thanks and you will like the next flesh rippin' post khalil unless I get distracted by something else which is always possible... I am intrigued by tryannosauroids as they seem to come in more flavors than tyrannosaurids. Also Dryptosaurus.

khalil beiting said...

I actually find Dryptosaurus really intriguing. Some recent suggestions point to it either being a close relative of Xionngunalong or possibly even being a Megaraptorid. I'm not taking a side until we find better remains though. And now I'm even more intrigued about the next post ;). By the way, just a reminder, but you should eventually do a post on Abelisaurids. They must have been doing something weird since they don't closely resemble other "vanilla" Theropods.

babehunter1324 said...

Very good post, I have to agree with the fact that this Tyrannosauridmania should go.

Duane Nash said...

@ khalil I would love to do one on abelisaurids but I don't really have anything to add on their feeding mechanism... I think that they really did just bite onto and hold tight like giant bull dogs. One funny trope I noticed in their art is that they always seem to run in pairs, just funny I thought.

Robert Haan said...

In general , i've always had a healthy respect for tyrannosaurs and their capabilities and have never tried to take anything away from them, but i've never put them up on a pedestal as being superior to every other archosaurian predator either , every theropod was awesome and special in their own way in surviving in their respective habitat and time, actually you can expand that statement to pretty much every organism that has existed on this planet , there are no failed experiments in nature as every living thing is equipped with the tools necessary to enable it to exploit its environment to its fullest capability , the extinction of a certain species does not necessarily mean that it was inferior to its replacements, it simply means that it just wasn't cut out to survive in the current time and place.

The Eurypterid said...

Perhaps tyrannosaur bites were designed for crippling prey via attacking the musculature?

We have bites aimed at the caudofemoralis (https://upload.wikimedia.org/wikipedia/commons/6/6a/DMNS_Edmontosaurus.png), which would do said crippling. Tyrannosaurs would need long teeth- which they do have, after a visual check versus Carchar- in order to penetrate the fat likely stored on the tail base (the deposits' existence suspected by Witton, http://markwitton-com.blogspot.co.uk/2015/09/humps-lumps-and-fatty-tissues-in.html).

The bite force, skull and teeth would also need to be much stronger in order to damage the deeper muscle without breaking the grip from stress or simply tearing out with superficial damage. This is also observed. Unlike abelisaurs, an extended period of stress on the skull is unlikely (due to the goal being disabling instead of wearing down), meaning the skull can afford to become very solid.

We know that ceratopsians did very well alongside tyrannosaurs. Perhaps their body-concealing frills, short legs and relatively sloped, stumpy tails were designed to make it as awkward as possible for a tyrannosaur to identify and disable any major locomotary muscle groups?

This is all speculation, so if someone who actually knows biology could comment and pick holes, I'd appreciate that. :)

khalil beiting said...

@The Eurypterid, I'm no proffesional biologist, but your theory seems pretty sound. A (somewhat) close modern day analogy would be the spotted Hyena. It can crush through bone, yet it doesn't nesecarilly go for said bone even when hunting. It uses it's bone crushing bite to cause mass trauma and damage to it's (usually) still alive prey. Like you said, the same method can be seen in the highly traumatized tail vertebra of a certiain Edmontosaurus specimen.

Duane Nash said...

Yes, a disabling bite to the caudemofemoralis has been suggested before: http://antediluviansalad.blogspot.com/2013/07/return-of-land-shark.html

Hadrosaurs with agility, speed, and a very thick/tough skin were probably more problematic prey than generally imagined. That they got away sometimes - as proven by haling of damaged bite trauma - suggests as such. Don't underestimate the quarry.

Bk Jeong said...


Bk Jeong said...

Also, sawing through the artery is a faster kill than pulverizing.

Bk Jeong said...

Also, screw tyrannosaurs. They can't kill anything bigger than themselves (though they definitely were not small-prey specialists) for Carcharodontosaurus's sake!

Luke said...

Among large terrestrial predators specializing on large prey, you find the highest carcass utilization among the giant constrictors and the Komodo dragon. Constrictors are probably not a good analogy for theropod feeding, but the dragons might be. Dragons dismember carcasses using a back-and-forth sawing motion as you have hypothesized for the blade-toothed theropods; dragons have ziphodont teeth; and dragons typically leave nothing but the gut contents of their prey - they consume all the bones, skull and all (and skin, tendons, organs, muscle, hair, horns ... everything). Could similar behavior among the theropods shed some light on the relative paucity of mid-sized sauropod remains?

Warren JB said...

Interesting as ever, Duane; and always good that someone points out that there were big theropods other than 'trex'.
Joe Pesci style, huh? Gives "Here's an arm. Here's a leg. Here's a wing!" an extra layer.

Luke: some good videos of komodo dragons feeding on large carcases, on youtube. Interesting that they pull back, as mentioned, but also 'saw' side to side. Not shaking like a shark, but a more deliberate 'turn head and bite laterally > pull back and straighten > reposition mouthful to other side > repeat'. Seemingly when presented with a wide, flat flank or limb surface that can't be easily bitten - at least not with the result of a decent mouthful - with the point of the snout. (Though I wonder if that has much to do with the suspended rather than freely lying joints of meat in some vids)

Brings up images in my head. I can imagine theropods plucking at soft underbellies and cloacal openings first, as Duane's talked about, and as vultures and dragons do. But when that's gone (or crowded) and there's only a sauropodal shoulder or side of ribs, the general size and shape of a barn door...?

Duane Nash said...

@Warren JB the extra wide gape of certain theropods, esp Allosaurus, may offer some clues into biting into wide surfaces. I suspect that there were "guilds" of theropods that acted in concert to dispose of such colossal mounds of flesh much as vultures show different specialties in accessing a carcass today. Some were good at or even necessary, to open up the thick and/or armored hide and then others may have concentrated on probing into the viscera or had a particular liking for cartilage/ligaments/skin. I want to explore this idea further in another post. I also suspect that this large carcass partitioning applied to not only species but different age groups of theropods.

Anonymous said...

A long time ago I went to Thermopolis in Wyoming. They have an Allosaurus feeding site there. (Not a nest they say, no egg shells). They know this because the parent Allosaurus left a big footprint in the mud. They tour guide said they thought the parent brought home pieces of leg bone home to the babies to eat. They have lots of shed baby Allosaurus teeth and pieces of shattered sauropod bone all over the place, as I remember.

Duane Nash said...

Yes thanks for comment anonymous. I have also heard Bakker mention of allosaur feeding lairs, I don't know if he is referring to same place that you visited. I have to admit that I am not quite sold on parent allosaurs provisioning the young. I think it is more a case of both the old and young feeding together on carcasses opportunistically.

D-man said...

This is untrue, Triceratops weighs 10 tons while T.rex weighs in at 7 tons. Also Edmomtosaurus is a bit taller and longer and a bit heavier too, though I have to agree that T.rex probably could not take down a fully grown or even sub adult

Tyrannosaurids are definitely amazing predators, but like Duan said their are many other predators in the same league. I believe that all carnivores are "winners" since they are all best suited for taking down the prey they have.

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