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:
|Alioramis. All the hallmarks of a true chainsaw mouth. credit SteveoC CC3.0
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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