Hello, patient readers. I've blogged about Raptors before, specifically Deinonychus and the problems of depicting dinosaurs in general. In an earlier post, I was wrestling with the then newly-popular preponderance of plumage on our favorite Terrible Lizards, and while I finally conceded that Deinonychus and Co. were probably fully feathered, I whined and hemmed about the amount of feathers and griped about how dinosaur lineages with no evidence for feathers at all were now being given fabulous coats. In the midst of this, I decried the new crop of bad paleo-art, using this image as my piéce de resistance:
Essentially my big scientific argument ran along the lines of, "Looks dumb, therefore wrong". It seems now that I might have to eat that argument, slathered in Nelson Muntz' Gourmet Ha-Ha Sauce...with one important caveat, which I'll get to later.
Since writing that blog post - in fact, several years later - I've stumbled across the amazing Antediluvian Salad, which has completely revolutionized my thinking on my favorite theropods and dinosaurs in general. Author Duane Nash's big claim is that, in terms of feeding, theropods - large and small - have their best contemporary analogue not in hawks, but in vultures. Vultures are superficially similar to hawks and eagles, but in terms of feeding - besides the whole scavenging thing, which has a lot more overlap than is generally acknowledged - vultures lead with their heads, rather than their feet.
This may seem like a technical distinction, or some kind of zoological nitpicking, but in fact it has immense implications for differences in attacking, feeding, and dominance behavior. Modern raptors attack and kill their prey with their feet; when battling over a carcass, they use their feet in preference to their beaks. Vultures, on the other hand - both Old- and New-World varieties - have much weaker talons, and attack with their heads (yes, they definitely kill things if the opportunity arises); around a carcass, they don't merely peck at rivals, but are known to latch onto other vultures' head-flesh, bite them mercilessly, and thrash them with their wings. An oft-repeated trope about vultures' naked heads states that "a feathered head would only get clotted with gore and cause infection", but in practice this doesn't necessarily follow: fully-feathered eagles and petrels, both notorious scavengers, plunge headlong into carcasses with as much gusto as their scavenger cousins. Instead, it appears that tough, hanging head-flesh is more important for dominance-biting situations.
In many cases, extant theropods (birds, that is) with extensive wattles around the face and neck are scrappy types, using their beaks to grab and hold onto a rival while they pummel or push them. The American turkey is an excellent example of this, as are black vultures. In mammalian species, bull elephant seals have enormous blubber pads around their neck to protect against the fangs of rivals; shar pei (Chineses mastiffs) feature voluminous skin folds to protect their necks against other dogs. While the "extra skin" rule doesn't apply to all face-biters in the animal kingdom (Tasmanian devils come to mind), it stands to reason that ancient theropod dinosaurs, being related to face-biting birds and engaging in a lot of face-biting of their own, should feature at least a little extra skin as protection around the carcass.
In my previous Deinonychus post I came up with the animal shown on the left. While my science was sound (especially with regards to the minimized neck plumage vis-a-vis ground hunting birds), I now feel my depiction is way too conservative - just a slightly more-feathered version of the old scaly 'Raptor (except for the cardinal-red feathers...what the heck was I thinking?). Note the scaly face, lizard lips, naked lower hindlimbs, and small primaries on the arms. The tail is outfitted with a begrudging little fan at the tip. The predator's overall body plan is simply too skinny and sectional. The only part I really stand by are the hands; I feel as though Raptor hands have been done a disservice in the name of distancing them from the curly-fingered "monster hands" of Jurassic Park's chimeras. I posit that they were way too robust and to just flap around uselessly; at the very least they would be effective grappling weapons when subduing large prey.
(In all this, I'm essentially rejecting Fowler et al's "Raptor Prey Restraint" model for dromaeosaurids; while certainly iconoclastic and a much-needed challenge to accepted dogma, upon closer review many of their conclusions are questionable at best. Deinonychus was neither a scaly wolf, nor a delicate ground-hawk; the truth is somewhere in the middle, and definitely weirder than anything we have today).
So I'm updating my Deinonychus depiction.
Below is my thought process, leading to my new Deinonychus model. The original skeletal reconstruction is based on the excellent sculpt by Jason Brougham, which is arguably the best and most complete reconstruction I've seen - most other reconstructions utilize the old "Allosaurid" skull Osborn produced, with its side-facing eyes and tall nasal arch. Dromeaosaurs were dog-faced, with binocular vision. In the initial stage I just threw some skin over the skeleton, much like the paleoart of the 90's; this is the depiction we're used to...and by God, do aesthetic preferences die hard.
But this is 2018! So I beefed up this predator with some extra flesh-bits, especially between the tail and the pubic bone, which is where the cloaca lies in birds. Dromaeosaurids have ridiculously huge pubic bones, sticking way out beyond their legs...what muscles attached here? Or was it just covered in cartilage, serving as a "butt pad" for sitting? The pubis is so weird and projecting, I almost want to draw a diagonal line from its tip to the middle of the tail, giving Deinonychus a massive "Hadrosaur ass". This also begs the question of how Deinonychus and other dromaeosaurids held their bodies; could they have possibly had a more upright posture? Would their anatomy allow for it? So many questions...
You will note I've added plenty of Nash-style colorful head wattlage...nothing too freaky, like cockscombs. I'm still a little too chicken (pun intended). But my Deinonychus is essentially a plucked bird in the third phase of my rendering, with "scaly" yellow feet and hands. The feet are given large pads, and the nails themselves are elevated off the ground (reconstructions put "claws" on dinosaur skeletons' feet, but what we actually see in fossils are more akin to fingertip-bones...the claws grow out of the fleshpad). I based the general amount of foot padding on similarly-sized ratites, like rheas and cassowaries. The arms are a little bonier, in keeping with their dinobird heritage - there's evidence dromaeosaurs evolved from flying dinosaurs, rather than the other way around.
Finally, the integument ("feathers", if you're nasty). I went conservative, giving it bald-eagle coloration, except for the head and neck area. Now, the bald eagle is an aerial hunter, and a piscivorian to boot; what would be the coloration of a ground-hunting, hypercarnivorous bird? Seriemas (which incidentally also have sickle-claws) have banded feathers on their underside and brown on top; Solitaires have blue-gray plumage with black accent feathers and bright red skin around the eyes. Roadrunners are a little more camouflaged, with mottled brown coloration. But none of these birds hunt prey larger than themselves, probably nothing bigger than a small rabbit. Would Deinonychus have taken after large-prey predators in its coloration? Wolflike grays? Leopard spots? Tiger stripes? Until we find feather impressions for these creatures, we just won't know. I'm banking on conservative colors with accents of white or black. I added an eyespot to its tailfan as well, since such a large organ as a dinosaur's tail must have been involved in signaling of some kind.
Do I owe Luis V. Rey an apology for calling his Deinonychus depiction "dumb"? Well...sort of. From the standpoint of how Deinonychus probably looked - at least in my current understanding, based on Duane Nash's ideas - Mr. Rey's depiction was correct. But this was not due to scientific rigor on his part: in his own words, "I depicted them with bald heads and looking like condors or vultures… why not?" I group Mr. Rey more in the category of "sensationalist" paleoart, and I feel like his depictions of dinosaur life and times, while flashy in the externals, are ultimately safe and run-of-the-mill. These commonplace, imagination-lacking scenes, repeated over and over, are exactly what I'm trying to get away from in my work.
PART II: My struggles with Deinonychus
Two Extremes
What's frustrating to me is, there's a weird "either-or" stance regarding Dromaeosaurid pack hunting, based completely on modern zöo-social archetypes and cultural assumptions, that amount to a failure of the imagination. We've assumed for so long that 'Raptors were hyperintelligent, hyperkinetic packhunters, we never really gave much thought to where the notion came from. Jurassic Park certainly popularized and, in a sense, codified the popular understanding about these animals. Then studies came out questioning the original assumption, and by the time of Fowler, et al., the pendulum swung in the complete opposite direction: Dromaeosaurids weren't very fast or intelligent, only circumstantially fed in groups, and in fact used their feet like hawks to squeeze small prey to death - the sickle claw was merely circumstantial. This was further justified by the assertion that no extant birds or reptiles hunt cooperatively (Eee...errr...ummm...yikes, let's unpack that later), and only mammals form actual cooperative packs in the modern biosphere (I'll give them that). Naturally this caused a sensation, and pretty much every hip young paleoartist jumped on the bandwagon, assuming it was the cutting edge of science. There's a lot of cultural and scientific baggage all knotted up here, and it's difficult to tease out where one thread begins and the next one ends. In fact, the more you look at it, the murkier the issue becomes.
In order to unravel this Gordian knot, let's start at the beginning.
Deinonychus was initially discovered in 1931, near Billings, Montana, by Barnum Brown - yes, he of Tyrannosaurus rex fame - and while the fossil was fairly complete, he didn't really have the antennae to register what he'd found. The focus on that time was on the big stuff - the diplodocids and Tyrannosaurs coming out of Western North American bone beds - and so the preparation of his Deinonychus (then called "Daptosaurus agilis") was begun, but never completed. It would be 33 years before more remains of the dromaeosaurid were found, when John Ostrom's expedition in the nearby Bridger, Montana unearthed the fragmentary remains of Deinonychus along with a 1-4 ton iguanadontid herbivore, Tenontosaurus. Similar fossilized scenes were discovered later in the Antlers Formation of Oklahoma. When the various remains of Deinonychus from different specimen beds were finally collated and described, it became apparent that this was a small, lithe predatory dinosaur, associated in groups with Tenontosaurus.
From Wikipedia:
Deinonychus teeth found in association with fossils of the ornithopod dinosaur Tenontosaurus are quite common in the Cloverly Formation. Two quarries have been discovered that preserve fairly complete Deinonychus fossils near Tenontosaurus fossils. The first, the Yale quarry in the Cloverly of Montana, includes numerous teeth, four adult Deinonychus and one juvenile Deinonychus. The association of this number of Deinonychus skeletons in a single quarry suggests that Deinonychus may have fed on that animal, and perhaps hunted it. Ostrom and Maxwell have even used this information to speculate that Deinonychus might have lived and hunted in packs.[39] The second such quarry is from the Antlers Formation of Oklahoma. The site contains six partial skeletons of Tenontosaurus of various sizes, along with one partial skeleton and many teeth of Deinonychus. One tenontosaur humerus even bears what might be Deinonychus tooth marks. Brinkman et al. (1998) point out that Deinonychus had an adult mass of 70–100 kilograms, whereas adult tenontosaurs were 1–4 metric tons. A solitary Deinonychus could not kill an adult tenontosaur, suggesting that pack hunting is possible.[12]
So already we have two major assumptions being made: 1) the Deinonychus in the area killed the associated Tenontosaurus, and 2) the Deinonychus were working together. This is not a huge stretch of the imagination: if you find the fossils of several lions around a cape buffalo skeleton, it's safe to assume they weren't all sitting down to tea together...but then we know how lions hunt. Dromaeosaurs, despite our assumed familiarity with them, are still patently mysterious creatures. We have a notion about how they killed - that huge claw is a pretty good clue - but any other evidence for their hunting behavior is extremely ambiguous. Even the famous "Fighting Dinosaurs" of Mongolia, a Velociraptor mongoliensis grappling with a Protoceratops, isn't "smoking gun" evidence that Velociraptor preyed upon this small ceratopsian - all it indicates is that the two were fighting (to the death!) for some reason when they were buried by a sand dune. With only a single small predator and a rather heftier herbivore, we don't know if the Velociraptor had help, or even who the primary aggressor was...for all we know, the Raptor may have been defending its nest from the Proto! Far-fetched, maybe (or maybe Protos were opportunistic omnivores like pigs, who the hell knows), but even this scenario illustrates how little we understand Dromaeosaurs and how they interacted with their prey. (Update - check out another piece of Velociraptor/Protoceratops interaction here).
We also have to unpack the cultural and scientific baggage surrounding dinosaur science at the time, in order to understand exactly why Ostrom et al came to these conclusions. Before the discovery of Deinonychus, it was pretty much assumed that dinosaurs were slow, cold-blooded brutes*, and even the smaller species were akin to two-legged lizards. I think the implications of a fast, warm-blooded dinosaur sent Ostrom reeling a little; in his giddy state he started making associations beyond what the evidence was actually showing. Group behavior associated with a carcass suddenly turned into group hunting, group hunting jumped to pack hunting, because what is the best-known pack hunter? Why the wolf, of course...! The lithe, lean mammalian killing machine, punching far above its weight, was the perfect analogue for this lithe, lean reptilian hunter. Pack hunting implied a high level of intelligence - never mind that a complete braincase of Deinonychus had not been found at that point. In essence, I believe, Ostrom was so overawed by the contrast between the tail-dragging lizards of yore and his new, tail-balancing little hunter that he overstated his case.
The discovery of Deinonychus kicked off what has been termed the "Dinosaur Renaissance" (or "First Dinosaur Renaissance", I think we're in the Second one...) Finding its articulation in Robert Bakker's The Dinosaur Heresies and Gregory S. Paul's Predatory Dinosaurs of the World, DR1 completely overturned the old order of things. The dinosaur-bird link was revived; fast, speedy, warm-blooded dinosaurs became the norm (often with crazy coloration to boot); soft fleshy bits were trimmed away until even T. rex became a shrinkwrapped, slimline Ferrari, capable of sprinting at 45 miles per hour. Pretty much all herbivores became herd animals, and pack life was extended to nearly every genus of carnivore, large and small. Feathers first started to make a tentative appearance on Dromaeosaurids, although the first feather impressions weren't discovered until 1996. The publication of the book and movie Jurassic Park, in 1989 and 1993 respectively, brought the Dinosaur Renaissance bursting into the popular imagination...bringing a whole host of problematic 'Raptor mythology along with it.
Now we're in the Second Dinosaur Renaissance (DR2), in which the conclusions of the first have come up for revision...and nothing is sacred. The bugbear of this new movement in dino-studies is definitely the Jurassic Park/World franchise: the Sins of the Fathers set up for ridicule and symbolic flogging. Once again we have rather extreme measures being taken to ensure a split from the past: Everybody gets feathers! Dinosaurs were terrible parents! Tyrannosaurs didn't have lips! And most importantly, Dromaeosaurs were nothing more than ground-living hawks, preying on small game and squabbling over carcasses! Legitimate research gets mixed in with dubious conclusions based on bad premises, and we're just now realizing how often science is stymied by the peer-review process, sensationalist journalism, and rather stagnant notions of ancient ecology and behavior. As above, so below: paleontology is facing a similar crisis to the general culture in terms of entrenched notions, misinformation, and uncertainty in constantly-shifting ground.
You can see from the history of Deinonychus that it's the most radical theories about these animals that gains the most traction in the popular (and popular-scientific) imagination. It's a rather unfortunate truth that, in many cases, the Fowler theory of Raptor Prey Restraint will be considered the most "cutting-edge science" simply because it is the most well-articulated: expect museums to start changing their Deinonychus displays completely over the next ten years, despite what real cutting-edge studies might say. There's always a lag in scientific understanding between paleontologists and the public. Drop an asteroid in middle of the Pacific Ocean, and hundred-foot tidal waves will hit the Pacific Rim coastlines repeatedly for days - even after the impact site has been swallowed up by calm seas: this rather tortured metaphor is about the size of the Fowler study. However much their claims might be refuted, the damage has already been done.
An Alternative Approach; or, Duane Nash to the Rescue.
I've been rather slavishly intoning "Antediluvian Salad" and "Duane Nash" like some kind of starry-eyed paleo-cultist recently, but I can't overstate how much this man's ideas about dinosaur appearance, behavior, and ecology need to be disseminated. I'd go so far as to call his radical reinterpretations "Dinosaur Renaissance 3", or at least "DR2.5".
He posits that theropod dinosaurs acted much like Old World vultures when approaching their prey.** Vultures descend upon carcasses a mob, with a head-oriented feeding style and a strict pecking order that results in much quarreling and face-biting between individuals. What may look like barbaric, desperate jostling for food is often more about establishing dominance; some vultures seem almost to neglect the carcass in order to go after lower-ranked vultures who get too uppity. The question of, "Did theropods hunt in groups?" is therefore sort of moot, because they went after their prey in gangs, with the largest and toughest individuals doing the grunt work while the smaller individuals predated the victim while it was still alive (vultures will do this too - they're opportunistic predators as well as scavengers, with young or sick livestock being especially vulnerable). Now, were these "packs" by any sense of the term? This is doubtful. The individuals in the mob would not be purposely related to one another. A proper pack is, after all, a family group. Theropod family units probably hunted together, but mostly as a means of feeding and training their young; when going after large prey, it was mostly an opportunistic, numbers-dependent game.
In Which I Attempt to Formulate My Own View of Deinonychus
My first proposition is that, no matter what the Morrison Formation and Antler Creek Formation remains actually preserved, we can infer there was at least some kind of relationship between Deinonychus and Tenontosaurus: was it predator-prey? Scavenger-carcass? Mutually antagonistic? The answer hinges upon three details: 1) How common were both species? 2) What was the full range of predators in these areas at this time? 3) What other specimens are available of both animals, and what do they show?
In order to understand Deinonychus and its ecosystem, we must first look at the much more abundant Tenontosaurus. Understanding how often Deinonychus and Tenontosaurus appear together will give us clues as to their relationship. Apparently the two most "important" specimens, found by John Osborne, are fairly typical of Deinonychus remains.
From Wikipedia:
Teeth and a number of skeletons belonging to the bird-like carnivorous theropod Deinonychus have often been discovered associated with Tenontosaurus tilletti remains. Tenontosaurus specimens have been found at over 50 sites, and 14 of those also contain Deinonychus remains. According to one 1995 study, only six sites containing Deinonychus fossils contain no trace of Tenontosaurus, and Deinonychus remains are only rarely found associated with other potential prey, like Sauropelta.[5] In all, 20% of Tenontosaurus fossils are found in close proximity to Deinonychus, and several scientists have suggested that this implies Deinonychus was the major predator of Tenontosaurus. Adult Deinonychus, however, were much smaller than adult Tenontosaurus, and it is unlikely a single Deinonychus would have been capable of attacking a fully grown Tenontosaurus. While some scientists have suggested that Deinonychus must therefore have been a pack hunter, this view has been challenged based on both lack of evidence for coordinated hunting (rather than mobbing behavior as in most modern birds and reptiles) as well as evidence that Deinonychus may have been cannibalizing each other, as well as the Tenontosaurus, in a feeding frenzy.[6] It is likely that Deinonychus favored juvenile Tenontosaurus, and that when Tenontosaurus reached a certain size, it passed out of range as a food source for the small theropods, though they may have scavenged larger individuals. The fact that most Tenontosaurus remains found with Deinonychus are half-grown individuals supports this view.[3][7] It also lived in the same area as the large carnivorous dinosaur Acrocanthosaurus.[8]
We have clues here that point to an important relationship between Deinonychus and Tenontosaurus, whatever that may be. The fact that the associated Tenontosaurus were consistently juveniles, in my mind, points to a predatory relationship: if the "next size up" of predators in the Antler Creek formation was the formidable Acrocanthosaurus, it begs the question of why such a large predator would be killing juvenile Tenontosaurus and leaving a large portion of the carcass, especially the fatty tail. One could posit that young Acros (as we know juveniles of large predators filled their own predatory niches) were doing the killing, at least at Antler Creek Formation in Oklahoma, but as far as we know this is the northern range of such sauropod-killers; what was doing the killing up in Montana?
It's important to make an aside here, and explain what exactly was going on during the Cretaceous in North America. This last and longest period in the Mesozoic Era - the so-called "Age of Dinosaurs" - is not as homogeneous as the public often presumes. For instance, Deinonychus would never have seen a Tyrannosaurus rex - even its later, larger cousin Utahraptor was probably long gone by the time the Tyrant Lizards arrived from Asia. Nor was North America the "typical" dinosaur spread we imagine it to be; in fact, certain parts of Western NA were cut off from the rest of the world for several million years, resulting in a flourishing of Hadrosaurids and Ceratopsians, for instance, and a dearth of sauropod Titanosaurs. For much of the Cretaceous, the entire continent from Texas to the Northwest Territories was split by the Western Interior Seaway; this enormous bodies of water would have split our beloved North America into at least two "continents", with the westernmost strip eventually connecting to Asia in the north and ending abruptly in southern Mexico in the south. In the Aptian and Albian ages of the Early Cretaceous, when Deinonychus and Tenontosaurus were exploring the intricacies of their relationship, the arid climate of the Jurassic/Cretaceous "Tithonian Event" that wiped out much of the diplodocid sauropods was just becoming hotter and wetter, resulting in a more jungly, subtropical environment. From what we can see, Tenontosaurus had arrived in the area during the bad times, and adapted well to the change in climate. It is during this humidifying period that Deinonychus appears in the fossil record.
Here's the important part: there were no Tyrannosaurids in the area as of yet. The same geographic location hosted several dromaeosaurids, associated with the earlier Barremian age, which included the now famous giant Raptor Utahraptor. Because the Beringian land bridge was open at the end of the Jurassic, then closed in the Early Cretaceous, then opened again in the Late Cretaceous, it is safe to assume that dromaeosaurids pulsed in from Asia, following waves of Iguanadontids and Ceratopsians, then were trapped in Western NA when the land bridge closed. Meanwhile, Tyrannosaurids evolved into larger, more powerful predators in Asia, and when the land bridge opened again, they flushed into North America and became the dominant superpredator. Could the influx of tyrannosaurids have spelled doom for the dromaeosaurids?
(I'm actually becoming really intrigued by this whole "dinosaur interchange" thing...there's a lot of unanswered questions. Expect another blog post dealing with this in the future!)
Since there's not a lot of hard evidence for Deinonychus predatory activity to go on, we'll have to use the old noggin and make several deductions:
1) Since there were few larger predators (except other dromaeosaurids, and the unlikely Acrocanthosaurus) to kill the associated Tenontosaurus, it is safe to conclude that, at least in some capacity, Deinonychus would predate juvenile Tenontosaurus.
2) If many Deinonychus are found around a Tenontosaurus carcass, and it is unlikely that one-on-one combat would turn out well for the predator, we can safely assume that several Deinonychus were involved in the kill.
3) If Deinonychus are rarely found without Tenontosaurus, we can also make the assumption that Tenontosaurus was a major prey animal for Deinonychus in both Montana and Oklahoma.
Therefore, from the evidence, I believe it is possible to conclude that groups of Deinonychus preyed regularly on Tenontosaurus.
I'm going to add some more evidence here: multiple Deinonychus skeletons have also been found in association with Sauropelta, an Ankylosaurid-like armored dinosaur. Furthermore, a Utahraptor predator trap has been discovered with several individuals of different ages predating an iguanadontid; whether this is direct evidence of group hunting, or if the individuals happened upon the carcasses of both predators and prey and became trapped themselves (a la the La Brea Tar Pits) is unknown, but it should be considered as a possibility when taken with the Deinonychus evidence. Added to this is the rightly famous but perhaps ambiguous "Fighting Dinosaurs" of the Gobi. Taken alone, each of these specimens tells us little about the predatory habits of dromaeosaurids; but when taken as a whole, the act of group-hunting becomes more plausible.
But is it pack hunting? Group hunting itself is, disappointingly, about as common as dirt. Lone-hunting predators are a quirk of the Quaternary; I'd argue that humans - the ultimate packhunters - killed off the majority of group-hunting predators, leaving canids and lions as the exceptions. It stands to reason that, in the absence of catastrophic interference from humans, even megapredators would gang up to increase their chances of hunting. We've found piles of Tyrannosaurid and Carcharodontosaurid bones of various ages all jumbled together, even in the absence of prey items; it's no stretch of the imagination to see at least the younger, spry-er juveniles forming gangs to hunt baby sauropods or Ceratopsians or Hadrosaurs. Crocodilians and Komodo dragons - hell, even turtles - will gang up and kill animals - and corvids and vulturines are notorious for their mobbing behavior.
But in terms of highly-coordinated assaults, the occurrence is far less frequent in the animal world. Canines, lions, whales, and hominids are pretty much the exception. Harris hawks and Aplomado falcons are known to coordinate in small family groups, with the latter assigning roles based on gender. While I won't rule out some level of coordination - especially from the large-brained Troodon - wolflike packhunting behavior among dinosaurs just wasn't that likely. I have to reluctantly agree. Especially since what first appears to be evidence for pack behavior in Deinonychus may actually be evidence against it.
You see, a true pack is known for its ability to quickly and efficiently hunt and kill a large prey animal with few casualties. Naturally deaths do occur, especially when dealing with dangerous prey, but usually the wounded will be nursed by the group and eventually recover. This is because a pack views each member as vital to the group. Food is apportioned according to rank, and while there is plenty of snarling around the carcass, the end result is that the whole pack is fed, with enough food to bring back to the offspring in the den.
So this begs the question with regards to the Deinonychus/Tenontosaurus remains: why the hell are there so many dead Deinonychus? If these predators were "frozen" in the act of a coordinated assault, we would see their articulated skeletons grappling with an articulated Tenontosaurus, as we do with the "Fighting Dinosaurs". Instead we see a jumble of bones of both species, sometimes interspersed or widely flung all over. The most abundant fossil in these specimens are Deinonychus teeth. This phenomenon is the rule, rather than the exception. When we see jumbled and spread-out skeletons like this, it's safe to conclude - from what we know of modern carcass sites - that the animals died in the open, and their skeletons were scattered by scavengers and the elements before being covered in mud and allowed to fossilize. Tenontosaurus was not a formidable opponent, especially when juvenile; barring some secret superpower - a venemous thumbspike? Fire breath? Eye-lasers? - such prey items could not be responsible for the level predator casualties seen at these sites.
The reluctant conclusion is that the Deinonychus killed one another. The number of teeth found scattered everywhere indicates that a lot more than feeding was going on; were they actively fighting one another over the carcass? If Darren Nash's vulture comparison is correct, we can infer that a vast number of Deinonychus - perhaps up to thirty individuals - descended upon the Tenontosaurus at once and tore it limb-from-limb; in the feeding frenzy, several Deinonychus were killed and eaten as well.
It's a pretty bad scene when you think about it:
Li'l Tonto the Tenontosaurus toddled along behind its family group, munching on lush foliage at the edge of a stream. The morning air was cool and steamy, and the insects were just beginning their sleepy chorus. The group was on edge, its older and wiser members feeling something wrong with the surrounding jungle; but Li'l Tonto was quite young and inexperienced, and so didn't register the lack of smaller dinosaurs feeding at the windfall of Gingko fruit, or the strange silence of the birds. Preoccupied with feeding, Li'l Tonto didn't notice that his relatives had moved off suddenly at a brisk pace, melting into the foliage of the surrounding woodland. Li'l Tonto's chewing is loud in the silence.
Then - branches snapping. A mob of Deinonychus poured in from all sides, some gliding down out of the trees, converging on the startled Tenontosaurus in seconds. Li'l Tonto squealed and bucked and slashed with his small thumb-claws, but the sheer weight of snapping Deinonychus pulled him to the ground. He feels the dull pain of their jaws stripping flesh from his hindquarters and digging into his underbelly, but shock is already setting in, and his whole body grows cold and numb. The Deinonychus near its neck region, probably the largest and toughest of the bunch, grapple him with their foreclaws and jaws, while their sickle-claws puncture his hide and begin to probe beneath his skin in quick stabbing motions, ripping open arteries and windpipe. Li'l Tonto goes down, whistling through his punctured trachea, fountains of blood squirting out of his perforated neck. His tail and thighs are already stripped to the bone before he hits the ground, and he disappears beneath a carpet of feathered backs and waving tails.
His death is only the beginning of what is turning into a feeding frenzy. The mob is nothing more than a dry-season hunting collective; they owe each other no loyalty. Snapping and clawing, shoving and screeching, the Deinonychus are keen to maintain a pecking order. They break from feeding to latch onto each others' loose face-flesh, ripping gashes and losing teeth in the process. As the meat diminishes the fighting becomes more desperate, not less; two or three will square off and tumble away from the carcass, snapping and growling; they latch with their forelimbs and mouths and kick one another like fighting cats. Their underbellies are thickened for this purpose, but with such powerful killing weapons, some are mortally wounded. The squirting blood attracts a detachment from the main mob, who rip apart their co-predators with as much enthusiasm as they destroyed Li'l Tonto.
At some point the flurry of activity begins to ebb. The larger Deinonychus, having taken the choice bits, have since stalked off to the bush to digest; the remaining group waddles away, until only the scrawniest Raptors are left to gnaw the bones. They've effectively skeletonized Li'l Tonto and the dead Deinonychus. They worked too fast for any larger predators to disrupt their feast, and with their cannibalistic tendencies, no smaller predators or even birds will attempt to feed until the last Deinonychus is sated.
This is dry-season behavior; in the good times, Deinonychus is a good parent, brooding its eggs, hunting small prey, and generally keeping to its family group. But as soon as the rains stop, Deinonychus begins whetting its claws, ready for the orgy of blood soon to follow.
In conclusion, I may owe Luis V. Rey an apology...but only for trashing his wattle-headed Deinonychus idea. I don't think he really thought it out, other than in a "why not?" sort of way. However, it just goes to show you how our ideas about dinosaurs can change if we let them, and how ultimately weird and fantastic these ancient creatures may turn out to be.
Rick Out.
*I need to check up on the accuracy of this statement. It's an oft-repeated trope - sort of like saying, "Victorians hated sex" - and needs more investigation and nuance than people are generally willing to apply. Every paleontological generation is convinced that the previous one is full of shit (coprolites, if you will) and are furthermore as dumb as the rocks they pick at. If you need any convincing that previous depictions of dinosaurs and ancient creatures weren't as idiotic or bereft of science as we assume they were, check out this book. Charles Knights' indescribably beautiful, breathtaking scenes alone - as inaccurate as we now know them to be - blow every modern paleoartist's work out of the water.
**Quick side-note about vultures: There are two types: Old-World Vultures, and New-World Vultures. Old-World Vultures are carrion-fowl, true, but their meals usually aren't that dead - that is, they are just as likely to gang up and steal a kill as they are to seek out something already dead. And they have been known to kill things. Vultures in India face immense persecution (and possible extinction) due to their calf- and lamb-killing habits. NWV's, on the other hand, tend not to be so pushy, although the bigger Condors have been known to throw their weight around.
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| Credit: Luis V. Rey, from his blog. |
Essentially my big scientific argument ran along the lines of, "Looks dumb, therefore wrong". It seems now that I might have to eat that argument, slathered in Nelson Muntz' Gourmet Ha-Ha Sauce...with one important caveat, which I'll get to later.
Since writing that blog post - in fact, several years later - I've stumbled across the amazing Antediluvian Salad, which has completely revolutionized my thinking on my favorite theropods and dinosaurs in general. Author Duane Nash's big claim is that, in terms of feeding, theropods - large and small - have their best contemporary analogue not in hawks, but in vultures. Vultures are superficially similar to hawks and eagles, but in terms of feeding - besides the whole scavenging thing, which has a lot more overlap than is generally acknowledged - vultures lead with their heads, rather than their feet.
This may seem like a technical distinction, or some kind of zoological nitpicking, but in fact it has immense implications for differences in attacking, feeding, and dominance behavior. Modern raptors attack and kill their prey with their feet; when battling over a carcass, they use their feet in preference to their beaks. Vultures, on the other hand - both Old- and New-World varieties - have much weaker talons, and attack with their heads (yes, they definitely kill things if the opportunity arises); around a carcass, they don't merely peck at rivals, but are known to latch onto other vultures' head-flesh, bite them mercilessly, and thrash them with their wings. An oft-repeated trope about vultures' naked heads states that "a feathered head would only get clotted with gore and cause infection", but in practice this doesn't necessarily follow: fully-feathered eagles and petrels, both notorious scavengers, plunge headlong into carcasses with as much gusto as their scavenger cousins. Instead, it appears that tough, hanging head-flesh is more important for dominance-biting situations.
In many cases, extant theropods (birds, that is) with extensive wattles around the face and neck are scrappy types, using their beaks to grab and hold onto a rival while they pummel or push them. The American turkey is an excellent example of this, as are black vultures. In mammalian species, bull elephant seals have enormous blubber pads around their neck to protect against the fangs of rivals; shar pei (Chineses mastiffs) feature voluminous skin folds to protect their necks against other dogs. While the "extra skin" rule doesn't apply to all face-biters in the animal kingdom (Tasmanian devils come to mind), it stands to reason that ancient theropod dinosaurs, being related to face-biting birds and engaging in a lot of face-biting of their own, should feature at least a little extra skin as protection around the carcass.
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| Out with the old...©2018 Rick Schlaack |
(In all this, I'm essentially rejecting Fowler et al's "Raptor Prey Restraint" model for dromaeosaurids; while certainly iconoclastic and a much-needed challenge to accepted dogma, upon closer review many of their conclusions are questionable at best. Deinonychus was neither a scaly wolf, nor a delicate ground-hawk; the truth is somewhere in the middle, and definitely weirder than anything we have today).
So I'm updating my Deinonychus depiction.
Below is my thought process, leading to my new Deinonychus model. The original skeletal reconstruction is based on the excellent sculpt by Jason Brougham, which is arguably the best and most complete reconstruction I've seen - most other reconstructions utilize the old "Allosaurid" skull Osborn produced, with its side-facing eyes and tall nasal arch. Dromeaosaurs were dog-faced, with binocular vision. In the initial stage I just threw some skin over the skeleton, much like the paleoart of the 90's; this is the depiction we're used to...and by God, do aesthetic preferences die hard.
But this is 2018! So I beefed up this predator with some extra flesh-bits, especially between the tail and the pubic bone, which is where the cloaca lies in birds. Dromaeosaurids have ridiculously huge pubic bones, sticking way out beyond their legs...what muscles attached here? Or was it just covered in cartilage, serving as a "butt pad" for sitting? The pubis is so weird and projecting, I almost want to draw a diagonal line from its tip to the middle of the tail, giving Deinonychus a massive "Hadrosaur ass". This also begs the question of how Deinonychus and other dromaeosaurids held their bodies; could they have possibly had a more upright posture? Would their anatomy allow for it? So many questions...
Finally, the integument ("feathers", if you're nasty). I went conservative, giving it bald-eagle coloration, except for the head and neck area. Now, the bald eagle is an aerial hunter, and a piscivorian to boot; what would be the coloration of a ground-hunting, hypercarnivorous bird? Seriemas (which incidentally also have sickle-claws) have banded feathers on their underside and brown on top; Solitaires have blue-gray plumage with black accent feathers and bright red skin around the eyes. Roadrunners are a little more camouflaged, with mottled brown coloration. But none of these birds hunt prey larger than themselves, probably nothing bigger than a small rabbit. Would Deinonychus have taken after large-prey predators in its coloration? Wolflike grays? Leopard spots? Tiger stripes? Until we find feather impressions for these creatures, we just won't know. I'm banking on conservative colors with accents of white or black. I added an eyespot to its tailfan as well, since such a large organ as a dinosaur's tail must have been involved in signaling of some kind.
Do I owe Luis V. Rey an apology for calling his Deinonychus depiction "dumb"? Well...sort of. From the standpoint of how Deinonychus probably looked - at least in my current understanding, based on Duane Nash's ideas - Mr. Rey's depiction was correct. But this was not due to scientific rigor on his part: in his own words, "I depicted them with bald heads and looking like condors or vultures… why not?" I group Mr. Rey more in the category of "sensationalist" paleoart, and I feel like his depictions of dinosaur life and times, while flashy in the externals, are ultimately safe and run-of-the-mill. These commonplace, imagination-lacking scenes, repeated over and over, are exactly what I'm trying to get away from in my work.
PART II: My struggles with Deinonychus
Two Extremes
What's frustrating to me is, there's a weird "either-or" stance regarding Dromaeosaurid pack hunting, based completely on modern zöo-social archetypes and cultural assumptions, that amount to a failure of the imagination. We've assumed for so long that 'Raptors were hyperintelligent, hyperkinetic packhunters, we never really gave much thought to where the notion came from. Jurassic Park certainly popularized and, in a sense, codified the popular understanding about these animals. Then studies came out questioning the original assumption, and by the time of Fowler, et al., the pendulum swung in the complete opposite direction: Dromaeosaurids weren't very fast or intelligent, only circumstantially fed in groups, and in fact used their feet like hawks to squeeze small prey to death - the sickle claw was merely circumstantial. This was further justified by the assertion that no extant birds or reptiles hunt cooperatively (Eee...errr...ummm...yikes, let's unpack that later), and only mammals form actual cooperative packs in the modern biosphere (I'll give them that). Naturally this caused a sensation, and pretty much every hip young paleoartist jumped on the bandwagon, assuming it was the cutting edge of science. There's a lot of cultural and scientific baggage all knotted up here, and it's difficult to tease out where one thread begins and the next one ends. In fact, the more you look at it, the murkier the issue becomes.
In order to unravel this Gordian knot, let's start at the beginning.
Deinonychus was initially discovered in 1931, near Billings, Montana, by Barnum Brown - yes, he of Tyrannosaurus rex fame - and while the fossil was fairly complete, he didn't really have the antennae to register what he'd found. The focus on that time was on the big stuff - the diplodocids and Tyrannosaurs coming out of Western North American bone beds - and so the preparation of his Deinonychus (then called "Daptosaurus agilis") was begun, but never completed. It would be 33 years before more remains of the dromaeosaurid were found, when John Ostrom's expedition in the nearby Bridger, Montana unearthed the fragmentary remains of Deinonychus along with a 1-4 ton iguanadontid herbivore, Tenontosaurus. Similar fossilized scenes were discovered later in the Antlers Formation of Oklahoma. When the various remains of Deinonychus from different specimen beds were finally collated and described, it became apparent that this was a small, lithe predatory dinosaur, associated in groups with Tenontosaurus.
From Wikipedia:
Deinonychus teeth found in association with fossils of the ornithopod dinosaur Tenontosaurus are quite common in the Cloverly Formation. Two quarries have been discovered that preserve fairly complete Deinonychus fossils near Tenontosaurus fossils. The first, the Yale quarry in the Cloverly of Montana, includes numerous teeth, four adult Deinonychus and one juvenile Deinonychus. The association of this number of Deinonychus skeletons in a single quarry suggests that Deinonychus may have fed on that animal, and perhaps hunted it. Ostrom and Maxwell have even used this information to speculate that Deinonychus might have lived and hunted in packs.[39] The second such quarry is from the Antlers Formation of Oklahoma. The site contains six partial skeletons of Tenontosaurus of various sizes, along with one partial skeleton and many teeth of Deinonychus. One tenontosaur humerus even bears what might be Deinonychus tooth marks. Brinkman et al. (1998) point out that Deinonychus had an adult mass of 70–100 kilograms, whereas adult tenontosaurs were 1–4 metric tons. A solitary Deinonychus could not kill an adult tenontosaur, suggesting that pack hunting is possible.[12]
So already we have two major assumptions being made: 1) the Deinonychus in the area killed the associated Tenontosaurus, and 2) the Deinonychus were working together. This is not a huge stretch of the imagination: if you find the fossils of several lions around a cape buffalo skeleton, it's safe to assume they weren't all sitting down to tea together...but then we know how lions hunt. Dromaeosaurs, despite our assumed familiarity with them, are still patently mysterious creatures. We have a notion about how they killed - that huge claw is a pretty good clue - but any other evidence for their hunting behavior is extremely ambiguous. Even the famous "Fighting Dinosaurs" of Mongolia, a Velociraptor mongoliensis grappling with a Protoceratops, isn't "smoking gun" evidence that Velociraptor preyed upon this small ceratopsian - all it indicates is that the two were fighting (to the death!) for some reason when they were buried by a sand dune. With only a single small predator and a rather heftier herbivore, we don't know if the Velociraptor had help, or even who the primary aggressor was...for all we know, the Raptor may have been defending its nest from the Proto! Far-fetched, maybe (or maybe Protos were opportunistic omnivores like pigs, who the hell knows), but even this scenario illustrates how little we understand Dromaeosaurs and how they interacted with their prey. (Update - check out another piece of Velociraptor/Protoceratops interaction here).
We also have to unpack the cultural and scientific baggage surrounding dinosaur science at the time, in order to understand exactly why Ostrom et al came to these conclusions. Before the discovery of Deinonychus, it was pretty much assumed that dinosaurs were slow, cold-blooded brutes*, and even the smaller species were akin to two-legged lizards. I think the implications of a fast, warm-blooded dinosaur sent Ostrom reeling a little; in his giddy state he started making associations beyond what the evidence was actually showing. Group behavior associated with a carcass suddenly turned into group hunting, group hunting jumped to pack hunting, because what is the best-known pack hunter? Why the wolf, of course...! The lithe, lean mammalian killing machine, punching far above its weight, was the perfect analogue for this lithe, lean reptilian hunter. Pack hunting implied a high level of intelligence - never mind that a complete braincase of Deinonychus had not been found at that point. In essence, I believe, Ostrom was so overawed by the contrast between the tail-dragging lizards of yore and his new, tail-balancing little hunter that he overstated his case.
The discovery of Deinonychus kicked off what has been termed the "Dinosaur Renaissance" (or "First Dinosaur Renaissance", I think we're in the Second one...) Finding its articulation in Robert Bakker's The Dinosaur Heresies and Gregory S. Paul's Predatory Dinosaurs of the World, DR1 completely overturned the old order of things. The dinosaur-bird link was revived; fast, speedy, warm-blooded dinosaurs became the norm (often with crazy coloration to boot); soft fleshy bits were trimmed away until even T. rex became a shrinkwrapped, slimline Ferrari, capable of sprinting at 45 miles per hour. Pretty much all herbivores became herd animals, and pack life was extended to nearly every genus of carnivore, large and small. Feathers first started to make a tentative appearance on Dromaeosaurids, although the first feather impressions weren't discovered until 1996. The publication of the book and movie Jurassic Park, in 1989 and 1993 respectively, brought the Dinosaur Renaissance bursting into the popular imagination...bringing a whole host of problematic 'Raptor mythology along with it.
Now we're in the Second Dinosaur Renaissance (DR2), in which the conclusions of the first have come up for revision...and nothing is sacred. The bugbear of this new movement in dino-studies is definitely the Jurassic Park/World franchise: the Sins of the Fathers set up for ridicule and symbolic flogging. Once again we have rather extreme measures being taken to ensure a split from the past: Everybody gets feathers! Dinosaurs were terrible parents! Tyrannosaurs didn't have lips! And most importantly, Dromaeosaurs were nothing more than ground-living hawks, preying on small game and squabbling over carcasses! Legitimate research gets mixed in with dubious conclusions based on bad premises, and we're just now realizing how often science is stymied by the peer-review process, sensationalist journalism, and rather stagnant notions of ancient ecology and behavior. As above, so below: paleontology is facing a similar crisis to the general culture in terms of entrenched notions, misinformation, and uncertainty in constantly-shifting ground.
You can see from the history of Deinonychus that it's the most radical theories about these animals that gains the most traction in the popular (and popular-scientific) imagination. It's a rather unfortunate truth that, in many cases, the Fowler theory of Raptor Prey Restraint will be considered the most "cutting-edge science" simply because it is the most well-articulated: expect museums to start changing their Deinonychus displays completely over the next ten years, despite what real cutting-edge studies might say. There's always a lag in scientific understanding between paleontologists and the public. Drop an asteroid in middle of the Pacific Ocean, and hundred-foot tidal waves will hit the Pacific Rim coastlines repeatedly for days - even after the impact site has been swallowed up by calm seas: this rather tortured metaphor is about the size of the Fowler study. However much their claims might be refuted, the damage has already been done.
An Alternative Approach; or, Duane Nash to the Rescue.
I've been rather slavishly intoning "Antediluvian Salad" and "Duane Nash" like some kind of starry-eyed paleo-cultist recently, but I can't overstate how much this man's ideas about dinosaur appearance, behavior, and ecology need to be disseminated. I'd go so far as to call his radical reinterpretations "Dinosaur Renaissance 3", or at least "DR2.5".
He posits that theropod dinosaurs acted much like Old World vultures when approaching their prey.** Vultures descend upon carcasses a mob, with a head-oriented feeding style and a strict pecking order that results in much quarreling and face-biting between individuals. What may look like barbaric, desperate jostling for food is often more about establishing dominance; some vultures seem almost to neglect the carcass in order to go after lower-ranked vultures who get too uppity. The question of, "Did theropods hunt in groups?" is therefore sort of moot, because they went after their prey in gangs, with the largest and toughest individuals doing the grunt work while the smaller individuals predated the victim while it was still alive (vultures will do this too - they're opportunistic predators as well as scavengers, with young or sick livestock being especially vulnerable). Now, were these "packs" by any sense of the term? This is doubtful. The individuals in the mob would not be purposely related to one another. A proper pack is, after all, a family group. Theropod family units probably hunted together, but mostly as a means of feeding and training their young; when going after large prey, it was mostly an opportunistic, numbers-dependent game.
In Which I Attempt to Formulate My Own View of Deinonychus
My first proposition is that, no matter what the Morrison Formation and Antler Creek Formation remains actually preserved, we can infer there was at least some kind of relationship between Deinonychus and Tenontosaurus: was it predator-prey? Scavenger-carcass? Mutually antagonistic? The answer hinges upon three details: 1) How common were both species? 2) What was the full range of predators in these areas at this time? 3) What other specimens are available of both animals, and what do they show?
In order to understand Deinonychus and its ecosystem, we must first look at the much more abundant Tenontosaurus. Understanding how often Deinonychus and Tenontosaurus appear together will give us clues as to their relationship. Apparently the two most "important" specimens, found by John Osborne, are fairly typical of Deinonychus remains.
From Wikipedia:
Teeth and a number of skeletons belonging to the bird-like carnivorous theropod Deinonychus have often been discovered associated with Tenontosaurus tilletti remains. Tenontosaurus specimens have been found at over 50 sites, and 14 of those also contain Deinonychus remains. According to one 1995 study, only six sites containing Deinonychus fossils contain no trace of Tenontosaurus, and Deinonychus remains are only rarely found associated with other potential prey, like Sauropelta.[5] In all, 20% of Tenontosaurus fossils are found in close proximity to Deinonychus, and several scientists have suggested that this implies Deinonychus was the major predator of Tenontosaurus. Adult Deinonychus, however, were much smaller than adult Tenontosaurus, and it is unlikely a single Deinonychus would have been capable of attacking a fully grown Tenontosaurus. While some scientists have suggested that Deinonychus must therefore have been a pack hunter, this view has been challenged based on both lack of evidence for coordinated hunting (rather than mobbing behavior as in most modern birds and reptiles) as well as evidence that Deinonychus may have been cannibalizing each other, as well as the Tenontosaurus, in a feeding frenzy.[6] It is likely that Deinonychus favored juvenile Tenontosaurus, and that when Tenontosaurus reached a certain size, it passed out of range as a food source for the small theropods, though they may have scavenged larger individuals. The fact that most Tenontosaurus remains found with Deinonychus are half-grown individuals supports this view.[3][7] It also lived in the same area as the large carnivorous dinosaur Acrocanthosaurus.[8]
We have clues here that point to an important relationship between Deinonychus and Tenontosaurus, whatever that may be. The fact that the associated Tenontosaurus were consistently juveniles, in my mind, points to a predatory relationship: if the "next size up" of predators in the Antler Creek formation was the formidable Acrocanthosaurus, it begs the question of why such a large predator would be killing juvenile Tenontosaurus and leaving a large portion of the carcass, especially the fatty tail. One could posit that young Acros (as we know juveniles of large predators filled their own predatory niches) were doing the killing, at least at Antler Creek Formation in Oklahoma, but as far as we know this is the northern range of such sauropod-killers; what was doing the killing up in Montana?
It's important to make an aside here, and explain what exactly was going on during the Cretaceous in North America. This last and longest period in the Mesozoic Era - the so-called "Age of Dinosaurs" - is not as homogeneous as the public often presumes. For instance, Deinonychus would never have seen a Tyrannosaurus rex - even its later, larger cousin Utahraptor was probably long gone by the time the Tyrant Lizards arrived from Asia. Nor was North America the "typical" dinosaur spread we imagine it to be; in fact, certain parts of Western NA were cut off from the rest of the world for several million years, resulting in a flourishing of Hadrosaurids and Ceratopsians, for instance, and a dearth of sauropod Titanosaurs. For much of the Cretaceous, the entire continent from Texas to the Northwest Territories was split by the Western Interior Seaway; this enormous bodies of water would have split our beloved North America into at least two "continents", with the westernmost strip eventually connecting to Asia in the north and ending abruptly in southern Mexico in the south. In the Aptian and Albian ages of the Early Cretaceous, when Deinonychus and Tenontosaurus were exploring the intricacies of their relationship, the arid climate of the Jurassic/Cretaceous "Tithonian Event" that wiped out much of the diplodocid sauropods was just becoming hotter and wetter, resulting in a more jungly, subtropical environment. From what we can see, Tenontosaurus had arrived in the area during the bad times, and adapted well to the change in climate. It is during this humidifying period that Deinonychus appears in the fossil record.
Here's the important part: there were no Tyrannosaurids in the area as of yet. The same geographic location hosted several dromaeosaurids, associated with the earlier Barremian age, which included the now famous giant Raptor Utahraptor. Because the Beringian land bridge was open at the end of the Jurassic, then closed in the Early Cretaceous, then opened again in the Late Cretaceous, it is safe to assume that dromaeosaurids pulsed in from Asia, following waves of Iguanadontids and Ceratopsians, then were trapped in Western NA when the land bridge closed. Meanwhile, Tyrannosaurids evolved into larger, more powerful predators in Asia, and when the land bridge opened again, they flushed into North America and became the dominant superpredator. Could the influx of tyrannosaurids have spelled doom for the dromaeosaurids?
(I'm actually becoming really intrigued by this whole "dinosaur interchange" thing...there's a lot of unanswered questions. Expect another blog post dealing with this in the future!)
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| Late Cretaceous North America (c) 1993 National Geographic Society...a classic! |
Since there's not a lot of hard evidence for Deinonychus predatory activity to go on, we'll have to use the old noggin and make several deductions:
1) Since there were few larger predators (except other dromaeosaurids, and the unlikely Acrocanthosaurus) to kill the associated Tenontosaurus, it is safe to conclude that, at least in some capacity, Deinonychus would predate juvenile Tenontosaurus.
2) If many Deinonychus are found around a Tenontosaurus carcass, and it is unlikely that one-on-one combat would turn out well for the predator, we can safely assume that several Deinonychus were involved in the kill.
3) If Deinonychus are rarely found without Tenontosaurus, we can also make the assumption that Tenontosaurus was a major prey animal for Deinonychus in both Montana and Oklahoma.
Therefore, from the evidence, I believe it is possible to conclude that groups of Deinonychus preyed regularly on Tenontosaurus.
I'm going to add some more evidence here: multiple Deinonychus skeletons have also been found in association with Sauropelta, an Ankylosaurid-like armored dinosaur. Furthermore, a Utahraptor predator trap has been discovered with several individuals of different ages predating an iguanadontid; whether this is direct evidence of group hunting, or if the individuals happened upon the carcasses of both predators and prey and became trapped themselves (a la the La Brea Tar Pits) is unknown, but it should be considered as a possibility when taken with the Deinonychus evidence. Added to this is the rightly famous but perhaps ambiguous "Fighting Dinosaurs" of the Gobi. Taken alone, each of these specimens tells us little about the predatory habits of dromaeosaurids; but when taken as a whole, the act of group-hunting becomes more plausible.
But is it pack hunting? Group hunting itself is, disappointingly, about as common as dirt. Lone-hunting predators are a quirk of the Quaternary; I'd argue that humans - the ultimate packhunters - killed off the majority of group-hunting predators, leaving canids and lions as the exceptions. It stands to reason that, in the absence of catastrophic interference from humans, even megapredators would gang up to increase their chances of hunting. We've found piles of Tyrannosaurid and Carcharodontosaurid bones of various ages all jumbled together, even in the absence of prey items; it's no stretch of the imagination to see at least the younger, spry-er juveniles forming gangs to hunt baby sauropods or Ceratopsians or Hadrosaurs. Crocodilians and Komodo dragons - hell, even turtles - will gang up and kill animals - and corvids and vulturines are notorious for their mobbing behavior.
But in terms of highly-coordinated assaults, the occurrence is far less frequent in the animal world. Canines, lions, whales, and hominids are pretty much the exception. Harris hawks and Aplomado falcons are known to coordinate in small family groups, with the latter assigning roles based on gender. While I won't rule out some level of coordination - especially from the large-brained Troodon - wolflike packhunting behavior among dinosaurs just wasn't that likely. I have to reluctantly agree. Especially since what first appears to be evidence for pack behavior in Deinonychus may actually be evidence against it.
You see, a true pack is known for its ability to quickly and efficiently hunt and kill a large prey animal with few casualties. Naturally deaths do occur, especially when dealing with dangerous prey, but usually the wounded will be nursed by the group and eventually recover. This is because a pack views each member as vital to the group. Food is apportioned according to rank, and while there is plenty of snarling around the carcass, the end result is that the whole pack is fed, with enough food to bring back to the offspring in the den.
So this begs the question with regards to the Deinonychus/Tenontosaurus remains: why the hell are there so many dead Deinonychus? If these predators were "frozen" in the act of a coordinated assault, we would see their articulated skeletons grappling with an articulated Tenontosaurus, as we do with the "Fighting Dinosaurs". Instead we see a jumble of bones of both species, sometimes interspersed or widely flung all over. The most abundant fossil in these specimens are Deinonychus teeth. This phenomenon is the rule, rather than the exception. When we see jumbled and spread-out skeletons like this, it's safe to conclude - from what we know of modern carcass sites - that the animals died in the open, and their skeletons were scattered by scavengers and the elements before being covered in mud and allowed to fossilize. Tenontosaurus was not a formidable opponent, especially when juvenile; barring some secret superpower - a venemous thumbspike? Fire breath? Eye-lasers? - such prey items could not be responsible for the level predator casualties seen at these sites.
The reluctant conclusion is that the Deinonychus killed one another. The number of teeth found scattered everywhere indicates that a lot more than feeding was going on; were they actively fighting one another over the carcass? If Darren Nash's vulture comparison is correct, we can infer that a vast number of Deinonychus - perhaps up to thirty individuals - descended upon the Tenontosaurus at once and tore it limb-from-limb; in the feeding frenzy, several Deinonychus were killed and eaten as well.
It's a pretty bad scene when you think about it:
Li'l Tonto the Tenontosaurus toddled along behind its family group, munching on lush foliage at the edge of a stream. The morning air was cool and steamy, and the insects were just beginning their sleepy chorus. The group was on edge, its older and wiser members feeling something wrong with the surrounding jungle; but Li'l Tonto was quite young and inexperienced, and so didn't register the lack of smaller dinosaurs feeding at the windfall of Gingko fruit, or the strange silence of the birds. Preoccupied with feeding, Li'l Tonto didn't notice that his relatives had moved off suddenly at a brisk pace, melting into the foliage of the surrounding woodland. Li'l Tonto's chewing is loud in the silence.
Then - branches snapping. A mob of Deinonychus poured in from all sides, some gliding down out of the trees, converging on the startled Tenontosaurus in seconds. Li'l Tonto squealed and bucked and slashed with his small thumb-claws, but the sheer weight of snapping Deinonychus pulled him to the ground. He feels the dull pain of their jaws stripping flesh from his hindquarters and digging into his underbelly, but shock is already setting in, and his whole body grows cold and numb. The Deinonychus near its neck region, probably the largest and toughest of the bunch, grapple him with their foreclaws and jaws, while their sickle-claws puncture his hide and begin to probe beneath his skin in quick stabbing motions, ripping open arteries and windpipe. Li'l Tonto goes down, whistling through his punctured trachea, fountains of blood squirting out of his perforated neck. His tail and thighs are already stripped to the bone before he hits the ground, and he disappears beneath a carpet of feathered backs and waving tails.
His death is only the beginning of what is turning into a feeding frenzy. The mob is nothing more than a dry-season hunting collective; they owe each other no loyalty. Snapping and clawing, shoving and screeching, the Deinonychus are keen to maintain a pecking order. They break from feeding to latch onto each others' loose face-flesh, ripping gashes and losing teeth in the process. As the meat diminishes the fighting becomes more desperate, not less; two or three will square off and tumble away from the carcass, snapping and growling; they latch with their forelimbs and mouths and kick one another like fighting cats. Their underbellies are thickened for this purpose, but with such powerful killing weapons, some are mortally wounded. The squirting blood attracts a detachment from the main mob, who rip apart their co-predators with as much enthusiasm as they destroyed Li'l Tonto.
At some point the flurry of activity begins to ebb. The larger Deinonychus, having taken the choice bits, have since stalked off to the bush to digest; the remaining group waddles away, until only the scrawniest Raptors are left to gnaw the bones. They've effectively skeletonized Li'l Tonto and the dead Deinonychus. They worked too fast for any larger predators to disrupt their feast, and with their cannibalistic tendencies, no smaller predators or even birds will attempt to feed until the last Deinonychus is sated.
This is dry-season behavior; in the good times, Deinonychus is a good parent, brooding its eggs, hunting small prey, and generally keeping to its family group. But as soon as the rains stop, Deinonychus begins whetting its claws, ready for the orgy of blood soon to follow.
In conclusion, I may owe Luis V. Rey an apology...but only for trashing his wattle-headed Deinonychus idea. I don't think he really thought it out, other than in a "why not?" sort of way. However, it just goes to show you how our ideas about dinosaurs can change if we let them, and how ultimately weird and fantastic these ancient creatures may turn out to be.
Rick Out.
*I need to check up on the accuracy of this statement. It's an oft-repeated trope - sort of like saying, "Victorians hated sex" - and needs more investigation and nuance than people are generally willing to apply. Every paleontological generation is convinced that the previous one is full of shit (coprolites, if you will) and are furthermore as dumb as the rocks they pick at. If you need any convincing that previous depictions of dinosaurs and ancient creatures weren't as idiotic or bereft of science as we assume they were, check out this book. Charles Knights' indescribably beautiful, breathtaking scenes alone - as inaccurate as we now know them to be - blow every modern paleoartist's work out of the water.
**Quick side-note about vultures: There are two types: Old-World Vultures, and New-World Vultures. Old-World Vultures are carrion-fowl, true, but their meals usually aren't that dead - that is, they are just as likely to gang up and steal a kill as they are to seek out something already dead. And they have been known to kill things. Vultures in India face immense persecution (and possible extinction) due to their calf- and lamb-killing habits. NWV's, on the other hand, tend not to be so pushy, although the bigger Condors have been known to throw their weight around.
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