T. rex Down!

It can be worthwhile revisiting what perhaps have become rather over-familiar scenes portraying dinosaur life. One of these is the much-pictured confrontation between a Tyrannosaurus rex and the armoured ankylosaur Euoplocephalus (my painting below).

Just how likely would such an encounter have been? And if so, then what would have been the probable outcome? If we place the two dinosaurs alongside each other (my painting below, with the skeletons giving a human scale), then one thing is clear straight away: Euoplocephalus, the largest of all the ankylosaurs, had at least as much body mass as the formidable predator. And it certainly was armoured - it even had a small bony plate covering its eyelid. In addition to the various spikes and plates, its most obvious weapon of defence was the bony 'club' at the end of its tail. This club (actually modified tail vertebrae) was not solid, but was honeycombed with spongy air pockets, making it in life both comparatively light and extremely strong and resilient, with the honeycombed bone acting as a shock absorber. That the fossilized tail club is so massively heavy is simply due to this honeycomb of air cells becoming filled with solid mineral deposits.

So how would a T. rex have tackled such an animal? *Studies have shown that the jaws of a T. rex could close with a staggering 2,900 pounds of bite force per side of the jaw: the most powerful bite of any animal ever known. This is certainly powerful enough to crunch straight through solid bone - and if a few teeth were broken in the process, then they were simply replaced, as was normal throughout a theropod's life. To put a Euoplocephalus on the menu, an experienced T. rex probably would go for the vulnerable neck or legs of the animal, or even *gulp* bite straight through the damage-dealing tail. But just how vulnerable was the T. rex itself?

The old-style reconstructions of tyrannosaurs portrayed them with legs as sturdy as tree trunks (by Charles R. Knight, above, painted almost a century ago), but we now know that T. rex would have had a 'chicken drumstick' leg, with hefty calf muscles, but with the ankle being little more than skin and sinew over bone. A well-timed blow from a tail club to a T. rex ankle surely would have done serious damage, injuring or even crippling the animal if wrong-footed. And a T. rex that went down after such a blow, even when its injury was not immediately fatal, might not get back up again.

My preparatory sketch for the scene (above) includes three T. rex, with one down and two still on the attack. Even such a top-of-the-food-chain predator might have scored better with such odds. My more finished drawing (below, prior to scanning and digital painting) narrows the odds down to two to one. Pathologies on the fossil of 'Sue', the largest T. rex known, suggest several partially-healed injuries, although at least some of these could be due to *parasitic infections.

So in the end, what would have been the outcome of such an encounter? As with animals today, it probably would have been down to the individual dinosaurs involved. A mature ankylosaur certainly might have downed a younger T. rex lacking the experience to know how well-enough to avoid a crippling blow. And a mature T. rex would have been on the lookout for easy-to-take-down young or sick prey. And as with anything else, that chance factor - a randomly-struck but lucky blow, a sudden well-aimed bite - could have drawn the line between living and dying.

Hawkwood 

*Breathing Life into Tyrannosaurus rex, by Gregory M. Erickson. Scientific American, Sept. 1999. *Paleontologists Assess T. rex Sue's Pathologies, by Kate Wong. Scientific American, Oct. 2001.

The Stones on Tour

It must have been one of the most dinosaur-intense environments in the world. During the last several million years of the Cretaceous, a shallow sea divided the eastern and western sides of the North American continent, with the western side stretching from the ice-free North Pole - then centered on land that is now northwest Alaska - all the way down to present-day Central America.

 

On the eastern side, Quebec's Manicouagan impact crater and the Appalachian mountain chain were already-ancient features of the

Cretaceous landscape. On the western side lived all the dinosaurs that have come to embody what the term 'dinosaur' represents to us: predatory tyrannosaurs, ceratopsians such as Triceratops, long-necked titanosaurs, and tank-like armoured ankylosaurs. In the wide skies above the flat Texas floodplain cruised the giant pterosaur Quetzalcoatlus (above), as large as a light aircraft. And in the shadows of volcanoes south of the present Canada-United States border, huge herds of hadrosaurs were on the move as they migrated to fresh grazing. With the discovery of the remains of a herd of the hadrosaur Maiasaurus estimated at a staggering 135 thousand individuals - apparently overcome by volcanic ash - we know that such migrations must have taken place: such herds would have been too large for a single location to have sustained them.

The waters of the central sea, known as the Western Interior Seaway or the Cretaceous Interior Seaway (my map, above), were home to marine reptiles as well-known to us now as the dinosaurs in the land to the west. Predatory mosasaurs, the giant turtle Archelon, with a shell as large as a Humvee, long-necked plesiosaurs - and the even-longer-necked Elasmosaurus. The teeth of Elasmosaurus (the skull, below) were well-adapted to grasping fish, and its meal certainly had a way to travel along the length of the neck before it reached the animal's gut. Now, there is more to tell about the gut of the elasmosaur, but first this:

An animal's fossil can teach us much, but it might not necessarily have a lot to offer when it comes to learning about that animal's social behavior. For this, analogs can be used. That is: the behavior of an extinct species can be inferred by comparing it with the behavior of a living animal with a similar morphology, or body shape. It was while watching a wildlife documentary of two snakes neck-wrestling that I thought of the snake-like necks of elasmosaurs, and later made a sketch (below) to illustrate the idea. We know from its neck vertebrae that an elasmosaur had more flexibility laterally than dorsally. That is: it could wave its neck from side to side more readily that it could up and down. So the two animals in my picture would have had to have been almost 'standing' in the water - an extra factor in such a trial of strength.

So would rival elasmosaurs, perhaps struggling for the right to mate with a female, really have fought in this way? As with any analog behavior, it can neither be proven nor disproven. But to me it does seem both reasonable and likely. The writhing serpentine necks weaving around each other among the white crests of the waves: this was the image in my mind as I began to draw. Strange creatures of another time and another place, like Moby Dick escorted by a cloud of white sea birds. Except in this case, the 'sea birds' are circling pterosaurs (Pterandon) excited by the struggle, as other animals often are in such situations.

Intriguingly, I came across in a *book the information that elasmosaurs apparently swam through present Kansas, Nebraska and the Dakotas to reach estuaries on the northeastern and northwestern coasts (the map detail, above). There they would swim upriver as much as 100 km (over 62 miles) away from the Seaway. But what drove them to do so? The question gnawed at me for a while. Then I remembered that elasmosaurs are associated with finds of gastroliths: stones which an animal swallows to aid digestion, using the stones like millstones to grind up hard-to-digest material before it passed to the animal's gut. Perhaps in the case of aquatic elasmosaurs these gastroliths served the important dual function of ballast to stabilise the animal's bouyancy.

All gastroliths wear down with use and need to be replaced. Were the reaches of these Cretaceous rivers the ideal source for these stones, pre-smoothed in the tumbling river waters, and lying on the riverbed for the taking? An elasmosaur *excavated in Kansas revealed gastroliths (above) whose source appears to have been these northern rivers. The river journeys of these animals clearly had a purpose, and that purpose would seem to have been to collect stones suitable for use as gastroliths. Stones from northern rivers found in the stomach region of an aquatic fossil reptile in Kansas can tell us much, both about the environment in which that animal lived, and about how that animal used the resources of that environment for its needs.

Hawkwood 

*An Odyssey in Time: The Dinosaurs of North America, by Dale A. Russell. The University of Toronto Press, 1989. *Cicimurri, D. J. and M. J. Everhart, 2001.

An elasmosaur with stomach contents and gastroliths from the Pierre Shale (late Cretaceous) of Kansas. Kansas Acad. Sci. Trans 104(3-4):129-143.

Gastroliths photograph from the Oceans of Kansas website (link on my sidebar). All other images © Hawkwood. The map of Cretaceous North America has been compiled from material drawn by Ron Blakey and Christopher R. Scotese, and from data by Dale A. Russell. Any misinterpretations of the data from these authors are entirely my own! The superimposed outline of contemporary North America is from D-Maps.

Hoots, Honks and Bellows

Some eight years ago I remember writing that, although the colors given to dinosaurs in artists' reconstructions are conjectural, it could only be a matter of time before some new imaging technology might provide us with real evidence of actual colors in their fossils. Well, last month's issue of *Nature contained news of exactly that. The discovery of cells known as melanosomes in the preserved fossil feathers of the dinosaur Sinosauropteryx indicated that the tail of this animal was a lemur-like striped russet brown. Although the colors themselves were not preserved in the fossil, the distinctive different shapes of the cells acted as a code that allowed each color to be determined. This is the first time ever that colors have been described in a dinosaur fossil, and of course it created much stir. But.. this particular fossil was in an exceptional state of preservation. We are still a long way from knowing - if indeed we ever will - just how colorful (or not) T. rex actually was. So the reality is that I find that my own stance as a reconstructional artist has not greatly changed.

Take a group of dinosaurs - the hadrosaurs - about which, thanks to partially mummified fossil specimens, we know a remarkable amount. Herbivorous hadrosaurs (sometimes informally known as 'duck-billed' dinosaurs) were extremely successful, ranging in the last few million years of the Cretaceous over several continents (the Parasaurolophus herd, above). Their crests contained a complex system of air passages that would have led between the nostrils and the lungs (the Lambeosaurus skull section, below), and they would have been capable of producing a variety of hoots, honks and bellows to fill the mists of a Mesozoic morning. Think of the passage through which a player must blow from lungs to mouthpiece through to the bell of an instrument such as a trombone or a french horn, and you have an analogy for a hadrosaur orchestra.

Hadrosaurs could also be large animals (my comparative skeletons of human and Lambeosaurus, below), and when we consider that fossil finds suggest evidence in some species of herd behaviour, plus the vocalizing abilities of these dinosaurs, then the picture emerges of animals with a reasonable degree of social interaction - and pehaps even complex social behaviour. But did color also play a role in this? We do not know, but it seems reasonable to assume that it did so. Snakes and birds have color vision. Mammals do not. Dinosaurs were certainly closer to reptiles than to mammals, and birds are the living equivalents of raptorial dinosaurs. Perhaps, in addition to vocalizing, the crests of hadrosaurs were used to send recognition signals of distinctive patterns and colors to others of their kind.

Such were my thoughts when I came to create my own 'portraits' of six hadrosaurs. With two of these (Anatotitan and Kritosaurus), it was an inflatable sac of skin rather than a crest which formed the vocalizing function, and the crest of one (Saurolophus) seems to have had limited vocalizing range. But the remaining three (Lambeosaurus, Parasaurolophus and Corythosaurus) all had distinctively individual head crests. My usual technique is first to make a detailed drawing in pencil (below), and to include in the drawing enough detail which commits me to establishing any skin patterns, which - however accurately I can portray the rest of the anatomy - clearly are speculative.

This detailed pencil drawing I then scan in and paint with a variety of digital brushes (below). And although this is the stage of creating the artwork that makes these animals seem the most alive, it also is the stage during which the most conjecture is used. From a purely palaeontological perspective, the reconstruction has by now become too conjectural to be of real value. Now, I can keep the thing within reasonable limits of zoological credibility by having a look through, and taking my lead from, my studio reference library of reptile and bird photographs and applying various analogous patterns, colors and textures.

Poring over such reference material - and studying the real thing in zoos and natural history museums - is a way of understanding generally the form and appearance of such skin markings in nature. Now, to build up the life appearance of a Lambeosaurus using the fossil skull as a basis on which to construct muscle and skin tissue: that's science. But to make you believe that a Lambeosaurus really did look the way in which I have portrayed it here, with patterns, colors, and all; that's where the art comes in!
Hawkwood


*Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds. Zhang, F., Kearns, S.L., Orr, P.J., Benton, M.J., Zhou, Z., Johnson, D., Xu, X. and Wang, X. Nature, advanced online publication, 27 January 2010.

Wings on its Fingers

It is of course an easy matter to get excited about the latest fossil find. A new species that supplies a previously-missing piece to the puzzle of where to fit what into the scheme of things deserves the attention that it receives in scientific circles and beyond. By way of contrast, other fossil specimens which might have been discovered decades ago, and which represent now-familiar fossil animals, perhaps run the risk of losing their edge through simple familiarity.

Recently I obtained (via the Internet, naturally!) a museum-quality cast of one of the best-known of all fossil pterosaur specimens (the original fossil, above, is here shown about life-size). This is the species Pterodactylus kochi, which was no larger than a common garden bird of today. The slender toothed skull is just 73mm (almost 3 inches) long, and in life the delicate animal would have had a wing span of some 40cm (16 inches). The fossil is one of the best-preserved of its kind; not only every bone can clearly be seen, but the fleshy outline of the animal, and even the indication of the wing membranes, have been preserved.

The extended fourth digit which formed the leading edge of the wing ('pterodactyl' means 'wing-finger') is perfectly articulated in the fossil, and even the sclerotic ring (the tiny circle of bony plates that supported the eyeball, below) is clearly visible. In life, the animal would have been covered with a thin layer of integuments similar to hairs in structure (my life reconstruction drawing, above), and the tiny teeth would have grasped and held insects on the wing.

Since dragonflies (below) have been found in the same fossil beds, it is reasonable to speculate that these would have been on the menu of this small pterodactyl. This pterosaur fossil comes from the famed deposits of Solnhofen limestone in Bavaria: the same fossil site where Archaeopteryx was discovered. Together with the small dinosaur Compsognathus and other species of pterosaurs, these creatures formed a community of Jurassic animals living in what was then an archipelago of islands lying in warm tropic seas.

It was among these islands that the pterosaur which my fossil cast portrays hunted and caught insects on the wing, living out its life until - for whatever reason - it died. The small body sank into the sheltered waters of a coastal lagoon, where, in the layer of oxygen-starved water lying in the deepest part of the lagoon, the body was hardly touched by the processes of decay - or by the actions of scavenging crustaceans - before being covered by silt. The covering of finely-compacted sediments provided further ideal conditions for fossilization to take place, and for the little pterosaur to begin its one hundred and fifty million year-long journey to our own time.

Hawkwood

Death in Montana

One of the most justly-famous fossil finds in dinosaur studies was the group unearthed in 1964 in Montana by the late Professor John Ostrom. The group consisted of the remains of the herbivore Tenontosaurus, together with between three to four individuals of a newly-discovered carnivorous dinosaur that was given the name of Deinonychus antirrhopus (literally: 'Terrible-claw/counterbalance'). What so excited the world of palaeontology was that the group appeared to show, not merely evidence of active predation, but a coordinated effort by predators to bring down a herbivore. In short: the Deinonychus were co-operating as a pack to hunt and kill the much larger Tenontosaurus.

Not surprisingly, this find was gratefully seized upon by palaeoartists as a worthy subject; not just because of its significance, but because of the possibilities which it offered for portraying some real down-and-dirty dinosaur action, while remaining faithful to the fossil material. When I came to produce my own version (above), I decided to use the tails of the animals as a compositional device to convey the drama of the kill. From their fossil remains, we know that Deinonychus had relatively inflexible tails, presumably to act as an effective counterbalancing rudder (hence 'antirrhopus') when running and turning. And for a herbivore of its type, Tenontosaurus had an unusually long tail.

My first rough pencil sketch (above) utilised these tails as a device for focusing the action towards the point of attack. This sort of worked, but with the predators coming from all sides, it did not completely convey the effect that I was after: that the Tenontosaurus was literally being knocked off balance by the ferocity of the attack. My second more detailed pencil drawing (below) placed the two Deinonychus at the hindquarters of their prey, which gave all four tails - both of predators and of prey - a uniform thrust, as if driven by an unstoppable force of fate. This seemed to work more effectively, and I scanned in the drawing and continued to work on it digitally, painting in the lighting effects and colors with digital brushes.

The deposits of the find indicate that the encounter took place on the bed of a dried-out river or delta, probably close enough to the undercut bank for the earth to have collapsed and hastened the animals' burial. I freely admit that using back-lit dust is a favorite device of mine for injecting atmosphere into such a scene, so this setting was from my point of view ideal. By altering the drawing so that the tenontosaur's forelegs were folded away out of balance, I now had the effect of it being knocked off its feet by the force of the Deinonychus impacting its body. The second Deinonychus was now also falling (the detail, below), and clearly in danger of having its skull crushed beneath its prey, which conveyed the idea that predators as well could be - and often are - the victims of their own attack. Active hunting can be a dangerous pursuit.

And so, in apparent faithfulness to the fossil material, I (and other paleoartists) dutifully portrayed one Tenontosaurus being attacked by three (or four) Deinonychus, with the clear implication that the raptors were coordinating their attack with each other. Thus portrayed (and whomever paints it), it has become one of the iconic images of paleo art; and the pack behaviour of raptors - and the implied intelligence required - was cheerfully made further use of in the Jurassic Park scripts. But is this really the way things were on that dusty Montana river bed some one hundred and thirteen million years ago? Even given the specifics of the fossil evidence, how can we be so sure?

It is both illuminating and rather sobering to look at Ostrom's original map of the site. This scattered tangle of fossil bones is what Ostrom actually had to work with. We know for certain that at least three Deinonychus and one Tenontosaurus died here. But that is all. There can be no way of knowing whether or not the raptors truly were acting co-operatively, or whether they were there just joining in an opportunistic meal when death, perhaps in the form of the collapsed river bank, overtook them. It is even possible, and has been *suggested, that a scavenging frenzy took place, in which other Deinonychus turned upon their own kind for a cannibalistic feast. But a truly coordinated pack attack, as practiced by wolves, wild dogs, and other such carnivorous mammals, is assumption.

And even if Deinonychus was intelligent as predatory dinosaurs go, this is still a long way from the intelligence and social interaction of mammals. And the fossils record only the dead. How many other animals were originally at the scene which simply lived and walked away? My painting depicts a lone tenontosaur, but there might have been several of these herbivores present, with only one falling victim, both to the raptors and to the processes of fossilization. Over the border in Wyoming another such site has been found. But this second site reveals the remains of no less than six tenontosaurs - and only one solitary Deinonychus. The scarily social and rationalising raptors of Jurassic Park were, after all, movie dinosaurs. Palaeontology must cope with situations which, as often as not, offer more than one viable scenario. 

Hawkwood 

 

Sources:

Ostrom, John H.: 'Osteology of Deinonychus antirrhopus, an unusual theropod dinosaur from the Lower Cretaceous of Montana'. New Haven: Peabody Museum of Natural History, Yale University, 1969. Series: Yale University. Peabody Museum of Natural History. Bulletin 30.

Parsons, William L., and Parsons, Kristen M.: 'Further descriptions of the osteology of Deinonychus antirrhopus (Saurischia, Theropoda)'. Bulletin of the Buffalo Society of Natural Sciences, Volume 38, 2009. 

*Roach, Brian T., and Brinkman, Daniel L.: 'A Reevaluation of Cooperative Pack Hunting and Gregariousness in Deinonychus antirrhopus and Other Nonavian Theropod Dinosaurs'. Bulletin of the Peabody Museum of Natural History 48(1):103–138, April 2007.

The Eye of a Raptor

This is the eye of a living raptor. But before anyone starts wondering whether some enterprising scientist has succeeded in turning a fictional Jurassic Park into reality, we need to define our terms. Raptors, as the word is understood and used in dictionary terms, are birds of prey. These can include the hawk whose eye is pictured here, as well as such birds as falcons, owls and eagles.

But since the release of the film Jurassic Park (below), the word raptor has become synonymous with a specific kind of dinosaur: middling-sized, it's true, but - at least as far as raptors are portrayed in Spielberg's films - ruthlessly predatory, alarmingly intelligent, and given to teaming up with others of their kind to hone their social hunting skills to a shocking efficiency.

And these dinosaur raptors had the armaments necessary to do this. The most obvious characteristic which such raptors had in common was the specialized second digit on their hind legs, which had evolved into a large killing claw (below). Raptors therefore used their third and fourth digits for walking and running, with the killing claw held upwards; it was simply too big to be functional for locomotion.

The word raptor comes from the Latin, meaning a ravisher or plunderer, and several dinosaurs carry the term in their name - Velociraptor, Utahraptor and Bambiraptor, to name just three (see the comparative sizes of *five of them, below) - although the name of one of the most typical 'raptors' of them all - Deinonychus - does not refer to the term.

Exactly how much we currently know and understand about these raptorial dinosaurs - and the other dinosaurs and animals which shared their world - is the subject of this weblog. Did raptors really hunt in packs, as portrayed in Spielberg's films? How can we know one way or the other? Indeed, were the 'velociraptors' in Jurassic Park really velociraptors at all? I have drawn and painted many life reconstructions of dinosaurs and other Mesozoic fauna, both professionally and for my own pleasure, and will be using these and related material to illustrate this weblog. And if a little philosophy creeps in along the way, well; what could be more viscerally existential than the thought of a real raptor chomping at your heels?

Hawkwood

*From left to right: Bambiraptor, Velociraptor, Deinonychus, Utahraptor, Megaraptor

Patience please!

The raptors are currently being fed. As soon as they are through with their meal, they will appear on this weblog, and those patient readers with a stout heart and a steady nerve are welcome to check back later to meet them.