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Wednesday, August 14, 2013

How Do Creationists Know What Dinosaurs Looked Like?

While watching a video of the Creationist Museum in Kentucky, with its impressively-detailed animatronic full-scale dinosaur models, I was struck by the thought: how do creationists know what dinosaurs looked like? I mean: there are these moving, snarling model dinosaurs in an institution which has elevated pseudoscience to the dubious level of a theme park attraction, and whose staff (at least, in the various interviews which I have seen them give) appear to have a near-pathological disdain for the scientific method. So how do creationists know what dinosaurs looked like?

Using a line grid to map a fossil site at the Bay of Fundy, Canada
Time on a museum field trip is a precious commodity. It has to be exploited to the maximum, and working hours need to be methodical and calculated. I recall on one field trip getting up at five in the morning, every morning. And weekends simply passed unnoticed. A field trip can by turns be fun, exciting, and tedious – but it is still hard work. How many excursions into the field did it take, over succeeding decades of time, and spanning many, many individual careers, for palaeontologists to reconstruct the dinosaurs’ world? And where did those scientists go to? From the Montana Badlands to arid Outer Mongolia, from Patagonia to Alaska’s North Slope, the destinations of such field trips usually demand  lobbying for the necessary funding, and in the cases involving some far-flung destination, as often as not some deft bureaucratic navigation through the acquiring of visas, permits, and other assorted red tape.

Freeing a fossil from its rock matrix
Safely back on base, the conservation work begins: the painstaking release from its matrix, with small hand-held power drill and sable brush, of some fragile fossil, perhaps over a series of weeks or even months, and the publishing of any findings, as well as the report to the board of the museum in question to justify the funds which have been sunk into both the field work and the subsequent in-museum research and restoration time. More often than not, a fossil will not be found in any great degree of articulation: it usually will be both disjointed and incomplete, or even scattered over a wide area. Maybe the skull is missing – or conversely, maybe the skull is the only part found. So what would the missing parts have looked like? And what does the surrounding fossil environment tell us about the fossil itself? Was it buried in a flash flood, or by a collapsed sand dune? Was it a victim of predation, or was it a predator fallen victim to another of its species? What might the fossil bones tell us about that individual dinosaur’s pathologies – its injuries and diseases – which it suffered in life?

Give this grid-defined fossil site map to a creationist, and tell them to restore the dinosaur(s) visible here, using only this map for reference. Click on the image to see the scale of the task!
These are just several of the many questions facing a palaeontologist when confronting a jumbled scattering of disarticulated fossil bones in a field location. And that scattering of bones might be from one individual or from several – and even then they might not be of the same species. Only later will someone like myself be brought in to flesh out the painstakingly restored bones as a life reconstruction, always recognising that there are lines between applied knowledge, reasonable assumption, and artistic licence. Applied knowledge would include such factors as the attachment points of muscles, which usually can be seen on bone as areas of rough pitted striations. Reasonable assumption could be the stance in which the animal is shown, which can be enhanced by the applied knowledge of the way in which the skeleton would have been articulated in life. And artistic licence would typically involve skin colour and patterns, which generally are speculative. But always when creating such a life reconstruction, I am aware of the untold research time of career scientists, both in the field and in the museum, behind what I am doing.

My life reconstruction of the head of a dryosaur: a mix of applied knowledge, reasonable assumption and artistic licence, and drawn with an awareness of the differences between these three factors.

So how do creationists know what dinosaurs looked like? They do not commit their time and *resources to the rigours of museum field work. They do not spend their working lives painstakingly piecing together the herculean puzzles of fossil bones tackled by professional palaeontologists. There is only one answer possible: they have acquired this knowledge by climbing over the backs of the very scientists whom they so openly despise. And the reason why creationists are able to include in their institution those crowd-pulling animatronic dinosaurs is because career scientists of all persuasions, philosophies and beliefs, but all of whom endorse evolutionary theory and geological time, have committed their working lives both to finding and restoring those jumbled scatterings of fossil bones.

Top image: Earthquake Dinosaurs. Second image: Australian Geographic, photo: Kara Murphy. Third image: Barnum-Brown Howe Quarry dinosaur bones map from Wikimedia Commons. Fourth image: original artwork © Hawkwood.

* Please don't mention the name 'Buddy Davis' to me. A scientist might play country music, but a country music singer does not a scientist make. Mr. Davis also considers himself to be a reconstructional artist of matters dinosaurean. Looking at his work is a chilling reminder of what can happen when reconstructional art is unsupervised by qualified professionals. So.. the Creation Museum organizes a 'field trip' to dinosaur country in Montana led by... Mr. Davis? Oh, spare me...

I wish to note here that some time ago a creationist took the time to write an extended response to this particular post. When I found it in my comments 'Awaiting moderation' I read it through carefully and clicked on 'Approve'. Alas, it failed to appear on the blog. My guess is that Blogger automatically rejected it as being overlong for a comment, as it was as long as any blog post, and additionally lacked any paragraphing or line breaks, making it something of a test in itself to read it.

My point is that I do not reject points of view simply because they might be contrary to my own. Nevertheless it seems worth making the further point that, to counter what I recall this person saying, there are no such things as 'creationist scientists', any more than there are 'Buddhist scientists' or 'Hindu scientists', or even 'atheist scientists'. 

There are just scientists. When science is being done, beliefs or non-beliefs rightly take a back seat. If they did not it wouldn't be science.

Monday, October 29, 2012

Ancient Wings

I began my previous post by speculating about keeping a pet dinosaur. It was only a short while after I posted it, however, before I realised that I already had done just that! When I lived in Australia I had a pet canary which, in a blaze of originality, I had christened Birdie. Despite his modest size, Birdie was as much of a dinosaur as any other bird alive today, for science now recognises no distinction. In fact, as far as scientific classification goes, there are no birds – just dinosaurs which are classified either as non-avian (all those dinosaurs which we traditionally think of as being just that) and avian (all dinosaurs which we now think of as birds). Or to put it another way: dinosaurs never actually became extinct – they just became birds.

In 1861, just two short years after Charles Darwin shook the prevailing world view with his publication On the Origin of Species, and as if on cue to reinforce all which he claimed, the fossil of a single perfect feather was found in a limestone quarry in Bavaria. The fossil beds were one hundred and fifty million years old, placing the bird within the Late Jurassic. But did the feather really belong to a bird? Nine subsequent finds from the same location (the specimen in the Berlin Museum, above) revealed remarkably preserved fossils of an animal no larger than a raven, which shared the characteristics of both dinosaurs and birds. The feathered wings and tail were clearly visible, but in place of a bird’s beak, this creature had a jawfull of sharp carnivore teeth (the claws and skull of the recently discovered 'Thermopolis' specimen, below).

And not only that: the sternum (breast bone), which in flying birds is massively developed as a distinctive  keel shape to anchor the strong pectoral muscles needed for the wing downstroke in flight, was comparatively small and flat. And this animal had a long bony tail, gastralia (belly ribs), and functional grasping claws on its forelimbs – all typical characteristics of raptorial dinosaurs – but not of birds. Science named the animal Archaeopteryx lithographicaArchaeopteryx meaning ‘Ancient Wing’, and lithographica, because the quality limestone quarried at the site was used in the then-prevailing lithographic printing process.

Whether we regard Archaeopteryx as a bird or as a dinosaur has very much to do with our own classifying mindset. In reality, the fluid evolutionary mechanisms of nature do not express themselves in these clear-cut terms. It is both and neither – although for science it is a dinosaur with flight capabilities. But how well could it fly, if at all? The clearly-defined wings of the fossil powerfully suggest the idea, but the skeletal anatomy speaks against it. With a good head wind it might have managed a brief glide, although probably not much more than this. When I made a rough sketch of the overall body shape (above) what became clear was that this animal was a good runner – another trait of its raptorial dinosaur connections. In fact, one fossil of Archaeopteryx which was preserved without feather impressions was for decades thought to be a fossil of the small carnivorous dinosaur Compsognathus, whose habitat Archaeopteryx shared.

Earlier this year, and just over a century and a half after its first discovery, the fossil of that compelling single feather (above, with below it, my drawing of a chicken feather for comparison) was re-examined. Using a powerful electron scanning microscope, the parts of the cells which produced pigmentation, known as melanosomes, were isolated and determined to be black. Black melanosomes would serve to strengthen the feather’s structure, making it more durable, and so aid any attempted flight. The discovery had its consequences for me personally, because some ten years earlier I had painted this ‘portrait’ of Archaeopteryx (below), and with the information which I then had to work with, my choice of colours was wholly speculative.

But in my reconstructional art I passionately believe that, as in science, I have to follow wherever the available evidence takes me. With this new evidence now to hand, a rethink was clearly in order. I scanned in my original acrylic painting and digitally repainted the colours (below) to reflect these latest findings. And interestingly – and contrary to my own expectations – I find this second updated version more convincing.

At the moment, we do not know whether Archaeopteryx was an overall black, or whether this applied only to the flight feathers, of which the single feather is one. But now I find that I rather enjoy the idea of a black Archaeopteryx, with its raven-dark wings catching a flash of iridescence in the sunlight as, hesitantly and experimentally on some far Jurassic Kitty Hawk beach, it took advantage of a strong onshore breeze and raised itself for a few momentous seconds above the sands.

Ryan M. Carney, Jakob Vinther, Matthew D. Shawkey, Liliana D'Alba & Jörg Ackermann:
New evidence on the colour and nature of the isolated Archaeopteryx feather
Published as Article #637 in Nature Communications, 24 January 2012

In his chapter on theropods in The Complete Dinosaur, edited by James O. Farlow and M. K. Brett-Surman, Philip J. Currie mentions that dinosaurs and birds share more than one hundred and twenty common characters in their anatomical features, and he concludes that '..the only character to define birds (from dinosaurs) is their ability to fly.' I would also add that all theropod dinosaurs and birds share the distinctive character of pneumatic (hollow) bones, and that it's worth remembering that feathers are simply modified reptile scales.

Tuesday, October 2, 2012

My Pet Dinosaur

Were I allowed by some chance of time and nature - and my tolerant wife - to keep a pet dinosaur, then this particular dinosaur would be high in the running for my choice. I have, however, no name to offer it, because science has not given it one. The reason for this is that it is known only by its tracks: not a single fossilized bone has been discovered which can be associated with these tracks.

Such fossils are known as trace fossils, because they are the indirect traces which an organism has left behind, rather than being actual fossilized remains. But trace fossils can still tell us much. If they are animal tracks, how was it walking - on two legs or on four? How fast was it travelling? Was it alone, or in a group? And of course tracks will also tell us with reasonable certainty whether it was herbivorous or carnivorous, and, depending upon the strata in which the tracks were found, how long ago it lived.
Tracks which cannot be associated with a specific animal are given their own name, and that is the case with our little dinosaur here. The dinosaur's name remains unknown. The tracks have been named by science as Atreipus, after their 19th century discoverer, Atreus Wanner. These little footprints (my drawing below, about life-size) have been known from eastern America's Connecticut Valley for some time, and we can deduce that they were made by a small herbivore walking on all fours: the prints of both fore- and hind feet are clearly visible. In fact, the tracks are so small that this dinosaur's body size could not have been much larger than that of a domestic cat's. It's style of locomotion is described as being 'habitually quadrupedal', which is just a way of saying that walking on all fours was the usual thing for it to do.

Reconstructing an animal from its tracks alone is a major challenge in itself, but these delicate, almost dainty tracks drew me to them, and I wanted to know how this little dinosaur might have appeared in life. The skin patterns and colours of my painted reconstruction above are conjectural, but the feet and limbs - long hind legs and shorter front legs - and the walking stance, are highly probable, and are what the Atreipus tracks themselves indicate. At some time in the very early Jurassic, around 205 million years ago, this unknown little dinosaur wandered over what is now the Connecticut Valley, living out its life, and in its wake leaving these modest tracks as our only record of its passing.

Paul E. Olsen and Donald Baird: The ichnogenus Atreipus and its significance for Triassic biostratigraphy: in K. Padian (ed.), The Beginning of the Age of Dinosaurs, Faunal Change Across the Triassic-Jurassic Boundary, Cambridge University Press, New York, 1986, p. 61-87.

Wednesday, July 18, 2012

Disproving Evolution

A couple of evenings ago I overheard the remark in a video phone-in interview that a Fundamentalist Christian creationist with something of a reputation on YouTube was considering becoming a scientist, apparently so that he could disprove evolutionary theory, as it were, from the inside. I won't embarrass him by naming him here, but such an aspiration demonstrates only a lack of any grasp of the way in which scientific method actually functions. To explain:

In science, there is no plan; you simply go wherever the evidence takes you. True enough, parameters can be set up, and based upon sound reasoning and experience, an extrapolated subatomic particle is discovered, or an expected fossil actually turns up in a specific locality. But science does not deal in negatives. So setting out actually to scientifically 'disprove' something is a non sequitur.

Still, let's for the sake of this point assume that it's possible (and allowable within the scientific community). You 'disprove' a theory - and a well-established and long-accepted one at that. What are you left with? A mere vacuum. You have done nothing actually to replace the quashed theory with anything new, with a viable alternative of your own that steps in to replace what you have trounced. To do that, you'd have to marshall your evidence and send a hypothesis of your own down the long and well-worn road that any scientific hypothesis has to tread in order to gain acceptance. In short: you'd actually have to practice science. Real science. And in science, things are neither *'proven' nor 'disproven', just accepted.

It's possible, of course, that some line of scientific reasoning might disprove something else, but it does so simply as a by-product of 'doing what it does', not as an intent. Like the way in which the mechanisms of evolution incidentally disprove creationism... :)

*While proof in the understood sense of the term is not part of the definition of what constitutes a scientific theory, it is true enough that some theories have shown themselves to be so robust that they are to all intents and purposes accepted as fact - evolutionary theory being one of them. And a 'theory' in science has a different meaning to the word in everyday use, which is why the creationist claim that 'evolution is just a theory' is yet another non sequitur.

And this clears up another widely-held misunderstanding by creationists: disproving something in science does not automatically 'prove' something else. So 'disproving' evolutionary theory would not by default establish that supernatural creation had occurred instead. The situation on the ground is that a supernatural means of creation would then have to be accepted and established as a scientific theory in its own right. Good luck with that one, creationists...

Thursday, May 6, 2010

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.

*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.

Wednesday, March 10, 2010

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.

*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.

Friday, February 5, 2010

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!

*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.

Saturday, December 26, 2009

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.

Thursday, November 26, 2009

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. 

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.