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.