Wednesday, October 08, 2008

The Virtual Art Show: Part 2


Pterosauria was the first vertebrate group to develop true flapping flight. Their origins are murky, because the oldest pterosaur fossils are already capable fliers! However, the fact that basal pterosaurs have both antorbital and mandibular fenestrae in their skulls indicate their archosaurian roots. Earlier pterosaurs, like Dimorphodon macronyx, had long, stiffened tails with bony rudders. Their wings were short, and the main wing surface ran from the end of the elongated fourth finger to the ankles. Furthermore, a hindlimb patagium ran between the elongated pinkie toes. This meant that early pterosaurs were clumsy on land, and may have spent all their time in the trees or on the wing.

Another group of pterosaurs, the Pterodactyloidea, arose during the Late Jurassic. They lost the long tails of their ancestors, elongated their wings, increased their walking abilities, and developed a menagerie of strange and wonderful headcrests. Two of the spectacular must have been Tupandactylus and Nyctosaurus. Pterodactyloids also diversified to tackle a wide range of foods and environments. Some, like Nyctosaurus, soared over the ocean, diving for fish like an albatross. Tupandactylus probably walked along the plains looking to scavenge or capture small vertebrates like an African hornbill. There was even a filter-feeding pterosaur from Argentina called Pterodaustro!

Artist Notes

Regular readers might remember that Nyctosaurus took an especially long time. Once again I must thank all my readers who commented and offered me tips and critiques on my drafts. Anyway, the final painting took its coloration from the Black Oystercatcher, a really beautiful Arctic seabird. Since Nyctosaurus is thought to have roosted around the Western Interior Seaway, I thought seabird colors would be fitting. However, gulls generally have pretty boring colors (although at one point I was considering the Black-Headed Gull) so I went with something more eye-catching. The toughest part was getting the crest to fit on the canvas--I was forced to shop off a few inches of the back-pointing portion to make it fit. The picture is almost life-size!

The Dimorphodon didn't require nearly as much work. Remember this awful attempt? It quickly evolved into a final draft which I turned into a transparancy and colored like a puffin. Why a puffin? Because ever since I was little, I'd thought that Dimorphodon's big ol' noggin looked puffin-esque. Ironically, it probably didn't live like a puffin. Puffins eat fish, Dimorphodon ate bugs and small terrestrial (and arboreal) vertebrates. Puffins roost on searocks and spend most of their time in the water, while Dimorphodon probably lived inland and, according to Mark Witton, may not have been the best flier. But I really like the color scheme, especially on the snout.

Another note: I wanted to try a range of media for the show. Dimorphodon was going to be on a piece of illustrator board and done up with illustrator markers. Unfortunately, illustrator board sucks, and flattened the look of my markers. I also bought cheap-ass markers because the good stuff (Prismacolor) was like $85. Anyway, the piece looked flat and faded, and I didn't like it at all, so I threw it out and started on canvas. I'm far happier with the canvas version!

Fun Facts

I didn't want to include Pterosauria in the show originally, because I wasn't convinced that the group should be included in the Archosauria! In fact, my position on their phylogenetic affinities is still tenuous, and rests solely on the skull features of Dimorphodon, who has both antorbiteal and mandibular fenestrae. Still, Euparkeria has both, too, and is not considered an archosaur proper. Nobody's done a good job of explaining to me why the group is currently placed close to, or within, the Ornithodira. I think Benton (I forget the year) did a good job of explaining why hindlimb features "shared" between ornithodirans and pterosaurs are convergences, and not the result of common ancestry.

Note: Once again, this format is FAIL.

Other posts in the Virtual Art Show:




ScottE said...

"Nobody's done a good job of explaining to me why the group is currently placed close to, or within, the Ornithodira."

Didn't they?

Seems reasonable enough to me.

Christopher said...

Well weather or not pterosaurs are archosaurs proper, archosauriformes, archosauromorps, basal diapsids of some general distinction or as far away from dinosaurs as you can get and still be reptiles they will always be Ornithodirans by definition. Gauthier 1986, the clade containing the last common ancestor of the dinosaurs and the pterosaurs and all of its descendants. Its not a particularly useful useful concept.

Nick Gardner said...

Ugh! Zach, you're forgetting that:
1. Many basal pterosaurs have antorbital fenestrae (like Eudimorphodon and Raeticodactylus).
2. Archosauria isn't an apomorphy-based clade, it's not defined by the presence or absence of the antorbital fenestra, but by the taxa within it.
3. Also, it wasn't Benton, but Bennett, rather.

Pterosaurs might not be archosaurs, but we'll have to wait til someone can demonstrate that they share more in common with some other taxa aside from dinosaurs and crocs. Until then, it's a safe bet to go with them being archosaurs. :-)

If you'd like a better explanation in person, then we could talk about this at SVP next week!

Zach said...

Yes, definately, Nick. As the snow piles up, I'm looking forward to it more and more!

(also, I know they all have antorbital's the mandibular fenestrae I'm concerned about)

Nick Gardner said...

Reversal. :-)