Flying Colors: Pterosaurs' Crests
by AMNH on
The incredible diversity of pterosaurs is perhaps best expressed in one of the prehistoric flying reptile’s most intriguing and mysterious features: the head crest.
Akin to a rooster’s comb, peacock’s crown, or the frill on some lizards’ necks, pterosaur crests were prominent anatomical features found across many species. But rather than flesh or feathers, these reptiles’ crests were made at least in part of bone—a boon to paleontologists, as hard bone tends to be preserved as a fossil.
Recent research also indicates that other horn-like material comprised part or even most of some pterosaur crests, with the thin, underlying bony structure supporting sometimes expansive membranes. Pterosaur crests are thought to have been fairly ubiquitous, appearing in many groups from the Triassic (252–201 million years ago) through the Jurassic (201–145 million years ago) and Cretaceous (145–66 million years ago) periods. In terms of size and dramatic effect, crests peaked in the Late Cretaceous, when the biggest pterosaurs also evolved.
Among pterosaur species known to have had crests, there is an amazing range of shapes and sizes. Pteranodon sternbergi, for example, had a high upright crest on its skull; Pteranodon longiceps, dagger-shaped blades at the back of its head; and Nyctosaurus, a fan-like structure at the rear of its head.
Dsungaripterus weii had two: a long, low crest on its snout and a short crest rising above the back of the head. The Anhanguera species had rounded disk shapes on both upper and lower jaws, while Gnathosaurus pterosaurs had long, low ridges running down the middle of their heads. Tupandactylus imperator had huge sail-like extensions that dwarfed the rest of its head.
Could something so flashy be all form and no function? The heavier crests cost the reptiles a lot in energy to grow and carry around. Reason suggests if they weren’t useful, they would have disappeared over millions of years of evolution. But just what that use was is a question that puzzles pterosaurologists to this day. There are competing theories, chief among them that crests serve as a form of species identification. Other possibilities include a role in sexual selection, heat regulation, as a rudder in flight, or as a keel in the water, stabilizing the reptile as it dove or skimmed for food.
The discovery in Brazil of wildly different crests among closely related species lends credibility to the theory of species identification: like a Mesozoic mohawk, a distinct crest would allow ready recognition of one’s own kind and, equally important, rule out others. Were the crests as brightly colored as shown in artists’ renderings? While scientists cannot know for certain, light and dark bands of color on the rare preserved tissue of a Pterorhynchus wellnhoferi crest found in China led to speculation that crests might indeed have been highly colored, especially if they served to communicate identity or attract mates. Still, without living descendants for comparison and the relative paucity of fossils, definitive proof has been elusive—so far.
The special exhibition Pterosaurs: Flight in the Age of Dinosaurs is now open, through January 4, 2015.
A version of this article appears in the Spring 2014 issue of Rotunda, the Member magazine.