Were Pterosaurs Dinosaurs?
UDATED Back when I recieved my copy of The Dinosaur Heresies by Robert Bakker for Christmas 1986 as a teen, the dinosaur renaissance was in full swing. I learned a lot of Bakker's then-revolutionary theories. The "Texas Pterosaur" Quetzalcoatlus was indeed "stupifyingly huge" as it was initially suspected of being. There was such a thing as a "pink pterodactyl", in the form of pterodaustro, a a sort of pterosaur answer to a modern flaming that used its bristle-lined lower beak jaw to strain for kill. Pigmentation of the krill would affect the pterosaur's fur in the same way it would a flamingo's feathers, Bakker convincingly theorized.
One of the minor ones was, unlike most other books I had read, Bakker classed pterosaurs among the true dinosauria. As a young child, I always called the winged reptiles "flying dinosaurs", even despite some children's texts assured me that flying and swimming Mesozoic reptiles were something other than dinosaurs, I insisted that they were--because of a science article on the success of dinosaurs my dad had read me. I have no idea what became of that article, but it had it completely wrong. Marine saurians had evolved wholely separate from dinoaurs. Ichthyosaurs go back to crocodile ancestors; mosasaurs are actually a type of lizard, and the term "dinosaur" would actually fit them much better--the oringinal "terrible lizards" of the sea. Pterosaurs, despite being close kin to dinosaurs, didn't quite qualify.
Bakker's theory was encouraging, as it suggested I may have been right after all! He had an entire chapter devoted to pterosaurs, "The Dinosaurs Take To The Air," and he wasn't talking about birds here, though Bakker was one of the leading champions of the idea that birds should be classed as surviving theropod, now an established fact among the vast majority of scientists. I already knew that that pterosaurs, partially due to the fact that they were active flyers were warm-blood and with large brains, possibly larger than dromeosaurs, the pack-hunting "raptor" dinosaurs. Most were also covered in fine, silky fur. Anne McCaffery's Dinosaur Planet depicted pteranodons, one of many Mesozoic species planted by aliens on the world of Ireta, as intelligent, communal and social creatures, who had a pecking order, and wove nets in order to catch fish. That's almost like how raptors are often portrayed in fiction today, their high intelligence greatly exaggerated.
Bakker's classification of the pterosauria among the dinosaur is based on the straight-ankle hinge that is present among all members of the dinosauria and pterosauria. It is not shared by the other main subclass of the class Archosauria, the crocodiles, who still have a sprawling or semi-erect gait. Bakker proposed that the possible ancestor of pterosaurs, and possibly the two classes of dinosaur, the sauricha and the Ornithichia, sharing this characteristic, was Lagasuchus, a small, fleet archosaur, with large hind legs. Lagasuchus was one of many species of Archosaurian bipedal reptiles, generally not classes as dinosaurs. But the ankle hinge betrays it as a possible ancestor. As lagasuchus probably leapt after its prey, some of its descendants may also have developed a winged membrane, according to Bakkerian theory, thus spurring the evolution of pterosaurs.
Bakker's theory of common pterosaur/dinosaur ancestry remains unaccepted by the majority of his colleages today. Not because it has been disproven, it seems. Classification is arbitrary by its very nature, and scientists don't want to rearrange the entire trasitional archosaurian cladagram just for this. So, as it stands, there are officially still three families of archosaurs, pterosaurs dinosaurs and crocodiles. Neither is lagasuchus officially "the first dinosaur." Could it have been? Maybe, though that species doubtless shared that same character with its cousins, but those archosaurs possessing it could easily have been ancestral. Pterosaurs were indeed close relatives of the ancestral dinosaurs. But how close were they?
Pterosaurs were undoubtedly warm-blooded, and it is now agreed that perhaps even the earliest theropods were as well. Feathers are agreed to have been present on most, if not all, the theropods, and this is to have gone back farther than previously thought, well into the Triassic. The bird Proavis seems to have been more advanced than Archeopteryx, though this has not been proven, as the fossil of this animal is so fragmentary. But given a Triassic ancestry of birds with fairly modern characteristics, and the shared lineage of pterosaurs with birds, might not a common ancestry sharing characters of both pterosaurs and theropods be probable? On one hand pterosaurs are bird-like in appearance enough to suspect there is more than merely parallel evolution at work here, especially knowing the close kinship with true dinosaurs. On the other, unlike theropods, certainly including avians, pterosaur retain a four-legged gait, suggesting that their ancestor, whatever it was, was not a theropod. It was once theorized that pterosaurs were more active and bird-like than previously supposed, and might have walked or run on their hindlimbs in bird-like fashion. This was soon disproven however, when trackways of pterosaur footprints revealed a four-legged gait. Tradition proved right this time.
So should pterosaurs be reclassed as dinosaurs? Or perhaps as something separate entirely? It often struck me that warm-blooded, furred, flying creatures of fairly high intelligence should not be classed as reptilian at all (their bone structure, supposedly, is what keeps them classed among the reptiles). We're increasingly finding that pterosaurs were more diverse, coming in all shapes, sizes and headcrests, and were doubtless as magnificent and awe-inspiring in their variety as are today's birds. They were definitely not the scaly "wing-lizards" of yore. They certainly wouldn't be if they were around today. If Bakker's proposal that dinosaurs, as warm-blooded active animals that include the birds should be re-classed as separate from reptiles (along with the therapsids or mammal-like reptiles), than shouldn't pterosaurs also be?
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