13 February 2008

Adorable Science

Scientists recently announced the discovery of one of the smallest pterosaurs of all. Pterosaurs were hairy, skin-winged, flying creatures commonly, and somewhat incorrectly, referred to as "pterodactyls". This adorable little guy has been named Nemicolopterus crypticus, meaning "hidden, forest-dwelling wing".

Painted restoration by Chuang Zhao. Taken from the New Scientist article, which has a larger version.

The wingspan is a mere 25 cm. Although the only known specimen is not a fully grown adult, it would not have gotten too much larger had it lived that long. Smaller pterosaur specimens are known, but they represent less mature individuals (i.e., hatchlings).

As I mentioned, pterosaurs are commonly known as "pterodactyls" outside of the paleontological community. "Ptero-dactyle" is an old term for Pterodactylus, a genus of pterosaur known from the Solnhofen deposits in Germany. That term and other terms like "ornithosaurs" have not been in use in paleontology for a very long time. There is, however, a large group of short-tailed pterosaurs called pterodactyloids; Nemicolopterus is not really a "pterodactyl", but it is a pterodactyloid.

Photo showing just how small this thing was. Taken from the ITN article, which erroneously calls it a "dinosaur".

A far more egregious mistake is being committed by many places reporting this creature, though: calling it a dinosaur. Pterosaurs are not dinosaurs, but are generally considered dinosaur cousins. Most scientists consider them non-dinosaurian stem-avians, although the possibility of a stem-archosaurian position has also been investigated. Unfortunately, primitive pterosauromorphs are not known (with the possible exception of Sharovipteryx mirabilis, a poorly-known Triassic animal seemingly having "leg-wings"), so it is difficult to pin down their exact relationships. But it is quite certain that they were not dinosaurs, that is, there is no way that they were descended from the final common ancestor of Iguanodon bernissartensis and Megalosaurus bucklandii.

|?-Pterosauromorpha (possible position)
|--Scleromochlus taylori
|--Pterosauromorpha (generally favored position)
| |?-Sharovipteryx (or in Prolacertiformes)
| `--Pterosauria
| |--Dromomeron romeri
| `--Lagerpeton chanarensis
|--Marasuchus lilloensis
`--+--Pseudolagosuchus major
|--Dinosauria (including Aves)
`--+--Eucoelophysis baldwini
`--Silesaurus opolensis

All these nomenclatural goof-ups aside, it's a pretty cool animal, and not just for its size. The toes are curved more than in any other pterosaur, and the authors interpret this as an adaptation to arboreality. I can just picture it hanging like a bat from a Mesozoic tree limb.

Preliminary anatomical reconstruction by John Conway. Click here for the full version.

What's interesting here is that it has arboreal adaptations, but it's not a primitive pterosaur. This same evolutionary pattern is seen in birds (avialans): the earliest members lack arboreal specializations, but some later members developer them. But this pattern is not, so far as we know, seen in bat (chiropteran) evolution. The earliest known stem-bats have arboreal adaptations, while the earliest pterosaurs and avialans do not. Might this reflect a fundamental difference in body plan between pan-mammals (including apo-chiropterans) and sauropsids (including pterosaurs and avialans)?

Two N. crypticus in a tree, by John Conway. Click here for the full version.

Wang, X., A. W. A. Kellner, Z. Zhou, and D. A. Campos. (2008 February 12). Discovery of a rare arboreal forest-dwelling flying reptile (Pterosauria, Pterodactyloidea) from China. Proceedings of the National Academy of Sciences 106(6):1983–1987. doi:10.1073/pnas.0707728105

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