【古生物学】水上生活をしていたカモ似の恐竜

A swan-necked and flipper-forelimbed new dinosaur species that spent at least some time living in water is described in a paper published in Nature this week. Halszkaraptor escuilliei lived during the Campanian stage of the Cretaceous (about 71-75 million years ago) in what is now Mongolia.

Maniraptora is a group of dinosaurs that includes birds and their closest relatives. During the Cretaceous, several maniraptoran lineages evolved different characteristics related to the ecosystems they inhabited, including active flight, gigantism, cursoriality (a specific adaptation for running) and herbivory.

Andrea Cau and colleagues use a high-resolution synchrotron radiation scanning method to examine a maniraptoran fossil still partially embedded in rock. The specimen, they find, has a number of strange features that are mostly absent among non-avian maniraptorans, but are shared by reptilian and avian groups with aquatic or semiaquatic ecologies.

The authors interpret these features as those of a new species of amphibious theropod that walked on two legs on land, with postural adaptations similar to short-tailed birds (like ducks), but used its flipper-like forelimbs to manoeuvre in water (like penguins and other aquatic birds), relying on its long neck for foraging and ambush hunting. The researchers group the new find with two other hitherto enigmatic and fragmentary specimens to produce a new dinosaur subfamily, the Halszkaraptorinae.