A Jurassic pterosaur from Patagonia and the origin of the pterodactyloid neurocranium

POL D.; PAULINA-CARABAJAL A.; CODORNIÚ L.; UNWIN D.

PeerJ

PeerJ-Inc

Lugar: London; Año: 2016 vol. 4 p. 1 - 22

2167-8359

Pterosaurs are an extinct group of highly modified flying reptiles that thrived dur- ing the Mesozoic. This group has unique and remarkable skeletal adaptations to pow- ered flight, including pneumatic bones and an elongate digit IV supporting a wing- membrane. Two major body plans have traditionally been recognized: the primitive, primarily long-tailed paraphyletic ??rhamphorhynchoids?? (preferably currently rec- ognized as non-pterodactyloids) and the derived short-tailed pterodactyloids. These two groups differ considerably in their general anatomy and also exhibit a remarkably different neuroanatomy and inferred head posture, which has been linked to different lifestyles and behaviours and improved flying capabilities in these reptiles. Pterosaur neuroanatomy, is known from just a few three-dimensionally preserved braincases of non-pterodactyloids (as Rhamphorhynchidae) and pterodactyloids, between which there is a large morphological gap. Here we report on a new Jurassic pterosaur from Argentina, Allkaruen koi gen. et sp. nov., remains of which include a superbly pre- served, uncrushed braincase that sheds light on the origins of the highly derived neu- roanatomy of pterodactyloids and their close relatives. A μCT ray-generated virtual endocast shows that the new pterosaur exhibits a mosaic of plesiomorphic and de- rived traits of the inner ear and neuroanatomy that fills an important gap between those of non-monofenestratan breviquartossans (Rhamphorhynchidae) and derived pterodactyloids. These results suggest that, while modularity may play an important role at one anatomical level, at a finer level the evolution of structures within a mod- ule may follow a mosaic pattern.