Zapalasaurus bonapartei, a new sauropod dinosaur from La Amarga Formation (Lower Cretaceous), northwestern Patagonia, Neuquen Province, Argentina

An incomplete skeleton from Puesto Morales (Neuquen Province, Argentina) is described as a new species of sauropod, Zapalasaurus bonapartei. The unit that yielded the holotype of this dinosaur is the Piedra Parada Member of the La Amarga Formation, whose age is regarded as Barremian-lower Aptian. Several characters are interpreted as autapomorphies of Zapalasaurus bonapartei: cervical vertebrae with a lamina uniting the prezygapophysis and the zygapophyscal portion of the postzygodiapophyseal lamina, cervical vertebrae with the diapophyseal portion of the postzygodiapophyseal lamina reduced, cervical vertebrae with poorly developed spinoprezygapophyseal laminae, mid and posterior caudal vertebrae with anteroposteriorly elongated neural spines, whose anterodorsal corners are higher than their posterodorsal ones, and caudal centrum length doubles over first 20 vertebrae. Zapalasaurus bonapartei is considered as the sister group of the other diplodocoids (excluding Haplocanthosaurus). Diplodocoids were abundant in the Early Cretaceous, becoming extinct by the early Late Cretaceous. The record of Zapalasaurus bonapartei shows that, at least in the Neuquina Basin, basal diplodocoids were more diverse than previously thought. (c) 2006 Elsevier Masson SAS. Tous droits reserves.