Duck-billed sauropods in the Cretaceous of Gondwana

SEBASTIÁN APESTEGUÍA

Oklahoma, EEUU

Congreso; Annual Meeting of the Society of Vertebrate Paleontology; 2004

Society of Vertebrate Paleontology

A new rather complete nemegtosaurid titanosaur from Upper Cretaceous beds of Patagonia combines squared lower jaws with anteriorly restricted narrow-crowned teeth arranged in comb like teeth batteries, definitively demonstrating that titanosaurs acquired a mandibular configuration similar to diplodocoids, as suggested by the controversial <i>Antarctosaurus</i>. Rebbachisaurid diplodocoids, the only other reported Late Cretaceous sauropods, could also have had a long square-snouted, spoon-shaped, hadrosaur-like head as that present in the remaining nemegtosaurids. The similarities in mouth configuration and corporal mobility (i.e. loss of hyposphene-hypantrum complex) among rebbachisaurids and derived titanosaurs suggest morphological constraints related to environmental stasis or resource particularities. The new sauropod also shows clear evidence of a sharp keratinous sheath over the non-dentigerous region that probably had a maxillary counterpart and worked to guillotine plant material. This ‘teeth and beak’ oral configuration renders these sauropods partially comparable to the highly diverse Laurasian ornithischian dinosaurs, poorly represented in Gondwanan landmasses, and whose success was related to the rise and diversification of flowering plants. Gondwanan Cretaceous sauropods probably dominated also the adaptive zones proper of Laurasian ornithischians. Their unusual features may help to explain the persistence of sauropods into the latest Cretaceous of southern continents. The presence of a beak-like structure in sauropod dinosaurs also reduces the morphological gap between birds and non-theropod dinosaurs.