Alvarezsaurid osteology: new data on cranial anatomy

Abstract

Alvarezsaurs were a group of theropod dinosaurs found in Asia, North America, South America and Europe during Jurassic and Cretaceous periods. In spite of being known by several specimens, diverse aspects of their anatomy remain poorly known. The aim of the present paper is to describe and analyse some points of the neuroanatomy of a newly collected alvarezsaurid specimen. A partial skeleton of an indeterminate Late Cretaceous alvarezsaurid theropod (HGM L08-59) from the collection of Henan Geological Museum in Zhengzhou, China, preserved a partial skull that allows to study some aspects of braincase anatomy. Anatomical features observed in HGM L08-59 and other alvarezsaurs indicate that members of this clade exhibited a notably enhanced somatosensory control during locomotion. The study of skull material of HGM L08-59 as well as that of other alvarezsaur skulls, sheds some doubts on the phylogenetic position of supposed Jurassic alvarezsaurs from China (i.e., Haplocheirus, Aorun and Shishugounykus). Further, some skull features of Haplocheirus are reminiscent to those of ornithomimosaurs and are dissimilar to alvarezsaurs. A comprehensive phylogenetic analysis will shed light on this complex topic that is highly relevant on discussions about early radiation of coelurosaurian theropods.