A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China

Abstract

A new titanosauriform sauropod, Ruixinia zhangi gen. et sp. nov., is described. It was recovered from the Lower Cretaceous Yixian Formation of Liaoning Province, northeastern China. Ruixinia is characterized by a unique combination of characters, including the following autapomorphies: distinct foramina present at the anterodorsal corner of the pleurocoels of the mid-posterior dorsals; anterior caudal neural spines bifid; anterior caudal neural spines with projecting subtriangular processes on the anterior margins of the neural spines; distinct grooves present on the lateral surface of neural arches in Caudals 2-12, just dorsal to the base of the caudal ribs; a transition point present between Caudal 22 and Caudal 23 with Caudals 1-22 much larger than more posterior caudals in size; distalmost six caudals fused; Chevron 18 with a bifurcated posterior process; Chevron 20 approximately pentagonal in lateral view; Chevrons 23-36 plank-shaped and unfused distally; lateral bulge developed on the lateral surface of the posterior lobe of the ilium; posterior margin of the tibial shaft strongly convex. Phylogenetic analysis places Ruixinia within the Titanosauriformes. The new find increases the diversity of early-branching Titanosauriformes in China and highlights the tail morphological diversity within this clade.