January 20 , 2017:

Highlights

We describe the caudal pneumaticity of saltasaurine titanosaurs.
We analyze the variability in the pneumaticity of the three saltasaurine taxa.
We assess the patterns of development of pneumaticity in saltasaurine titanosaurs.
We discuss changes in the level of pneumaticity in saltasaurine titanosaurs and non-saltasaurine titanosaurs.

Abstract

Among extant vertebrates, only birds have a respiratory system associated with pneumatic diverticula. However, several extinct clades also had pneumatic diverticula, including the sauropod dinosaurs. Among sauropods, Saltasaurini are characterized by extreme postcranial pneumaticity, which extends as far down the spinal column as the posterior caudal vertebrae. In this paper the pneumatic foramina in both the neural arches and the centra are described in detail, and the relative proportion of air spaces in the caudal vertebrae is established, revealing that the skeleton of Rocasaurus muniozi was more pneumatized than that of Neuquensaurus australis, with Saltasaurus loricatus intermediate. The level of pneumatization varies between the three saltasaurine taxa: in Neuquensaurus, only the neural arch is pneumatized, whereas in the other two saltasaurines both neural arches and centra are pneumatized. This allows us to hypothesize that the timing of pneumatization varied between the three species, with Rocasaurus muniozi pneumatized earliest in ontogeny. This ontogenetic pattern is correlated with evolutionary derivation: the most derived taxa show pneumatization in both the neural arch and the centrum.