Comparision of the endocranial morphology of the nodosaurid Pawpawsaurus and ankylosaurids from North America and Mongolia, with comments on the presenc of the flocculus in the brain of non-theropod dinosaurs

PAULINA CARABAJAL, A.; LEE, Y-N.; JACOBS, L.; KOBAYASHI, Y.; CURRIE, P. J.

Berlin

Congreso; Society of Vertebrate Paleontology annual meeting; 2014

Society of Vertebrate Paleontology

The cranial endocasts of Pawpawsaurus, a nosodosaurid ankylosaur from the Lower Cretaceous of North America, and Tarchia and Talarurus both ankylosaurids from the Upper Cretaceous of Mongolia, were studied using CT scans. The goal of this study is the identification of evolutionary pattern change among the two ankylosaur families and here we report the preliminary results. The general morphology of the brain and inner ear of the three taxa resembles that described for other ankylosaurs such as Euoplocephalus or Sauropelta. The development of the olfactory bulbs is similar in both families, and theelongated lagena indicates that hearing was probably an important sense. However, the brain has a more sigmoidal shape in nodosaurids, whereas ankylosaurids have less marked angles between hind-mid-andforebrains. Compared with Pawpawsaurus, the studied ankylosaurids have more laterally marked and expanded cerebral hemispheres. A remarkable trait is the presence of the flocculus in Euoplocephalus and Tarchia. The flocculus is not recongnized in Talarurus and is absent in Pawpawsaurus, Struthiosaurus, Sauropelta, Hungarosaurus, Panoplosaurus, and an unnamed specimen from Japan,suggesting that its absence is characteristic of nodosaurids. Since recent studies on bird brain evolution state that the development of the flocculus is not just related with flight capabilities but with gaze stabilization, we suggest that its presence in quadrupedal non-theropod dinosaurs responds to capabilities related with fast movements of the head (feeding and/or defense behavior, and in the particular case of ankylosaurids, also related to the movement and stabilization required for the active use of a heavy clubtail.