New insights on the development of the flocculus on Pseudosuchia (Archosauria)

VON BACZKO, M.B.; BARRIOS, F.; DESOJO, J.B.; PAULINA CARABAJAL, A.; BONA, P.

Diamante

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

CICYTTP

The flocculus is a cerebellar structure associated to the occulomotor reflex, whichintegrates the movement of the neck, eyes and balance organs. Historically, the flocculushas been related to bipedalism and flying capabilities within Archosauria given its greatdevelopment on birds and pterosaurs, although recently it has been regarded as a centre of gaze stabilization. We present a review on the presence of this structure within thecrocodilian lineage Pseudosuchia. The flocculus is distinguishable in several noncrocodylomorph pseudosuchians, except in the ornithosuchid Riojasuchus because of itspoor preservation. Among aetosaurs, is present in Neoaetosauroides and Desmatosuchus asa semispherical structure anterior to the semicircular canals. The floccular recess is presentin the endocranium of the poposaurids Arizonasaurus, Effigia, and Shuvosaurus, and it islarger than that of the non-crocodylomorph loricatans Batrachotomus and Postosuchus. Onthe contrary, the flocculus of the mesoesucrocodilian crocodilomorphs is barely noticeableon the nothosuchians (e.g. Simosuchus, Rukwasuchus). On continental neosuchians (e.g.Crocodylus, Caiman), as well as on marine ones (?Metriorhynchus? westermanni), it is notpresent. We can conclude that, 1- the development of the flocculus within archosaurs is notstrictly related to bipedalism (poposaurids) or flight since it is present in quadrupedalpseudosuchians (aetosaurs, loricatans); 2- the reduction of the flocculus on continental(terrestrial and aquatic) and marine neosuchians and nothosuchians indicates that itsdevelopment is not associated to any particular environment. The development of theflocculus might be driven by a higher capacity for gaze stabilization, probably not related toa specific habit.