Endocranial anatomy of Madrynornis mirandus (Aves, Sphenisciformes), a crown-penguin from the early late Miocene of Patagonia

DEGRANGE, F.J.; TAMBUSSI, C.P.

Dallas

Congreso; 75th Society of Vertebrate Paleontology Meeting; 2015

By studying the brain and inner ear anatomy of the early late Miocene (Tortonian, 11.6 - 7.2 Ma) crown penguin Madrynornis mirandus (MEF-PV100), it was our aim to find out more about the transition from stem to crown penguins. Previous phylogenetic studies show Madrynornis mirandus as closely related to the living Yellow-eyed Penguin and the crested penguins of the genus Eudyptes. The three-dimensional visualization of its endocranial anatomy in a comparative frame (stem and extant penguins and outgroups) reveals some shared characteristics with extant penguins while others with the stem penguins (Patagonian Miocene Paraptenodytes + Antarctic Eocene penguins). Among the first, the brain is airencephalic, the wulst are less caudally expanded but more dorsally extended than in extant penguins, the optic lobes are cranially located but relatively less developed, the interaural pathway (the contralateral connection between the paired rostral tympanic recesses) is absent, the general pattern of the tympanic recesses is simple without cancellae, the carotid anastomosis is X-type (similar to Spheniscus). Secondly, the telencephalon is relativelly longer and narrower and the flocculi are stouter and more laterally disposed than in extant penguins. Because the posterior portion of the skull is broken, brain volume and consequently encephalization quotient, could not be estimated. Madrynornis mirandus also shows the retention of primitive morphologies such as large olfactory bulbs and high olfactory ratio (35.7) suggesting higher levels of olfactory sensitivity than extant taxa. The latter may indicate exceptional smell sensory abilities that would be expected from predatory animals. These new data holds a large potential to learn more about the evolution of the brain in penguins. Research support was provided by CONICET (PIP 112 20130100059 CO) and UNLP N671.