Comparative brain anatomy of fossil and living Pygoscelis

ACOSTA HOSPITALECHE, C.; PAULINA CARABAJAL, A.

Bristol

Conferencia; 8 International Penguin Conference; 2013

Anatomical descriptions of penguin brains are scarce in the literature, and fossil brains are even rarer. Brain anatomy of fossil birds can be studied using cranial endocasts that closely reflect the brain anatomy and blood vessels, since the brain is almost completely filling the endocranial cavity. Here, we use CT scans of three specimens, including the holotype of Pygoscelis calderensis (SGO-PV 792, SGO-PV 791 and SGO-PV 790) and the three extant species, P. adeliae, P. antarctica, and P. papua to obtain virtual reconstructions and describe the endocranial anatomy. In all species, the olfactory tract is slender and long and anteroventrally projected, although the fossil Pygoscelis calderensis shows olfactory tracts relatively longer than the extant species. The olfactory bulbs are oval-shaped and slightly divergent from the midline in P. calderensis and Pygoscelis antartica, whereas the bulbs are markedly divergent in Pygoscelis papua and P. adeliae. Each cerebral hemisphere is markedly expanded laterally occluding the optic lobe in dorsal view, as in most living birds. P. calderensis have more pointy lateral margins than the extant species, which have rounded lateral margins. In all species, there is an evident eminentia sagittalis dorsally, which is oval shaped and separated from the rest of the hemispherium by a conspicuous vallecula. The cerebellum and the auricular cerebelli are large, and the pituitary body is small and exhibits an oval shape. Cranial nerve VI has a short passage that runs from the floor of the medulla oblongata to enter the pituitary fossa. The internal carotid arteries also enter the pituitary body through separate foramina. The passages for the arteries diverge from the midline in a wide angle in ventral view of the endocast. The medulla oblongata is elongate and its ventral surface presents a rostro-caudally oriented mark that we interpret as a blood vessel. The inner ear in the living forms has the general avian morphology, with large and slender semicircular canals and a long and slender lagena. The semicircular canals are oval-shaped. The anterior semicircular canal is larger and taller than the posterior semicircular canal. The large and slender canals are related with high manouvrability in Archaeopteryx and comparatively acrobatic flight in extant birds. The lagena is simple, long and tubular-shaped.