MicroCT , birds and brains: insights on the endocranial morphology of Tyrannides (Aves, Australaves)

DEMMEL FERREIRA, MARÍA MANUELA; DEGRANGE, FEDERICO JAVIER; TIRAO, GERMÁN ALFREDO

Congreso; ll Virtual Meeting of Systematics, Biogeography, and Evolution; 2021

Tyranni (Aves, Passeriformes) is a clade considered basal among the order Passeriformes. The infraorder Tyrannides or New World suboscines include one of the greatest endemic vertebrate radiations of South America with more than 1200 species. Although its ecology has been well studied, little is known about its endocranial morphology. The aim of this work is to explore the endocranial morphology of the Tyrannides, in an attempt to establish morphological differences between the different families and its relationship with macroevolutionary aspects. Fifteen skulls of adult Furnariidae and Tyrannidae were CT scanned and 3D models of the endocast were generated. Phylogenetical corrected regression analysis shows that only one furnariid (Syndactyla rufospuerciliata) has a brain volume larger than expected for their body mass, whereas the rest of the furnarids and all tyranids have smaller brains. All species have an airencephalic type of brain. The telencephalon of Furnariidae and Tyrannidae is wider than longer (except for Coryphistera alaudina and Agriornis montanus, respectively). In all the species studied here, the eminentiae sagittales correspond to type A (i.e., rostrally placed). These structures are extensive and elongated. The bulbus olfactorius is short and small in both families. The hypophysis is oriented perpendicularly to the horizontal semi-circular canal of the inner ear. The optic lobes of furnarids are laterocaudally partially overlaped by the telencephalic hemispheres, but in tyrannids this condition is not that noticeable. When observed in lateral view, the optic lobes are placed rostrally; equally developed in both families. The cerebellum is elongated with marked and variable number of folia in all species. In furnarids, this structure has a sub-rectangular shape. Among tyrannids, the shape of the cerebellum is variable: in some species is squarer and in others is rhomboidal. The medulla oblongata of Furnariidae has an elongated aspect, whereas in Tyrannidae is globose and it is in most cases as long as wide. The mean hearing ranges varies greatly in both families, ranging from 2899.20 Hz to 3567.61 Hz in furnarids, and from 2996.93 Hz to 3228.29 Hz in tyrannids. Phylogenetical signal is poor in all of the features measured in the endocraniums (brain volume, Wulsts, optic lobe and olfactory ratio, width over height of cerebellum and telencephalic hemispheres). These preliminary results provide key information that contribute to a better understanding of Tyranni radiation, and subsequently to the evolution of the largest order of birds, the Passeriformes.