Inner ear morphology and sensory capabilities of terror birds (Aves, Cariamiformes).

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

La rioja

Jornada; xxvii Jornadas Argentinas de paleontología Vertebrados; 2013

Terror birds (Phorusrhacidae) comprise the most outstanding group of the South American Cenozoic avifauna. In order to understand better their hunting skills, the endosseous labyrinth of the inner ear of terror birds is reconstructed. Semicircular canals are aligned in approximately orthogonal planes. The lateral canal origin lies on the lateral surface of the common crus. Interestingly, the three canals leave the vestibular system together in their extant relatives, the Cariamidae. The cochlear duct is a long, straight finger-like tube, with the distal tip strongly directed medially in Mesembriornithinae, whereas it is shorter and almost perpendicular to the basicranium in Patagornis. The vestibular fenestra is conspicuously marked and the cochlear fenestra is wide, oval, and especially large in Patagornis. Our estimations of hearing sensitivity put the Mesembrionithinae below the average for living species. Because the vocalization range of most birds falls within the lower half of their hearing sensitivity, terror birds may have had a narrower and lower vocalization frequency range. It seems plausible to hypothesize that phorusrhacids had enhanced acoustic abilities at lower frequency registers, using them for intraspecific communication or prey detection. Vestibular organs also provide sensations of gravity, motion, and vibration. If the activity during an attack involved rapid hatching movements of the head, then the length of its canals should be adequate to respond to such higher angular amplitudes. Interestingly, canals of Patagornis are notoriously shorter and stouter and, therefore, it is valid to assume more sluggish head movements that turn requiring enhanced sensitivity to low-amplitude motions. CICTERRA (CONICET-UNC), Av. Vélez Sársfield 1611, X5016GCA, Córdoba, Provincia de Córdoba, Argentina. fjdino@gmail.com *Contribution PIP 0437 and UNLP N671.