A revision of skull morphology in Phorusrhacidae (Aves, Cariamiformes)

ABSTRACT

Phorusrhacidae, popularly known as ‘terror birds’, are the most speciose clade within the avian order Cariamiformes, with a fossil record that ranges from the Eocene to the Pleistocene. Although several species have preserved skulls, our understanding of their cranial morphology remains incomplete. Here, a comprehensive overview of the current knowledge of phorusrhacid skull anatomy is presented. The phorusrhacid skull bauplan includes salient features such as deep, triangular fossae temporales, a complex basipterygoid articulation and the loss of bending zones related to kinesis. Two skull morphotypes can be discriminated: the psilopterine and the ‘terror bird’ type. The ‘terror bird’ skull type is here considered an evolutionary specialization, indicating that among phorusrhacids, medium-size to large phorusrhacids show more rigid and stiffer skulls. Nevertheless, studies have shown that the two morphotypes may have handled prey in a similar manner, suggesting that a trophic specialization with a unique hunting technique was the key driver of the evolution of the phorusrhacid skull.

ACKNOWLEDGMENTS

My warmest acknowledgment belongs to C. P. Tambussi for her constant support, advice and friendship. L. Chiappe and K. Johnson from the Natural History Museum of Los Angeles County (Los Angeles); W. Simpson, J. Holstein, and K. Lawson from the Field Museum of Natural History (Chicago); C. Norris, D. Brinkman, and M. Fox from Yale Peabody Museum (New Haven); C. Mehling from the American Museum of Natural History (New York); L. Witmer from Ohio University (Athens); S. Chapman from the Natural History Museum (London); E. Ruigomez from the Museo Paleontológico Egidio Feruglio (Trelew); A. Kramarz from the Museo Argentino de Ciencias Naturales Bernardino Rivadavia (Buenos Aires); M. Reguero from the Museo de La Plata (La Plata); and A. Dondas, M. Taglioretti, and F. Scaglia from the Museo Tradicional Lorenzo Scaglia (Mar del Plata) allowed and facilitated the consult of the collections under their management. I am grateful to the Editor V. De Pietri, the Technical Editor J. M. Harris, and to T. Worthy and an anonymous reviewer who provided helpful feedback on the manuscript. This research was part of my doctoral dissertation (National University of La Plata) realized at the División Paleontología de Vertebrados (Museo de La Plata) and funded by two CONICET doctoral scholarships. This is a contribution to PICT 2330, PICT 1319 and PUE 2016 – CONICET – CICTERRA.