Meeting Abstract

25.1  Monday, Jan. 5  Evolution of Avian Compound Rhamphothecae: Homology of Simple and Compound Horny Beaks in Birds HIERONYMUS, T.L.*; WITMER, L.M.; Ohio University Department of Biological Science; Ohio University College of Osteopathic Medicine th108702@ohiou.edu

The topology of separate elements in avian compound rhamphothecae is strongly similar within different clades, not only in external appearance but in how these elements conform to underlying structures. We conducted a morphological survey of 81 extant bird species, and tested superficial similarities between external beak morphology in compound and simple rhamphothecae for substantive similarity in associated skeletal structures and nerve courses. A revised set of morphological characters for compound rhamphothecae was optimized onto three recent phylogenetic hypotheses to assess the relationships of homology and homoplasy in rhamphothecal morphology. Osteological correlates of rhamphothecae from fossil basal ornithurine birds Hesperornis, Parahesperornis, and Ichthyornis show that compound rhamphothecae are the primitive state for living birds (Neornithes). Simple rhamphothecae are the result of the loss of softer keratinous grooves between rhamphothecal components, and there are many examples of transitional forms between compound and simple rhamphothecae in which the grooves remain as shallow depressions without a pronounced edge. Ancestral character state reconstructions of rhamphothecal morphology within Neornithes also show a considerable amount of homoplasy. We suggest that the frequent occurrence of homoplastic characters in rhamphothecal morphology is the result of underlying similarity in facial development.