Comparative anatomy of the passerine carpometacarpus helps illuminate the early fossil record of crown Passeriformes

• Published in: Journal of anatomy 2023-03, Vol.242 (3), p.495-509
• Main Authors: Steell, Elizabeth M., Nguyen, Jacqueline M. T., Benson, Roger B. J., Field, Daniel J.
• Format: Article
• Language: English
• Subjects: Anatomy; Anatomy, Comparative; Animals; Biological Evolution; carpometacarpus; Europe; Fossils; Homoplasy; Morphology; Oligocene; Original; Passeri; Passeriformes; Passeriformes - anatomy & histology; passerines; Phylogeny; songbirds; Tyranni
• ISSN: 0021-8782; 1469-7580; 1469-7580
• DOI: 10.1111/joa.13761

The hyper‐diverse clade Passeriformes (crown group passerines) comprises over half of extant bird diversity, yet disproportionately few studies have targeted passerine comparative anatomy on a broad phylogenetic scale. This general lack of research attention hinders efforts to interpret the passerine fossil record and obscures patterns of morphological evolution across one of the most diverse clades of extant vertebrates. Numerous potentially important crown passeriform fossils have proven challenging to place phylogenetically, due in part to a paucity of phylogenetically informative characters from across the passerine skeleton. Here, we present a detailed analysis of the morphology of extant passerine carpometacarpi, which are relatively abundant components of the passerine fossil record. We sampled >70% of extant family‐level passerine clades (132 extant species) as well as several fossils from the Oligocene of Europe and scored them for 54 phylogenetically informative carpometacarpus characters optimised on a recently published phylogenomic scaffold. We document a considerable amount of previously undescribed morphological variation among passerine carpometacarpi, and, despite high levels of homoplasy, our results support the presence of representatives of both crown Passeri and crown Tyranni in Europe during the Oligocene. Here, we bolster knowledge of passerine evolution by presenting a comparative framework for a morphologically variable, functionally important and frequently‐fossilised skeletal component of the wing, the carpometacarpus. We show that some of the earliest crown passerines, including the enigmatic and controversial Wieslochia weissi, were crown‐group suboscines—a diverse radiation of extant passerines completely absent from Europe in the present day. Our study constitutes an important first step towards illuminating passerine skeletal evolution by revealing that widespread homoplasy characterises the passerine carpometacarpus.