New fossil mousebird (Aves: Coliiformes) with feather preservation provides insight into the ecological diversity of an Eocene North American avifauna DANIEL T. KSEPKA 1,2 * and JULIA A. CLARKE 3 1 Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Campus Box 8208, Raleigh, NC 27695, USA 2 Department of Paleontology, North Carolina Museum of Natural Sciences, Raleigh, NC 27601, USA 3 Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 1 University Station C1100, Austin, TX 78712, USA Received 11 June 2009; accepted for publication 27 August 2009 Coliiformes (mousebirds) are represented by just six extant species. These species, restricted to sub-Saharan Africa, are all primarily frugivorous and are among the most sedentary of living birds. Previously described fossil Coliiformes preserving feather traces share the short, rounded wing shape of extant mousebirds. Along with osteological evidence, these observations have been proposed to support poor sustained flight capabilities across the stem mousebird lineage. We report a new species of Coliiformes from the early Eocene (51.66 ± 0.09 Ma) Fossil Butte Member of the Green River Formation, represented by one of the comparatively few fossils from these deposits preserving carbonized traces of the wing and tail feathering. Feather traces indicate an elongate, tapering wing shape similar to that of some extant aerial insectivores, and suggestive of a capacity for sustained and agile open-air flight. Traces of the rectrices reveal the tail accounted for approximately two-thirds of the total length of the bird, a proportion similar to that in living mousebirds. Phylogenetic analysis places the new species as a stem representative of Coliiformes, demonstrating for the first time that the two major clades of Coliiformes – Sandcoleidae and Colii – co-occurred at Fossil Lake. Based on the recovered phylogeny, as well as the osteology and feathering of extant and fossil Coliiformes, the wing shape of the new species is interpreted as apomorphic. In addition to documenting unexpected morphological specialization within stem-lineage Coliiformes, the new species adds yet another taxon to the emerging reconstruction of the diverse Paleogene avifauna from the tightly dated and nearly synchronous fossiliferous deposits of the Fossil Butte Member. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160, 685–706. doi: 10.1111/j.1096-3642.2009.00626.x ADDITIONAL KEYWORDS: Fossil Butte Member – Green River Formation – paleontology – phylogeny – wing. INTRODUCTION Coliiformes are a clade of small, arboreal birds. Extant representatives of Coliiformes (Coliidae) are primarily frugivorous, highly social, and capable of entering a temporary state of torpor (McAtee, 1947; Rowan, 1967; Bartholomew & Trost, 1970; Fry, Keith & Urban, 1988; de Juana, 2001). Morphologically, all extant species are characterized by a prominent feathered head crest, short and rounded wings, highly elongate tails, and a specialized foot. The plumage of these birds also shows several interesting modifica- tions, including a lack of down, restriction of apteria to the head, and loose contour feather barbs that contribute to a hair-like quality (Rowan, 1967; de Juana, 2001). Modifications of the tarsometatarsus and phalanges facilitate rotation of the first and fourth digit, allowing the foot to attain facultatively anisodactyl, zygodactyl, and pamprodactyl configura- tions, which these birds employ adeptly in clinging, *Corresponding author. E-mail: ksepka@gmail.com Zoological Journal of the Linnean Society, 2010, 160, 685–706. With 9 figures © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160, 685–706 685 Downloaded from https://academic.oup.com/zoolinnean/article-abstract/160/4/685/2625581 by guest on 09 June 2020