A large collection of Presbyornis (Aves, Anseriformes, Presbyornithidae) from the late Paleocene and early Eocene of Mongolia

Abstract

We describe a large collection of fossil ‘waterfowl’ bones that are referable to the extinct clade Presbyornithidae (Anseriformes). All of these fossils were collected between 1971 and 1994 from Upper Paleocene and Lower Eocene sediments at the Tsagaan Khushuu site in the Gobi Desert of southern Mongolia. The collection includes specimens referred to a new small species within the genus Presbyornis Wetmore, 1926 as well as large numbers of bones that we place in the genus Presbyornis. On this basis of the Tsagaan Khushuu collection we suggest that several species of Presbyornis likely coexisted in this region; indeed, the presence of large numbers of middle‐sized, morphologically consistent but probably ecologically disparate species at the Tsagaan Khushuu site is consistent with the range of variation seen, for example, in taxa of extant dabbling ducks (Anatini). Although the anatomy and phylogenetic position of Presbyornithidae (in particular Presbyornis) are well known, this material from Mongolia further demonstrates the prevalence of these birds in aquatic and semi‐aquatic habitats by the earliest Paleogene. Because presbyornithids are also well documented from the late Cretaceous, their palaeoecology and morphological diversity provides a clue to selective avian survivorship across the Cretaceous‐Paleogene (K‐Pg) boundary. Copyright © 2009 John Wiley & Sons, Ltd.

More evidence for plesiomorphy of the quadrate in the Eocene anseriform avian genus Presbyornis

“…1A 7 , B 7 ). The only pneumatic foramen that is present in either of the two specimens, but has not been mentioned by Kurochkin and Dyke (2010), is in the basiorbital position.…”

“…2). A striking feature of the caudal view is the caudomedial depression that is extensive and deep ventrally but, in contradiction to Kurochkin and Dyke (2010), does not contain a foramen (Fig. 1A 7 , B 7 ).…”

“…Galliforms differ from modern anseriforms in the pattern of quadrate pneumatization: galliforms have two foramina, rostromedial and basiorbital, and modern anseriforms have only a single, caudomedial foramen. The presence of the caudomedial foramen would be a likely synapomorphy of Presbyornis and modern anseriforms, as assumed by Elzanowski and Boles (2012) who relied on Kurochkin and Dyke's (2010) suggestive and unequivocal report of this foramen in the Asiatic specimens. This stresses the importance of our observation that there is no foramen in the caudomedial depression in either of these specimens (Fig.…”

“…The two quadrates were recovered by screen-washing and sieving from a single sedimentary lens at the Tsagaan Khushuu locality, Mongolia, among numerous postcranial bones of presbyornithids (Kurochkin and Dyke 2010). While there is no explicit information on whether any other bird bones were found in the same deposits, the prevalence of presbyornithid postcranial bones and a detailed, specific similarity to the American presbyornithid quadrates (Elzanowski and Stidham 2010: fig.…”

“…The cranial anatomy of Presbyornis is in need of a thorough revision, which is likely to result in a more basal placement of this taxon relative to Anseranas and Anatidae (Elzanowski and Boles 2012).The preservation and variation of Presbyornis quadrates from North American collections left some essential details uncertain (Elzanowski and Stidham 2010). Meanwhile, Kurochkin and Dyke (2010) published four photographs of two Presbyornis quadrates from the Early Eocene of the Gobi Desert (Central Asia), but failed to describe them except for some erroneous information (reinforced by a misleading photograph) that "each bears a large pneumatic foramen on its posterior surface". Here I correct this error, describe in detail the two specimens, and show the significance of characters that they help to define.…”