A new zygodactylid species indicates the persistence of stem passerines into the early Oligocene in North America

Abstract

BackgroundThe lake deposits of the informal Ruby Paper Shale unit, part of the Renova Formation of Montana, have yielded abundant plant fossils that document Late Eocene – Early Oligocene global cooling in western North America. A nearly complete small bird with feather impressions was recovered from this unit in in 1959, but has only been informally mentioned.ResultsHere we describe this fossil and identify it as a new species of Zygodactylus, a stem lineage passerine with a zygodactyl foot. The new taxon shows morphological traits that are convergent on crown Passeriformes, including an elongate hallux, reduced body size, and a comparative shortening of proximal limb elements. The fossil documents the persistence of this lineage into the earliest Oligocene (~ 33 Ma) in North America. It is the latest occurring North American species of a group that persists in Europe until the Miocene.ConclusionsEocene-Oligocene global cooling is known to have significantly remodeled both Palearctic and Nearctic mammal faunas but its impact on related avifaunas has remained poorly understood. The geographic and temporal range expansion provided by the new taxon together with avian other taxa with limited fossil records suggests a similar pattern of retraction in North America followed by Europe.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1319-6) contains supplementary material, which is available to authorized users.

New bird remains from the early Eocene Nanjemoy Formation of Virginia (USA), including the first records of the Messelasturidae, Psittacopedidae, and Zygodactylidae from the Fisher/Sullivan site

“…This small species from the Green River Formation is unusual in that the ulna distinctly exceeds the tarsometatarsus in length. A putative zygodactylid from the early Oligocene of Montana (USA), which was described as Zygodactylus ochlurus, has a tarsometatarsus length of 15.5 mm (Hieronymus et al 2019).…”

Linking ecological specialization to its macroevolutionary consequences: An example with passerine nest type

“…Fossil records for passerines suggest rapid turnover of diversity over time, with high species diversity and diversification rates (Jetz et al 2012; Marshall 2017) despite the extinctions of entire early passerine lineages (Hieronymus et al 2019; Ksepka et al 2019), high turnover of passerines within Europe between the Oligocene and the present (Manegold 2008; Bochenski et al 2021), and the impact of late Pleistocene species extinctions (Steadman et al 2015; Oswald and Steadman 2018). Diversification models using phylogenetic trees with only extant taxa often appear to underestimate the rates of extinction (Höhna et al 2011; Louca and Pennell 2021), producing error in many diversification analyses (Stadler 2013).…”

“…However, some fossil evidence for passerines suggests that extinction rates and turnover have been high. This evidence includes the extinctions of entire early lineages (Hieronymus et al 2019; Ksepka et al 2019), high turnover within Europe between the Oligocene and the present (Mayr 2005; Manegold 2008; Bochenski et al 2021), and Pleistocene-Holocene species extinctions (Rando 1999; Seguí 2001; Claramunt and Rinderknecht 2005; Rando et al 2010; Oswald and Steadman 2015; Stefanini et al 2016; Rando et al 2017; Steadman and Oswald 2020). In addition, evidence from molecular phylogenies of extant taxa suggests passerine turnover has been high (Greenberg et al 2021).…”

“…However, some fossil evidence for passerines suggests that extinction rates and turnover have been high. This evidence includes the extinctions of entire early lineages (Hieronymus et al 2019 (Stadler 2013). Thus, we sought to examine whether our results were robust to assumptions about extinction rate.…”