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

Abstract

We report new avian remains from the early Eocene Nanjemoy Formation of the Fisher/Sullivan site in Virginia, USA. The fossil material includes the first records of the Messelasturidae, Psittacopedidae, and Zygodactylidae from the Nanjemoy Formation, with these taxa being widespread and fairly common in coeval North American and European sites. Psittacopedidae and Zygodactylidae are stem group representatives of the Passeriformes, and a tibiotarsus assigned to the Psittacopedidae is unusual in that it lacks a supratendinal bridge (this bridge is, however, also absent in the psittacopedid taxon Pumiliornis). We further report more material of the Charadriiformes and corroborate a previous tentative referral of a tarsometatarsus to the Parvicuculidae. It is noted that this latter bone is likewise very similar to the tarsometatarsus of the Fluvioviridavidae, which indicates close affinities between the two higher-level clades. Because of the comparatively small extent of the new avian material, it is remarkable that it includes a comparatively high number of fossils that represent previously unknown taxa. This supports the hypothesis that early Eocene avifaunas featured a high taxonomic diversity, but that higher-level clades showed low species richness. We hypothesise that this may indicate low rates of cladogenetic diversification in a rather homogenous paleoenvironment.

Early Eocene fossils elucidate the evolutionary history of the Charadriiformes (shorebirds and allies)

“…As noted by Mayr (2022), the Charadriisimilis essexensis holotype exhibits a Charadrii-like morphology, and affinities to the Charadrii are also suggested by our phylogenetic analyses. Analysis of the unconstrained dataset resulted in three most parsimonious trees (L = 143; CI = 0.57; RI = 0.70) and showed Charadriisimilis to be the sister group of the Burhinidae (Fig.…”

“…The distal humerus of the new species is distinctly larger than that of an unnamed charadriiform from the North American Nanjemoy Formation (Mayr, 2016a;Fig. 4.15), but the proximal humerus corresponds to that of another unnamed charadriiform described by Mayr et al (2022). The occurrence of a concave notch in the proximal humerus from the Nanjemoy Formation and in that of The Charadrii are the sister taxon of a clade including the Scolopaci and Lari and have a scarce fossil record (Bochenski et al, 2019;Mayr, 2022).…”

“…According to studies of molecular data (e.g., Paton et al, 2003; Prum et al, 2015; Kuhl et al, 2021; Černý and Natale, 2022), the Charadriiformes (shorebirds and allies) include three extant higher-level taxa, the Charadrii (plovers and allies), Scolopaci (jacanas, sandpipers, and allies), and Lari (gulls, terns, and allies). Although the interrelationships of these taxa are now congruently resolved in sequence-based analyses, their evolutionary history remains elusive owing to a poor early Paleogene fossil record, which consists mainly of fragmentary remains of uncertain affinities (Mayr, 2022).…”

“…Articulated wing and pectoral girdle elements of an unnamed charadriiform bird are known from the latest early or earliest middle Eocene (∼48 million years ago [Ma]) of the Messel fossil site in Germany (Mayr, 2000), and partial humeri of charadriiforms were reported from the early Eocene (53–54 Ma) Nanjemoy Formation in Virginia, USA (Mayr, 2016a; Mayr et al, 2022) and the early Eocene (∼55 Ma) of Mongolia (Hood et al, 2019). Although these fossils represent unambiguous modern-type (i.e., crown-group-like) charadriiforms, their exact affinities are difficult to determine (an analysis by Musser and Clarke, 2020 recovered them as part of crown group Charadriiformes, but in our opinion the fragmentary nature of the fossils and their generalized morphology impede a well-founded phylogenetic placement).…”

“…In addition to the preceding specimens, there are a few early Paleogene charadriiform-like birds of uncertain affinities (Mayr, 2022; see also Panteleyev, 2011 for the description of unnamed fragmentary remains from the middle Eocene of the Crimea Peninsula, which were overlooked by Mayr, 2022). A well-preserved partial skeleton from the early Eocene Fur Formation in Denmark was described as Scandiavis mikkelseni Bertelli et al, 2013 (see also Heingård et al, 2021, who referred a partial skull to the species).…”