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We report charadriiform and charadriiform-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). A partial skeleton of a small modern-type charadriiform is described as a new species, Charadriisimilis essexensis n. gen. n. sp., and most closely resembles taxa of the Charadrii (plovers, stilts, oystercatchers, and other “wader-like” shorebirds). Affinities to this clade were also supported by phylogenetic analyses, which placed the fossil as the sister taxon of either the Burhinidae or all crown group Charadrii. In addition, we identify specimens of the charadriiform-like taxon Scandiavis, which was before known only from the early Eocene Fur Formation in Denmark. Associated limb elements of two individuals are classified as Scandiavis cf. mikkelseni Bertelli et al., 2013, and remains of two further individuals are tentatively assigned to Scandiavis. The presence of a processus supracondylaris dorsalis on the previously unknown humerus corroborates charadriiform affinities of Scandiavis, whereas a plesiomorphic hypotarsus morphology indicates a position outside crown group Charadriiformes. Charadriisimilis essexensis is one of the earliest modern-type charadriiforms, and the holotype of the species is the most substantial early Paleogene fossil record of a charadriiform bird. Together with Scandiavis, as the best-represented taxon to be considered as a stem group charadriiform, it provides the basis for an improved understanding of the evolutionary history of charadriiform birds.
We report new specimens of the Plotopteridae from Washington State (USA), an area where these flightless seabirds underwent significant diversification during the late Eocene and Oligocene. To date, five plotopterid species from western Washington have been formally named. Specimens previously assigned to Tonsala buchanani Dyke, Wang, and Habib, 2011 belong to at least two, but probably even three, different species. One of these, the large-sized “Whiskey Creek specimen” from late Eocene deposits mapped as the Makah Formation, is the oldest known plotopterid and is here tentatively assigned to ?Klallamornis clarki Mayr and Goedert, 2016. Another specimen originally referred to T. buchanani is also likely to belong to a different species and is among the most substantial records for North American plotopterids. We formally transfer T. buchanani to the taxon Klallamornis and show that the only unambiguously identified specimen of the species—the holotype—is currently poorly diagnosed from Klallamornis abyssa Mayr and Goedert, 2016, which is from coeval strata of the Pysht Formation. Although the holotype of K. abyssa is larger than that of K. buchanani, there remains a possibility that plotopterids were sexually dimorphic in size. We describe the first ungual phalanx of a plotopterid, which is referred to K. buchanani, and report previously unknown elements of the large ?K. clarki and the first records of this species from the Lincoln Creek Formation. Current data indicate that plotopterids originated in the middle or late Eocene on islands off western North America, and we hypothesize that the radiation of these birds in the North Pacific Basin may have been related to the evolution of kelp forests.
We revisit the holotype of Calcardea junnei Gingerich, 1987 from the latest Paleocene (Clarkforkian) of the Willwood Formation (Wyoming, USA). The species is based on a partial skeleton and was originally assigned to the Ardeidae (herons). As we show, this classification cannot be upheld and Calcardea Gingerich, 1987 more closely resembles the taxon Vastanavis Mayr et al., 2007 (Vastanavidae), a parrot-like bird from the early Eocene of India. Even though C. junnei is a large bird, its long wings and short tarsometatarsus argue against a predominantly terrestrial way of living, and the morphology of the tarsometatarsus and pedal phalanges instead suggest strong grasping feet. We conclude that an assignment of Calcardea to the landbird clade (Telluraves) is better supported than its classification into the waterbird clade (Aequornithes), which includes Ardeidae and other ‘ciconiiform’ and ‘pelecaniform’ taxa. Calcardea junnei is one of the oldest known representatives of Telluraves and its morphology shows plesiomorphic features, which contributed to its previous misidentification as a heron. Calcardea exhibits a distinctive osteology and affords a glimpse of a previously unknown late Paleocene avian morphotype.
The Paleocene locality of Menat (Puy-de-Dôme, France) has yielded several avian fossils, which remained poorly studied, even though some were found almost a century ago. Here, we review some of the material in public collections and show that those birds from Menat, which are at least tentatively identifiable, resemble taxa from early Eocene fossil localities. A largely complete skeleton of a medium-sized bird with strong feet shows affinities to the early Eocene Halcyornithidae and Messelasturidae, which are considered to be representatives of the clade including Psittaciformes and Passeriformes. Another skeleton of a small species resembles the Songziidae from the lower Eocene of China, which are representatives of Ralloidea, the clade including Rallidae and Heliornithidae. A new and previously unreported specimen exhibits exceptional soft tissue preservation, in that the bones appear to be largely dissolved but the podotheca of the feet and even the soft parts around the shank are visible; the plumage remains of this specimen furthermore show an unusual bluish hue.
Bathornis (“Neocathartes”) grallator (Wetmore, 1944) from the middle Eocene of Wyoming is based on a partial skeleton, which is the most substantial record of the North American Bathornithidae and one of the most complete fossils of a Paleogene stem group representative of the Cariamiformes. So far, however, an assessment of the evolutionary significance of this important fossil has been hampered by the limited published osteological data. Moreover, cariamiform affinities of B. grallator and its true “genus”-level identity were recognized after the last comprehensive revision of the Bathornithidae, and some of its features were incorrectly portrayed in the original description. Here, the B. grallator holotype is restudied and the taxonomic composition and phylogenetic affinities of bathornithids are revised. It is suggested to restrict Bathornithidae to the taxon Bathornis, from which the putative bathornithid Paracrax differs in numerous features, with even cariamiform affinities of this latter taxon not having been established beyond doubt. B. grallator was a flightless bird and has recently been hypothesized to be the sister taxon of the likewise flightless South American Phorusrhacidae. The present analysis, however, supports a position outside a clade including Phorusrhacidae and Cariamidae (the cariamiform crown clade). Owing to their terrestrial way of living, Cariamiformes appear to have been prone to a loss of flight capabilities. B. grallator shows close similarities to a flightless cariamiform bird from the Paleogene of Europe, but the phylogenetic significance of this resemblance is difficult to assess owing to the limited material known of the latter species.
A partial skeleton of a pelagornithid bird found in latest Oligocene or earliest Miocene marine strata in Oregon consists of a pelvis fragment, thoracic vertebrae, and leg bones of a single individual. It is the most completely preserved pelagornithid from the late Oligocene/early Miocene, and one of the few bony-toothed birds from this time period in general. The new fossil is from the Nye Mudstone and shows some previously unknown features that contribute to a better understanding of the osteology of pelagornithids. Because Paleogene and late Neogene pelagornithids differ in several osteological features and the temporally intermediate forms are poorly known, it further bridges a gap in our knowledge of character evolution in pelagornithids. The interrelationships within Pelagornithidae are still poorly resolved, but we detail that a clade of Neogene species, which the Oregon pelagornithid is not part of, can be supported by a derived morphology of the femur. To ease description of Neogene pelagornithids, we synonymize Palaeochenoides Shufeldt, 1916 and Tympanonesiotes Hopson, 1964 with Pelagornis Lartet, 1857, and suggest classification of all Neogene pelagornithids in the latter taxon.
The Paleogene (Paleocene–Oligocene) fossil record of birds in Europe is reviewed and recent and fossil taxa are placed into a phylogenetic framework, based on published cladistic analyses. The pre-Oligocene European avifauna is characterized by the complete absence of passeriform birds, which today are the most diverse and abundant avian taxon. Representatives of small non-passeriform perching birds thus probably had similar ecological niches before the Oligocene to those filled by modern passerines. The occurrence of passerines towards the Lower Oligocene appears to have had a major impact on these birds, and the surviving crown-group members of many small arboreal Eocene taxa show highly specialized feeding strategies not found or rare in passeriform birds. It is detailed that no crown-group members of modern ‘families’ are known from pre-Oligocene deposits of Europe, or anywhere else. The phylogenetic position of Paleogene birds thus indicates that diversification of the crown-groups of modern avian ‘families’ did not take place before the Oligocene, irrespective of their relative position within Neornithes (crown-group birds). The Paleogene fossil record of birds does not even support crown-group diversification of Galliformes, one of the most basal taxa of neognathous birds, before the Oligocene, and recent molecular studies that dated diversification of galliform crown-group taxa into the Middle Cretaceous are shown to be based on an incorrect interpretation of the fossil taxa used for molecular clock calibrations. Several taxa that occur in the Paleogene of Europe have a very different distribution than their closest extant relatives. The modern survivors of these Paleogene lineages are not evenly distributed over the continents, and especially the great number of taxa that are today restricted to South and Central America is noteworthy. The occurrence of stem-lineage representatives of many taxa that today have a restricted Southern Hemisphere distribution conflicts with recent hypotheses on a Cretaceous vicariant origin of these taxa, which were deduced from the geographical distribution of the basal crown-group members.
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