Search

All extant birds are toothless, and recent molecular evidence suggests that edentulism in extant birds is the product of a single evolutionary transition to toothlessness on the line to crown birds in the Cretaceous. However, a fossil crown bird premaxilla from the Palaeogene of North America (assigned to the gastornithid Omorhamphus storchii) has been interpreted as bearing alveoli for teeth, an observation that would cast doubt on a single loss of teeth preceding the extant avian radiation. However, the identity of these putative alveoli has never been reinvestigated in detail. Here, we re-examine this problematic juvenile specimen, using non-invasive x-ray microtomography, enabling the assessment of the true identity of the large, alveolus-like pits on the ventral side of this premaxilla. Although superficially alveolus-like, we illustrate that these pits represent openings of large neurovascular canals communicating with both the medullary cavity as well as other canals opening along the dorsal and lateral surfaces of the upper jaw, and that none of these openings appear to represent tooth alveoli. Further, we demonstrate that claims of an adult gastornithid specimen (Gastornis parisiensis) exhibiting tooth alveoli are similarly unfounded. By rejecting the hypothesis of dentition in these gastornithids, we eliminate any lingering uncertainty regarding the persistence of teeth within the avian crown group. We illustrate the presence of similar large vascular openings along the ventral surface of the beak of juvenile Gastornis russelli/parisiensis, and smaller versions in the juvenile premaxillae of Sylviornis neocaledoniae. We suggest that the large vascular canals in gastornithid specimens such as O. storchii are a feature associated with rapid growth of the juvenile beak, allowing the attainment of a large and dorsoventrally deep beak early in ontogeny. This may have enabled young gastornithids to become autonomous early, consistent with a presumably precocial developmental strategy.

The early Eocene locality of La Borie is located near the village of Saint-Papoul, in southwestern France. It consists of clay deposits that have yielded numerous vertebrate fossils, including remains of the giant flightless bird Gastornis. These remains were initially attributed to the species G. parisiensis , which is otherwise recorded from the late Paleocene and earliest Eocene of the North Sea Basin. New fossil birds collected in the La Borie clay pit in 2018 include an almost complete mandible of Gastornis. We describe a new species of Gastornis based on this mandible and we show that the previously described remains from La Borie must be assigned to this new species. The new species differs from other species of Gastornis in the morphology of the mandible, maxilla and quadrate. The morphological diversity of the genus Gastornis , which existed in Europe for at least 17 million years, is emphasized. LSID of publication : urn:lsid:zoobank.org:pub:10E7938B-C972-4127-94DC-169D35977B11. [ABSTRACT FROM AUTHOR]

The early Eocene locality of La Borie is located in the village of Saint-Papoul, in southern France. These Eocene fluvio- lacustrine clay deposits have yielded numerous vertebrate remains. Mammalian taxa found in the fossiliferous levels indicate an age near the reference level MP 8-9, which corresponds to the middle Ypresian, early Eocene. Here we provide a detailed description of the avian remains that were preliminarily reported in a recent study of the vertebrate fauna from La Borie. A maxilla, a quadrate, cervical vertebrae, a femur and two tibiotarsi are assigned to the giant ground bird Gastornis parisiensis (Gastornithidae). These new avian remains add to the fossil record of Gastornis, which is known from the late Paleocene to middle Eocene of Europe, early Eocene of Asia and early Eocene of North America. Gastornis parisiensis differs from the North American Gastornis giganteus in several features, including the more ventral position of the narial openings and the slender orbital process of quadrate. Two tibiotarsi and one tarsometatarsus are assigned to a new genus and species of Geranoididae, Galligeranoides boriensis gen. et sp. nov. So far, this family was known only from the early and middle Eocene of North America. The fossils from La Borie constitute the first record of the Geranoididae in Europe. We show that Gastornis coexisted with the Geranoididae in the early Eocene of both Europe (La Borie) and North America (Willwood Formation). The presence of Geranoididae and the large flightless bird Gastornis on either side of the present-day North Atlantic provides further evidence that a high-latitude land connection existed between Europe and North America in the early Eocene. [ABSTRACT FROM AUTHOR]

The stratigraphic distribution of the three main groups of large flightless birds known from the Palaeogene of Europe, Gastornithidae, Phorusrhacidae and Ratitae, is reviewed. The huge, herbivorous gastornithids, represented by the single genus Gastornis , are known from the Selandian (Middle Palaeocene) to the late Lutetian (Middle Eocene), being recorded from reference levels MP5 to MP13. The carnivorous phorusrhacids are represented by a single species, Eleutherornis cotei , from the late Lutetian (MP14, late Middle Eocene). The ratites have a patchy distribution, being represented by two species of moderate size, Remiornis heberti from the Thanetian (MP6, Late Palaeocene) and Palaeotis weigelti from the Lutetian (MP11 to MP13, Middle Eocene). The stratigraphic distributions of large eggs referred to gastornithids in the Late Palaeocene and Early Eocene of southern Europe and the occurrence of enigmatic large avian footprints in the Late Eocene of France are discussed. Whereas gastornithids and ratites co-existed in both the Palaeocene and the Middle Eocene, phorusrhacids seem to have been the only large ground birds in Europe at the end of the Middle Eocene. The palaeobiogeographical and evolutionary implications of the stratigraphic distributions of those groups of large birds in Europe are discussed. As Gastornis first appears in North America and in Asia in the Early Eocene, it is likely that gastornithids originated in Europe and later spread to other land masses during a dispersal event close to the Palaeocene–Eocene boundary. Prior to that, gastornithids evolved on the European “island continent”, where they were the largest terrestrial tetrapods during the Palaeocene. Gastornithids do not seem to have been significantly affected by the PETM. Ratitae have a more patchy record and relationships between Remiornis and Palaeotis remain unclear. Nevertheless, those European forms are among the earliest known ratites and this should not be overlooked in discussions of ratite evolution and palaeobiogeography. Phorusrhacids appear to have been present in Europe for only a short time and are interpreted as the result of dispersal from Africa followed by local extinction. [ABSTRACT FROM AUTHOR]