Femora from an exceptionally large population of coeval ornithomimosaurs yield evidence of sexual dimorphism in extinct theropod dinosaurs

Sexual dimorphism is challenging to detect among fossils due to a lack of statistical representativeness. The Angeac-Charente Lagerstätte (France) represents a remarkable 'snapshot' from a Berriasian (Early Cretaceous) ecosystem and offers a unique opportunity to study intraspecific variation among a herd of at least 61 coeval ornithomimosaurs. Herein, we investigated the hindlimb variation across the best-preserved specimens from the herd through 3D Geometric Morphometrics and Gaussian Mixture Modeling. Our results based on complete and fragmented femora evidenced a dimorphism characterized by variations in the shaft curvature and the distal epiphysis width. Since the same features vary between sexes among modern avian dinosaurs, crocodilians, and more distant amniotes, we attributed this bimodal variation to sexual dimorphism based on the extant phylogenetic bracketing approach. Documenting sexual dimorphism in fossil dinosaurs allows a better characterization and accounting of intraspecific variations, which is particularly relevant to address ongoing taxonomical and ecological questions relative to dinosaur evolution.

The Missing Late Pleistocene Ostrich Femur from Zhoukoudian (China): New Information Provided by a Rediscovered Old Cast

A complete ostrich femur from the Late Pleistocene deposits of the Upper Cave at Zhoukoudian (China) was referred by Shaw to Struthio anderssoni in the 1930s, but its present whereabouts are unknown. A good quality plaster cast of the missing specimen has been found in the collections of the Natural History Museum (London). This cast provides interesting information about the morphology of this large ostrich femur, which had previously been only summarily described and not illustrated. Although smaller than the femora of the Early Pleistocene giant ostrich Pachystruthio, the robust femur from Zhoukoudian shows morphological similarities with them, and it is suggested that ‘Struthio’ anderssoni should be placed in the genus Pachystruthio. The importance of old palaeontological casts is emphasized, as well as the need to preserve and curate them properly.

The First-Named Fossil Ostrich: A Revision of Struthio asiaticus, from the Siwaliks of India

The first fossil ostrich to have been named, by Milne-Edwards in 1869–1871, was Struthio asiaticus, a taxon based on a specimen collected by Colonel Colvin in the Siwaliks of India, consisting of associated postcranial elements (vertebrae, forelimb elements, a fragmentary tarsometatarsus and first phalanx of the third toe). Although it was described as least twice in some detail in the 19th century, the specimen has since then been interpreted in conflicting ways. A revision of the type material and its history shows that it came in all likelihood from the Siwaliks of present-day India, not Pakistan. The exact locality is unknown and the stratigraphic position of the specimen is uncertain (the frequent attribution to the Dhok Pathan Formation is not based on solid evidence). Contrary to what has sometimes been claimed, Struthio asiaticus was neither a small nor an especially large ostrich. It was apparently comparable in size with the modern S. camelus, but had slightly more robust cervical vertebrae and carpal bones. It seems to have been relatively short-toed. Because of the incompleteness of the material and uncertainties about its geological age, it is difficult to assess the place of Struthio asiaticus in the evolutionary history of the ostriches. Reports of Struthio asiaticus from Africa and north-eastern Asia are based on misinterpretations and should be discarded.