A carpometacarpus from the upper cretaceous of patagonia sheds light on the Ornithurine bird radiation

We report the discovery of an isolated avian carpometacarpus from the Upper Cretaceous Allen Formation (Campanian-Maastrichtian), Salitral Moreno, Rio Negro Province, Argentina. This specimen is referred to cf. Neornithes because it presents a distinct but shallow infratrochlear fossa, a shortened ventral rim of the carpal trochlea that does not contact the base of the extensor process, and an extensor process conspicuously surpassing cranially the articular facet for digit I. The isolated nature of the specimen precludes its inclusion within the main neornithine lineages. Although it may represent part of the crown clade Neornithes, the limited data available do not confidently support placement within any particular lineage. The carpometacarpus constitutes one of the few records of Mesozoic Neornithine-like birds for South America.