A new therizinosaur from the Early Cretaceous Jehol Biota and ecomorphological patterns among early therizinosaurians

Le résumé fourni par la source

Therizinosauria is a highly specialized clade of maniraptoran theropods, notable for a suite of unusual traits in late-branching taxa. These paradoxical anatomical features contributed to the complex taxonomic history of the clade, which remained unresolved until the discovery of early branching taxa. Here, we describe a new early branching species, Kayrasaurus changliensis, based on a nearly complete, skeletally immature specimen (IVPP V 18597) recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China. This taxon is notably larger than other penecontemporaneous Jehol therizinosaurians (at least 1.6 times larger than the second-largest taxon, Beipiaosaurus inexpectus) and exhibits a unique combination of features (e.g. extremely small and densely packed teeth, cervical centra markedly longer than dorsal centra, and a dorsally extended ‘lip’ on manual ungual IV). We evaluate the phylogenetic position of K. changliensis using an expanded dataset with increased character and taxon sampling. Our results allow us to revise the diagnosis of B. inexpectus and provide new insights into therizinosaurian evolution, provisionally recovering two subclades within Therizinosauridae that are differentiated by their manual ungual morphology. By integrating morphological traits, body mass estimates, and biomechanical data, we infer the possibility of at least two distinct ecological niches among Jehol therizinosaurians. One ecological group, represented by B. inexpectus and possibly K. changliensis, exhibits features indicative of enhanced bite force and a more robust, less cursorial body plan. In contrast, Jianchangosaurus yixianensis and Lingyuanosaurus sihedangensis display traits associated with greater cursoriality and a reliance on forelimb-based foraging. Kayrasaurus changliensis, together with the results of our phylogenetic analysis, provides new insights into the morphological evolution and ecological adaptations of therizinosaurians in the Jehol Biota. However, further analyses and the discovery of more complete, well-preserved specimens are essential to rigorously test and refine these hypotheses. https://zoobank.org/urn:lsid:zoobank.org:pub:505B2A92-F877-490D-AA80-7CE5A21242B9

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.