The recent discovery of a dense, paucispecific bonebed from the Early Cretaceous Cedar Mountain Formation, central Utah, has yielded new information on the morphology and evolution of therizinosaurs. Detailed description of the pectoral girdle and forelimb of Falcarius utahensis—the predominant taxon recovered from this site—provides the basis for a species-level, phylogenetic investigation of this enigmatic group. The analysis, consisting of 32 characters arrayed among 13 taxa, supports previous assertions that Falcarius represents the basal-most known member of the clade. The analysis further supports a monophyletic Therizinosauroidea on the basis of seven unambiguous synapomorphies of the pectoral girdle and forelimb. Contrary to previous hypotheses, analysis of the pectoral girdle and forelimb suggests that Therizinosauridae is more appropriately defined as a derived clade including Nothronychus, Erlicosaurus, Neimongosaurus, Therizinosaurus, and Segnosaurus. Equally strong support is recovered for a clade containing these five genera plus “Alectrosaurus” and Erliansaurus. The morphology of primitive therizinosauroids—characterized by Falcarius, Beipiaosaurus, and Alxasaurus—suggests that Early Cretaceous taxa already exhibited the beginnings of a trend toward increased robustness and altered range of motion of the pectoral girdle and forelimb. Derived therizinosaurs exhibit an amplification of these evolutionary trends as well as increased dorsal reach, increased wrist flexibility, and severe reduction in manual digit length. The functional reorganization of the pectoral girdle and forelimb throughout the evolutionary history of therizinosaurs can be reasonably attributed to a shift from obligatory predation to a novel paleoecological role that reached its pinnacle in derived Late Cretaceous members.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 26 • No. 3