The second mamenchisaurid dinosaur from the Middle Jurassic of Eastern China

A new mamenchisaurid dinosaur, <i>Anhuilong diboensis</i> gen. et sp. nov. from the Middle Jurassic of Eastern China is reported here. The holotype consists of complete left humerus, ulna and radius of an individual. Comparative study and cladistic analysis shows this new taxon belongs to Mamenchisauridae and bears a unique combination of characters, such as low ratios of the average of the greatest widths of the proximal end, mid-shaft and distal end of the humerus/length of the humerus, total length of ulna to humerus and total length of radius to humerus; the lateral edge of the deltopectoral crest directs caudolaterally, the lateral accessory condyle on the craniodistal edge of humerus is more robust than the medial one, and the cross-sectional shape of the ulna at mid-shaft is elliptical with highest ratio of transverse to craniocaudal diameter among mamenchisaurids. Phylogenetically, <i>Anhuilong</i> is the sister taxon of <i>Huangshanlong</i>, and with <i>Omeisaurus</i> they together form the sister clade to all other members of Mamenchisauridae. Including <i>Huangshanlong</i>, two mamenchisaurids have been found in eastern China, and indicates that Mamenchisauridae was already a diverse sauropod clade in China by the Middle Jurassic.