Yongjiacaris

Yongjiacaris is an extinct genus of shrimp, which had only one species, Yongjiacaris zhejiangensis.^[1] Yongjiacaris represents the second report of freshwater caridean shrimp from the Mesozoic.^[1]

The name of the genus Yongjiacaris refers to Yongjia County, in the Zhejiang Province of China, while the species name Y. zhejiangensis is derived from the province name.^[1] Yonjiacaris was formally described by Alessandro Garassino, Shen Yanbin, Frederick R. Schram, and Rod S. Taylor in 2002.^[1] It is described from 138 specimens discovered in the C Member of the Moshishan Formation of Yongjia County, and from specimens found in the Showchang Formation near Jiande, both in southeastern China.^[1] These two correlative rock units date to the Barremian age of the Early Cretaceous; volcanic rocks in the C Member of the Moshishan Formation are dated to 120 million years old, and volcanic rocks in the Showchang Formation are dated to 118 million years ago.^[1] The C Member of the Moshishan Formation is a heterogeneous rock unit including sandstone, shale, tuff, conglomerate, and rhyolite, while the Showchang Formation is dominantly sandstone and mudstone.^[1] The types of plants present in the C Member and the Showchang Formation (relatively abundant ferns and Bennettitales, rare members of the Ginkgoaceae) and characteristics of the plants, such as leaf form and cuticle thickness, indicate a relatively hot and dry climate.^[1] The two rock units have fossil assemblages including plants, charophytes, bivalves, ostracods, conchostracans, and insects.^[1]

While other genera from the family Palaemonidae are known from the Aptian age in the lower Cretaceous period, Yongjiacaris represents the first member described from the Barremian age.^[1] It measured from 1.5 to 2 centimetres (0.6 to 0.8 in) in length.^[1]