Reassessing Concavicaris (Pancrustacea: Thylacocephala) from the Carboniferous of USA

Thylacocephalans are a peculiar group of fossil pancrustaceans characterized by a shield enveloping most of the body, large compound eyes, three pairs of raptorial appendages, eight pairs of gills, and a posterior trunk consisting of 8–22 segments. With a fossil record spanning the Silurian to Cretaceous, thylacocephalans have a wide distribution, both in time and space. However, there has been limited examination of specimens from different time periods, and, as such, thylacocephalan systematics remains controversial, preventing a detailed study on their evolution and diversification. One period that requires further study is the Carboniferous. Almost all known Carboniferous thylacocephalans originate from the USA, including Concavicaris —the most iconic Paleozoic thylacocephalan taxon, which has functioned as a wastebasket genus. Further, there are several Carboniferous thylacocephalan occurrences mentioned in the literature from the USA that have not formally been described. To have a more detailed understanding of Carboniferous thylacocephalan diversity dynamics, as well as underlying evolutionary processes, a thorough systematic review is needed. To rectify this, we performed a detailed review of Carboniferous Concavicaris from the USA. In doing so, we describe a new genus and species, Triangulusinus pustulosus n. gen. n. sp., and present a detailed revision of Concavicaris —a taxon that we split into Concavicaris sensu stricto , Paraconcavicaris , Quadrangulucaris n. gen., and Rotundaparma n. gen. This revision opens new perspectives on the systematics and diversification of thylacocephalans. UUID: http://zoobank.org/3371e3b9-3b57-4df1-897e-37cc8be201ce