A redescription and phylogenetic position of Adocus planus, an adocid turtle from the Late Cretaceous of Mongolia

Abstract

In this paper we present a detailed description of the holotype of Adocus (orig. Shineusemys) planus from the Late Cretaceous of Mongolia. The holotype, originally reported to be a plastron, is actually represented by a partial shell with an almost complete plastron and few carapace fragments on the steinkern. The reexamination of the holotype of A. planus allows us to present new images of this specimen, improve its diagnosis and include it in a phylogenetic analysis of Adocusia (Adocidae + Nanhsiungchelyidae) for the first time. The phylogenetic analysis places A. planus within the Adocus clade in polytomy with other species of this genus. This result confirms our previous suggestion that Shineusemys should be considered a junior subjective synonym of Adocus.