LAUSR

Abstract This paper presents the detailed description of a remarkable skull and partial postcranial skeleton of a very juvenile elasmosaurid referred to Tuarangisaurus keyesi (CD 427), from the upper Campanian-lower Maastrichtian levels of the Tahora Formation, New Zealand. The following points are discussed: i) the conspecific status of CD 427 with T. keyesi, ii) clarification of several cranial sutures in the adult holotype of T. keyesi by comparison with the clearly open sutures in the juvenile specimen; iii) morphologic changes undergone by the skull during the ontogeny of T. keyesi; iv) a first look at the postcranial skeleton of T. keyesi. The studied specimen holds a great significance because it represents one of the rarely-available juvenile elasmosaurid skulls known worldwide. As a result, we provide the first insights regarding the skull ontogeny of an austral elasmosaurid plesiosaurian.