Abstract

An indeterminate aristonectine elasmosaurid is recorded from a lower Maastrichtian bed of the Conway Formation, Waipara River, South Island, New Zealand. The described specimen (CM Zfr 104), previously considered part of the hypodigm of Mauisaurus haasti, came from the upper part of the Alterbidinium acutulum biozone, the same zone from which the only well-known aristonectine from New Zealand, Kaiwhekea katiki, is recorded. The cervical vertebrae of CM Zfr 104 have the same distinctive features (i.e., with extremely broad rather than long centra) as those from previously recorded juvenile aristonectines from Argentina, Chile and Antarctica. This new record is congruent with the biogeographic relationships of Cretaceous marine amniotes from the Weddellian Palaeobiogeographic Province (i.e., Patagonia, western Antarctica, New Zealand and southeastern Australia). Therefore, this type of vertebra is regarded as a distinctive feature of the Weddellian aristonectine elasmosaurids.