Leptocleidus and Umoonasaurus had round bodies and triangle-shaped heads.

Leptocleidids have been found in what were shallow nearshore, freshwater and brackish habitats.

[2] Hilary F. Ketchum and Roger B. J. Benson (2010), transferred Brancasaurus, Kaiwhekea, Nichollssaura and Thililua to this family.

[3] However, Ketchum and Benson (2011) reassigned Kaiwhekea and Thililua to their original positions, as an elasmosaurid and a polycotylid, respectively.

[1] Kaiwhekea Nichollssaura Thililua Brancasaurus Umoonasaurus L. capensis L. superstes Cladogram based on Ketchum and Benson (2011):[1] Nichollssaura Brancasaurus Umoonasaurus L. capensis L. superstes