The morphology of the single preserved molar of the holotype of the Australian Early Cretaceous (Aptian) mammal Teinolophos trusleri shows that it is a monotreme and probably a steropodontid, rather than a 'eupantothere' as originally proposed. The structure of the rear of the jaw of T. trusleri supports the molecular evidence that previously formed the sole basis for recognising the Steropodontidae as a distinct family.

Thomas H. Rich [trich@museum.vic.gov.au ], Museum Victoria, P.O. Box 666E, Melbourne, Victoria 3001, Australia; Patricia Vickers-Rich [prich @mail. earth. monash. edu. au ], Andrew Constantine [andrew.constantine@nre.vic.gov.au ], and Lesley Kool[1kool@mail.earth.monash.edu.au ], Earth Sciences Department & Monash Science Centre, Monash University, Clayton, Victoria 3168, Australia; Peter Trusler, 9 Whitehorse Road, Blackburn, Victoria 3130, Australia; Timothy F. Flannery Iflannery.tim@saugov.sa.gov.au ], South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia; Richard Cifelli [rlc@ou.edu ], Oklahoma Museum of Natural History, 2401 Chautauqua, Norman, Oklahoma 7301 9-0606, USA; Nicholas van Klaveren [nvk@zx.net ], 1/6 Lucerne Avenue, Mornington, Victoria 3931, Australia.