A synopsis of the Early Miocene St Bathans Fauna of New Zealand

Abstract

The St Bathans Fauna, from sites near the village of St Bathans, Central Otago, South Island, is the first substantive pre-Quaternary terrestrial vertebrate fossil fauna discovered in New Zealand. This fauna derives from 33 sites or discrete sedimentary beds located in the lower 50 m of the lacustrine Bannockburn Formation, Manuherikia Group, and is generally accepted as local stage Altonian (19–15.9 Ma; Burdigalian, Early Miocene) in age. Investigations since 2001 have revealed an abundant and diverse fauna from over 9000 catalogued lots that is herein reviewed. Invertebrates notably include eight genera and species of terrestrial molluscs. Among vertebrates, freshwater fish remains dominate with 17 species evidenced by 16,500 analysed otoliths (genera Neochanna, Galaxias, Prototroctes, and Mataichthys) and many thousands of bones. Birds (minimally 45 species, several thousand bones) are the most common non-fish vertebrates, among which waterfowls dominate all assemblages (10 species). Co-occurring with these was a diverse herpetofauna, including undetermined crocodylians and a terrestrial turtle, both absent in Recent faunas. Significantly, the St Bathans Fauna evidences that Zealandia already had all of New Zealand’s ‘old’ endemic Recent taxa (sphenodontids, leiopelmatids, dinornithiforms, apterygids, aptornithids, strigopoid parrots, acanthisittids, and mystacinids) during the Early Miocene. Furthermore, it includes Australasia’s oldest ardeids, two flightless rallids, a novel higher landbird family, a greater diversity of bats, and terrestrial mammals. All sites reflect a single fauna, except that the ducks Manuherikia lacustrina (stratigraphically lower in section) and M. primadividua (higher) have a mutually exclusive distribution that is not yet correlated with any other biotic distribution differences.