St Bathans fauna

rdf:langString St Bathans fauna

rdf:langString The St Bathans fauna is found in the lower Bannockburn Formation of the Manuherikia Group of Central Otago, in the South Island of New Zealand. It comprises a suite of fossilised prehistoric animals from the late Early Miocene (Altonian) period, with an age range of 19–16 million years ago. The layer in which the fossils are found derives from littoral zone sediments deposited in a shallow, freshwater lake, with an area of 5600 km2 from present day Central Otago to Bannockburn and the Nevis Valley in the west; to Naseby in the east; and from the Waitaki Valley in the north to Ranfurly in the south. The lake was bordered by an extensive floodplain containing herbaceous and grassy wetland habitats with peat-forming swamp–woodland. At that time the climate was warm with a distinctly subtropical Australian climate and the surrounding vegetation was characterised by casuarinas, eucalypts and palms as well as podocarps, araucarias and southern beeches. The fossiliferous layer has been exposed at places along the Manuherikia River and at other sites in the vicinity of the historic gold mining town of St Bathans. The fauna consists of a variety of vertebrates, including fish, a crocodilian, a rhynchocephalian (a relative of tuatara), geckos, skinks, and several kinds of birds, especially waterbirds. Of tree-dwelling birds, parrots outnumber pigeons thirty to one. Proapteryx, a basal form of kiwi, is known from there. The Miocene ecosystem was recovering from the ‘Oligocene drowning’ a few million years earlier, when up to 80% of the current land area of New Zealand was submerged. The wildlife that lived in, on, and around the palaeolake Manuherikia was uniquely New Zealand, which strongly suggesting that some emergent land remained during this near drowning event. Marked global cooling and drying during the Miocene, Pliocene and the Pleistocene Ice Ages resulted in the extinction of the ‘subtropical’ elements of the St Bathans’ fauna. Those that survived adapted to the dynamic geological and climatic changes, and would form part of the enigmatic fauna that characterised New Zealand when humans arrived in the late 13th century.