A preliminary assessment of the diversity of songbirds (Aves, Passeriformes) from the Miocene St. Bathans Fauna, New Zealand

The passerines or songbirds (Passeriformes) of the Early Miocene St. Bathans Fauna (Otago, New Zealand) have received little attention since studies of this lacustrine fauna began, with just one species, Kuiornis indicator (Acanthisittidae), formally described. In this preliminary study, we assess the species diversity of passerines in the fauna based primarily on size and features of the tarsometatarsus, one of the most commonly preserved elements. Our results demonstrate the presence of between 10 and 17 passerine species in the fauna. These included a meliphagid (honeyeaters), larger than the extant Tui Prosthemadera novaeseelandiae, and newly discovered specimens that further support the previously reported presence of a large cracticid, the size of the Australian Magpie Gymnorhina tibicen. Despite the presence of seven acanthisittids in Holocene faunas and studies that hypothesize that at least four acanthisittid genera were present in the Miocene, we only found evidence for K. indicator, possibly due to a collecting bias. Excluding acanthisittids, the passerine diversity in the St. Bathans Fauna was similar to that of the entire South Island prior to human arrival, all of which suggests that Zealandia had a greater diversity of songbirds during the Early Miocene than in the Holocene, with numbers declining possibly as a result of subsequent losses in floral diversity.