Flightless rails (Aves: Rallidae) from the early Miocene St Bathans Fauna, Otago, New Zealand

Abstract

While known for over a decade to exist, fossil rails of the early Miocene (19–16 Ma) St Bathans Fauna, from the South Island of New Zealand, have not previously been described taxonomically or studied in detail. Here we use qualitative osteological features and analyse measurements from wing and leg bones to determine the number of taxa represented, their flight ability, and the presence and nature of sexual dimorphism within the identified taxa. We describe two new rail species in monospecific genera from the St Bathans Fauna: Priscaweka parvales gen. et sp. nov., which is extremely common, and Litorallus livezeyi gen. et sp. nov., a distinctly larger, uncommon species. Priscaweka parvales exhibited a significant degree of sexual dimorphism and was tiny, being the size of the extinct Chatham Island Rail Cabalus modestus. Both newly described species exhibit skeletal proportions and osteological features that indicate they had reduced wings and were flightless. These observations reveal that flightless rallid species have been present in New Zealand for millions of years. The distinctiveness of the St Bathans rails from their closest geographical and chronological neighbours suggests some hidden diversity of volant rails in Australia's fossil record. However, the combined data from Australasian and European records reveal no evidence for a diverse early Miocene crown rallid fauna as predicted by some molecular studies. A subsequent, middle Miocene radiation for crown rallids seems more likely, and appears to have produced the high taxonomic diversity seen in Holocene Australasian rail faunas.

http://zoobank.org/urn:lsid:zoobank.org:pub:9F638A1E-C17D-4A85-9D6E-3D0F24D5AE1E

Keywords:

• fossil birds
• sexual dimorphism
• diversity
• Zealandia

Acknowledgements

We thank A. and E. Johnstone of Home Hills Station, St Bathans, Otago, and Tony Enright of Dunstanburn Station, Southern Lakes Holdings Ltd, for their co-operation and generosity in allowing the excavation of fossils on their land; this study and many others would not have been possible without them. Many thanks go to Jennifer P. Worthy, who has sacrificed hundreds of hours of her time sorting fossils from sediment over the years, many of which were used in this study. Grateful thanks also go to the South Australian Museum, Museum Victoria, Australian Museum, Northern Territory Museum, Museum of New Zealand Te Papa Tongarewa, and the Canterbury Museum for allowing us to borrow specimens for use in this study. Finally, we would like to extend our gratitude to Gerald Mayr and an anonymous reviewer for their feedback and editing advice regarding the manuscript. This work was supported by the Australian Research Council, grants DP0770660 (MA, SH) and DP120100486 (THW).

Additional information

Funding

This work was supported by the Australian Research Council, grants DP0770660 (MA, SH) and DP120100486 (THW)