Fossils of treecreepers and a new species of a sittella add to the growing picture of Australia's past songbird diversity.

Songbirds, also known as passerines or perching birds, make up nearly 60% of all living birds. These include the small birds that are often seen in trees and shrubs, such as fairy-wrens, robins and finches, as well as larger birds including crows, magpies and birds-of-paradise. Even though songbirds are now widespread and diverse, little is known about their evolutionary past. This is because very few songbird fossils have been identified and studied, which has implications for our knowledge about their biodiversity into the future.

The oldest known fossils of two groups of songbirds have recently been discovered: sittellas and Australo-Papuan treecreepers. These two groups of songbirds are not closely related to each other, but both are adapted to climbing tree trunks in search of insects. Sittellas spiral up and down tree trunks and along branches, whereas treecreepers only climb from the bottom to the top of trees.

Sittellas and Australo-Papuan treecreepers are very similar in their appearance and their tree-climbing behaviour to the nuthatches and treecreepers found in the Northern Hemisphere. For this reason they were thought to be closely related to their northern counterparts. It wasn't until the 1960s that sittellas and Australo-Papuan treecreepers were recognised as uniquely Australian and New Guinean birds.

The fossils of a sittella and Australo-Papuan treecreepers were identified from leg bones that were discovered in the Riversleigh World Heritage Area in Queensland, Australia. To identify these fossils, I compared them with the skeletons of living songbirds in the Australian Museum's bird collection. These fossils share many similarities in their form and structure with living sittellas and treecreepers.

One of the fossils represents a new species of sittella named Daphoenositta trevorworthyi (Trevor's Sittella), in honour of bird palaeontologist Dr Trevor Worthy. This species lived during the early Miocene, about 10-16 million years ago. Trevor's Sittella looked very similar to its living relatives but it was nearly twice their size.

The discovery of these fossils confirms the long history of sittellas and Australo-Papuan treecreepers in Australia. New fossil discoveries such as these help us to reveal the amazing diversity of birds that lived in this part of the world millions of years ago. These fossils provide a glimpse into how Australia's bird fauna has changed through time, and how it might change in the future.

Dr Jacqueline Nguyen
Chadwick Biodiversity Fellow

More information:

Nguyen, J.M.T. (2016). Australo-Papuan treecreepers (Passeriformes: Climacteridae) and a new species of sittella (Neosittidae: Daphoenositta) from the Miocene of Australia. Palaeontologia Electronica 19.1.1A: 1-13.