The late Cenozoic passerine avifauna from Rackham’s Roost Site, Riversleigh, Australia

The Riversleigh World Heritage Area, north-western Queensland, is one of the richest Cenozoic deposits in Australia for passerine fossils. Most of the Riversleigh passerine remains derive from the late Cenozoic Rackham’s Roost Site. Here we describe 38 fossils from this site, which represent eight extant families of passerine birds. These fossils include the oldest records of Maluridae (fairywrens and allies), Acanthizidae (acanthizid warblers), Pomatostomidae (Australo-Papuan babblers), Petroicidae (Australasian robins), Estrildidae (estrildid finches), Locustellidae (songlarks and grassbirds) and Acrocephalidae (reed warblers) in Australia, and the oldest records globally of Maluridae, Acanthizidae, Pomatostomidae, Petroicidae and Estrildidae. The fossils also include the oldest known representatives of the major radiation Passerida sensu stricto in the Australian fossil record, indicating that the second dispersal event of this group had already occurred in this region at least by the early Pleistocene. In describing the Rackham’s Roost fossils, we have identified suites of postcranial characters that we consider diagnostic for several Australian passerine families. These osteological characters can be used in future palaeontological, morphological and phylogenetic studies. The overrepresentation of small animals and the fragmentary condition of their remains suggests that the extant carnivorous Ghost Bat, Macroderma gigas (Megadermatidae) was the primary accumulator of the Rackham’s Roost assemblage. The taxonomic composition of the Rackham’s Roost passerine avifauna corroborates the palaeoenvironmental interpretation of this site as open woodland with a grassy understorey, perhaps next to a riparian forest. These passerine remains also provide a record of the avian component of the endangered Ghost Bat’s diet in this part of northern Australia, an area from which it has recently disappeared. KeywordS. Passeriformes; fossil bird; osteology; late Cenozoic; Riversleigh; Australia nguyen, Jacqueline M. T. , Suzanne J. Hand, and MicHael arcHer. 2016. The late Cenozoic passerine avifauna from Rackham’s Roost Site, Riversleigh, Australia. Records of the Australian Museum 68(5): 201–230. http://dx.doi. org/10.3853/j.2201-4349.68. 2016.1668 202 Records of the Australian Museum (2016) Vol. 68 The Riversleigh World Heritage Area, which lies within Boodjamulla (Lawn Hill) National Park in north-western Queensland, is one of the most significant Cenozoic fossil regions in Australia. These fossil deposits are exceptional because they document regional biodiversity and faunal and environmental change over the last 25 million years, from the late Oligocene to the Holocene (Archer et al., 1989, 2000). The Riversleigh deposits have yielded a spectacularly diverse fauna, including insects, ostracods, molluscs, fish, amphibians, reptiles, birds and mammals (Archer et al., 2006; Arena, 2008 and references therein). Much of its rich and diverse mammalian fauna has been the focus of palaeontological, palaeoecological and phylogenetic studies (e.g., Black et al., 2012). There have been considerably fewer studies on the Riversleigh avifauna, particularly the passerines (perching birds). Numerous passerine fossils have been recovered from Riversleigh. Only a fraction of these fossils have been described so far, but they reveal a diversity of taxa. Fossil passerines from early Miocene sites in Riversleigh include: a lyrebird, Menura tyawanoides Boles, 1995; Australo-Papuan treecreepers, Cormobates sp. and Climacteris sp. (Nguyen, 2016); an oriolid, Longmornis robustirostrata Boles, 1999a; a cracticid, Kurrartapu johnnguyeni Nguyen, 2013; and a corvid-like passerine, Corvitalusoides grandiculus Boles, 2006. Middle Miocene deposits at Riversleigh have yielded a sittella, Daphoenositta trevorworthyi Nguyen, 2016 and indeterminate honeyeaters (Boles, 2005). Fossils of a logrunner, Orthonyx kaldowinyeri Boles, 1993 have been recovered from Riversleigh sites that span the late Oligocene to the late Miocene (Nguyen et al., 2014). Fossils representing three indeterminate honeyeater taxa have been reported from the late Cenozoic Rackham’s Roost Site (Boles, 2005), one of the richest sites at Riversleigh for small bird bones. Most of the known Riversleigh passerine material derives from this site. The Rackham’s Roost fossils, which form the basis of this paper, present an opportunity to improve our understanding of the evolutionary history and past diversity of Australia’s passerine avifauna. In this study, our main aim is to describe the Rackham’s Roost passerine fossils and interpret aspects of the taphonomy and palaeohabitat of this site. Our secondary aim is to identify and describe characters of postcranial bones that are informative for distinguishing selected passerine families.