Morphometric analysis confirms the presence of the Plains-wanderer (Aves: Pedionomus torquatus) in fossil deposits at Naracoorte Caves, South Australia

The Plains-wanderer (Pedionomidae: Pedionomus torquatus) is a species of Australian shorebird that exclusively inhabits open grasslands. The reported presence of this species in the fossil deposits of Naracoorte Caves suggests that it once inhabited a wooded environment. It was therefore important to assess whether the fossils are indeed conspecific with P. torquatus before inferences on the past palaeoecological preferences of the species are made. This study reassessed the identity of fossils identified as P. torquatus using both qualitative observations and morphometric analyses to test for proportional differences of fossil specimens which might indicate taxonomic distinction. Measurements were collected from fossils attributed to Pedionomus from Blanche Cave (45-15 ka) and Victoria Fossil Cave (>400-220 ka), and compared with modern skeletal specimens through univariate and principal component analyses. Fossil elements were significantly larger than the modern specimens, although marked overlap was consistently observed, precluding unambiguous differentiation on size. No qualitative traits distinguishing the two groups could be identified. The Naracoorte fossil Pedionomus are therefore considered to represent a population of P. torquatus, wherein birds were slightly larger than extant ones. The Naracoorte deposits sampled a forest and woodland-dominated environment over the last 400,000 years, one which would be deemed unsuitable for modern Plains-wanderers, indicating that P. torquatus may have formerly occupied a much broader range of habitats than its present distribution suggests. It is inferred that the Plains-wanderer underwent a marked contraction in occupied habitat during the Holocene.