Palaeoecology and preliminary taphonomy of the Robertson Cave entrance chamber fauna, Naracoorte

Abstract

The entrance chamber of Robertson Cave contains the most complete Holocene vertebrate deposit yet found at Naracoorte Caves, South Australia. The deposit dates from ~946 to 24090 Cal yr BP, spanning the ‘youngest’ part of the ~500,000 year Naracoorte fossil record. This study examined previously unstudied entrance chamber material, focussing primarily on the mammal fauna. Fossils were first sorted for diagnostic specimens and then identified to taxon. Taphonomic analysis of bone breakages, corrosion, manganese staining and hairline fracturing were completed. Statistical significance of faunal community composition across 12 excavation layers was analysed using chi-squared tests, along with comparisons between a similar, contemporaneous site, Wet Cave, and the modern mammal faunas for the region. Rarefaction was undertaken to ensure that the sample size from the deposit was sufficient to assess community structure. Palaeoecological analysis revealed the mammal fauna was composed largely of small herbivores and insectivores, with larger herbivores and only two larger carnivores. Assessment of the abundance of Anura in comparison with the mammalian fauna showed that in excavation layers 3 and 4, there was a much higher ratio of mammals; particularly Muridae, to Anura, which correlates to ~3819 to 10224 years ago. Taphonomic analysis of corrosion and breakages suggest the faunal assemblage was accumulated primarily as an owl deposit, aligning with prior work. The owl species was likely Tyto novaehollandiae, as indicated by the prey size range. Limited manganese staining and hairline fracturing of the bones suggest the cave environment remained relatively dry over time and has not experienced frequent significant wetting and drying. The inferred vegetation for the area immediately around the cave entrance was open, dry sclerophyll forest. Additionally, open mallee heathland was likely present in the region. Overall, Robertson Cave has a well-preserved diverse fossil assemblage that warrants further research.