Taphonomic and palaeoecological investigations of Riversleigh Oligo-miocene fossil sites: mammalian palaeocommunities and their habitats

The palaeoecology of selected fossil sites from the Riversleigh World Heritage Area, northwestern Queensland, Australia, was studied with the aim of describing the palaeohabitats of the sites through the use of characteristics of mammalian community structure. Taphonomic analyses were carried out to determine whether the study sites represent allochthonous or autochthonous assemblages. Subsequently, ecological attributes of the mammalian fossil assemblages were inferred from functional morphology. Trophic and locomotor behaviours were used to describe the adaptive structure of communities and a method was established for inferring the locomotor behaviour of fossil taxa from morphometrics of their calcanea. Such ecological attributes of the assemblages can be used in reconstructing habitats. This is possible because modern mammalian community structure (as represented by ecological diversity/attribute characteristics) has been found to correlate with habitat structureand thus has predictive value, directly applicable in palaeoecology. Modern mammalian faunas from a variety of habitats around the world were used as possible analogues for the Riversleigh fossil faunas. Multivariatestatistical techniques were explored for identifying potential similarities between the community structure of the fossil faunas and that of the modern faunas. Annual rainfall was then estimated for the fossil sites throughregression analysis allowing climatic inference from the faunal palaeocommunities. On the basis of similarities in community structure, general habitat or vegetation structure was proposed for the fossil assemblages. The results of the analyses undertaken indicate that Riversleigh early-middle Miocene habitats were densely forested.The late Oligocene Quantum Leap Site local fauna and the late Miocene Encore Site local fauna suggest mixed vegetation, or more open environments. The trend of decreasing annual rainfall through the Miocene and the palaeohabitats of the Miocene sites proposed here fit the general pattern of vegetation and climate change during this period for the Australian continent as a whole