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 structure and 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. Multivariate statistical 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 through regression 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.

Riversleigh, World Heritage Property, located in North-western Queensland, Australia, contains over 200 fossil bearing localities from the Oligo-Miocene. The study presented here aims at finding new methods to improve the accuracy of palaeoecological and biochronological studies and describe the palaeoenvironmental and chronological settings of the Riversleigh fossil deposits. One of the methods developed in this thesis, Minimum Sample Richness (MSR), determines the minimum number of species that must be present in a fauna to allow meaningful comparisons using multivariate analyses. Using MSR, several Riversleigh localities were selected for a palaeoecological study using the cenogram method to determine the palaeoenvironment during the Oligo-Miocene. Finally, the Numerical ages method was used to refine the relative ages of the Riversleigh localities and a re-diagnosis of the Riversleigh Systems is proposed.

The marsupial family Pseudocheiridae is currently known from seventeen species of six genera in Australia and New Guinea. These small to medium-sized arboreal animals are nocturnal and folivorous. Extinct pseudocheirids are recognised from several mid to late Cenozoic fossil localities across Australia and New Guinea. The single largest collection of pseudocheirid fossils has been recovered from the Oligo-Miocene freshwater carbonates of the Riversleigh World Heritage Area in northwest Queensland. This collection, which includes the first pseudocheirid cranial fossils, forms the basis of this investigation. Three new extinct pseudocheirid genera together containing four species are identified and described. Six new species of Paljara, Marlu and Pildra are also described from Riversleigh. Two of the new Marlu species are reported from South Australia??s Leaf Locality. From Riversleigh, Marlu kutjamarpensis is identified and additional material of Paljara tirarensae and P. nancyhawardae documented. New species attributed to Marlu and Pildra necessitate revision of those genera. Cranial material is identified for three of the new species. The rostrum of archaic pseudocheirids is shorter than in extant forms but cranial morphology is similar overall. Phylogenetic relationships of all extinct pseudocheirids are analysed. They include all new and previously described species, most of which have never been examined in a parsimony-based analysis. Two hypotheses of pseudocheirid evolution are presented: a paired lineage hypothesis and a single lineage hypothesis. Both hypotheses demonstrate that species of Paljara are not the most plesiomorphic pseudocheirids, Marlu praecursor does not cluster with other species of Marlu, the new genus Gawinga is most closely related to Paljara and there are no representatives of the extant genus Pseudochirops in any pre-Pliocene locality. All extant pseudocheirids cluster to form a crown clade sister to a stem lineage of Pseudokoala and Marlu species. Pseudocheirids are found in all Oligo-Miocene faunal zones of Riversleigh. Species of Paljara and Marlu are most frequently recovered from Faunal Zone B and C deposits respectively. Four pseudocheirid species biostratigraphically correlate the Kutjamarpu local fauna of the Leaf Locality with Faunal Zones B and C of Riversleigh, suggesting an early to middle Miocene age for both deposits. Modern pseudocheirids first evolved no later than the late Miocene from a descendant of the Marlu + Pseudokoala lineage when all other Oligo-Miocene pseudocheirids became extinct. At least three pseudocheirid lineages dispersed to New Guinea approximately five million years ago, but ecological barriers probably prevented subsequent migrations between the two landmasses.

Riversleigh, World Heritage Property, located in North-western Queensland, Australia, contains over 200 fossil bearing localities from the Oligo-Miocene. The study presented here aims at finding new methods to improve the accuracy of palaeoecological and biochronological studies and describe the palaeoenvironmental and chronological settings of the Riversleigh fossil deposits. One of the methods developed in this thesis, Minimum Sample Richness (MSR), determines the minimum number of species that must be present in a fauna to allow meaningful comparisons using multivariate analyses. Using MSR, several Riversleigh localities were selected for a palaeoecological study using the cenogram method to determine the palaeoenvironment during the Oligo-Miocene. Finally, the Numerical ages method was used to refine the relative ages of the Riversleigh localities and a re-diagnosis of the Riversleigh Systems is proposed.

The marsupial family Pseudocheiridae is currently known from seventeen species of six genera in Australia and New Guinea. These small to medium-sized arboreal animals are nocturnal and folivorous. Extinct pseudocheirids are recognised from several mid to late Cenozoic fossil localities across Australia and New Guinea. The single largest collection of pseudocheirid fossils has been recovered from the Oligo-Miocene freshwater carbonates of the Riversleigh World Heritage Area in northwest Queensland. This collection, which includes the first pseudocheirid cranial fossils, forms the basis of this investigation. Three new extinct pseudocheirid genera together containing four species are identified and described. Six new species of Paljara, Marlu and Pildra are also described from Riversleigh. Two of the new Marlu species are reported from South Australia??s Leaf Locality. From Riversleigh, Marlu kutjamarpensis is identified and additional material of Paljara tirarensae and P. nancyhawardae documented. New species attributed to Marlu and Pildra necessitate revision of those genera. Cranial material is identified for three of the new species. The rostrum of archaic pseudocheirids is shorter than in extant forms but cranial morphology is similar overall. Phylogenetic relationships of all extinct pseudocheirids are analysed. They include all new and previously described species, most of which have never been examined in a parsimony-based analysis. Two hypotheses of pseudocheirid evolution are presented: a paired lineage hypothesis and a single lineage hypothesis. Both hypotheses demonstrate that species of Paljara are not the most plesiomorphic pseudocheirids, Marlu praecursor does not cluster with other species of Marlu, the new genus Gawinga is most closely related to Paljara and there are no representatives of the extant genus Pseudochirops in any pre-Pliocene locality. All extant pseudocheirids cluster to form a crown clade sister to a stem lineage of Pseudokoala and Marlu species. Pseudocheirids are found in all Oligo-Miocene faunal zones of Riversleigh. Species of Paljara and Marlu are most frequently recovered from Faunal Zone B and C deposits respectively. Four pseudocheirid species biostratigraphically correlate the Kutjamarpu local fauna of the Leaf Locality with Faunal Zones B and C of Riversleigh, suggesting an early to middle Miocene age for both deposits. Modern pseudocheirids first evolved no later than the late Miocene from a descendant of the Marlu + Pseudokoala lineage when all other Oligo-Miocene pseudocheirids became extinct. At least three pseudocheirid lineages dispersed to New Guinea approximately five million years ago, but ecological barriers probably prevented subsequent migrations between the two landmasses.

Wombats (Vombatidae, Marsupialia) are fossorial marsupials that are most closely related to koalas amongst living marsupials. The cheek teeth of wombats are unique amongst Australian marsupials in being hypselodont (the condition where the teeth continue to grow throughout life and the formation of roots is suppressed). Hypselodonty is an adaptation to high degrees of tooth wear. The fossil record of vombatids is largely restricted to Pliocene to recent deposits and is largely represented by isolated teeth. Six genera are currently recognised from these deposits, all of which have hypselodont teeth. To date, a single isolated vombatid tooth has been described from pre-Pliocene deposits of South Australia and is the only example of a vombatid cheek tooth that possesses roots. Seventy specimens, representing five species of vombatid, have been recovered from Oligo-Miocene deposits in the Riversleigh World Heritage Site in northwestern Queensland and are described here. Among these are four new species and one new genus. A new species of Warendja from Riversleigh is described. It represents the oldest known hypselodont vombatid. This species is compared with additional specimens of the Pleistocene species of Warendja (W wakefieldi). Three species of Rhizophascolonus and a new monotypic genus are also described. Phylogenetic analysis of these taxa indicates that Rhizophascolonus may represent a sister taxon to the other vombatids. These specimens comprise almost all known examples of Oligo-Miocene vombatids. Most of the specimens are isolated teeth and are highly variable in size and morphology. Cusp detail is clearly preserved on many, allowing for omparison with the cusp morphology on juvenile cheek teeth of the common wombat (Vombatus ursinus). All of the taxa found in the deposits at Riversleigh share a number of characters such as marked differences in enamel thickness and height around the cheek teeth. It is argued here that these shared characters are indicative of high amounts of tooth wear and/or occlusal stresses acting on the trailing edge enamel. Combined with evidence of scratch-digging adaptations of the forelimbs it is suggestive of a rhizophagous niche for at least some of these early vombatids.