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Is the modern koala ( Phascolarctos cinereus) a derived dwarf of a Pleistocene giant? Implications for testing megafauna extinction hypotheses

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Abstract

The modern Australian koala (Phascolarctos cinereus) is commonly regarded as a dwarf descendent of a Late Pleistocene giant koala (Ph. stirtoni). The implication of that hypothesis is that the giant koala survived the Late Pleistocene megafaunal extinction “event”, albeit as a smaller body-sized form. It is important to be able to constrain rates of Late Pleistocene faunal turnover, an aspect reliant on having accurate taxonomic information of extinct species. The koala dwarfing hypothesis is tested here by using a temporally-constrained biogeographical record of fossil koalas, and a morphological character analysis. The contemporary occurrence of both taxa in pre-Late Pleistocene deposits and significant differences in dental morphologies between those forms suggests that the modern koala is not a derived dwarf of the Pleistocene giant koala. Thus, the giant-form was among a number of other giant mammals, lizards and birds that suffered extinction sometime during the Late Pleistocene. The potential phenomenon of dwarfing of other Late Pleistocene and Recent faunas, such as grey kangaroos, is commonly used as a test for or against various megafaunal extinction hypotheses. However, the results of this study also demonstrate that the dwarfing hypothesis has not been adequately tested for a suite of other taxa. Thus, until the dwarfing hypothesis can be more fully tested, a clear understanding of the fate of Late Pleistocene faunas that apparently survived the extinction “event”, and the origins of many extant forms will remain elusive.

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... The modern genus has a fossil record dating back to the late Miocene or Pliocene (Pledge, 1992) of South Australia and the modern species to 350 ka, with numerous Quaternary records in all states except Tasmania and the Northern Territory (Price, 2008a). Today, P. cinereus occupies temperate, sub-tropical and tropical forests and moist to semi-arid woodlands from northeastern Queensland to the southeastern corner of South Australia (Fig. 1). ...
... The specific distinction of P. stirtoni and P. maris from each other, and from P. cinereus, has been the subject of much debate (e.g., Archer and Hand, 1987;Black, 1999;Piper, 2005;Price, 2008a). Few morphological features distinguish the species Black, 1999;Piper, 2005) and those previously noted (e.g., Bartholomai, 1968;Price, 2008a; appear to fall within the range of variation exhibited in the dentitions of the living species (see Black et al., 2013a). ...
... The specific distinction of P. stirtoni and P. maris from each other, and from P. cinereus, has been the subject of much debate (e.g., Archer and Hand, 1987;Black, 1999;Piper, 2005;Price, 2008a). Few morphological features distinguish the species Black, 1999;Piper, 2005) and those previously noted (e.g., Bartholomai, 1968;Price, 2008a; appear to fall within the range of variation exhibited in the dentitions of the living species (see Black et al., 2013a). Morphological comparisons between P. stirtoni and P. maris cannot be made directly because the former is known from its upper dentition and the latter from an isolated lower molar. ...
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The modern Koala Phascolarctos cinereus is the last surviving member of a once diverse family Phascolarctidae (Marsupialia, Phascolarctomorphia). Nine genera and at least 16 species of koala are known. Late Oligocene sediments of central Australia record the oldest fossils and highest species diversity. Five species are known from the early to middle Miocene rainforest assemblages of the Riversleigh World Heritage Area, Queensland. With the onset of dryer conditions after the middle Miocene climatic optimum (~ 16 Ma), rainforest habitats contracted resulting in the apparent extinction of three koala lineages (Litokoala, Nimiokoala, Priscakoala). Phascolarctos first appears in the fossil record during the Pliocene and the modern species around 350 ka. Despite a dramatic decline in taxonomic diversity to a single extant species, the fossil record indicates that at most only three koala species coexisted in any given faunal assemblage throughout their 24 million year history. Within these assemblages, the vast majority of extinct koalas are extremely rare (some known from only a single specimen) which may reflect a general rarity within their palaeohabitats compared with the modern species which is represented by an estimated 400,000 individuals spread over most of eastern mainland Australia. Be that as it may, Phascolarctos cinereus, although once geographically more widespread, occurring for example in Western Australia in the Pleistocene, underwent significant range contractions and localized population extinctions during the stressful climatic conditions of the late Pleistocene and more recently through human-induced habitat destruction. Combined with threats of disease, reduced genetic diversity and climate change, the survival of this iconic Australian marsupial is arguably a cause for concern.
... 50 ka (Price et al., 2009b) whilst the oldest records are ca. 500 ka (Price, 2008). This suggests that the deposit is mid-late Pleistocene, and thus in agreement with the age suggested by the presence of the giant devil. ...
... In general, koalas are rare components of the Australian fossil record (Black, Louys & Price, 2014), and this is especially true of Phascolarctos stirtoni. The species was described on the basis of a single maxillary fragment (Bartholomai, 1968), with only scant specimens referred to it since (Price, 2008). ...
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Fossils from caves in the Manning Karst Region, New South Wales, Australia have long been known, but until now have never been assessed for their palaeontological significance. Here, we report on late Quaternary faunal records from eight caves in the region. Extinct Pleistocene megafaunal taxa are recognised in two systems and include giant echidnas (Tachyglossidae gen. et sp. indet.), devils ( Sarcophilus laniarius ), koalas ( Phascolarctos stirtoni ), marsupial ‘lions’ ( Thylacoleo carnifex ), and kangaroos ( Macropus giganteus titan ). Some caves contain skeletal remains of introduced exotics such as sheep and dogs, but also provide a rich record of small-bodied native species including Eastern Bettongs ( Bettongia gaimardi ), Eastern Chestnut Mice ( Pseudomys gracilicaudatus ), and White-footed Rabbit Rats ( Conilurus albipes ). These endemics are either locally extirpated or have suffered total extinction in the historic period. Their skeletal and dental remains were recorded as unmineralised surface specimens in the caves, indicating that they are recent in age. Extant populations have never been recorded locally, thus, their probable loss from the region in historic times had gone unnoticed in the absence of palaeo-evidence. Our findings suggest that the supposed habitat tolerances of such species have been substantially underestimated. It is highly likely that modern populations have suffered niche contraction since the time of European colonisation of the continent. The local extirpations of several species of digging mammal has likely led to decreased functionality of the current ecosystem.
... Louys et al. 2007; this paper) from the Riversleigh World Heritage Area, north-western Queensland (Fig. 1), the genus was known from a few isolated teeth (see Stirton et al. 1967;Springer 1987). Assessment of species boundaries and intraspecific variation in previous systematic studies of koalas by Black & Archer (1997), Louys et al. (2007) and Price (2008b) have been based on unpublished qualitative accounts of variation in P. cinereus dentitions by the authors (e.g. unpublished thesis of Black 1992). ...
... This approach is consistent with numerous other morphometric dental studies of not only koalas (e.g. Bartholomai 1968;Price 2008b;Pledge 2010), but marsupials in general (e.g . Freedman 1967;Freedman & Joffe 1967a, b;Bartholomai 1971;Price 2002Price , 2005Price , 2008aEaston 2006;Black & Hand 2010), and allows for direct comparison of results between respective investigations. ...
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We document morphological variation (both geographical and sexual) in the dentition of the extant koala, Phascolarctos cinereus, in order to facilitate discrimination of species boundaries in extinct phascolarctids. Considerable variation is evident in dental structures previously used to diagnose several phascolarctid fossil species. Consistent patterns of morphological variation are not evident between sexes or geographic regions, with variation as great between samples as within them. Metric variation is evident between the sexes in upper molar dimensions with Victorian (southern) males significantly larger than Victorian females, although this is not reflected in lower molar dimensions or in the Queensland (northern) sample. Male koalas from southern populations generally display significantly larger molars than their northern counterparts; however this trend is not evident in female upper molar dimensions. In both males and females, some, but not all, lower molar dimensions are larger in southern populations than northern. In light of these results, a systematic revision of species of Litokoala suggests L. dicktedfordi' is a junior synonym of L. kutjamarpensis, and the poorly known L. thurmerae is regarded to be a nomen dubium. Further, we describe a partial cranium of a new species of koala from Early Miocene sediments in the Riversleigh World Heritage Area, northern Australia. Litokoala dicksmithi sp. nov. is the fifth koala species recorded from the diverse rainforest assemblages of Riversleigh and the third species referred to the Oligo-Miocene genus Litokoala. Aspects of cranial morphology, including a shortened robust rostrum and broad, irregular nasal aperture, confirm placement of Litokoala as sister taxon to the modern genus Phascolarctos. Relatively large orbits and small body size suggest the possibility that L. dicksmithi was nocturnal, had enhanced visual acuity, and was a more agile arboreal species than the relatively sedentary extant koala.
... Due to the broad temporal span of the P. cinereus fossil records (< 1 to 569 thousand years ago) (Price 2008), these fossil data were not considered reliable for use in our modelling. We therefore used the contemporary distribution data of P. cinereus with its contemporary climate envelope and then used it to predict the past distribution of this species at the LGM. ...
... Published fossil sites containing relatively well-dated records of koalas since the Late Miocene, 11-5.3 million years ago (followingPrice 2008). ...
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The koala Phascolarctos cinereus is the only member of the once diverse marsupial family Phascolarctidae to have survived the Last Glacial Maximum. A climate envelope model for P. cinereus was developed to predict the range for this species at present and at the Last Glacial Maximum. The model was compared to the contemporary koala records and the known fossil records of P. cinereus during the Quaternary. The predicted current core range for koalas was concentrated in southeast Queensland, eastern New South Wales and eastern Victoria. At the Last Glacial Maximum their predicted core range contracted significantly to southeast Queensland and northeast New South Wales. Our findings concord with other studies that find species experienced range contractions during glacial maxima. In the context of the future conservation planning for koalas in the wild, our historical perspective demonstrates the past adaptations of koalas to changes in climate and their probable range contraction to climatic refugia. The future survival of wide-ranging specialist
... stirtoni, are known from Pliocene and Pleistocene deposits of southern and eastern Australia (Pledge 1992; Archer et al. 1997; Price et al. 2009a, b). The extant Ph. cinereus has a fossil record extending back until at least the middle Pleistocene (Price 2008). Phascolarctos cinereus was originally considered to have been a late Pleistocene-Holocene dwarf of the extinct Ph. stirtoni (Archer 1984; Archer and Hand 1987; Murray 1984), thus implying that the later taxon did not suffer extinction in the late Pleistocene as a suite of other large-bodied 'megafauna' did (e.g., Price and Sobbe 2005;). ...
... Yet the fossil record demonstrates that it was not entirely resilient to such impacts through the Pleistocene–Holocene transition. Fossil records demonstrate that the modern koala once had a near continent-wide distribution (Price 2008), being found not only through eastern and southeastern Australia (including its modern geographic range), but also across southern central and southwestern Australia (e.g., Archer 1972; Lundelius and Turnbull 1982; Prideaux et al. 2010). For example, late Pleistocene fossils of Ph. cinereus have been recorded from Madura Cave, part of the Nullarbor Plains ('the treeless plains') (Lundelius and Turnbull 1982) (Fig. 9.2). ...
Chapter
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Understanding phylogenetic diversity over large temporal scales as afforded by the fossil record allows for the identification of the history of taxonomic diversity in extant taxa. Identification of such long-term trends in lineage 'health' is a critical, but commonly underutilized method for helping to prioritize species for conservation. The modern Australian koala (Phascolarctos cinereus) is a case in point. It is widely debated whether the modern koala should be an immediate candidate for conservation. Although modern populations have seen recent declines in some regions, in other areas koalas are overabundant, with translocation, con-traceptive, and evening culling programs suggested as population control measures. The view from the fossil record is that koalas (family Phascolarctidae) have suffered a dramatic, progressive long-term decline in diversity (e.g., four genera and eight species in the late Oligocene, compared to only one genus and species at present). At no time in the known history of the Phascolarctidae has phylogenetic diversity been as low as today. Climate change, leading to enhanced variability in seasonality, increased aridfication, and habitat change has had a negative impact on phascolarctid diversity through time, and has been a determining factor in the geographic range of the modern koala. Do such observations warrant adding the modern koala to the list of threatened species? Although the answer to this question remains outside the scope of this chapter, it should be remembered that extinction of the extant koala would mark the loss of not only of a single species, but also of an entire family of endemic Australian marsupial.
... Recently, Johnson et al. [21] integrated long and short read sequencing by PacBio and Illumina to generate the highest quality reference genome assembly of any marsupial species for the modern koala (Phascolarctos cinereus), the sole extant member of the marsupial family Phascolarctidae [22]. To leverage and compliment this resource, here we have generated whole-genome bisulfite sequencing (WGBS) maps across tissues of both sexes, capturing the DNA methylation state of nearly all cytosines in koala genome. ...
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X chromosome inactivation (XCI) mediated by differential DNA methylation between sexes is an iconic example of epigenetic regulation. Although XCI is shared between eutherians and marsupials, the role of DNA methylation in marsupial XCI remains contested. Here, we examine genome-wide signatures of DNA methylation across fives tissues from a male and female koala ( Phascolarctos cinereus ), and present the first whole-genome, multi-tissue marsupial ‘methylome atlas’. Using these novel data, we elucidate divergent versus common features of representative marsupial and eutherian DNA methylation. First, tissue-specific differential DNA methylation in koalas primarily occurs in gene bodies. Second, females show significant global reduction (hypomethylation) of X chromosome DNA methylation compared to males. We show that this pattern is also observed in eutherians. Third, on average, promoter DNA methylation shows little difference between male and female koala X chromosomes, a pattern distinct from that of eutherians. Fourth, the sex-specific DNA methylation landscape upstream of Rsx , the primary lnc RNA associated with marsupial XCI, is consistent with the epigenetic regulation of female-specific (and presumably inactive X chromosome-specific) expression. Finally, we use the prominent female X chromosome hypomethylation and classify 98 previously unplaced scaffolds as X-linked, contributing an additional 14.6 Mb (21.5%) to genomic data annotated as the koala X chromosome. Our work demonstrates evolutionarily divergent pathways leading to functionally conserved patterns of XCI in two deep branches of mammals.
... While the extinction of L. webbi appears to be tied to climate-change driven habitat loss, the causes for the wider decline of the genus in recent times is unclear. It is, however, a pattern also apparent in other Australian mammal groups such as koalas (Price, 2008a;Black et al., 2014;Price, 2012a). This present study adds to the growing list of small-bodied mammal extinctions that occurred in Australia, alongside the extinction of the megafauna, throughout the late Quaternary. ...
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The genus Leggadina (colloquially known as ‘short-tailed mice’) is a common component of Quaternary faunas of northeastern Australia. They represent a member of the Australian old endemic murid radiation that arrived on the continent sometime during the late Cenozoic. Here we describe two new species of extinct Leggadina from Quaternary cave deposits as well as additional material of the extinct Leggadina macrodonta . Leggadina irvini sp. nov. recovered from Middle-Upper (late) Pleistocene cave deposits near Chillagoe, northeastern Queensland, is the biggest member of the genus, being substantially larger than any other species so far described. Leggadina webbi sp. nov. from Middle Pleistocene cave deposits at Mount Etna, central eastern Queensland, shares features with the oldest species of the genus, the Early Pleistocene L. gregoriensis . Based on the current palaeoecological interpretation of the type locality, L. webbi , represents the only member of the genus that inhabited rainforest. The succession of Leggadina species through the late Quaternary suggests an ecological replacement of the extinct large-bodied L. irvini with the extant, small-bodied L. lakedownesis at Chillagoe. At Mt. Etna, the extinct rainforest species L. webbi is replaced with the extant xeric-adapted L. forresti during the latest Middle Pleistocene. This replacement is associated with a mid-Pleistocene shift towards progressive intensifying seasonal and arid climates. Our study adds to the growing list of small-bodied faunal extinctions during the late Quaternary of northern Australia.
... Although the preponderance of grazing taxa suggests a dominatingly open paleohabitat, large-bodied browsing kangaroos such as " Simosthenurus " , Sthenurus (both short-faced kangaroos of the Sthenurinae) and Troposodon (Lagostrophinae), and diprotodontoids (Palorchestes parvus) have also been recorded from the Chinchilla Sands (Prideaux, 2004). Medium-sized (10–40 kg) forest wallabies (Silvaroo), arboreal tree kangaroos (Bohra) and koalas (Phascolarctos) are also known (Dawson, 2004a, b; Price, 2008a; Price et al., 2009a). Today, tree kangaroos are restricted only to NE Australian and New Guinean tropical rainforests. ...
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have a detrimental impact on the last surviving megafauna, it is likely that they simply compounded upon longer-term climate-driven processes. Independent paleoclimate information suggests that Plio-Pleistocene climates were complex beyond glacial-interglacial cyclicity, and hence, faunal responses were similarly complex.
... Paleoenvironmental reconstructions based on faunal components within the assemblage suggest that a mosaic of habitats occurred around the area during the Pliocene. For instance, the presence of tree kangaroos, koalas and forest wallabies implies the presence of forests3456. Large-bodied grazing marsupials suggest the presence of widespread, open grasslands [7]. ...
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The Chinchilla Local Fauna is a diverse assemblage of both terrestrial and aquatic Pliocene vertebrates from the fluviatile Chinchilla Sand deposits of southeastern Queensland, Australia. It represents one of Australia's few but exceptionally rich Pliocene vertebrate localities, and as such is an important source of paleoecological data concerning Pliocene environmental changes and its effects on ecosystems. Prior inferences about the paleoenvironment of this locality made on the basis of qualitative observations have ranged from grassland to open woodland to wetland. Examination of the carbon and oxygen isotopes in the tooth enamel of marsupials from this site represents a quantitative method for inferring the paleoenvironments and paleoecology of the fossil fauna. Results from Chinchilla show that Protemnodon sp. indet. consumed both C3 and C4 photosynthesis plant types (mean δ(13)C = -14.5±2.0‰), and therefore probably occupied a mixed vegetation environment. Macropus sp. indet. from Chinchilla also consumed a mixed diet of both C3 and C4 plants, with more of a tendency for C4 plant consumption (mean δ(13)C = -10.3±2.3‰). Interestingly, their isotopic dietary signature is more consistent with tropical and temperate kangaroo communities than the sub-tropical communities found around Chinchilla today. Other genera sampled in this study include the extinct kangaroo Troposodon sp. indet. and the fossil diprotodontid Euryzygoma dunense each of which appear to have occupied distinct dietary niches. This study suggests that southeastern Queensland hosted a mosaic of tropical forests, wetlands and grasslands during the Pliocene and was much less arid than previously thought.
... Many such local faunas lack physical dating that allows the assemblages to be placed in a temporally constrained biogeographical context relevant to the understanding of faunal evolution and extinction. Therefore , it is difficult to test hypotheses relating to, for example , mammalian response(s) to the late Cenozoic long-term contraction of Australia's rainforests (Hocknull et al. 2007) and the cause(s) of Quaternary faunal extinctions (Price 2008; Price & Webb 2006; Price et al. 2009b ). Understanding this biological history provides the fundamental background , if not basis, for understanding the major evolutionary and extinction events of the Quaternary. ...
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Koalas (Phascolarctidae) are uncommon elements within the Australian fossil record. The earliest representatives are recorded from late Oligocene rainforest assemblages of central Australia. In contrast, the extant Koala Phascolarctos cinereus Blainville, 1816 (the only surviving member of a once diverse family) is found only in eastern Australian open woodlands. Extinction of koalas from rainforests was previously thought to have occurred after the middle Miocene. Recent systematic cave excavations at Mt. Etna, central eastern Queensland, Australia, have revealed several remarkable new middle Pleistocene vertebrate assemblages that are dominated by rainforest-adapted taxa. Within one of the deposits, we have identified a new, but archaic, genus and species of koala. Invictokoala monticola gen. et sp. nov. shares affinities with the most plesiomorphic member of the family, Madakoala Woodburne et al., 1987 (late Oligocene), but is distinguished by possessing higher-crowned upper molars, with a tricsupate (rather than linear) paraconule on M2 (autapomorphic condition within koalas), closely positioned stylar cusps, and better-developed posterior cingulae. Thus, not only does I. monticola represent a ‘holdover’ from an Oligocene ancestor, but the Madakoala–Invictokoala stem represents a ‘ghost’ lineage within the Phascolarctidae, with no representatives known between the late Oligocene and middle Pleistocene. Previously, it was thought that the post-middle Miocene loss of koalas from rainforests may have been a result of a co-evolved dependence of koalas to open eucalypt woodlands, and/or competitive exclusion with koala-like rainforest-adapted ringtail possums. However, the inferred diet of middle Pleistocene I. monticola (i.e. non-Eucalyptus) and coeval occurrence with numerous rainforest-adapted ringtail possums does not support that hypothesis. It appears more likely that koalas had always been closely associated with rainforests, at least until the late Quaternary extinction of I. monticola. Generally, the paucity of rainforest faunal assemblages, and specifically, records of fossil koalas through the late Cenozoic drastically limits our understanding of their evolution.
... Late Pleistocene extinctions in Australia, attributed to the impacts of Aboriginal arrival, climate change, or their combination, resulted in the extinction of most of the continent's larger animals (megafaunal marsupials, birds, and reptiles), as well as the extinction or decline of some medium-sized species, including koalas [15]. Prior to this extinction event, two koala species (both the modern P. cinereus and the larger P. stirtoni) co-existed in Australia, and the modern koala had a wider distribution that extended to south-western Western Australia [16,17]. The extinction of one koala species and the reduction of the geographic range of the living koala since the Pleistocene provide strong indications of Late Pleistocene koala declines, which in addition to reducing the taxonomic diversity of koalas, would also have likely impacted the genetic diversity of P. cinereus. ...
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Background The koala (Phascolarctos cinereus) is an arboreal marsupial that was historically widespread across eastern Australia until the end of the 19th century when it suffered a steep population decline. Hunting for the fur trade, habitat conversion, and disease contributed to a precipitous reduction in koala population size during the late 1800s and early 1900s. To examine the effects of these reductions in population size on koala genetic diversity, we sequenced part of the hypervariable region of mitochondrial DNA (mtDNA) in koala museum specimens collected in the 19th and 20th centuries, hypothesizing that the historical samples would exhibit greater genetic diversity. Results The mtDNA haplotypes present in historical museum samples were identical to haplotypes found in modern koala populations, and no novel haplotypes were detected. Rarefaction analyses suggested that the mtDNA genetic diversity present in the museum samples was similar to that of modern koalas. Conclusions Low mtDNA diversity may have been present in koala populations prior to recent population declines. When considering management strategies, low genetic diversity of the mtDNA hypervariable region may not indicate recent inbreeding or founder events but may reflect an older historical pattern for koalas.
... er reflected reworking which had caused apparent association. This reduces the number of Pleistocene megafaunal sites with human associations in South America, and it is now difficult to assert a human cause for the extinction of Megafauna in Southern Patagonia. This further reduces the weight of argument for the ''overkill'' hypothesis as a whole. Price (2008) discusses dwarfing in the koala lineage Phascolarctos sp. which has been used in the past to suggest that the large koala Phascolarctos stirtoni had not become extinct towards the end of the Pleistocene. Instead intraspecific evolution had been proposed, implying that the extant koala Phascolarctos cinereus had evolved by size reduction ...
Article
Quaternary palaeoecology, as a discipline, involves the analysis of a large range of fossil organisms from the last ca. 2 million years. This paper considers the role that these Quaternary records can take in better understanding the evolution of those organisms. We also discuss the surprisingly low uptake of evolutionary biology in Quaternary palaeoecological studies. This leads us to encourage an advance on both these fronts with a greater degree of collaboration with phylogeographic and ancient DNA researchers. These discussions accompany a summary of a special issue of Quaternary Science Reviews representing the proceedings of the XVII INQUA held in Cairns Australia in 2007. This special issue includes papers on a wide variety of Quaternary evolutionary palaeoecological and population dynamic subjects including extinct Pacific Island palm trees, Beringian beetles, Scandinavian trees, and the effects on human and animal populations of an extraterrestrial impact event in the Late Glacial of North America.
... Many of those of intermediate size did survive, but in altered form with the most pronounced cases of time-dwarfing occurring in the largest surviving species (the body mass of red and grey kangaroos decreasing by about 30%, while that of much smaller species such as spotted quolls and rock wallabies declined by less than 10%; see Flannery, 1994, pp. 208-216;and Lomolino et al., 2006, p. 559; but see Price, 2008). ...
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Charles Darwin's observations and insights continue to inspire nearly all scientists who are captivated by both the marvels and the perils of island life. Here I feature four themes inspired by Darwin's singular insights: themes that may continue to provide valuable lessons for understanding the ecological and evolutionary development of insular biotas, and for conserving the natural character and evolutionary potential of all species restricted to isolated ecosystems (natural or anthropogenic).
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The phenomenon of X chromosome inactivation (XCI) mediated by sex-specific differences in DNA methylation is well characterized in eutherian mammals. Although XCI is shared between eutherians and marsupials, the role of marsupial DNA methylation in this process remains contested. Here we examine genome-wide signatures of DNA methylation from methylation maps across fives tissues from a male and female koala (Phascolarctos cinereus) and present the first whole genome, multi-tissue marsupial "methylome atlas." Using these novel data, we elucidate divergent versus common features of marsupial and eutherian DNA methylation and XCI. First, tissue-specific differential DNA methylation in marsupials primarily occurs in gene bodies. Second, the marsupial X chromosome is significantly globally less methylated (hypomethylated) in females compared to males. We show that this pattern is also observed in eutherian X chromosomes. Third, on average, promoter DNA methylation shows little difference between male and female koala X chromosomes, a pattern distinct from that of eutherians. Fourth, the sex-specific DNA methylation landscape upstream of Rsx, the primary lncRNA associated with marsupial X chromosome inactivation, is consistent with the epigenetic regulation of female- (and presumably inactive X chromosome-) specific expression. Finally, we utilize the prominent female X chromosome hypomethylation and classify 98 previously unplaced scaffolds as X-linked, contributing an additional 14.6 Mb (21.5 %) to genomic data annotated as the koala X chromosome. Our work demonstrates evolutionarily divergent pathways leading to the functionally conserved pattern of X chromosome inactivation in two deep branches of mammals.
Book
Extinctions have always occurred and always will, so what is so surprising about the megafauna extinctions? They were caused by humans and were the first of many extinctions that eventually led to the extinction of the Moa, Stellers Sea Cow, the Dodo, Great Auk and countless other species great and small, all attributed to human agency. Therefore, the megafauna were humans first great impact on the planet. There is now an increasing realization that the blitzkrieg view of these extinctions may have been wrong. A growing body of evidence and long-term field work is beginning to show that at least Australias megafauna did not succumb to human agency, not because humans probably did not hunt the odd animal but because the an infinitely more logical reason lies in the climatic conditions of the Quaternary Ice Ages and the affect they had on continental geography, environment, climate and, most importantly, the biogeography of the megafauna. This book presents the evidence of this theory, demonstrating the biogeographic approach to Australia s megafauna extinction. Written clearly to benefit a diverse level of readers, from those with a passing interest to professionals in the field. Examines future climate change and its effects on the planet by looking at examples buried in the pastPresents new evidence from extensive field research.
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The origins, evolution and palaeodiversity of Australia’s unique marsupial fauna are reviewed. Australia’s marsupial fauna is both taxonomically and ecologically diverse comprising four extant orders Dasyuromorphia, Peramelemorphia, Notoryctemorphia and Diprotodontia) and one extinct order Yalkaparidontia). Molecular divergence dates estimate a Palaeocene origin for the Australian marsupial orders yet ordinal differentiation is obscured by significant gaps in the fossil record with a single terrestrial mammal-bearing deposit known between the late Cretaceous and the late Oligocene. This deposit, the 55 million-year-old early Eocene Tingamarra Local Fauna of southeastern Queensland, contains Australia’s oldest marsupial (Superorder Australidelphia) as well as taxa tentatively interpreted to represent South American groups (Order Polydolopimorphia). Palaeobiogeographic hypotheses regarding the distribution and interordinal relationships of Australian and South American marsupials are discussed. Dasyuromorphia and Peramelemorphia were possibly also present in the early Eocene, Diprotodontia in at least the late Oligocene and Notoryctemorphia and Yalkaparidontia in the early Miocene. Palaeobiodiversity was highest during the early to middle Miocene as evidenced by a spectacular array of marsupial groups in the rainforest assemblages of the Riversleigh World Heritage Area. The onset of icehouse conditions during the middle Miocene saw significant faunal turnover with loss of many archaic groups and the emergence of a range of modern lineages. Few deposits of late Miocene age are known. Development of Australia’s first grasslands and arid habitats occurred in the Pliocene, accompanied by an explosive radiation of grazing kangaroos. The Pleistocene was characterised by severe and unpredictable climatic conditions and the extinction of the Australian megafauna. Lowered sea levels allowed faunal interchange between mainland Australia and neighbouring New Guinea as well as the arrival of the first humans. Resolution of the role of humans and/or climate change in megafaunal extinction requires more precise dating of late Pleistocene deposits. We reflect on the predictive power of the fossil record to enhance understanding of the effects of climate change and humans on the future of the Australian marsupial fauna.
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Around 88 large vertebrate taxa disappeared from Sahul sometime during the Pleistocene, with the majority of losses (54 taxa) clearly taking place within the last 400,000 years. The largest was the 2.8-ton browsing Diprotodon optatum, whereas the ∼100- to 130-kg marsupial lion, Thylacoleo carnifex, the world's most specialized mammalian carnivore, and Varanus priscus, the largest lizard known, were formidable predators. Explanations for these extinctions have centered on climatic change or human activities. Here, we review the evidence and arguments for both. Human involvement in the disappearance of some species remains possible but unproven. Mounting evidence points to the loss of most species before the peopling of Sahul (circa 50-45 ka) and a significant role for climate change in the disappearance of the continent's megafauna.
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Koalas (Phascolarctidae, Marsupialia) are generally rare components of the Australian fossil record. However, new specimens of fossil koalas were recovered during recent systematic excavations from several eastern Plio-Pleistocene deposits of Queensland, eastern Australia, including the regions of Chinchilla, Marmor and Mt. Etna. The new records are significant in that they extend the temporal and geographic range of Plio-Pleistocene koalas from southern and southeastern Australia, to northeastern central Queensland. We provide the first unambiguous evidence of koalas in the Pliocene Chinchilla Local Fauna (phascolarctid indet. and Ph. ?stirtoni): important additions to an increasingly diverse arboreal mammalian assemblage that also includes tree kangaroos. The persistence of koalas and local extinction of tree kangaroos in the Chinchilla region today suggests that significant habitat and faunal reorganization occurred between the Pliocene and Recent, presumably reflecting the expansion of open woodlands and grasslands. Other koala records from the newly U/Th-dated Middle Pleistocene Marmor and Mt. Etna fossil deposits (Phascolarctos sp. and Ph. ?stirtoni), along with independent palaeohabitat proxies, indicate the former presence of heterogeneous habitats comprised of rainforests, open woodlands and grasslands. The lack of such habitat mosaics in those regions today is likely the product of significant Middle Pleistocene climate change.
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The Henschke Fossil Cave was discovered in a quarry near Naracoorte in 1969. The fossiliferous silt was excavated systematically from the upper levels of the cave during the next 11yr. The resulting fossils from each designated area and arbitrary level were analysed for species, and minimum numbers calculated. Relative abundance of each species was calculated for each level in the combined central areas of the deposit, and is presented graphically. Opposing trends of relative abundance are revealed for some species, and might reflect environmental changes. Age determinations on charcoal indicate that this part of the cave filled between 32 000 and 40 000yr ago, before becoming sealed. Interpreted environmental changes from a wetter, denser, forest to drier, more open, shrubby woodland, agree with climatic and vegetational data obtained elsewhere in the region. Comparisons are made with the fauna of the nearby Victoria Fossil Cave. -Author
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Catastrophic hypotheses for mass extinctions are commonly criticized because many taxa gradually disappear from the fossil record prior to the extinction. Presumably, a geologically instantaneous catastrophe would not cause a reduction in diversity or a series of minor extinctions before the actual mass extinction. Two types of sampling effects, however, could cause taxa to appear to decline before their actual biotic extinction. The first of these is reduced sample size provided in the sedimentary record and the second, which we examine in greater detail, is artificial range truncation. The fossil record is discontinuous in time and the recorded ranges of species or of higher taxa can only extend to their last known occurrence in the fossil record. If the distribution of last occurrences is random with respect to actual biotic extinction, then apparent extinctions will begin well before a mass extinction and will gradually increase in frequency until the mass extinction event, thus giving the appearance of a gradual extinction. Other factors, such as regressions, can exacerbate the bias toward gradual disappearance of taxa from the fossil record. Hence, gradual extinction patterns prior to a mass extinction do not necessarily eliminate catastrophic extinction hypotheses. The recorded ranges of fossils, especially of uncommon taxa or taxa in habitats not represented by a continuous record, may be inadequate to test either gradual or catastrophic hypotheses.
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A method, based on femoral circumference, allowed us to develop body mass estimates for 11 extinct Pleistocene megafaunal species of macropodids (Protemnodon anak, P. brehus, P. hopei, P. roechus, Procoptodon goliah, ‘P.’ gilli, Simosthenurus maddocki, S. occidentalis, Sthenurus andersoni, S. stirlingi and S. tindalei) and three fossil populations of the extant eastern grey kangaroo (Macropus giganteus). With the possible exception of P. goliah, the extinct taxa were browsers, among which sympatric, congeneric species sort into size classes separated by body mass increments of 20–75%. None show evidence of size variation through time, and only the smallest (‘P.’ gilli) exhibits evidence suggestive of marked sexual dimorphism. The largest surviving macropodids (five species of Macropus) are grazers which, although sympatric, do not differ greatly in body mass today, but at least one species (M. giganteus) fluctuated markedly in body size over the course of the Pleistocene. Sexual dimorphism in these species is marked, and may have varied through time. There is some mass overlap between the extinct and surviving macropodid taxa. With a mean estimated body mass of 232 kg, Procoptodon goliah was the largest hopping mammal ever to exist.
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Historical concepts of the generic status of the macropodines commonly known as kangaroos and wallabies are reviewed in this paper. A new diagnosis is provided for the genus Macropus, encompassing both living and fossil forms, and using cladistic principles to assess the phylogenetic value of diagnostic characters where possible. Cytological, biochemical and anatomical characters are used. Fourteen living and 11 extinct species of Macropus are recognized. Of these, 20 species have been classified into three subgenera, M.(Macropus), M.(Osphranter) and a new subgenus, M.(Notamacropus), as follows: M.(M.) giganteus, M.(M.) fuliginosus, M.(M.) mundjabus, M.(M.) pan, M.(M.) pearsoni and M.(M.) ferragus; M.(O.) antilopinus, M.(O.) bernardus, M.(O.) robustus, M.(O.) rufus and M.(O.) pavana; ,M.(N.) rufogriseus, M.(N.) eugenii, M.(N.) parryi, M.(N.) dorsalis, M.(N.) irma, M.(N.) agilis, M.(N.) greyi, M.(N.) parma, M.(N.) wombeyensis and M.(N) thor. Four poorly known extinct species, M. dryas, M. rama, M. woodsi and M. narada, have not yet been allocated to a subgenus. Prionotemnus palankarinnicus Stirton, 1957 is shown to belong outside Macropus. Because it is the type-species of Prionotemnus, that name is not available for a subgenus of Macropus. A current synonymy is presented for fossil species and the known stratigraphic range is given for each species. A phylogeny is presented expressing our view that M. (,Votamacropus) is the most plesiomorphic subgenus and M. (Macropus) is the most derived.
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The accumulation of mammals in McEachern's Deathtrap Cave (G-49) was not a selective process because the specimens characterise a relatively diverse fauna with a large mean body weight distribution and all age classes being represented in three taxa. The fossil assemblage demonstrates a strong representation of small-bodied species that include arboreally adapted species as well as ground dwelling species. The activity of predatory accumulators has been ruled out because the pitfall morphology of the cave has prevented its utilisation as either a den or roosting place. The taphonomic characteristics of the naturally accumulated fossil assemblage in McEachern's Deathtrap Cave highlights the ambiguities of separating predatory versus natural accumulation.
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Reappraisal of the reliability of numerical dating results for Australian extinct megafauna and archaeology reveals that many still-quoted ages are incorrect and should be eliminated from databases and discussions. We estimate that the megafauna-human overlap period on mainland Australia was about 3900 years (95% confidence interval 3158 to 4642 years) centred ~44,000 calendar years ago. Our results rule out climatic and environmental changes associated with the Last Glacial Maximum as contributing factors in Australian late Pleistocene megafauna extinctions, whereas the short overlap suggests instead that anthropogenic factors are likely to be dominant.
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This paper provides a summary of the Pleistocene vertebrate fossil sites of the South East region of South Australia and builds upon an earlier paper by Williams (1980). It also provides the first detailed review of all known Pleistocene faunal sites of the Naracoorte Caves World Heritage Area. Each known site in the region is listed with details of the site and faunal assemblage, fossil collections made from it and references to previous literature. The representation of the major vertebrate groups in the Pleistocene sites of the South East and the level of scientific attention they have received are discussed.
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Grant Hall chamber in Victoria Fossil Cave, Naracoorte, South Australia, contains a late Pleistocene faunal assemblage, dated at between 206 and 76 Ka. Taphonomic and faunal analyses indicate that the predominant mode of accumulation was via a surface exposed pitfall trap. An avian predator, such as Tyto alba, may have been responsible for the accumulation of small mammal remains. The faunal assemblage is taxonomically diverse containing at least 47 taxa. It includes many browsing species such as Wallabia bicolour and the extinct Sthenurine kangaroos and Zygomaturus trilobus, as well as small mammals that require trees and a thick understorey. The Grant Hall fauna thus indicates the presence of densely vegetated woodland, interspersed with small patches of open and thickly grassed areas in the proximal vicinity of the old cave entrance. The relative abundances and species composition of the Macropodidae fauna in Grant Hall are significantly different from other faunal assemblages found at Naracoorte. This study has provided palaeoecological information for a time period not previously investigated at the Naracoorte Caves; detailed surveying of the chamber was undertaken as part of the study.
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The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial-interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric;and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric: concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.
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New dating confirms that people occupied the Australian continent before the earliest time inferred from conventional radiocarbon analysis. Many of the new ages were obtained by accelerator mass spectrometry 14C dating after an acid–base–acid pretreatment with bulk combustion (ABA-BC) or after a newly developed acid–base–wet oxidation pretreatment with stepped combustion (ABOX-SC). The samples (charcoal) came from the earliest occupation levels of the Devil's Lair site in southwestern Western Australia. Initial occupation of this site was previously dated 35,000 14C yr B.P. Whereas the ABA-BC ages are indistinguishable from background beyond 42,000 14C yr B.P., the ABOX-SC ages are in stratigraphic order to ∼55,000 14C yr B.P. The ABOX-SC chronology suggests that people were in the area by 48,000 cal yr B.P. Optically stimulated luminescence (OSL), electron spin resonance (ESR) ages, U-series dating of flowstones, and 14C dating of emu eggshell carbonate are in agreement with the ABOX-SC 14C chronology. These results, based on four independent techniques, reinforce arguments for early colonization of the Australian continent.
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The date for the initial colonization of Sahul is a key benchmark in human history and the topic of a long-running debate. Most analysts favor either a 40,000 BP or 60,000 BP arrival time, though some have proposed a much earlier date. Here we review data from more than 30 archaeological sites with basal ages >20,000 years reported since 1993, giving special attention to five sites with purported ages >45,000 years. We conclude that while the continent was probably occupied by 42–45,000 BP, earlier arrival dates are not well-supported. This observation undercuts claims for modern human migrations out of Africa and beyond the Levant before 50,000 BP. It also has critical but not yet conclusive implications for arguments about a human role in the extinction of Sahul megafauna.
Article
Many forms are represented only by isolated bone fragments, and comparatively little has been accomplished in the way of functional morphology and detailed description of the extinct beasts. Consequently interpretations are speculative and subject to revision. Observations imply that Australian fauna was (and still is) less able to withstand the impact of ecological change in the presence of man, even with the small numbers of men that were present 50 000-30 000 yr ago. -from Author
Chapter
Ontogenetic analysis of the dentition in a wide range of marsupials and eutherians provides valuable criteria for assessing tooth homologies among extant therian mammals. In addition, these developmental data offer evidence for the loss of teeth during mammalian evolution. Such studies can distinguish the deciduous or successional nature of individual teeth, even when replacement does not occur postnatally. Ontogenetic analyses also provide evidence for the formation of vestigial deciduous teeth that do not erupt; these rudiments serve as valuable clues to the homologies of some tooth positions that have been lost during mammalian phylogeny. The continued accumulation of developmental data on the pattern of early budding and differentiation of deciduous tooth germs offers useful criteria for identifying tooth class homologies of highly modified teeth, in addition to their bony and occlusal relationships.
Article
Excavation of the floor of Cathedral Cave, Wellington Caves, was undertaken between 1982 and 1986. Three major phases of deposition are recognised, representing the end of the last interglacial (Phase 1), the last glacial maximum (Phase 2) and a Holocene phase (Phase 3). Radiocarbon dating of small amounts of charcoal in Phase 1 gave dates ranging from 33,800 BP to 21,000 BP, while dates of 2,590 BP and 2,950 BP were obtained from Phase 3 sediments. Within these Phases stratigraphic, sedimentological and taphonomic changes are apparent. Phase 1 has the characteristics of an attritional entrance facies deposit. Large taxa (>1.5 kg body weight) are represented by juveniles only, except for scavengers and carnivores, suggesting a pitfall trap. The abundance of small mammals is consistent with their accumulation due to owls and the Ghost Bat, which is present in the bottom 1.25 m of the deposit. In Phase 2 a high degree of disturbance is suggested by the inclusion of large limestone boulders and rocks and the highly fragmented nature of the bone. Two distinct heavily indurated 'floors' dip toward the south-east and suggest entry of the sediments from a point in the roof of the cave co-incident with the apex of the present 'altar' formation. The sediments of Phase 3 are not indurated and contain no large boulders or bone fragments, larger species being represented by isolated teeth only. The entrance source of Phase 3 sediments is unknown. At least 38 marsupial taxa have been identified of which 10 are extinct. Of the remaining 28 extant marsupial taxa only 9 may still occur west of the Great Dividing Range today. Of the non-marsupial taxa rodents are most abundant. Microchiropteran bats are represented in several strata, as are reptiles and small birds. Pleistocene 'megafauna' taxa are represented in Phase 1 and Phase 2. 'Megafaunal' species include Macropus (Osphranter) altus, M. (M.) titan, M. (M.) ferragus, M. (Notamacropus) n. sp., Protemnodon sp., Simosthenurus oreas, and Thylacoleo carnifex. The fauna of medium and smaller sized mammals exhibits disharmonious assemblages typical of other late Pleistocene/Holocene faunas of eastern and south-eastern Australia. The presence of the Ghost Bat, Macroderma gigas, in Phase 1 suggests a suitable configuration of the cave and cave entrance at that time, and a warmer, wetter climate than Phase 2. Fauna of Phase 3 lacks extinct species and is representative of conditions which existed at the time of first European settlement of the Wellington region.
Chapter
As an island continent restricted to the Southern Hemisphere, Australia's physiographic, climatic, and biotic histories are unique. This article reviews the records of Australian vertebrates in the middle Pleistocene, an interval of oscillating climate and high faunal diversity, most conspicuously among the larger species composing the ‘Pleistocene megafauna’. Australia is divided into eight provinces (major regions) based on modern climatic zones, and the distributions of vertebrates across these provinces are examined. Given the more complete nature of the records for Australian mammals (especially marsupials) compared with those of other vertebrate groups, these species are considered in most detail. Several major ‘time-averaged’ distribution patterns are evident, particularly among the herbivorous marsupials. These patterns are likely to have been determined by climatically and edaphically controlled distribution of major vegetation types.
Article
A unifying, predictive hypothesis is developed that explains many facets of late Quaternary biotic change in Australia. Pleistocene faunal extinction (commonly called megafaunal extinction) is envisaged as the precipitating mechanism for much environmental change. The extinction is thought to be of the “blitzkrieg” type as presented by Martin (1973), and was followed by suppression through human hunting of the remaining large herbivores. Much vegetation was left uneaten because of these events, resulting in an increased standing crop of fuel. Increased fuel continuity and mass ensured that fires could become much larger and hotter than was usually possible previously. The changed fire regime eventually eliminated fire sensitive Gondwanan rainforest elements from almost all parts of the continent that were not protected. Aborigines responded to the changed fire regime with firestick farming. This maintained a high diversity as it ameliorated the worst effects of fires on medium-sized mammals and possibly some plants. Twentieth century Australian mammal extinctions are the result of a trophic cascade that followed the cessation of firestick farming.
Article
Evolutionary “dwarfism” or “nanism” is the phenomenon in which a significant decrease in mean body size of a lineage (an ancestral-descendant sequence of populations) occurs through time. A detailed analysis of several Late Quaternary dwarfed marsupial lineages from Australia is given. Based on linear tooth dimensions of the dwarfed lineages, four points are considered: 1) percent dwarfing; 2) evolutionary rates of change of tooth dimensions; 3) variation within lineages before and after dwarfing; and 4) several aspects of multivariate dental allometry. [The lineages include Macropus titan (fossil)— M. giganteus (Recent) and Osphranter cooperi (fossil)— O. robustus (Recent) in the family Macropodidae (kangaroos), and Sarcophilus laniarius (fossil)— S. harrisii (Recent) in the family Dasyuridae (Tasmaniandevil).] Dental measurements led to these conclusions: 1) Species with the largest body size show the greatest size reduction, and the species with the smallest body size change the least. 2) Evolutionary rates for this reduction in Australian lineages are similar to comparable Post-Pleistocene dwarfed lineages in Europe. 3) Tooth width, especially posterior width, changes more rapidly than length. The first molar changes relatively slowly, especially in length. 4) Variability is higher in the dwarfed forms than in the larger ancestors. 5) Multivariate allometric rates of dwarfing are consistent with results for rates of change calculated in darwins for the relation between change in length and maximum width (and less so for the relation between M1 and M4 reduction). This pattern of dwarfing allometry is broadly similar to within-species allometry, and is quite dissimilar to synchronous interspecific allometry. Brief consideration is also given to taxonomy of dwarfing lineages and to problems of concurrent megafaunal extinctions. It is concluded that dwarfism is an adaptive process which is probably the result of a density-dependent factor(s) (i.e. a resource limited system).
Article
Examines the ecology and behaviour of modern elephants to create models for reconstructing the lives and deaths of extinct mammoths and mastodonts. The sources for these models are long-term studies of elephants Loxodonta africana in Zimbabwe, which are described with respect to the implications of anatomical, behavioural and ecological similarities between past and present proboscideans. The first section deals with the classification of fossil and living forms; the physical appearance of mammoths, mastodonts and modern elephants; and a model for understanding mammoths and mastodonts from the social structure and habitat use by modern elephants. The second section has two chapters on actualistic studies of mass deaths and mass kills, and the final section looks at the meaning of sites from the world fossil record, and at the extinctions in North America at the end of the Pleistocene. A lengthy appendix details methods for age determination, and is followed by an extensive reference list and index. -J.W.Cooper
Article
Lake Victoria, 13 km long and 10 km wide, is the largest lunette lake attached to the Murray River in southeastern Australia. The lake occupies the western part of a larger basin at least twice the size of the present lake. The larger basin has been incised nearly 30 m into the regional sand plain surface and into the early-middle Pleistocene Blanchetown Clay. Within the larger basin (east of the lunette of the present Lake Victoria), various landforms have developed, including alluvial terraces, salt pans, small dry basins and multiple small lunettes. Among these, an arcshaped sand ridge, possibly an old lunette, was dated by TL as 82 ka. The present lunette of Lake Victoria is up to 40 m high and consists of 3 units: Nulla Nulla Sand (30 m thick), Talgarry Sand (up to 10 m thick) and the reworked Dunedin Park Sand. The Nulla Nulla Sand consists dominantly of pure medium to fine-grained sand sequences with a few red palaeosols, indicating long-standing high lake levels with a few lunette stable intervals. Deposition of the Nulla Nulla Sand ended around 20 ka, starting at least 40 ka ago and probably much earlier. The Talgarry Sand, overlying a prominent red palaeosol on top of the Nulla Nulla Sand, consists of pure sand horizons interbedded with at least 3 gypseous clayey silt layers. The gypseous sediments indicate a major change of hydrologic conditions in the lake basin, fluctuation of lake levels and periodically high salinity. The Talgarry Sand was deposited from 17 to 10 ka as dated by TL and previous 14C dates. After 10 ka, lunette accretion stopped, possibly the result of incision of the Murray River channel, reducing the water and sediment input to the basin. However, erosion and deflation of the lunette formed an apron of sediment on the lower lake-facing slope and sand transport to the lee-side long slope, leaving “islands” of old sediment along the lunette crest zone.
Article
The mystery of vanishing species has occupied the minds of palaeontologists and neontologists for more than a century. In more recent times the exponential growth of the human population with accompanying habitat destruction and shrinking biodiversity is an inescapable reality. Could humans have also been responsible for the extinction of the ice-age megafauna? Martin & Wright (1967) attributed the extinction of North American megafauna to the spread of humans. It was a theme echoed in Australia by Merrilees (1968) in his keynote paper 'Man the destroyer' and revisited by Flannery (1994) in 'The Future Eaters'. A confounding variable in the Ice-age extinctions has been the role of climate. Contemporary research into past climates is providing temporal resolution approaching biological time scales and now sheds new light on a number of single cause hypotheses. Chris Johnson's book, 'Australia's Mammal Extinctions: a 50,000 year history', is both timely and comprehensive. It aims to bring a scientific approach to a multidisciplinary problem. The author outlines the importance of multiple working hypotheses and refutation in arriving at a best fit explanation. An approach perhaps obvious to readers with a scientific background but all too often missed or misunderstood in an adversarial society. Whether you agree or disagree with Johnson you have a framework in which to test his interpretations. The structure of the book invites debate not blind acceptance, indeed the author's bias is clear and the conclusions in many sections are built on so many 'ifs', 'mays' and 'mights' that one can lose count. Paradoxically this is a strength not a weakness for it provides not only an endless array of research questions but should also sound a cautionary note to those who would blindly invoke the conclusions to frame management policy. Johnson has surveyed an impressive body of literature in many disparate fields and this well written and referenced book should appeal to both the general reader as well as specialists seeking a broader context for their own research. What will not be so apparent to the general reader are the assumptions underpinning the interpretation of evidence from the sub-discipline areas. The book is well illustrated with some elegant paintings of extinct mammals.
Article
slightly worn and details of the crown morphology are well preserved. P3 is as in the extant P. cinereus except that it is larger, the posterolabial cusp is absent, the longitudinal crest is only slightly sinuous, and the lingual and labial accessory ridges are more numerous and better defined. The molars, M1 and M2, are also relatively large, but are otherwise very similar to P. cinereus. All cusps are moderately high and sharply defined. M1 is distinguished from M2 by the possession of an additional ridge that extends posterolingually from about half way along the postprotocrista to contact with the centre of the lingual cingulum, dividing the lingual moiety of the transverse median valley into two pockets. A low, rounded ridge also ascends directly labially from the apex of the metacone, dividing the labial stylar ridge. This ridge is absent in M2, but the stylar ridge is discontinuous posteriorly from the point where it would have contacted the ridge. The labial base of the paracone is also narrower in M2, and a groove ascends from the apex of the paracone directly labially dividing the labial stylar ridge.
Article
A long term overview is taken of patterns of speciation and extinction among Australian marsupial herbivores. Three generalised periods are considered; the Pliocene, early to early-late Pleistocene and the last 100 ka. Available data indicate no single extinction event occurred, rather, each morphophysiological herbivore guild (foregut and hindgut fermenters, browsers, grazers and mixed-feeders) exhibit very different patterns of speciation and extinction. Extinctions that occurred prior to ~100 ka are attributed to the direct influence of climate, compounded by the complex interaction of the herbivores themselves on vegetation. Eight genera (15 species) of mega-herbivore survived all earlier climatic and environmental stresses, only to become extinct during the last ~55 ka. Late survival of this group is attributed to their large body size. However, ecophysiological attributes associated with large body size would also have increased their vulnerability to human impact, which eventually caused their extinction. Modern large kangaroos, particularly the wallaroos, euros and red kangaroos have superb anatomical, physiological and reproductive adaptations, which evolved or were honed during the middle Pleistocene glacial cycles. These features, and their ability to survive on poor quality grasses, have ensured their status as Australia's surviving ‘megafauna’.
Article
A new radiometric date of 3.6 Ma for the basalt overlying fossiliferous units of the Allingham Formation, provides a minimum age for the Bluff Downs Local Fauna. Ground studies and interpretation of aerial photography has clarified the volcanic history of the area and a new basalt flow has been identified and named. Although the age of the capping basalt permits a younger age for the Bluff Downs Local Fauna than originally described, the stratigraphy,combined with the interpreted stage of evolution of the fauna, still supports an Early Pliocene age for the site.
Article
The caves near Naracoorte, South Australia, contain one of the richest and most diverse fossil faunal assemblages on the Australian continent. Three sites were selected for electron spin resonance (ESR) dating because clastic, fossiliferous sediments were sandwiched between speleothem layers. This allows independent age control by highly precise thermal ionization mass-spectrometry (TIMS) U-series dating. We find that all ESR results agree within the constraints given by the U-series dates, and allow further refinement of the age of the fauna analysed, indicating that most of the fauna in the large Victoria Cave Fossil Chamber is twice as old as reported previously.Our dating results, spanning from 280 to 500 ka for the Fossil Chamber, Victoria Cave, to about 125 ka for the Grant Hall, Victoria Cave, and 170 to 280 ka for the Fossil Chamber, Cathedral Cave, indicate little change, if any, in the megafaunal assemblage from the early Middle to the early Late Pleistocene. This changed dramatically after the last interglacial, when a large proportion of the megafauna suddenly disappeared. Copyright © 2001 John Wiley & Sons, Ltd.
Article
The limestone caves of the Naracoorte region in South Australia contain extensive deposits of megafauna-rich sediments and intercalated cave formation (speleothems). High-precision thermal ionisation mass spectrometry (TIMS) U/Th dating of flowstones directly associated with several large deposits reveals a distinct cyclicity in the timing of sediment and flowstone depositional events in the Naracoorte caves. This pattern parallels a cyclical alternation of ‘Wet Phases’, and intervening periods with a water deficit over the last 500 ka (Ayliffe et al., 1998. Geology 26, 147). Dates from flowstone interlayers in the fossil deposits coincide with the massive speleothem growth events which characterise Wet Phases. Hiatuses in flowstone deposition correlatable through several cave systems imply that water deficits were initiated by regional aridity during full glacial and then extended into the succeeding warmer, wetter interglacials. Clastic deposits in caverns with restricted entrance shafts correlate with hiatuses, suggesting many of these deposits contain fauna representative of full glacial and interglacial climates. Caverns with small openings have often been sealed from the surface and dating has constrained the length of accumulation episodes in several fossil deposits, one to less than 20 ka. The hydrological regimes and environmental conditions inferred from the timing of speleothem deposition have been used to develop a model for cyclic sediment and bone accumulation in the caverns at Naracoorte over the last 400 ka. The giant Victoria Fossil Chamber deposit accumulated prior to 200 ka and because its entrance is large it may contain faunas representative of all climatic phases. There has been no apparent change in faunal diversity at Naracoorte over at least three glacial–interglacial cycles of the Middle Pleistocene.
Article
Cebuella, Callithrix, Leontopithecus, andSaguinus share five distinguishing features. All of these features are best interpreted as derived character states within Platyrrhini, and these animals are phyletic dwarfs. These derived traits may form a single complex that evolved as a result of dwarfing. Two changes in the dentition are shown to be correlated with dwarfing in mammals. These four platyrrhine genera may or may not form a monophyletic group. It is suggested thatCallimico is an “incipient dwarf platyrrhine.” Causes of dwarfing in mammals are discussed.
Article
A new middle Pleistocene vertebrate fossil record from eastern Australia, dated by U disequilibrium series, records the first Quaternary record of an Australian tropical rainforest fauna. This exceptionally rich fauna underwent extinction after a long period of relative faunal stability, spanning several glacial cycles, and persisted probably until 280 000 years ago. Some time between 280 000 and 205 000 years ago the rainforest fauna was replaced by a xeric-adapted fauna. Since that time, the xeric-adapted fauna was replaced by a mesic-adapted fauna which was established by the Holocene. This is the first vertebrate faunal evidence in Australia of the middle Pleistocene Mid-Brunhes Climatic Event (MBE), a major climatic reorganisation that led to increased aridity in northern Australia from around 300 000 years ago. Several independent palaeoclimate proxies suggest that the climatic shift to aridity was due to increased climatic variability and weakened northern monsoons, which may be manifested in the extinction of the aseasonal rainforest fauna and its replacement by an arid-adapted fauna. We extend the temporal ranges of several taxa from the Pliocene into the middle Pleistocene. We also reveal a longer palaeobiogeographic connection of rainforest taxa and lineages shared between New Guinea and Australia than was previously thought and show that their extinction on mainland Australia occurred sometime after 280 000 years ago.
Article
Three to seven oriented paleomagnetic samples were collected from 16 sites in the Nelson Bay and Bridgewater formations at Portland, Victoria, which contains the recently discovered Nelson Bay local fauna (L.F.). The entire section has reversed polarity. These results, along with Globorotalia truncatulinoides within the section, and the presence of underlying middle Pliocene-dated basalts, indicate that the Portland section, and the included Nelson Bay L.F., was deposited within the late Matuyama Chron between 1.66 and 0.73 myr ago. This represents the first well-documented pre-14C Pleistocene mammalian fauna in Australia calibrated in direct stratigraphic context with absolute dating methods. In addition, the reversed polarity for the Bridgewater Formation confirms the previous hypothesis that the depositional history of this beach-sand deposit is time-transgressive across the Brunhes-Matuyama boundary.