Aaron B. Camens

Strong morphological support for the molecular evolutionary tree of placental mammals.

The emerging molecular evolutionary tree for placental mammals differs greatly from morphological trees, leading to repeated suggestions that morphology is uninformative at this level. This view is here refuted empirically, using an extensive morphological and molecular dataset totalling 17 431 characters. When analysed alone, morphology indeed is highly misleading, contradicting nearly every clade in the preferred tree (obtained from the molecular or the combined data). Widespread homoplasy overrides historical signal. However, when added to the molecular data, morphology surprisingly increases support for most clades in the preferred tree. The homoplasy in the morphology is incongruent with all aspects of the molecular signal, while the historical signal in the morphology is congruent with (and amplifies) the historical signal in the molecular data. Thus, morphology remains relevant in the genomic age, providing vital independent corroboration of the molecular tree of mammals.

Were early Tertiary monotremes really all aquatic? Inferring paleobiology and phylogeny from a depauperate fossil record

The recent study of monotreme paleobiology and phylogeny by Phillips et al. (1) emphasized that the crown group Monotremata may have diverged relatively recently. However, they failed to discuss several aspects of the monotreme fossil record and functional morphology that may have a significant bearing on their conclusions.

Herds Overhead: Nimbadon lavarackorum (Diprotodontidae), Heavyweight Marsupial Herbivores in the Miocene Forests of Australia

The marsupial family Diprotodontidae (Diprotodontia, Vombatiformes) is a group of extinct large-bodied (60–2500 kg) wombat-like herbivores that were common and geographically widespread in Cenozoic fossil deposits of Australia and New Guinea. Typically they are regarded to be gregarious, terrestrial quadrupeds and have been likened in body form among placental groups to sheep, rhinoceros and hippopotami. Arguably, one of the best represented species is the zygomaturine diprotodontid Nimbadon lavarackorum which is known from exceptionally well-preserved cranial and postcranial material from the middle Miocene cave deposit AL90, in the Riversleigh World Heritage Area, northwestern Queensland. Here we describe and functionally analyse the appendicular skeleton of Nimbadon lavarackorum and reveal a far more unique lifestyle for this plesiomorphic and smallest of diprotodontids. Striking similarities are evident between the skeleton of Nimbadon and that of the extant arboreal koala Phascolarctos cinereus, including the powerfully built forelimbs, highly mobile shoulder and elbow joints, proportionately large manus and pes (both with a semi-opposable digit I) and exceedingly large, recurved and laterally compressed claws. Combined with the unique (among australidelphians) proportionately shortened hindlimbs of Nimbadon, these features suggest adept climbing ability, probable suspensory behaviour, and an arboreal lifestyle. At approximately 70 kg, Nimbadon is the largest herbivorous mammal to have occupied the forest canopies of Australia - an ecological niche that is no longer occupied in any Australian ecosystem and one that further expands the already significant niche diversity displayed by marsupials during the Cenozoic.

Late Pleistocene Australian Marsupial DNA Clarifies the Affinities of Extinct Megafaunal Kangaroos and Wallabies

Understanding the evolution of Australias extinct marsupial megafauna has been hindered by a relatively incomplete fossil record and convergent or highly specialized morphology, which confound phylogenetic analyses. Further, the harsh Australian climate and early date of most megafaunal extinctions (39-52 ka) means that the vast majority of fossil remains are unsuitable for ancient DNA analyses. Here, we apply cross-species DNA capture to fossils from relatively high latitude, high altitude caves in Tasmania. Using low-stringency hybridization and high-throughput sequencing, we were able to retrieve mitochondrial sequences from two extinct megafaunal macropodid species. The two specimens, Simosthenurus occidentalis (giant short-faced kangaroo) and Protemnodon anak (giant wallaby), have been radiocarbon dated to 46-50 and 40-45 ka, respectively. This is significantly older than any Australian fossil that has previously yielded DNA sequence information. Processing the raw sequence data from these samples posed a bioinformatic challenge due to the poor preservation of DNA. We explored several approaches in order to maximize the signal-to-noise ratio in retained sequencing reads. Our findings demonstrate the critical importance of adopting stringent processing criteria when distant outgroups are used as references for mapping highly fragmented DNA. Based on the most stringent nucleotide data sets (879 bp for S. occidentalis and 2,383 bp for P. anak), total-evidence phylogenetic analyses confirm that macropodids consist of three primary lineages: Sthenurines such as Simosthenurus (extinct short-faced kangaroos), the macropodines (all other wallabies and kangaroos), and the enigmatic living banded hare-wallaby Lagostrophus fasciatus (Lagostrophinae). Protemnodon emerges as a close relative of Macropus (large living kangaroos), a position not supported by recent morphological phylogenetic analyses.

DIPROTODONTID FOOTPRINTS FROM THE PLIOCENE OF CENTRAL AUSTRALIA

ABSTRACT The first Pliocene marsupial fossil trackways from Australia are described. The trackways, attributed to Euowenia grata (De Vis) (Diprotodontoidea, Marsupialia), occur in the middle Pliocene Tirari Formation, Warburton River, northern South Australia. The trackways were formed as the animals made their way across a soft claypan. Pad impressions, subsequently infilled by a gypsum-cemented clay, indicate how weight was distributed within the pes.

Palaeobiology of Euowenia grata (Marsupialia: Diprotodontinae) and its presence in northern South Australia

Recovery of a specimen of Euowenia grata (De Vis, 1887) from mid Pliocene sediments of the Tirari Formation on the bank of the Warburton River in the Lake Eyre Basin provides the first recorded account of this species in South Australia. The specimen comprises a partial skull including left and right premaxillae, maxillae, and left zygomatic arch, along with an almost complete upper dentition (missing the left I2). An articulated hind leg and pes found downstream at the same stratigraphic level, as well as both fore- and hind-feet of a single individual, are also referred to E. grata and represent the first postcranial material assigned to the species. A reconstruction of the pes indicates that much more of the body weight was borne by the tarsus in this species than in plesiomorphic diprotodontids, such as Nimbadon Hand et al., 1993, or Ngapakaldia Stirton, 1967, although E. grata does not exhibit the more extreme enlargement of the tarsus seen in graviportal Pleistocene diprotodontids. E. grata is found here also to be the only known Australian marsupial, extant or extinct, to exhibit fusion of all three cuneiform bones in the tarsus. We suggest that the diprotodontine hind limb and pes had evolved graviportal adaptations in the Pliocene as well as in the Pleistocene members. We also suggest that E. grata may have been able to rear up against trees while browsing.

Vertebrate Trace Fossils from the Late Pleistocene of Kangaroo Island, South Australia

ABSTRACT It is rapidly becoming apparent that the Late Pleistocene vertebrate trace fossil record of southern Australia is much more comprehensive than previously understood, and complements the skeletal fossil record with regard to the distribution of taxa in coastal environments and the palaeobiology of both extinct and extant organisms. We surveyed the majority of prospective Bridgewater Formation outcrops on Kangaroo Island in South Australia and discovered a trace fossil site preserving hundreds of individual traces. A minimum of ten different reptile, bird, and mammal taxa, as well as invertebrates, are represented at the site. Single-grain optically stimulated luminescence dating indicates that the dune in which the traces imprinted was deposited at the beginning of Marine Isotope Stage 5e (135.4 ± 5.9 ka). The traces were made by several extinct taxa including large quadrupeds (most probably diprotodontids), short-faced (sthenurine) kangaroos, and thylacines, as well as extant taxa including possums, the Tasmanian Devil, goannas, shorebirds, and a variety of kangaroos. This site demonstrates that, even though vertebrate trace fossil sites do not often allow the same level of taxonomic differentiation as skeletal fossil deposits, they can nevertheless provide important information about taxon distribution and behavior that can be correlated and contrasted with skeletal fossil assemblages.

Contemporaneous trace and body fossils from a late Pleistocene Lakebed in Victoria, Australia, allow assessment of bias in the fossil record.

The co-occurrence of vertebrate trace and body fossils within a single geological formation is rare and the probability of these parallel records being contemporaneous (i.e. on or near the same bedding plane) is extremely low. We report here a late Pleistocene locality from the Victorian Volcanic Plains in south-eastern Australia in which demonstrably contemporaneous, but independently accumulated vertebrate trace and body fossils occur. Bite marks from a variety of taxa are also present on the bones. This site provides a unique opportunity to examine the biases of these divergent fossil records (skeletal, footprints and bite marks) that sampled a single fauna. The skeletal record produced the most complete fauna, with the footprint record indicating a markedly different faunal composition with less diversity and the feeding traces suggesting the presence, amongst others, of a predator not represented by either the skeletal or footprint records. We found that the large extinct marsupial predator Thylacoleo was the only taxon apparently represented by all three records, suggesting that the behavioral characteristics of large carnivores may increase the likelihood of their presence being detected within a fossil fauna. In contrast, Diprotodon (the largest-ever marsupial) was represented only by trace fossils at this site and was absent from the sites skeletal record, despite its being a common and easily detected presence in late Pleistocene skeletal fossil faunas elsewhere in Australia. Small mammals absent from the footprint record for the site were represented by skeletal fossils and bite marks on bones.

New evidence of megafaunal bone damage indicates late colonization of Madagascar

The estimated period in which human colonization of Madagascar began has expanded recently to 5000–1000 y B.P., six times its range in 1990, prompting revised thinking about early migration sources, routes, maritime capability and environmental changes. Cited evidence of colonization age includes anthropogenic palaeoecological data 2500–2000 y B.P., megafaunal butchery marks 4200–1900 y B.P. and OSL dating to 4400 y B.P. of the Lakaton’i Anja occupation site. Using large samples of newly-excavated bone from sites in which megafaunal butchery was earlier dated >2000 y B.P. we find no butchery marks until ~1200 y B.P., with associated sedimentary and palynological data of initial human impact about the same time. Close analysis of the Lakaton’i Anja chronology suggests the site dates <1500 y B.P. Diverse evidence from bone damage, palaeoecology, genomic and linguistic history, archaeology, introduced biota and seafaring capability indicate initial human colonization of Madagascar 1350–1100 y B.P.