Academic literature on the topic 'Notoryctidae – Evolution'

The phylogenetic position of the marsupial mole, Notorcytes typhlops, has been difficult to ascertain with morphological characters because of its highly specialised fossorial lifestyle. On the basis of serological data, Kirsch (1977b) suggested that this species was sufficiently different from other marsupials to warrant placing it in its own suborder. Using the DNA-DNA hybridisation technique on single-copy DNA to assess sequence differences over the entire genome, I confirm that N. typhlops is not closely related to any other marsupial family, and warrants placement in its own order.

Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely ‘transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these—the dental morphology known as zalambdodonty—was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages—marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene.

Most heterothermic marsupials appear to display one of the two patterns of torpor that have been described in placental mammals. During shallow, daily torpor body temperature (T(b)) falls for several hours from about 35-degrees-C to values between 11 and 28-degrees-C, depending on the species, and metabolic rates fall to about 10-60% of the basal metabolic rate (BMR). In contrast during deep and prolonged torpor (hibernation), T(b) falls to about 1-5-degrees-C, metabolic rates to about 2-6% of BMR and torpor bouts last for 5-23 days. Shallow, daily torpor has been observed in the opossums (Didelphidae), the carnivorous marsupials (Dasyuridae) and the small possums (Petauridae). Daily torpor may also occur in the numbat (Myrmecobiidae) and the marsupial mole (Notoryctidae). Deep and prolonged torpor (hibernation) has been observed in the pygmy possums (Burramyidae), feathertail glider (Acrobatidae) and Dromiciops australis (Microbiotheriidae). The patterns of torpor in marsupials are paralleled by those of monotremes, placentals and even birds. These similarities in torpor patterns provide some support to the hypothesis that torpor may be plesiomorphic. However, as endothermy and torpor in birds apparently has evolved separately from that in mammals and as torpor occurrence in mammals can change within only a few generations it appears more likely that torpor in endotherms is convergent.

The musculoskeletal system of marsupial mammals has numerous unusual features beyond the pouch and epipubic bones. One example is the widespread absence or reduction (to a fibrous “patelloid”) of the patella (“kneecap”) sesamoid bone, but prior studies with coarse sampling indicated complex patterns of evolution of this absence or reduction. Here, we conducted an in-depth investigation into the form of the patella of extant marsupial species and used the assembled dataset to reconstruct the likely pattern of evolution of the marsupial patella. Critical assessment of the available literature was followed by examination and imaging of museum specimens, as well as CT scanning and histological examination of dissected wet specimens. Our results, from sampling about 19% of extant marsupial species-level diversity, include new images and descriptions of the fibrocartilaginous patelloid in Thylacinus cynocephalus (the thylacine or “marsupial wolf”) and other marsupials as well as the ossified patella in Notoryctes ‘marsupial moles’, Caenolestes shrew opossums, bandicoots and bilbies. We found novel evidence of an ossified patella in one specimen of Macropus rufogriseus (Bennett’s wallaby), with hints of similar variation in other species. It remains uncertain whether such ossifications are ontogenetic variation, unusual individual variation, pathological or otherwise, but future studies must continue to be conscious of variation in metatherian patellar sesamoid morphology. Our evolutionary reconstructions using our assembled data vary, too, depending on the reconstruction algorithm used. A maximum likelihood algorithm favours ancestral fibrocartilaginous “patelloid” for crown clade Marsupialia and independent origins of ossified patellae in extinct sparassodonts, peramelids, notoryctids and caenolestids. A maximum parsimony algorithm favours ancestral ossified patella for the clade [Marsupialia + sparassodonts] and subsequent reductions into fibrocartilage in didelphids, dasyuromorphs and diprotodonts; but this result changed to agree more with the maximum likelihood results if the character state reconstructions were ordered. Thus, there is substantial homoplasy in marsupial patellae regardless of the evolutionary algorithm adopted. We contend that the most plausible inference, however, is that metatherians independently ossified their patellae at least three times in their evolution. Furthermore, the variability of the patellar state we observed, even within single species (e.g. M. rufogriseus), is fascinating and warrants further investigation, especially as it hints at developmental plasticity that might have been harnessed in marsupial evolution to drive the complex patterns inferred here.

Marsupial moles (genus Notoryctes) are the most highly specialised burrowing marsupials. The specialisations of the appendicular musculo-skeletal system of the marsupial moles are extensive and widespread; the major alterations are concentrated in, but not restricted to, the forelimb. Many of the derived features of the muscular system appear to be adaptations for improving the mechanical advantage of the limbs for burrowing. A number of the specialisations of the muscular system of the marsupial moles are convergent with those previously documented in other fossorial mammals, including golden moles, rodents and armadillos. There are, however, a number of unique specialisations of the musculo-skeletal system of Notoryctes. The functional morphology of the locomotor apparatus of marsupial moles is interpreted on the basis of the descriptions of the anatomy of the skeletal and muscular systems. The burrowing technique of the marsupial moles is a modified form of the parasagittal digging method that is used by other fossorial mammals, such as golden moles, armadillos and some rodents including pocket gophers. Differences in the functional morphology of the hindlimb between marsupial moles and other fossorial mammals are a reflection of the fact that marsupial moles do not construct permanent open burrow systems, but instead constantly dig through loose soil, backfilling as they progress. The functional morphology of the tail is uniquely specialised in the marsupial moles to function as the fifth limb during the pentapedal burrowing locomotion of marsupial moles. The remains of Miocene fossil marsupial mole, while clearly pleisiomorphic with respect to the appendicular skeletal morphology of modern notoryctids, demonstrate a high degree of specialisation for digging. It is hypothesised that the Miocene marsupial mole was already substantially specialised for a fossorial lifestyle, and thus pre-adapted for a subterranean lifestyle developed in correlation with the desertification of the Australian continent. Phylogenetic affinities of marsupial moles within the Marsupialia have long been enigmatic. While specialisation of the musculo-skeletal system have been so widespread as to obscure almost any phylogenetically relevant patterns, there is some evidence to support an association between notoryctids and peramelid bandicoots. Interspecific differences between the two species of marsupial moles, Notoryctes typhlops and N. caurinus, are minor but do support the separation of the two species.