Marsupial moles, theNotoryctidae/noʊtəˈrɪktɪdiː/ family, are two species of highly specializedmarsupial mammals that are found in the Australian interior.[2] They are smallburrowing marsupials that anatomically converge on fossorialplacental mammals, such as extantgolden moles (Chrysochloridae) and extinctepoicotheres. The species are:
In an example ofconvergent evolution, notoryctids resemble (and fill theecological niche of) thetalpid or true moles from North America and Eurasia and the Chrysochloridae orgolden moles from Southern Africa. Like chrysochlorids andepoicotheres, notoryctids use their forelimbs and enlarged central claws to dig in a parasagittal (i.e., up and down) plane, as opposed to the "lateral scratch" style of digging that characterizes talpid moles.[4][5]
Marsupial moles spend most of their timeunderground, coming to the surface only occasionally, probably mostly after rains. They are functionallyblind, their eyes having become reduced tovestigial lenses under the skin that lack a pupil. They have no external ears, just a pair of tiny holes hidden under thick hair. The head is cone-shaped, with a leathery shield over the muzzle, the body is tubular, and the tail is a short, bald stub encased in leathery skin. They are between 12 and 16 centimetres (4.7–6.3 in) long, weigh 40 to 60 grams (1.4–2.1 oz), and are uniformly covered in fairly short, very fine pale cream to white hair with an iridescent golden sheen. Theirpouch is small but well developed and has evolved to face backwards so it does not fill with sand. It contains just twoteats, so the animal cannot support more than two young at a time. They are the only marsupials with a truecloaca.[6]
The limbs are very short, with reduced digits. The forefeet have two greatly enlarged, spade shaped, flat claws on the third and fourth digits, which are used to excavate soil in front of the animal. The hindfeet are flattened, and bear three small claws; these feet are used to push soil behind the animal as it digs.Epipubic bones are present but small and as in some other fossorial mammals (e.g.,armadillos), the last five cervicalvertebrae are fused, giving the head greater rigidity during digging. The animal swims through the soil and does not leave behind a permanent burrow.
The teeth of the marsupial moles are degenerate and bear no resemblance to polyprotodont or diprotodont teeth. Their dental formula varies, but is usually somewhere near4–3.1.2.43.1.3.4 × 2 = 42–44. The upper molar teeth are triangular andzalambdodont, i.e., resembling an inverted Greek letterlambda in occlusal view, and the lower molars appear to have lost their talonid basins.[7][8][9] Marsupial moles are the only marsupials that aretesticond.[10]
Notoryctids are represented by earlyMiocene fossils ofNaraboryctes fromRiversleigh in Queensland, Australia, which show themosaic acquisition of dental and skeletal features of the livingNotoryctes from a more surface-dwelling ancestor.[11]The notoryctid fossil record demonstrates that the primary cusp of the molars is the metacone,[11] distinct from the paracone characteristic of zalambdodont tenrecs, golden moles, andSolenodon.[12] Regarding the number of teeth in each dental quadrant (ordental formula), the fossil record demonstrates polymorphism of tooth number, both between specimens and within the same specimen.[11] Nonetheless, older studies concluded[13] there are four molars (typical for marsupials) in each quadrant both in livingNotoryctes and the fossil notoryctidNaraboryctes.[11]
American paleontologistWilliam King Gregory wrote that "Notoryctes is a true marsupial"[14]: 209 and this view has been repeatedly verified by phylogenetic analyses of comparative anatomy,[15][16]mitochondrial DNA,[17][18][19] nuclear DNA,[20][21] rare genomic events,[22] and combined datasets of nuclear and mitochondrial DNA[23] and morphology and DNA.[24][25][26] The largest phylogenetic datasets strongly support the placement ofNotoryctes as the sister taxon to adasyuromorph-peramelian clade, within theAustralidelphian radiation.[27]
^Rose KD, Emry RJ (1 January 1983). "Extraordinary fossorial adaptations in the Oligocene palaeanodonts Epoicotherium and Xenocranium (Mammalia)".Journal of Morphology.175 (1):33–56.doi:10.1002/jmor.1051750105.PMID30053775.S2CID51727274.
^Gadow, Hans (2009). "On the Systematic Position ofNotoryctes typhlops".Proceedings of the Zoological Society of London.60 (3):361–433.doi:10.1111/j.1469-7998.1892.tb06835.x.
^Burk, A; Westerman, M; Kao, DJ; Kavanagh, JR; Springer, MS (1999). "An analysis of marsupial interordinal relationships based on 12S rRNA, tRNA valine, 16S rRNA, and cytochrome b sequences".Journal of Mammalian Evolution.6 (4):317–334.doi:10.1023/A:1027305910621.
^Amrine-Madsen, H; Scally, M; Westerman, M; Stanhope, MJ; Krajewski, C; Springer, MS (2003). "Nuclear gene sequences provide evidence for the monophyly of australidelphian marsupials".Molecular Phylogenetics and Evolution.28 (2):186–196.doi:10.1016/S1055-7903(03)00122-2.PMID12878458.
^Meredith, RW; Janečka, JE; Gatesy, J; Ryder, OA; Fisher, CA; Teeling, EC; Goodbla, A; Eizirik, E; Simão, TL; Stadler, T; Rabosky, DL (2011). "Impacts of the Cretaceous Terrestrial Revolution and KPg extinction on mammal diversification".Science.334 (6055):521–524.doi:10.1126/science.1211028.PMID21940861.
^Phillips, MJ; McLenachan, PA; Down, C; Gibb, GC; Penny, D (2006). "Combined mitochondrial and nuclear DNA sequences resolve the interrelations of the major Australasian marsupial radiations".Systematic Biology.55 (1):122–137.doi:10.1080/10635150500481614.PMID16507529.
^Asher, RJ; Horovitz, I; Sánchez-Villagra, MR (2004). "First Combined Cladistic Analysis of Marsupial Mammal Interrelationships".Molecular Phylogenetics and Evolution.33 (1):240–250.doi:10.1016/j.ympev.2004.05.004.PMID15324852.
^O’Meara, RN; Thompson, RS (2014). "Were there Miocene meridiolestidans? Assessing the phylogenetic placement ofNecrolestes patagonensis and the presence of a 40 million year meridiolestidan ghost lineage".Journal of Mammalian Evolution.21 (3):271–284.doi:10.1007/s10914-013-9252-3.
^Mitchell, KJ; Pratt, RC; Watson, LN; Gibb, GC; Llamas, B; Kasper, M; Edson, J; Hopwood, B; Male, D; Armstrong, KN; Meyer, M (2014). "Molecular phylogeny, biogeography, and habitat preference evolution of marsupials".Molecular Biology and Evolution.31 (9):2322–2330.doi:10.1093/molbev/msu176.PMID24881050.
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