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Marsupial mole

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Marsupial moles[1]
Temporal range: 20–0 Ma Miocene to Recent
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Infraclass:
Marsupialia
Superorder:
Australidelphia
Order:
Notoryctemorphia

Kirsch, in Hunsaker, 1977
Family:
Notoryctidae

Ogilby, 1892
Genus:
Notoryctes

Stirling, 1891
Species

N. typhlops
N. caurinus

Ranges of marsupial mole species

Marsupial moles (Marsupialia, Australidelphia, Notoryctidae) are specialized marsupial mammals, known from two species distributed in the Australian interior. Notoryctids are small, fossorial mammals that anatomically converge on other fossorial (and distantly related) mammals, such as living golden moles (Chrysochloridae) and extinct epoicotheres (Pholidota). These fossorial mammals utilize 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[2][3] Notoryctids are represented by early Miocene fossils of Naraboryctes from site of Riversleigh in Queensland, Australia, which document the mosaic acquisition of dental and skeletal features of the living Notoryctes from a more terrestrial ancestor.[4]

There are two extant species:[1]

Marsupial moles spend most of their time underground, coming to the surface only occasionally, probably mostly after rains. They are blind, their eyes having become reduced to vestigial lenses under the skin, and they have no external ears, just a pair of tiny holes hidden under thick hair.

Characteristics

The head is cone-shaped, with a leathery shield over the muzzle, the body is tubular, and the tail is a short, bald stub. They are between 12 and 16 cm long, weigh 40 to 60 grams, and are uniformly covered in fairly short, very fine pale cream to white hair with an iridescent golden sheen. Their pouch has evolved to face backwards so it does not fill with sand, and contains just two teats, so the animal cannot bear more than two young at a time.

The limbs are very short, with reduced digits. The forefeet have two large, 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. In a feature unique to this animal, the neck vertebrae are fused to give the head greater rigidity during digging.[6]

Their molar teeth are triangular, or "zalambdodont", i.e., resembling an inverted Greek letter "lambda" in occlusal view. The notoryctid fossil record demonstrates that the primary cusp of the molars is the metacone[4], distinct from the paracone characteristic of zalambdodont tenrecs, golden moles, and Solenodon[7]. Regarding the number of teeth in each dental quadrant (or dental formula) Archer et al. reported that "the dental formula for species of Notoryctes is controversial because of considerable polymorphism in tooth number, both between specimens and within the same specimen." Nonetheless, reflecting the consensus of older studies[8], Archer et al. report the presence of four molars (typical for marsupials) in each quadrant both in living Notoryctes and the fossil notoryctid Naraboryctes.

Evolution

Phylogenetic tree of marsupials derived from retroposon data, showing placement of marsupial moles within Euaustralidelphia[9]

American paleontologist William King Gregory wrote in 1910 (p. 209) that "Notoryctes is a true marsupial" and this view has been repeatedly verified by phylogenetic analyses of comparative anatomy[10][11], mitochondrial DNA[12][13],[14],nuclear DNA[15][16], rare genomic events [9] and combined datasets of morphology and DNA (Asher et al. 2004; Beck et al 2008; O'Meara & Thompson 2014). The largest phylogenetic datasets strongly support the placement of Notoryctes close to dasyuromorph marsupials, within the Australidelphian radiation (Meredith et al. 2011; Mitchell et al. 2014).

References

  1. ^ a b Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 22. ISBN 0-801-88221-4. OCLC 62265494.
  2. ^ Yalden DW. The anatomy of mole locomotion. Journal of Zoology. 1966 May 1;149(1):55-64.
  3. ^ Rose KD, Emry RJ. Extraordinary fossorial adaptations in the Oligocene palaeanodonts Epoicotherium and Xenocranium (Mammalia). Journal of Morphology. 1983 Jan 1;175(1):33-56
  4. ^ a b Archer, M.; et al. (2011-05-22). "Australia's first fossil marsupial mole (Notoryctemorphia) resolves controversies about their evolution and palaeoenvironmental origins". Proceedings of the Royal Society of London B: Biological Sciences. 278: 1498–1506. doi:10.1098/rspb.2010.1943. Retrieved 2017-02-26. {{cite journal}}: Cite has empty unknown parameter: |1= (help); Explicit use of et al. in: |last2= (help)
  5. ^ "Mole Patrol". The Marsupial Society. 2004. Retrieved 2006-11-09.
  6. ^ Gordon, Greg (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. p. 842. ISBN 0-87196-871-1.
  7. ^ Asher RJ, Sánchez-Villagra MR. Locking yourself out: diversity among dentally zalambdodont therian mammals. Journal of Mammalian Evolution. 2005 Jun 1;12(1):265-82.
  8. ^ Thomas O. XI.—Notoryctes in North-west Australia. Journal of Natural History. 1920 Jul 1;6(31):111-3.
  9. ^ a b Nilsson, M.; et al. (2010-07-27). "Tracking marsupial evolution using archaic genomic retroposon insertions". PLoS Biol. 8: e1000436. doi:10.1371/journal.pbio.1000436. Retrieved 2017-02-26. {{cite journal}}: Explicit use of et al. in: |last2= (help)CS1 maint: unflagged free DOI (link)
  10. ^ Horovitz I, Sánchez‐Villagra MR. A morphological analysis of marsupial mammal higher‐level phylogenetic relationships. Cladistics. 2003 Jun 1;19(3):181-212.
  11. ^ Beck RM, Warburton NM, Archer MI, Hand SJ, Aplin KP. Going underground: postcranial morphology of the early Miocene marsupial mole Naraboryctes philcreaseri and the evolution of fossoriality in notoryctemorphians. Memoirs of Museum Victoria. 2016;74:151-71.
  12. ^ Springer MS, Westerman M, Kavanagh JR, Burk A, Woodburne MO, Kao DJ, Krajewski C. The origin of the Australasian marsupial fauna and the phylogenetic affinities of the enigmatic monito del monte and marsupial mole. Proceedings of the Royal Society of London B: Biological Sciences. 1998 Dec 22;265(1413):2381-6.
  13. ^ Kjer KM, Honeycutt RL. Site specific rates of mitochondrial genomes and the phylogeny of eutheria. BMC Evolutionary Biology. 2007 Jan 25;7(1):8.
  14. ^ Burk A, Westerman M, Kao DJ, Kavanagh JR, Springer MS. An analysis of marsupial interordinal relationships based on 12S rRNA, tRNA valine, 16S rRNA, and cytochrome b sequences. Journal of Mammalian Evolution. 1999 Dec 1;6(4):317-34.
  15. ^ Amrine-Madsen H, Scally M, Westerman M, Stanhope MJ, Krajewski C, Springer MS. Nuclear gene sequences provide evidence for the monophyly of australidelphian marsupials. Molecular phylogenetics and evolution. 2003 Aug 31;28(2):186-96.
  16. ^ Meredith RW, Janečka JE, Gatesy J, Ryder OA, Fisher CA, Teeling EC, Goodbla A, Eizirik E, Simão TL, Stadler T, Rabosky DL. Impacts of the Cretaceous Terrestrial Revolution and KPg extinction on mammal diversification. Science. 2011 Oct 28;334(6055):521-4.
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