Temporal range:
Monotreme collage.jpg
Four of the five extant monotreme species: platypus (top-left), short-beaked echidna (top-right), western long-beaked echidna (bottom-left), and replica eastern long-beaked echidna (bottom-right)
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Monotremata
C.L. Bonaparte, 1837[2]

Monotremes (/ˈmɒnətrmz/) are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. In addition, they lay eggs rather than bearing live young, but, like all mammals, the female monotremes nurse their young with milk.

Monotremes have been considered members of Australosphenida, a clade that contains extinct mammals from the Jurassic and Cretaceous of Madagascar, South America, and Australia, though this is disputed.

The only surviving examples of monotremes are all indigenous to Australia and New Guinea, although there is evidence that they were once more widespread, as Monotrematum is known from the Paleocene of South America.[6] The extant monotreme species are the platypus and four species of echidnas. There is currently some debate regarding monotreme taxonomy.

The name monotreme derives from the Greek words μονός (monós 'single') and τρῆμα (trêma 'hole'), referring to the cloaca.

  1. ^ 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. pp. 1–2. ISBN 0-801-88221-4. OCLC 62265494.
  2. ^ Bonaparte, C.L. (1837). "A New Systematic Arrangement of Vertebrated Animals". Transactions of the Linnean Society of London. 18 (3): 258. doi:10.1111/j.1095-8339.1838.tb00177.x.
  3. ^ Thomas H. Rich; Timothy F. Flannery; Patricia Vickers-Rich (2020). "Evidence for a remarkably large toothed-monotreme from the Early Cretaceous of Lightning Ridge, NSW, Australia". In Guntupalli V.R. Prasad; Rajeev Patnaik (eds.). Biological consequences of plate tectonics. New perspectives on post-Gondwana break-up–A tribute to Ashok Sahni. Vertebrate Paleobiology and Paleoanthropology. Springer. pp. 77–81. doi:10.1007/978-3-030-49753-8_4. ISBN 978-3-030-49752-1. S2CID 229647914.
  4. ^ Thomas H. Rich; Timothy F. Flannery; Alistair R. Evans; Matt White; Timothy Ziegler; Alanna Maguire; Stephen Poropat; Peter Trusler; Patricia Vickers-Rich (2020). "Multiple hypotheses about two mammalian upper dentitions from the Early Cretaceous of Australia". Alcheringa: An Australasian Journal of Palaeontology. 44 (4): 528–536. doi:10.1080/03115518.2020.1829042. S2CID 230531306.
  5. ^ Flannery, T. F.; Rich, T. H.; Vickers-Rich, P.; Ziegler, T.; Veatch, E. G.; Helgen, K. M. (2022). "A review of monotreme (Monotremata) evolution". Alcheringa: An Australasian Journal of Palaeontology. 46: 3–20. doi:10.1080/03115518.2022.2025900. S2CID 247542433.
  6. ^ Pascual, Rosendo; Archer, Michael; Jaureguizar, Edgardo Ortiz; Prado, José L.; Godthelp, Henk; Hand, Suzanne J. (23 April 1992). "First discovery of monotremes in South America". Nature. 356 (6371): 704–706. Bibcode:1992Natur.356..704P. doi:10.1038/356704a0. S2CID 4350045.

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