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Evolution of macropodidae

The Macropodidae are an extant family of marsupial with the distinction of the ability to move bipedally on the two hind legs sometimes via saltation, as well as quadrupedally. They are herbivores, but some fossil species like Ekaltadeta are hypothesised to have been carnivores.[1] This can not be proven as it can not be compared with an extant species. The taxonomic affiliations with each other and other groups of marsupials is still in flux and under debate.

Earliest macropods

In Australia there are various fossil taxa described from the Oligocene-Miocene boundary from Riversleigh of Queensland, Lake Tarkarooloo, Namba, Etabunna and Wipajiri formations of South Australia.[2] Currently no fossils Macropodidae have been found that predate the Late Oligocene, and their taxonomic relationship with other marsipial families is under debate.[3] According to Burk et al (1998) using 12S ribosomal RNA transversions the Hypsiprymnodontids diverged from the other macropodids about 45 million years ago, the Macropodines and potoroines about 30 million years ago and the New Guinea Dorcopsis and Dorcopsulus about 10 million years ago when they inhabited the Australian mainland.[4] The fossils that have been found are a plesiomorphic form of kangaroo, indicating it is likely that the family dates back even earlier. The earliest post K-T extinction is the Tingamarra Fauna of the Eocene, but no taxa described as Macropodidae have been found in these deposits, and these Eocene species are of uncertain relationship to any Oligocene taxa.

All current families are represented in these Oligocene deposits, but not all sub-families and those that are not (Sthenidae, Macropodidae) are found during the rapid evolution of Kangaroos in the Mid to Late Miocene deposits. Of those that are, the Hypsiprymnodontidae genus Ekaltadeta, and isolated molars from the genus Hysiprymnodon spp. are known. Of the Macropodidae only the subfamily plesiomorphic Bulundamayinae are known, with the species Wakiewakie lawsoni, Gumardee pascuali, Purtia and Palaeopotorous priscus known.[3] There are Potoidae represented by Bettongia moyesi from the Middle Miocene. The last family from the Oligocene-Miocene boundary are species that could be described as a plesiomorphic macropodoids, and are ascribed to the extinct family Balbaridae in the genus Nambaroo and Balbaroo.[3]

Nambaroo occurs in fossil formations from the Bullock Creek local fauna, that were found in freshwater limestone of the Camfield beds.[5] Other Balbarines have been found in Riversleigh and Alcoota fossil deposits.[6] Other families that date back to this era are the Hypsiprymnodontidae, which includes the two subfamilies Propleopinae and Hypsiprymnodontinae.[3] Both subfamily members have genera of Oligocene age with the genus Hypsiprymnodontinae extending that far.[3]

The family balaridae is considered to be primitive in dental morphology, and shares these common features only seen in Hypsiprymnodon moschatus, some other phalangeroids and primitive macropdines.[6] These features discount all potoroids from being ancestors to the macropodids based on these structural grounds. These features are the compressed trigonid on the first lower molar, straight molar row and a strongly twisted dentary.[6] Primitive Macropodines have the straight molar row in common.[6] Ekaltadeta also has pleisiomorphic features in that the dental canal and meaaeteric canal are separated at their anterior, below premolar three and the first molar. With the messeteric canal terminating in a cul-de-sac. This it shares with no other Macropodoids. Another feature that it only shares with Hypsipromnodon is that the lower second premolar is not eviceted by the third premolar.[7]

Pleistocene developments

Extinctions

Balbaridae, Bulungamayinae, Sthernuridae all became extinct by the Pleistocene. The reason for their extinctions are unknown but hypotheses include outdated model, climate and habitat changes. Some species of Sthenurus could have been around when humans arrived in Australia, but by this time they were already progressing towards extinction.[citation needed]

Current speciation

References

  1. ^ Stephen Wroe, Jenni Brammall, and Bernard N. Cooke "The Skull of Ekaltadeta ima (Marsupialia, Hypsiprymnodontidae?): An Analysis of Some Marsupial Cranial Features and a Reinvestigation of Propleopine Phylogeny, With Notes on the Inference of Carnivory in Mammals Journal of Paleontology. 72(4), 1998, pp. 738-751
  2. ^ Cooke. B. N., "Cranial remains of a new species of Balbarine kangaroo (Marsupiala: Macropodoidea) from the Oligo-Miocene freshwater limestone deposits of Riversleigh World Heritage area, Northern Australia" Journal of Paleontology., 74(2), 2000, pp.317-326 doi:10.1017/S0022336000031528
  3. ^ a b c d e Kear. B. P., Cooke. B. N . A review of macpropodoid (Marsupialia) systematics with the inclusion of a new family. Memoirs of the Association of Australasian Palaeontologists 25, 83-101. ISSN 0810-8889
  4. ^ Angela Burk, Michael Westerman, and Mark Springer "The Phylogenetic Position of the Musky Rat-Kangaroo and the Evolution of Bipedal Hopping in Kangaroos (Macropodidae: Diprotodontia)" 47(3): 457 ± 474, 1998
  5. ^ Schwartz L R S and Megirian D., "A New Species of Nambaroo (Marsupialia; Macropodoidea) from the Miocene Camfield Beds of Northern Australia with Observations on the Phylogeny of the Balbarinae", Journal of Vertebrate Paleontology 24(3):668–675, September 2004
  6. ^ a b c d Flannery. T, Archer. M & Plane. P 1982 "Middle Miocene Kangaroos (Macropoidea:Marsupialia) from three localities in Northern Australia, with a description of two new subfamilies". Journal of Geology and Geophysics, 7, 287-302.
  7. ^ Archer. M. Flannery. T 1985 "Revision of the extinct Giant Rat Kangaroo (Potoroidae:Marsupialia), with description of a new Miocene genus and species and a new Pleitocene species of Propleopus, Journal of Paleontology, Vol. 59, No 6, pp. 1331-1349.