Evolution of Macropodidae
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The Macropodidae are an extant family of marsupial with the distinction of the ability to move bipedally on the hind legs, sometimes by jumping, as well as quadrupedally. They are herbivores, but some fossil genera like Ekaltadeta are hypothesised to have been carnivores.[1] The taxonomic affiliations within the family and with other groups of marsupials is still in flux.[2]
Earliest macropods
[edit]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.[3] No fossils Macropodidae have been found that predate the Late Oligocene.[2] Using 12S ribosomal RNA transversions, the Hypsiprymnodontidae were found to have diverged from the other macropodids about 45 million years ago, the Macropodinae and Potoroinae about 30 million years ago, and Dorcopsis and Dorcopsulus of New Guinea 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 assigned to the 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 (Sthenurinae, Macropodinae) are found during the rapid evolution of kangaroos in Mid-Miocene to Late Miocene deposits. Of those that are, the hypsiprymnodontid genus Ekaltadeta and isolated molars from the genus Hysiprymnodon are known. Of the Macropodidae, only the plesiomorphic subfamily Bulungamayinae is known, represented by Wakiewakie lawsoni, Gumardee pascuali, Purtia and Palaeopotorous priscus.[2] There are Potoridae, represented by Bettongia moyesi, from the Middle Miocene. The last family from the Oligocene–Miocene boundary consists of species that could be described as a plesiomorphic macropodoids and are ascribed to the extinct family Balbaridae in the genera Nambaroo and Balbaroo.[2]
Nambaroo occurs in fossil formations from the Bullock Creek fauna, which are found in freshwater limestone of the Camfield beds.[5] Other balbarids have been found in Riversleigh and Alcoota fossil deposits.[6] Another family that dates back to this era is the Hypsiprymnodontidae, which includes the two subfamilies Propleopinae and Hypsiprymnodontinae.[2] Both subfamilies have genera of Oligocene age, with the genus Hypsiprymnodon extending that far.[2]
Balaridae is primitive in dental morphology and shares features seen in common with only Hypsiprymnodon moschatus, some other Phalangeroidea and primitive macropodines.[6] These features discount all potoroids from being ancestors to the macropodids on these structural grounds. They consist of a compressed trigonid on the first lower molar, straight molar row and strongly twisted dentary.[6] Primitive macropodines have the straight molar row in common.[6] Ekaltadeta also has plesiomorphic features in that the dental canal and masseteric canal are separated anteriorly, below premolar three and the first molar, with the masseteric canal terminating in a cul-de-sac. This it shares with no other macropodids. Another feature that it only shares with Hypsipromnodon is that the lower second premolar is not evicted by the third premolar.[7]
Pleistocene developments
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Extinctions
[edit]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. The taxonomic affiliations within the family and with other groups of marsupials is still in flux.[2]
Current speciation
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References
[edit]- ^ 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
- ^ a b c d e f g Kear. B. P., Cooke. B. N . A review of macropodoid (Marsupialia) systematics with the inclusion of a new family. Memoirs of the Association of Australasian Palaeontologists 25, 83-101. ISSN 0810-8889
- ^ 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
- ^ 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)" Systematic Biology 47(3): 457 ± 474, 1998
- ^ 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
- ^ 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.
- ^ 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 Pleistocene species of Propleopus, Journal of Paleontology, Vol. 59, No 6, pp. 1331-1349.