TheMacropodidae are an extant family ofmarsupial with the distinction of the ability to move bipedally on the hind legs, sometimes by jumping, as well as quadrupedally. They areherbivores, but some fossil genera likeEkaltadeta are hypothesised to have beencarnivores.[1] The taxonomic affiliations within the family and with other groups of marsupials is still in flux.[2]
In Australia there are various fossil taxa described from the Oligocene–Miocene boundary fromRiversleigh ofQueensland,Lake Tarkarooloo,Namba,Etabunna andWipajiri formations ofSouth Australia.[3] No fossils Macropodidae have been found that predate theLate Oligocene.[2] Using12S ribosomal RNAtransversions, theHypsiprymnodontidae were found to have diverged from the other macropodids about 45 million years ago, theMacropodinae andPotoroinae about 30 million years ago, andDorcopsis andDorcopsulus ofNew Guinea about 10 million years ago, when they inhabited the Australian mainland.[4] The fossils that have been found are aplesiomorphic form of kangaroo, indicating it is likely that the family dates back even earlier. The earliest post-K–T extinction is theTingamarra fauna of theEocene, 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 genusEkaltadeta and isolated molars from the genusHysiprymnodon are known. Of theMacropodidae, only the plesiomorphic subfamilyBulungamayinae is known, represented byWakiewakie lawsoni,Gumardee pascuali,Purtia andPalaeopotorous priscus.[2] There arePotoridae, represented byBettongia moyesi, from theMiddle Miocene. The last family from the Oligocene–Miocene boundary consists of species that could be described as a plesiomorphicmacropodoids and are ascribed to the extinct familyBalbaridae in the generaNambaroo andBalbaroo.[2]
Nambaroo occurs in fossil formations from theBullock Creek fauna, which are found in freshwater limestone of the Camfield beds.[5] Other balbarids have been found inRiversleigh andAlcoota fossil deposits.[6] Another family that dates back to this era is the Hypsiprymnodontidae, which includes the two subfamiliesPropleopinae andHypsiprymnodontinae.[2] Both subfamilies have genera of Oligocene age, with the genusHypsiprymnodon extending that far.[2]
Balaridae is primitive in dental morphology and shares features seen in common with onlyHypsiprymnodon moschatus, some otherPhalangeroidea and primitive macropodines.[6] These features discount all potoroids from being ancestors to themacropodids on these structural grounds. They consist of a compressedtrigonid on the first lower molar, straight molar row and strongly twisteddentary.[6] Primitive macropodines have the straight molar row in common.[6]Ekaltadeta also has plesiomorphic features in that thedental canal andmasseteric canal are separated anteriorly, below premolar three and the first molar, with the masseteric canal terminating in acul-de-sac. This it shares with no other macropodids. Another feature that it only shares withHypsipromnodon is that the lower second premolar is not evicted by the third premolar.[7]
![[icon]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aWiki_letter_w_cropped.svg) | This section is empty. You can help byadding to it.(November 2019) |
TheBalbaridae,Bulungamayinae andSthenurinae all became extinct by thePleistocene. The reasons for their extinctions are unknown, but hypotheses include outdated model climate and habitat changes.[citation needed] Some species ofSthenurus could have been around when humans arrived in Australia, but by this time, they were already progressing towards extinction.[citation needed] As of 2001[update], the taxonomic affiliations within the family and with other groups of marsupials is still in flux.[2]