Congruus kitcheneri, an extinct species of kangaroo that lived in Australia between 2.6 million and 12,000 years ago, was adapted for climbing trees, although it was larger and not as specialized for arboreal living as the tree-kangaroos.
Congruus kitcheneri was adapted to climb through powerful forelimbs and hindlimbs, grasping hands and strongly curved claws. This image shows the living swamp wallaby (Wallabia bicolor). Image credit: John O’Neill / CC BY-SA 3.0.
“Kangaroos and their relatives (family Macropodidae) descended from arboreal possum-like ancestors during the Paleogene period before becoming the main ground-dwelling mammalian herbivores of the Australian continent over the past 20 million years,” said Flinders University’s Professor Gavin Prideaux and Dr. Natalie Warburton of Murdoch University.
“There are more than 60 living species, including bettongs, wallabies and kangaroos, and many more extinct species, including giant short-faced kangaroos.”
“Smaller extant macropodids are mainly solitary fungivores or browsers, while larger species tend to be grass consumers.”
“Eleven of the 12 living macropodine genera are characterized by species that are principally ground dwelling.”
“They employ a bipedal hopping when moving at speed, and a pentapedal mode, involving the use of the tail as a ‘fifth limb’ when moving slowly. These locomotory styles are facilitated by striking adaptations in physiology and skeletal anatomy, including elongation of the hindlimbs and feet, and reconfiguration of the ankle joint to minimize lateral and rotational movement during hopping.”
“They descended from ground-dwelling ancestors by ascending into the trees. Tree-kangaroos can hop bipedally as well as move their hindlimbs alternately.”
Exquisite preservation of hands and feet of Congruus kitcheneri from the Nullarbor Plain of Western Australia. Image credit: Natalie Warburton, Murdoch University.
In a paper published in the journal Royal Society Open Science, the researchers presented the first published skeletal description of an extinct Australian macropodine that is not a tree-kangaroo.
“The specimens we analyzed suggest this species would climb and ‘move slowly’ through trees,” Dr. Warburton said.
The team examined several cranial specimens and two near-complete kangaroo skeletons, a male and a female, from the Thylacoleo Caves of the Nullarbor Plain in south-central Australia.
“The Thylacoleo Caves are famous for both the remarkably complete preservation of the fossil remains and the insights they provide into the unexpectedly high level of diversity of large marsupial species that inhabited what is now an arid treeless plain,” Professor Prideaux said.
“Despite purportedly being an expert in fossil kangaroos, it took me most of that time to work out that these two skeletons belonged to a species first described decades earlier from jaw fragments from a cave in southwestern Australia.”
“By undertaking a painstaking process of identifying and describing the anatomical details of every single bone that was recovered from the skeletons, we have been able to reveal that this species of extinct kangaroo was adapted for climbing trees in order to browse on plant material not available to animals that are stuck on the ground,” Dr. Warburton said.
Professor Prideaux and Dr. Warburton reallocated it to the previously monotypic genus Congruus.
“These fossils have unusually long fingers and toes with long, curved-claws, in comparison to other kangaroos and wallabies, for gripping; powerful arm muscles to raise and hold themselves up in trees, and a longer, more mobile neck than other kangaroos that would be useful for reaching out the head in different directions for browsing on leaves,” Dr. Warburton said.
“This is really interesting, not just from the point of view of unexpected tree-climbing behavior in a large kangaroo, but also as these specimens come from an area that is now bare of trees, and so tells us that the habitat and environment in the area were really different to what they are now, and perhaps different to what we might have previously interpreted for that time.”
“This is unexpected and exciting and it provides us with new information as we try to understand the changing environments of Australia through time.”
Natalie M. Warburton & Gavin J. Prideaux. 2021. The skeleton of Congruus kitcheneri, a semiarboreal kangaroo from the Pleistocene of southern Australia. R. Soc. open sci 8 (3): 202216; doi: 10.1098/rsos.202216