Tree-kangaroos (genus Dendrolagus) today are found only in tropical forests of Queensland and New Guinea, but between 3.5 million and 250,000 years ago, at least seven species of the extinct giant tree-kangaroo genus Bohra lived in unexpected places all over Australia.
Life reconstruction of Bohra illuminata, a species of giant tree-kangaroo that lived in Nullarbor region, Australia, 250,000 years ago. Image credit: Peter Schouten.
“Bohra tree-kangaroos lived in central, southern and eastern Australia,” said Flinders University’s Professor Gavin Prideaux.
“Habitats in these areas at the time included woodland and savannah.”
“The association between living tree-kangaroos and rainforest is a recent phenomenon, and has come about only because of the extinction of giant tree-kangaroos from non-forest habitats.”
“Tree-kangaroos first evolved around 5 million years ago as forests spread during a greenhouse phase.”
“Later, as Australia dried out again, some species of Bohra adapted to more open habitats.”
Professor Prideaux and colleagues examined more than 100 teeth and bones of Bohra tree-kangaroos.
The specimens came from fossil sites extending from southern Victoria to central Australia to the New Guinea highlands.
“The tree-kangaroo story is an intriguing one,” Professor Prideaux said.
“They are a result of what is sometimes called evolutionary reversal, but not in a literal sense.”
“The earliest members of the kangaroo family descended from possum-like ancestors, and then kangaroos became specialized for hopping along the ground.”
“So, tree-kangaroos returned to where it all started for their distant ancestors many millions of years ago.”
“To do this, they needed to undo some adaptations. The characteristic body plan of kangaroos that hop on two oversized hindlegs became increasingly specialized over time.”
“Kangaroos have long feet and legs, and their ankle bones lock together to limit sideways movement. This helps ensure that hopping across the ground is energetically efficient.”
“However, flexibility and strength are advantages for climbing, so tree-kangaroos evolved shorter, more flexible legs and feet, and more powerful arms and claws,” said Murdoch University’s Dr. Natalie Warburton.
Subtle differences between the extinct species, the largest of which may have weighed as much as 40 kg, suggests that their climbing abilities differed.
“Modern tree-kangaroos spend most of their time in the canopy,” Dr. Warburton said.
“However, different species of Bohra probably differed in the proportion of time they spent living in trees and on the ground. This is similar to larger monkeys in Africa and Southeast Asia today.”
“These important findings enable us to see how environmental change over time has shaped the evolution of Australia’s unique fauna,” Professor Prideaux said.
“Studies of newly discovered fossils provide critical evidence that can change our understanding of the animals in the modern world.”
A paper describing this research was published in the journal Zootaxa.
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Gavin J. Prideaux & Natalie M. Warburton. 2023. A review of the Late Cenozoic genus Bohra (Diprotodontia: Macropodidae) and the evolution of tree-kangaroos. Zootaxa 5299 (1); doi: 10.11646/zootaxa.5299.1.1
