In the early 1980s, paleontologists found unusual molars in a dry salt lake in the northern part of South Australia. While these researchers believed the molars were from an ancient ancestor of the kangaroo—the Palaeopotorous priscus, which is Latin for “ancient rat kangaroo”—they had to wait more than 30 years before computer-based analysis could confirm the significance of their discovery.
“The teeth of Palaeopotorous were initially described in 1986. Even then they were stated as representing possibly the most primitive relative of the entire modern kangaroo radiation,” said study author Wendy den Boer, PhD, of Uppsala University. “Yet nobody ever evaluated this claim, and despite being occasionally mentioned in the scientific literature, they were never again examined in detail.”
“The name Palaeopotorous was established using a single molar tooth, although 11 other anatomically very similar teeth were recovered during the expedition. None of these fossils were found in association, so it is still unclear whether we are dealing with one or more species,” said coauthor Benjamin Kear, PhD, of Uppsala University. “This uncertainty means that we have had to use a complex series of analyses to assess its morphological similarity and evolutionary relationships relative to other members of the kangaroo family tree.”
“Our results showed that Palaeopotorous was most similar to living rat-kangaroos as well as some other extinct kangaroo relatives. Using information from fossils, and the DNA of living species, we were able to further determine that at around 24 million years old, Palaeopotorous is not just primitive, but likely represents the most distant forerunner of all known kangaroos, rat-kangaroos, and their more ancient ancestors,” said den Boer.
“Palaeopotorous was about the size of a small rabbit and probably did not hop, but would have bounded on all four legs. Nevertheless, a few bones found at the same site in central Australia indicate that the earliest kangaroos already possessed some key adaptations for hopping gaits,” said Kear.
Palaeopotorous lived when central Australia was much wetter than it is today. Its fossils were buried in clay deposits left by a river, but these earliest kangaroo ancestors would have foraged among vegetation growing nearby and along the banks. The teeth were washed into the river after the Palaeopotorous died, along with the remains of many other ancient marsupials.
The study, “Is the Fossil Rat-Kangaroo Palaeopotorous priscus the Most Basally Branching Stem Macropodiform,” was published by the Journal of Vertebrate Paleontology.