The Marsupial Lion Family Was Diverse And Complex

Peter Schouten's rendering of the marsupial lion. Peter Schouten/The Journal of Systematic Paleontology

An extra member has been added to the marsupial lion family. Like its relatives, Wakaleo schouteni was unrelated to lions, or indeed any cats, but in Australia's ancient forests it filled a somewhat similar niche to some modern big cats. W. Schouteni was only a fifth the size of the largest marsupial lion, the fearsome Thylacoleo carnifex, but you still wouldn't want to meet one in a dark wood. That's unlikely, however, since they've been dead some 18 million years.

In the late Oligocene and early Miocene eras 18-26 million years ago, Australia's rainforests teemed with life, most of which has long gone as the continent dried out. Fortunately, the remarkable fossil fields of the Riversleigh World Heritage area have preserved remnants of this abundance. W. schouteni, named for the artist Peter Schouten who brought Riversleigh's wonders to our eyes, is the latest such discovery.

At 23 kilograms (50 pounds), it was more of a Eurasian lynx than a lion. Like other Thylacoleonidae, however, it had vicious pre-molars that have been compared to bolt cutters.

Lacking competition from placental mammals, the Thylacoleonidae diversified in size and prey, from the cute little Microleo attenboroughi, the size of a house cat, to the last survivor Thylacoleo carnifex, which was indeed a rival to lions in its size and fearsome nature.

The Journal of Systematic Palaeontology paper, in which schouteni is first described, also reclassifies a slightly smaller member of the family, previously known as Priscileo pitikantensis. Based on the similarities between schouteni and its smaller relative, the authors argue for moving P. pitikantensis into the Wakaleo genus.

Dr Anna Gillespie of the University of New South Wales told IFLScience that when pitikantensis was discovered only a few species of Wacolea were known. These species were larger and with teeth that did not closely resemble pitikantensis. The discovery of schouteni – clearly a Wacaleo, but with strong resemblances to pitikantensis – has forced a rethink. The discoveries show Wacolea first appeared in the Australian environment millions of years earlier than previously suspected, raising questions of just how old they are.

Indeed, Gillespie expects the entire Priscileo genus will now go. The only other member of the genus, a possum-sized species she herself first described as a relative of pitikantensis, will get a new genus in a paper she's now working on.

The fiddling with the classifications of long-dead species reflects the challenges of paleontology, where we often have just a few fragments of a long-lost species. Our picture of W. schouteni is relatively good, since Gillsepie had around a dozen fragments to work from, including the rare luxury of a skull. Where the fossil record is sparser, paleontologists must do a lot of guesswork, updating as new information arrives.

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