A team of researchers from the University of New South Wales has discovered a new species of the extinct marsupial Thylacoleonidae lion family that weighed just 600 grams, making it smaller than its younger relative, Thylacoleo carnifex. The size of the new "micro-lion" and its success living alongside its larger relatives suggests a unique nature and lifestyle of the tiny carnivorous creature in comparison to standard-sized marsupial lions during the same time period.

Contrary to what their name implies, marsupials do not actually bear any close relationship to lions – while lions are members of the order Carnivora, marsupial lions belong to the order Diprotodontia and lived largely among the trees, possessing retractable claws that allowed them to climb trees and scoop up their prey with ease. As of now, they are the largest carnivorous mammals known to have existed in Australia, as well as one of the largest carnivorous marsupials known in the world.

The new animal has been named Microleo attenboroughi after the famous naturalist Sir David Attenborough. Attenborough advocated for the Riversleigh World Heritage Area of northwestern Queensland in Australia where the fossil remains were found. The remains are believed to date back 19 million years to the Miocene epoch, when the tiny beast roamed the local rainforests and preyed on smaller-sized animals.

"Microleo attenboroughi would have been more like the cute, but still feisty kitten of the family," says Anna Gillespie, lead author of the study. "It was not lion-size or even bob-cat-size. Weighing only about 600 grams, it was more like a ringtail possum in size."

The species was identified through a fossil specimen consisting of part of the lion's skull and teeth, which revealed unique features common to marsupial lions that belong to the carnivorous Thylacoleonidae family.

The remains came from the fossil deposit called Neville's Garden Site, which to date has led to the unearthing of thousands of ancient bones and teeth from fauna including bats, turtles and lizards.

Despite the tiny size of the M. attenboroughi, it was forced to share the landscape of the northern Miocene rainforests with two species of marsupial lion that were much larger in size. The researchers believe that it was likely able to compete with these creatures by focusing on a different size range of prey, such as small vertebrates, although they believe that it is also possible that they competed with each other.

Further research on this tiny micro-lion species will aim to uncover additional fossil specimens in order to shed light on the finer details of the animal's way of life and clarify exactly how it co-existed among its larger carnivorous relatives and how successful it was at surviving in the face of such heftier competition.

"Tantalizing questions about the rest of its skull and skeleton which could further clarify aspects of its lifestyle – such as whether it had an enlarged 'killing' thumb claw like its Pleistocene relative – must await discovery of more complete specimens," says study co-author Mike Archer.

The findings were published in the journal Palaeontologia Electronica.

Source: University of New South Wales