Little Leo Attenborough: A new mini marsupial lion from Australia

August 25, 2016 PLOS Blogs Mammals

Researchers from the University of New South Wales in Australia have discovered a new miniature marsupial lion and published it in the Open Access journal Palaeontologia Electronica. The adorable little critter, honorably named Microleo attenboroughi after the famed naturalist Sir David Attenborough, is the ninth species of marsupial lion to be discovered in the Riversleigh World Heritage Area of Queensland.

The study’s lead author, Dr. Anna Gillespie, commented on the tiny size of Microleo, which would have weighed in at a mere 1.3 pounds (600 g). “It was not lion-size or even bobcat size….it was more ringtail possum in size.”

“Microleo attenboroughi would have been more like the cute but still feisty kitten of the family,” she adds.

The family? Well, Microleo is part of an impressive pedigree. Its relatives include the much larger Thylacoleo carnifex, first described by Richard Owen in 1858. Thylacoleo is notable for being the size of a lion, with massive third premolars described by Gillespie et al (2016) as “resembling a pair of bolt-cutting blades.” Others in this group, including Priscileo and Wakaleo, are intermediate in size between their smaller (Microleo) and larger (Thylacoleo) relatives.

Size differences between Microleo attenboroughi and the three other genera of marsupial lions, Priscileo, Wakaleo and Thylacoleo. Image: UNSW — Size differences between *Microleo attenboroughi* and the three other genera of marsupial lions, *Priscileo*, *Wakaleo* and *Thylacoleo*. Image: UNSW

This family of marsupial lions, the Thylacoleonidae, are notable because of evolutionary modifications to their premolars, which, as mentioned previously, are massive, elongate, and knife-like. Thylacoleo is noted as having one of the strongest bite forces of any animal.

Gillespie et al (2016) investigated the evolutionary relationship of Microleo to its thylacoleonid relatives via a phylogenetic analysis in PAUP*. They recovered Microleo as the sister-group to all other marsupial lions.

Cladistic relationships of *Microleo* attenboroughi within Thylacoleonidae and Vombatiformes: 1) strict consensus tree of nine most parsimonious trees obtained in the phylogenetic analysis (tree length = 272 steps; see Appendices 1, 2); 2) time-tree of thylacoleonid phylogeny. From Gillespie et al (2016).

Microleo is much older than its relatives; it was recovered form a limestone deposit representing a lush rainforest ecosystem during the Miocene, about 19 million years ago. Thylacoleo, its larger but younger relative, hails from the late Pliocene (2 Ma) to late Pleistocene (~46,000 years ago).

The fossil deposit where Microleo was discovered, named Neville’s Garden Site, has only produced only one specimen of Microleo, but is a trove of fossils for other organisms, including bandicoots, possums, kangaroos, toothed platypuses, koalas, bats, fish, turtles, lizards, pythons, and birds, including the earliest-known Australian parrot.

Suzanne Hand, co-author of the study, said, “The early Miocene of northern Australia, as documented by the thousands of fossils from Riversleigh, was a time of mild, very wet climatic conditions with mammal diversity more like that seen in Borneo than anywhere in Australia today.”

24_marsupial_nevillesgardentoday_3 — The Neville’s Garden Site as it is today, with researchers and volunteers from UNSW. Photo: UNSW

The researchers speculate that Microleo likely was arboreal, living among the trees and tearing other creatures apart with its molars. Maybe not so cute anymore? But with limited material to go off of, many questions still remain about Microleo and its lifestyle.

“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 [Thylacoleo] – must await discovery of more complete specimens,” says Michael Archer, co-author of the study.

Reference:

Gillespie AK, Archer M, Hand SJ (2016) A tiny new marsupial lion (Marsupialia, Thylacoleonidae) from the early Miocene of Australia. Palaeontologia Electronica 19.2.29A: 1-25.

This article has been produced using press material supplied by the University of New South Wales.