Largest marsupial ever

The largest marsupial ever to exist was Diprotodon optatum, a rhino-sized cousin of modern wombats that lived in Australia between 1.6 million and 44,000 years ago, during the Pleistocene epoch. Research carried out by Dr Stephen Wroe (University of Sydney, Australia) on a complete skeleton of this megaherbivore, over 3.7 m (12 ft 2 in) long from nose to tail, produced an estimated mass of around 2.8 tonnes (6,170 lb) for an average-sized 3-m-long (9-ft 9-in), 2-m-tall (6-ft 6-in) adult.

By contrast, the red kangaroo (Osphranter rufus), today’s largest marsupial, has a head-body length of 1.4 m (4 ft 7 in), typically propped up by 1–1.2m (3 ft 3 in–3 ft 11 in) further of tail length. Large specimens can stand up to 2.2 m (7 ft 3 in) on two legs, and weigh up to 90 kg (200 lb).

It remains very fiercely debated whether D. optatum was still present when the first ancestors of Australian aboriginals settled on the island continent. The conservative credible date for human arrival in Australia is about 47,500 years ago, too short a timeframe for humans to have had plausible influence in Diprotodon’s extinction in the eyes of some experts; the case for human culpability is further weakened here when the error margin in estimating the age of Australian archaeological and palaeontological sites from this time interval (typically a few thousand years) is considered. Recently, however, evidence of early human settlement dating back 65,000 years was identified from a cave shelter site in Northern Territory, making staggered, human-driven extinction of the biggest ever marsupial a possibility that merits further investigation.

Dr Wroe is now based at the University of New England in Armidale, NSW, Australia.