Swimming with dinos

24 January, 2008

A platypus
A platypus
Image: Gary Lewis
Source: Gary Lewis

After more than 25 years hard work digging the 112-120 million year old Cretaceous rocks of Victoria, Dr Tom Rich, Curator of Vertebrate Palaeontology at Museum Victoria, has hit pay dirt with another big discovery.

Analysis using a high-resolution CT scanner in Texas, USA, has revealed that one of the fossil jaws retrieved from Flat Rocks near Inverloch, thought to be a monotreme or egg-laying mammal, is actually a close relative of the platypus.

Scans showed a large canal running through the jaw, evidence the animal probably had a bill lined with many electrosensors, as occurs in the modern platypus.

This finding, published on 29 Jan in the prestigious journal Proceedings of the National Academy of Sciences (USA) implies that the platypus represents the oldest living family of mammals on the planet.

The jaws of Teinolophos trusleri were first described by Tom and his team in 2001. With teeth showing similar features to the milk teeth of the modern platypus, they were confident it was at least a monotreme. In 2005 they published on an arm bone thought to belong to an ancient relative of the echidna, which they named Kryoryctes.

The most significant aspect of their research was that some 11 independent molecular biology studies had predicted a split between the platypus and echidna families taking place between 11 and 80 million years ago, but their fossil evidence pushed the age of the split back another 40 million years. This places them well into the age of dinosaurs.

Tom began digging along the south-eastern coast of Victoria some 25 years ago in his original quest to find Australia’s oldest mammals. He kept finding dinosaur bones, but in 1996 the first mammal jaw finally turned up, causing international scientific headlines when it was published in 1997 in Science.

In 2005 a close study of the Teinolophos jaws revealed that monotremes had an independent evolution of their hearing mechanism, a study also published in Science that received world-wide media attention. Since then Tom’s team have turned up 40 or more mammal fossils that fit into four or five kinds of early mammals. 

These new results demonstrate how persistent digging coupled with state-of-the-art analytical techniques are vital in making palaeontologic breakthroughs.

Excavations will continue at Inverloch in February 2008.

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Image Gallery

The team digging at Inverloch, February 2007 Teinolophos jaw from Inverloch, Victoria