BURIED beneath a dirt road in the middle of the New South Wales central tablelands lie a few thousand of our ancestors. About 370 million years ago, a billabong teaming with ancient fish promptly dried up, preserving an ancient aquarium in layers of earth.

When an Australian Museum palaeontologist, Alex Ritchie, excavated the road in 1993 he unearthed 80 tonnes of material and discovered 4000 fish of eight different species, making the site one of Australia's richest fossil deposits.

Alex Ritchie. Credit:Ben Rushton

''I knew we were onto a good thing,'' Dr Ritchie said. ''Within three hours of digging along the road we hit a layer of fish.''

Now, new research suggests the site, 10 kilometres west of Canowindra, could contain some of the most complete fossils of the first vertebrates to walk on land - a group known as tetrapods.