Main Club, 5 June 2026

Our speaker was Kailah Thorn, Collections Manager for Herpetology at the WA Museum. Kailah’s interest, first in vertebrate zoology and then in palaeontology, stemmed from being a “dinosaur nerd” as a child. She now crawls through caves looking for the bony remains of skinks and other reptiles that have fallen in.

Kailah defines a fossil as any evidence of past life, whether bones, mummified bodies, footprints, coprolites (fossilised droppings) or casts and moulds. Fossil lizards are hard to reconstruct because they are often part of a jumble of small bones in a cave or a dig. The various bones of the skull may form part of the jumble because they don’t fuse, as mammal bones do. Kailah decided to focus on skinks – a challenge because they are often hard to identify. She said that to make sense of fossils, it is useful to be familiar with similar modern species.

Of the three tribes of Australian skinks, Kailah has looked into the Tiliquini – the group that includes our familiar Bobtail Tiliqua rugosa. Half of a lower jaw, discovered in a dense layer of bones on the edge of a lake, showed that members of this group existed in Australia at 25Ma (25 million years ago). This was discovered by Kailah & colleagues from Flinders University during a field trip in 48-degree heat in the Lake Frome Basin. Fossils of skinks from Riversleigh in NW Queensland show that they began to resemble Australian skinks by 15 Ma. These were the first “social skinks”, which belong to the genus Egernia. Then some unusually big skinks, another species of Bluetongue, but 30% bigger, Tiliqua wilkinsonorum, appeared about 3.6 Ma.

An old mine spoil heap at Wellington Caves near Dubbo revealed a single dentary – that is, one side of a lower jaw bone, and later a frontal bone – from a large, broad-headed skink Tiliqua frangens. Kailah applied for a grant to investigate this species. A surprising number of the bones of this species showed healed fractures on the lower back, suggesting that they had been trodden on! Some were huge, with a snout-to-vent length of 60cm and weighing 2.3kg. This is very unusual in skinks. Kailah showed us an osteoderm (a hard, bony dermal structure from inside a scale) from Tiliqua frangens.

Evidence suggests that two major events occurred in Australian skink history – a major burst at 35Ma, when the climate was drying out, and then at 10Ma, with the evolution of larger body sizes that lived in open vegetation. Australia now has 470 species of skink (and 263 species of gecko). Evidence from cave fossils shows that the Nullarbor has lost 85% of its mammal species, so Kailah is trying to determine whether skinks have had a similar extinction history. Unfortunately, bones from Nullarbor caves collected in the 1960s by an American palaeontologist have been returned to the US.

Kailah reminded us that present-day Bobtail skinks mate for life, reproduce slowly and bear live young.

Mike Gregson