Meet Ligulalepis, our common fishy ancestor.

Searching in limestone outcrops of New South Wales, Australia, a team led by scientists from Flinders University recently unearthed the second skull found to date — and the most complete one yet — of this tiny prehistoric bony fish.

The researchers applied modern scanning techniques and powerful X-rays to these two preserved specimens — each only about a centimetre across — to reveal hidden features of Ligulalepis’ brain cavity. The 3D anatomical picture helped the team place the 400-million-year-old creature at the base of the evolutionary tree that leads to all bony fish, one offshoot of which includes humans and all other four-limbed vertebrates.

“This resolves the big question about what the ancestor of all modern bony fish looked like,” said Flinders paleontologist and lead study author, Alice Clement, in a press release. The results were published in the journal eLife.