Measuring a tiny 2 centimeters (0.8 inches) in length, two 400-million-year-old fossilized fish skulls are providing a big clue into the evolutionary tree and our origins, according to new research published in eLIFE Sciences.

Found more than two decades apart in Australia, the Ligualelepis skulls were preserved in three-dimensions, allowing for researchers to scan and piece together their bone structure. Not only did the scans reveal never-before-seen details of skull bones, the shape of the brain cavity, and soft tissues (including nerves and blood vessels also found in humans) they also provide some of the first anatomical evidence of how humans evolved from fish. Researchers say the first ever digital restoration of this species’ brain cavity helps to place their important position in the vertebrate evolutionary tree.

“Our research reveals previously unknown details about the pattern of dermal skull bones, the shape of the brain and other soft tissue features,” said research associate Dr Alice Clement in a statement. “It resolves the big question about what the ancestor of all modern bony fish looked like."

In short, Ligualelepis is the ancestor of all bony fish, living right before two major groups split and evolved into different species that paved the way for the evolution of mammals, reptiles, and amphibians 400 million years ago, Ligualelepis began to change and evolve; fins started developing at the front of its body with bones that would later become our humerus, ulna, and radius.

“Not many people would think humans evolved parts of their bone structure from a fish. We are all just highly advanced fishes, that’s the point of our story,” said paleontology professor Dr John Long, who was involved in the study.

The team at Flinders University prepared the specimens using acetic acid to expose the bone from the rock they were embedded in. CT scans and “powerful X-rays” then created 3D visuals showcasing their anatomy.

“The scans illustrate the changes early fish went through to achieve their current body plan,” said Long. “This includes fish we most like to eat like salmon, tuna, and trout as well as those we keep as pets like goldfish.”

When the first fossil was discovered 20 years ago, researchers say it fueled debate about the fish’s evolution. A second discovery two years ago helped the team to provide an accurate description and recreation of where the fish belongs in the evolutionary tree.