Australian scientists have discovered a 400-million-year-old fish fossil featuring a human-like jaw structure. Paleontologists believe the ancient fish species' jaw bones represent an evolutionary antecedent of the human jaw.

"The fossil reveals, in intricate detail, the jaw structure of this ancient fish, which is part of the evolutionary lineage that ultimately led to humans," Yuzhi Hu, a postdoctoral researcher at the Australian National University, said in a news release.

Researchers discovered the fish among limestone strata along the coast of Lake Burrinjuck, near Canberra, Australia's capital. The specimen's exact species is unclear, but researchers believe the fossil represents a type of armored fish known as a placoderm and belongs to the Buchanosteidae family.

Scientists used high-resolution CT scanning and a 3D printer to replicate the fish's jaw bones. The process helped paleontologists piece the fish's jaws back together and better understand the specimen's unique jaw structure.

The fossil was remarkably well preserved, and the 3D imaging process revealed the presence of internal jaw cartilages.

"The amazing preservation of the fossil allows us to trace the grooves carrying the blood supply to the jaws and brain," Hu said.

The positioning and structure of the fish's carotid arteries recall the flow of blood to the face, jaws and brain in humans and mammals.

Until recently, scientists believed extinct placoderms represented an evolutionary dead end -- an isolated lineage. But the discovery of a group of Chinese maxillate placoderms revealed a much closer relationship to humans than previously expected. The group is named for the presence of an upper jaw bone called maxilla, similar to humans' upper jaw bone.

The latest Australian placoderm discovery confirms the link between humans and placoderms, and its exceptional preservation offers more anatomical context.

"The Australian fossil helps us to interpret these aspects in the Chinese maxillate placoderms," researcher Jing Lu said.

Scientists detailed their analysis of the placoderm fossil in a new paper published this week in the journal Scientific Reports.

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