Chinese paleontologists have discovered the world’s oldest complete teleost fossil, dating back 436 million years. These specimens, including the small Eosteus and the predatory Megamastax, reveal the early evolution of the jaws and teeth that characterize nearly all modern vertebrates.

Two groundbreaking cover stories published in Nature on March 4, 2026 settle long-standing issues. Questions about the origin of teleosts, the ancestors of 98% of modern vertebrates, Including humans.

A research team from the Chinese Academy of Sciences has unearthed the oldest known complete fossil of a teleost fish in southern China. These discoveries fill a critical gap in the ‘fish-to-human’ evolutionary timeline and show that core features of modern vertebrates evolved millions of years earlier than previously thought.

Discover the world’s oldest fish

A research team has identified a new species, Eosteus chongchingensis, in 436-million-year-old sediments in Chongqing. At only 3 centimeters long, this tiny specimen is the oldest complete teleost fossil ever discovered. Despite their small size, they provide a “mosaic” of traits that link early jawed vertebrates with modern fishes.

Eosteus has the streamlined body and scales of modern fish, but it also has anatomical features previously found only in extinct cartilaginous fishes and armored placoderms. This combination suggests that this fish is at the very base of the teleost family tree, just before the major evolution of ray-finned fishes (which make up most modern species) and lobe-finned fishes (the group that eventually migrated to land).

Silurian “Big Mouth”

In the second study, researchers used high-resolution CT scans to reconstruct the skull of Megamastax ambriodus, a giant of the time discovered in Yunnan province. At more than 1 meter long, Megamastax was the largest vertebrate of the Silurian period (about 423 million years ago).

By creating a 3D digital model, the researchers revealed the intricate “dental cushions” – dull, honed structures inside the jaw. The discovery resolves a 50-year-old controversy over isolated fossilized teeth found in Europe, confirming that they belong to primitive teleost fishes. Megamastax’s enormous size challenges the idea that early vertebrates were exclusively small, suggesting instead that a complex predator-prey ecosystem existed long before the “age of fishes.”

Southern China as the cradle of life

A series of studies reinforces the theory that southern China was a major center of early vertebrate evolution. these Fossils offer an unusual look An ancestral anatomy shared by all modern bony creatures.

By identifying these “stem” species, scientists are now able to map how complex jaws and teeth were originally formed. These discoveries do more than just add new names. fossil record. They reveal the lineage trajectory that ultimately led to the human body project.