Ancient fossils from South China are changing what we know about the first bony fishes. These discoveries shed new light on how jaws, teeth, and other key features of vertebrates evolved. This happened before the main fish groups split apart.
A research team from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) at the Chinese Academy of Sciences led this work. Their findings were published in two Nature articles. The team included Professors Min Zhu, Jing Lu, and You’an Zhu.
Scientists found the oldest known fossils of bony fishes. These fossils show important details like jaws, teeth, and braincases. They come from two early species that lived hundreds of millions of years ago.
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Start Your News DetoxAnalysis shows both species belong to a group of bony fishes that was not well understood before. They are the most primitive examples found from before the two main branches of bony fishes split. These branches are ray-finned fishes and lobe-finned fishes.
These discoveries help fill a big gap in the evolutionary story that connects early fishes to humans. They also strengthen the idea that southern China was very important in early vertebrate evolution.
Why Early Bony Fish Matter
Bony fishes are central to the story of vertebrates. Today, there are two main groups: ray-finned fishes and lobe-finned fishes. They adapted to different environments in water and on land.
Ray-finned fishes include over 30,000 living species. They make up most of the fish species we see today. One branch of lobe-finned fishes eventually moved onto land during the Devonian period. This group ultimately led to tetrapods, which include humans.
Despite their importance, the origins of bony fishes have been a mystery. Most early fossils studied were already specialized ray-finned or lobe-finned fishes from the Devonian period. Fossils of earlier, more primitive bony fishes, called stem osteichthyans, were very rare. These existed before the two main groups diverged. This lack of fossils left scientists unsure what the common ancestor of these groups looked like.
After more than ten years of fieldwork and lab analysis, the research team made two big discoveries. In Early Silurian deposits in Xiushan, Chongqing, they found Eosteus chongqingensis. This is the oldest complete fossil of a bony fish found anywhere.
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New Fossils Push Back Fish Evolution
Researchers also used high-resolution computed tomography (HRCT) to rebuild the skull and teeth of Megamastax amblyodus. This was the largest known vertebrate from the Silurian period. This fossil comes from the Late Silurian Kuanti Formation in Qujing, Yunnan. The new data solved a puzzle that had lasted over 50 years about its tooth plates.
Eosteus chongqingensis lived about 436 million years ago. It was tiny, only about 3 centimeters long. But the fossil is very well preserved. It shows the entire body from head to tail. It is older than all other large bony fish fossils found before. It even predates the earliest known microfossils of bony fishes.
The fossil shows a mix of old and more advanced features. Its sleek body, single dorsal fin, and special scales (caudal fulcra) are like those in early ray-finned fishes. However, it lacks the bony fin rays usually seen in bony fishes. It also has an anal fin spine, which was only seen before in cartilaginous fishes and placoderms.
These traits suggest that key features of bony fishes developed earlier than scientists thought.
Megamastax Anatomy Solves Tooth Puzzle
Megamastax amblyodus lived during the Late Silurian, about 423 million years ago. It lived in what is now Qujing, Yunnan. It could grow to over 1 meter long, making it the largest known vertebrate of its time. After almost a decade of study, researchers used advanced imaging and 3D computer reconstruction. This revealed the animal’s full head structure and internal anatomy.
Its teeth are in inner and outer rows, called dental arcades. The inner row has tooth cushions on blunt bases. This is a primitive form of bony fish teeth. This structure solves a long-standing debate about isolated tooth cushions found in Silurian rocks in the Baltic region. It clarifies how those fossils should be classified.
Analysis places both Eosteus and Megamastax in the stem group of bony fishes. They show an ancestral state that existed before ray-finned and lobe-finned fishes split. These fossils help reveal the original body plan of modern bony fishes. This group includes most living fish species and all tetrapods, including humans.
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South China: A Cradle of Vertebrate Evolution
These discoveries offer new insights into how jawed vertebrates first diversified. They challenge the idea that the earliest bony fish looked like lobe-finned fishes. They also help explain how jaws and teeth evolved in this important group.
The researchers say these findings also confirm that South China was a major center for the origin and early evolution of bony fishes and jawed vertebrates.
Deep Dive & References
The oldest articulated bony fish from the early Silurian period - Nature, 2026
Largest Silurian fish illuminates the origin of osteichthyan characters - Nature, 2026
This study received support from the Key Program of the National Natural Science Foundation of China, the International Research Center of Big Data for Sustainable Development Goals, and other funding.
