Historic fossils from South China reveal the earliest bony fishes and shed new mild on how jaws, tooth, and key vertebrate options developed earlier than the main fish lineages diverged.
A analysis workforce led by Profs. Min Zhu, Jing Lu, and You’an Zhu from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) on the Chinese language Academy of Sciences reported the findings in two consecutive cowl articles revealed within the journal Nature. Their work reveals main new clues concerning the origin of bony fishes.
The scientists uncovered the oldest-known fossils belonging to bony fishes. These fossils protect vital anatomical particulars, together with jaws, tooth, and braincases, from two early species that lived hundreds of millions of years ago.
Phylogenetic analysis indicates that both species belong to a previously poorly understood stem group of bony fishes. They represent the most primitive examples identified so far from the time before the evolutionary split between the two main branches of bony fishes: ray-finned fishes and lobe-finned fishes.
The discoveries help fill an important gap in the evolutionary story connecting early fishes to humans and strengthen evidence that southern China played a key role in early vertebrate evolution.
Why the Origin of Bony Fishes Matters for Vertebrate Evolution
Bony fishes occupy a central position in the vertebrate tree of life. Today, they are represented by two major lineages: ray-finned fishes and lobe-finned fishes, which adapted to different environments in water and on land.
Ray-finned fishes include more than 30,000 living species and account for most of the fish species people recognize today. According to the study, one branch of lobe-finned fishes eventually moved onto land during the Devonian period and ultimately gave rise to tetrapods, including humans.
Despite their importance, the origins of bony fishes have long been unclear. Most early fossils studied by scientists already belong to specialized ray-finned or lobe-finned fishes from the Devonian period. Fossils representing earlier primitive forms of bony fishes, known as stem osteichthyans that existed before the two lineages diverged, have been extremely rare. This absence left scientists uncertain about the appearance of the common ancestor of these two groups.
After more than ten years of fieldwork and laboratory analysis, the research team made two major discoveries. In Early Silurian deposits in Xiushan, Chongqing, they uncovered Eosteus chongqingensis, the oldest complete fossil of a bony fish found anywhere in the world.
Eosteus Discovery Pushes Again the Timeline of Bony Fish Evolution
The researchers additionally used high-resolution computed tomography (HRCT) to reconstruct the cranium anatomy and tooth of Megamastax amblyodus, the most important identified vertebrate from the Silurian interval. This fossil comes from the Late Silurian Kuanti Formation in Qujing, Yunnan. The newly obtained anatomical information has solved a puzzle that had persevered for greater than fifty years relating to the origin of its tooth plates.
Eosteus chongqingensis lived round 436 million years in the past and was tiny, measuring solely about 3 centimeters lengthy. Regardless of its measurement, the fossil is remarkably effectively preserved and exhibits the whole physique from head to tail. It’s older than all beforehand described giant bony fish fossils and even predates the earliest identified microfossils of bony fishes.
The fossil reveals a combination of primitive and extra superior traits. Its streamlined physique, single dorsal fin, and specialised scales referred to as caudal fulcra resemble these seen in early ray-finned fishes. Nevertheless, it lacks the lepidotrichia (bony fin rays) usually related to bony fishes and possesses an anal fin backbone that had beforehand been noticed solely in cartilaginous fishes and placoderms.
These traits point out that key options of bony fishes developed sooner than scientists had beforehand believed.
Megamastax Anatomy Solves Lengthy-Standing Tooth Plate Puzzle
Megamastax amblyodus lived through the Late Silurian (about 423 million years in the past) in what’s now Qujing, Yunnan. It may develop to greater than 1 meter in size, making it the most important identified vertebrate of its time. After almost a decade of research and quite a few makes an attempt, researchers used superior imaging strategies and three-dimensional (3D) laptop reconstruction to disclose the animal’s full cranial construction and inside anatomy.
Its tooth are organized in inside and outer rows often known as dental arcades. The inside row incorporates tooth cushions that sit on blunt bases, representing a primitive type of bony fish dentition. This anatomical construction resolves a long-standing debate about remoted tooth cushions found in Silurian rocks within the Baltic area and clarifies how these fossils needs to be categorised.
Phylogenetic evaluation locations each Eosteus and Megamastax throughout the stem group of bony fishes. They symbolize an ancestral situation that existed earlier than ray-finned and lobe-finned fishes diverged. These fossils, due to this fact, assist reveal the ancestral physique plan of recent bony fishes, a gaggle that features most residing fish species and all tetrapods, together with people.
South China Confirmed as a Cradle of Early Vertebrate Evolution
The discoveries present new perception into the early diversification of jawed vertebrates. They challenge the idea that the earliest bony fish resembled lobe-finned fishes and help clarify how jaws and teeth evolved in this important group.
According to the researchers, the findings also strengthen evidence that South China was a major center for the origin and early evolution of bony fishes and jawed vertebrates.
References:
“The oldest articulated bony fish from the early Silurian period” by You-An Zhu, Yang Chen, Qiang Li, Wen-Jin Zhao, Zheng-Da Zhou, Lian-Tao Jia, Yi-Lun Yu, Han-Xin Yu, Guang-Biao Wei, Per E. Ahlberg, Jing Lu and Min Zhu, 4 March 2026, Nature.
DOI: 10.1038/s41586-026-10125-2
“Largest Silurian fish illuminates the origin of osteichthyan characters” by Jing Lu, Brian Choo, Wenjin Zhao, You-an Zhu, Xindong Cui, Zhaohui Pan, Donglei Chen, Xiaoyue Liu, Yilun Yu, Tuo Qiao, Qiang Li, Liantao Jia, Per Ahlberg and Min Zhu, 4 March 2026, Nature.
DOI: 10.1038/s41586-025-10008-y
This study was supported by 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 sources.
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