Abstract Physics Light Waves Evolution

Shocking 439-million-year-old ‘shark’ is forcing scientists to rethink evolutionary timeline

These findings provide hard evidence of the massive diversification of vertebrate groups tens of millions of years before the onset of what is known as the “Age of Pisces”, around 420 million years ago.

The ancient shark was found in China and is the oldest jawed ancestor of man.

Top predators in the ocean are often depicted as living sharks. Paleontologists have been able to locate ancient ancestor remains that originate from the Paleozoic era, which dates back hundreds of millions of years. These ancient “sharks”, often called acanthodians, were covered in spines. Unlike modern sharks, they have evolved bony “armor” around their paired fins.

Scientists have been shocked by the age of a newly discovered acanthodian species in China. The find is the oldest undisputed jawed fish and predates the earliest acanthodian body fossils by about 15 million years.

The researchers’ findings were recently published in the journal Nature.

Fanjingshania renovata

Reconstruction of the life of Fanjingshania renovata. Credit: Zhang Heming

Reconstructed from thousands of tiny skeletal fragments, Fanjingshanianamed after the famous UNESCO World Heritage Site Fanjingshan, is a bizarre fish with external bony “armor” and several pairs of fin spines that distinguish it from living jawfish, cartilaginous sharks and rays , and bony lines and lobes. finned fish.

review of Fanjingshania by a team of researchers from the Chinese Academy of Sciences, Qujing Normal University and the University of Birmingham revealed that the species is anatomically close to groups of extinct spiny ‘sharks’ collectively known as the acanthodians. Unlike modern sharks, acanthodians have cutaneous ossifications of the shoulder region which occur primitively in jawed fish.

Fanjingshania renovata in the ocean

A reconstruction of Fanjingshania renovata in the ocean Credit: Fu Boyuan and Fu Baozhong

The fossil remains of Fanjingshania were discovered in bone bed samples from the Rongxi Formation in Shiqian County, Guizhou Province, China.

These findings provide verifiable evidence that major groupings of vertebrates began to diversify tens of millions of years before the onset, 420 million years ago, of what is known as the “age of fish”. “.

Scientists have discovered characteristics that distinguish Fanjingshania of all other known vertebrates. It has pectoral, pre-pectoral, and pre-pelvic spines that fuse into a single unit with dermal shoulder girdle plates. Additionally, the ventral and lateral portions of the shoulder plates have been found to extend to the posterior edge of the pectoral fin spines. The species has distinctive trunk scales and the crowns of these scales consist of a row of tooth-like elements (odontodes) adorned with irregular nodular ridges. Strangely, dentin growth is recorded in scales but not in other parts of the dermal skeleton, such as fin spines.

Fanjingshania renovata

An alternative view of Fanjingshania renovata. Credit: Zhang Heming

“It is the oldest jawed fish whose anatomy is known,” said Professor Zhu Min of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences. “The new data allowed us to locate Fanjingshania into the phylogenetic tree of early vertebrates and gain much-needed insight into the evolutionary steps leading to the origin of important vertebrate adaptations such as jaws, sensory systems, and paired appendages.

From the start, it was clear to scientists that by Fanjingshania The shoulder girdle, with its array of fin spines, is key to identifying the position of the new species in the evolutionary tree of early vertebrates. They found that a group of acanthodians, known as the climatiids, possess the full range of shoulder spines recognized in Fanjingshania. Moreover, contrary to the normal development of the dermal plate, the pectoral ossifications of the Fanjingshania and climatiids are fused to modified trunk scales. This is considered to be a specialization of the primitive condition of jawed vertebrates where the bony plates develop from a single center of ossification.

Pectoral dermal skeleton fragment

Fragment of the pectoral dermal skeleton (part of a pectoral spine fused to the plate of the shoulder girdle) of Fanjingshania renovata shown in ventral view. Credit: Andreev, et al

Unexpectedly, the fossil bones of Fanjingshania show evidence of extensive resorption and remodeling that is commonly associated with skeletal development in bony fishes, including humans.

“This level of hard tissue modification is unprecedented in chondrichthyans, a group that includes modern cartilaginous fishes and their extinct ancestors,” said lead author Dr Plamen Andreev, a researcher at Qujing Normal University. “This speaks to developmental plasticity beyond what is currently understood of the mineralized skeleton in early diversification of jawed fishes.”

The resorption characteristics of Fanjingshania are most apparent in isolated trunk scales which show evidence of loss of tooth-like crown elements and removal of dermal bone from the base of the scale. Thin sections and tomography sections show that this resorption step was followed by the deposition of replacement crown elements. Surprisingly, the closest examples of this skeletal remodeling are found in the dentition and dermal teeth (denticles) of extinct and living bony fishes. In Fanjingshania, however, the resorption did not target individual teeth or denticles, as occurred in bony fishes, but rather removed an area that included multiple scaly denticles. This particular replacement mechanism is more like skeletal repair than the typical tooth/denticle substitution of jawed vertebrates.

The Chongqing Fish Fossil Repository is the only Ancient Silurian Lagerstätte in the world that preserves full-jawed fish head to toe, offering an unparalleled chance to peek into the proliferating “dawn of the fish”. Credit: NICE Tech/ScienceApe

A phylogenetic hypothesis for Fanjingshania that uses a numerical matrix derived from observable characters confirmed the researchers’ initial hypothesis that the species represents an early evolutionary branch of primitive chondrichthyans. These results have profound implications for our understanding of the origin of jawed fishes, as they align with morphological clock estimates for the age of the common ancestor of cartilaginous and bony fishes, dating it to he about 455 million years ago, during a period known as the Ordovician.

These results indicate that the absence of undisputed Ordovician jawfish remains could be explained by the undersampling of sedimentary sequences of comparable age. They also indicate a strong preservation bias against teeth, jaws, and articulated vertebrate fossils in contemporary strata of Fanjingshania.

“The new finding challenges existing models of vertebrate evolution by dramatically condensing the timeframe for the emergence of jawed fish from their closest jawless ancestors. This will have a profound impact on how we assess the rates evolution of early vertebrates and the relationship between morphological and molecular changes in these groups,” said Dr. Ivan J. Sansom of

University of Birmingham
Founded in 1825 as the Birmingham School of Medicine and Surgery, the University of Birmingham (informally the University of Birmingham) is a public research university located in Edgbaston, Birmingham, United Kingdom. It is a founding member of the Russell Group, an association of public research universities in the UK, and of Universitas 21, an international network of research-intensive universities.

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Reference: “Spiny chondrichthyan from the lower Silurian of South China” by Plamen S. Andreev, Ivan J. Sansom, Qiang Li, Wenjin Zhao, Jianhua Wang, Chun-Chieh Wang, Lijian Peng, Liantao Jia, Tuo Qiao, and Min Zhu, 28 September 2022, Nature.
DOI: 10.1038/s41586-022-05233-8

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