The shock of the 439-million-year-old “shark” forces scientists to rethink the timeline of evolution

These discoveries provide concrete evidence of the enormous diversity of the group of vertebrates tens of millions of years before the start of the so-called “Age of Fish” around 420 million years ago.

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

Ocean top predators often appear as live sharks. Paleontologists have been able to find the remains of ancient ancestors originating from the Paleozoic era, dating back hundreds of millions of years. These ancient “sharks”, often referred to as acanthodians, were covered with spines. Unlike modern sharks, they have developed a bony “shield” around their paired fins.

Scientists were shocked by the age of a newly discovered acanthodian species from China. This discovery is the undisputed oldest jawed fish, and predates the first acanthodian body fossils by about 15 million years.

The researchers’ findings were recently published in the journal temper nature.

Fanjingshania renovata

rebuilding life Fanjingshania renovata. Credit: Zhang Heming

Reconstructed from thousands of minute skeletal fragments, FanjingchanyaNamed after the UNESCO World Heritage site Fanjingshan, it is a peculiar fish with an external bony “shield” and multiple pairs of fin spines that distinguish it from live jawless fish, cartilaginous sharks, rays, bony rays, and lobes. Fin fish.

test in Fanjingchanya By a team of researchers from the Chinese Academy of Sciences, Qujing Normal University, and the University of Birmingham, it was revealed that the species is anatomically close to the extinct groups of spiny sharks known collectively as acanthodians. In contrast to modern sharks, acanthodians have dermal ossification in the shoulder region that occurs rudimentally in jawed fish.

Fanjingshania renovata in the ocean

Rebuilding Fanjingshania renovata in the ocean. Credit: Fu Boyuan and Fu Baozhong

fossil remains Fanjingchanya They were detected in bone bed samples from the Rongxi Formation in Xiqian County, Guizhou Province, China.

These discoveries provide verifiable evidence that major vertebrate assemblies began diversifying tens of millions of years before the 420 million years before the start of the so-called ‘Age of Fish’.

Scientists have discovered the characteristics that distinguish Fanjingchanya of all other known vertebrates. It has thoracic, pre-thoracic and pre-pelvic spines fused together as a single unit with the lamellae of the dermal girdle. Moreover, it was found that the ventral and lateral parts of the shoulder plates extend to the posterior edge of the spines of the pectoral fin. The species has distinctive trunk scales, and the crowns of these scales consist of a row of tooth-like (dental) elements decorated with irregular edges. Oddly enough, dentin growth is recorded in the scales but not in other parts of the cutaneous skeleton, such as the fin spine.

Fanjingshania renovata

An alternative view of Fanjingshania renovata. Credit: Zhang Heming

“This is the oldest fish with a known dissected jaw,” said Professor Zhou Min of the Institute of Vertebrate Paleontology and Anthropology (IVPP) of the Chinese Academy of Sciences. “The new data allowed us to put Fanjingchanya in the phylogenetic tree of early vertebrates and gain much-needed information about the evolutionary steps that lead to the origin of important vertebrate adaptations such as jaws, sensory systems, and paired appendages.”

From the start, it was clear to scientists that In Fangjingchanya The shoulder girdle, with its set of fin spines, is key to locating new species in the evolutionary tree of early vertebrates. They found that a group of acanthodians, known as climatids, possessed the full set of shoulder spines recognized in Fanjingchanya. Moreover, in contrast to the normal development of the skin plate, the thoracic ossification of Fanjingchanya Climatic organisms are fused in modified trunk scales. This is seen as a specialization of the primitive case of jawed vertebrates where bony plates grow from a single ossifying center.

Thoracic cutaneous skeleton part

Part of the thoracic cutaneous skeleton (part of the thoracic spine fused to the shoulder girdle plate) from Fanjingshania renovata Appears in ventral presentation. Credit: Andreev et al

Unexpectedly, bones of fossils Fanjingchanya They show evidence of extensive resorption and remodeling typically associated with skeletal development in bony fish, including humans.

“This level of hard tissue modification is unprecedented in cartilage, a group that includes modern cartilaginous fish and their extinct ancestors,” said lead author Dr. Plamen Andreev, a researcher at Qujing Normal University. “It speaks to a greater flexibility of growth than is currently understood for the mineral skeleton at the beginning of jawed fish diversification.”

resorption features Fanjingchanya Most evident in isolated stem scales that show evidence of loosening of crown elements such as teeth and removal of dermal bone from the base of the scale. Thin cut specimens and computed tomography slides show that this resorptive phase was followed by deposition of replacement crown elements. Surprisingly, the earliest examples of skeletal remodeling are found in the dentition and dermal dentition (teeth) of extinct and living bony fish. in FanjingchanyaHowever, the resorption did not target individual teeth or teeth, as it did in bony fish, but instead removed an area that included multiple dental veneers. This peculiar replacement mechanism is more similar to skeletal repair than the typical replacement of teeth/tooths for jawed vertebrates.

The Chongqing Fish Fossil Repository is the world’s first and only Lagerstätte Silurian Repository that preserves full-jawed fish from head to tail, providing an unparalleled opportunity to peek into the breeding ‘dawn of the fish’. Credit: NICE Tech/ScienceApe

The phylogenetic hypothesis of Fanjingshania using a numerical matrix derived from observable characters confirmed the researchers’ initial hypothesis that the species represented an early evolutionary branch of primitive cartilage. These findings have profound implications for our understanding of the evolutionary history of jawed fish because they are consistent with morphological clock estimates of the age of the common ancestor of cartilaginous and bony fish, dating to about 455 million years ago, during a period known as the Ordovician.

These results tell us that the lack of undisputed remains of jawed fishes from the Ordovician period can be explained by the lack of sampling of sediment sequences from similar antiquity. They also indicate a strong preservation bias in teeth, jaws, and articulated vertebrate fossils in intestinal layers with Fanjingchanya.

“The new discovery calls into question current models of vertebrate evolution by significantly intensifying the time frame for the emergence of jawed fish from their closest jawless ancestors,” said Dr. Evan J.

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

“data-gt-translate-attributes=”[{” attribute=””>University of Birmingham.

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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