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Chinese paleontologists have discovered a new species of extinct shark ancestors – acanthodes. The 439 million-year-old find is about 15 million years older than the earliest acanthod fossils, making the fossil "shark" the oldest jawed fish, according to the Chinese Academy of Sciences.

The discovered shark–like fish was named Fanjingshania - in honor of the UNESCO World Heritage Site Fanjingshan, the highest peak of the Wulin Mountains in southeastern China. The new species is anatomically close to the groups of extinct spiny fish known by the common name acanthodes. Unlike modern sharks, acanthodes had skin ossifications in the shoulder girdle, which in a primitive form are found in jawed fish.

Fanjingshania is a bizarre fish with an external bony "armor" and several pairs of fin spikes that distinguish it from modern jawed fish, sharks and rays, as well as bony ray-finned and brush-finned fish.

The researchers also identified features that distinguish Fanjingshania from any known vertebrate. She had skin plates in the area of the shoulder girdle, which merge as a whole with a number of thorns. In addition, in the fossil bones of Fanjingshania, the researchers saw signs of extensive resorption of hard tissues (destruction by the action of multidimensional cells, osteoclasts), which is usually associated with the development of the skeleton in bony fish (in humans, this natural process also occurs during development).

"This level of modification of hard tissues is unprecedented for chondrichthyans, a group that includes modern cartilaginous fish and their extinct ancestors," the authors of the work are quoted in a press release. "This indicates a greater plasticity of the mineralized skeleton development than is currently believed at the beginning of the diversification of jawed fish."

The results of the study confirm that the Fanjingshania species represents an early evolutionary branch of primitive chondrichthyans, that is, cartilaginous fish. They are of great importance for understanding when jawed fish and, in general, jawed vertebrates arose.

The article was published in the journal Nature
PHOTO: Reconstruction of Fanjingshania renovata © ZHANG Heming

The information is taken from the portal "Scientific Russia" (https://scientificrussia.ru /)

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