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recently, the chongqing municipal planning and natural resources bureau and the institute of vertebrate paleontology and paleoanthropology, chinese academy of sciences, led a new research on new fish fossil materials from chongqing's unique buried fossil deposits.discovery of armored fishforkmiao familyfishthe research results were published online in the journal of vertebrate paleontology.

in september 2022, the chongqing municipal planning and natural resources bureau and the team of academician zhu min of the chinese academy of sciences reported the discovery of chongqing's unique buried fossil reservoir in the form of a cover article in the international academic journal nature. in order to protect and study chongqing's unique buried fossil reservoir, the chongqing institute of geology and mineral resources, as the responsible unit, carried out in-depth research work.the well-preserved, large-scale, and highly diversejawfish and jawless fish。

the armored fish, diplodocus bifurcata, discovered this time, belongs to the true armored fish among the armored fish. it has the typical slender dorsal pore and lateral line system arrangement of the head carapace of true armored fish. the end of the lateral transverse tube of the head carapace is in a bifurcated state, hence the species name "diplodocus".

△ sketch of the double-forked miao fish head armor

through detailed comparative anatomical studies, the research team found that the two-forked miaojia fish and the agile tujia fish, which appeared on the cover of the journal nature in 2022, are closely related. the two have many similar characteristics, such as a short middorsal tube and bifurcated ends of the lateral transverse tube. phylogenetic analysis shows that the two-forked miaojia fish and the agile tujia fish together form a monophyletic group named tujia fish family.the tujia fish family has been extinct for nearly 436 million years, which consists of two genera, tujia fish and miao fish (both genera are named from xiushan tujia and miao autonomous county). it is the second family-level paleontological classification unit named by chongqing after the "yongdong fish family". the establishment of the tujia fish family has added primitive and strong branches to the tree of vertebrate life evolution.

△ a simplified diagram of the phylogeny of true armored fish

the bifurcated miaojia fish has preserved part of the body connected to the head armor, as well as the paired fin folds on both sides of the ventral surface of the body. the discovery of paired fin folds in armored fish provides key fossil evidence for the "fin fold theory" of the origin of paired appendages of vertebrates. following the agile tujia fish, the existence of fin folds in the bifurcated miaojia fish may mean that abdominal fin folds are widely present in armored fish. sixty million years later, it was this pair of fin folds that evolved into the limbs of vertebrates to land on land, becoming the "left and right arms" of vertebrates to dominate the earth. it can be said that the fin folds are the "prototype of the limbs" of vertebrates.

△ the lateral line and paired ventral fin folds of the double-forked miao fish

in addition, a pair of lateral lines running vertically through the body of the double-forked miao fish were found.this is the first time this has been found in armored fishthe lateral line is an important sensory organ found in fish and amphibians. like a radar, vertebrates can sense the direction and pressure of water flow, detect the surrounding environment and other organisms, and respond quickly through the lateral line.this doubleforkmiao familyfishthe paired lateral lines discovered in the fish provide new key scientific information for understanding the morphology of the lateral line system of armored fish and the connection between the body lateral line and the head lateral line.

it is reported that the 436 million-year-old ancient fish in the "chongqing special buried fossil repository" have been preserved intact in a special way, which is very rare. this gives scientific researchers the opportunity to take a glimpse of the peculiar appearance of the "ancestors" of vertebrates hundreds of millions of years ago, and study some previously unknown evolutionary information, such as the origin of jaws, the prototype of paired fins, and other early evolution of body configurations. it fills the missing initial link in the evolutionary history of "from fish to humans" and changes the world's traditional understanding of the evolution of life.

(reporters xia siwei and zhang yuncheng)