China News Service, Beijing, April 12 (Reporter Sun Zifa) Compared with other fish, lungfish is more closely related to tetrapods including humans. It usually has specialized developed tooth plates and self-connecting type. The jaws, coupled with a strong bite, are ideal for preying on shelled invertebrates.
However, this traditional cognition was rewritten by the latest research on the discovery of ancient fish fossils by the team of Academician Zhu Min of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (Institute of Paleoanthropology, Chinese Academy of Sciences). A new genus of lungfish fossil that "eats soft but not hard" was discovered, dating back about 390 million years ago, named "Huize Dian Bi-wing".
As the most important result of this fossil discovery study, the research team found that the Huizedian bipterus has a new type of tooth plate. The special structure makes it impossible to eat hard shell food like other lungfish, but may Feeding on aquatic mollusks and even other fish by sucking and other methods.
The important results of this paleontological research paper were recently published online in the international academic journal "Systems Paleontology".
The author of the paper and associate researcher Qiao Tuo of the Institute of Ancient Spine of the Chinese Academy of Sciences introduced the research results of the team.
Photo by China News Agency reporter Sun Zifa
Provide new materials for clarifying the phylogenetic relationship of early lungfish
Luo Yanchao, the first author of the paper and a doctoral student at the Institute of Paleovertebra of the Chinese Academy of Sciences, said that the fossils of Huize Dianbi-wing fish were collected from the Middle Devonian (about 390 million years ago) strata in Huize County, Qujing, Yunnan, and its genus name "Dian Bi-wing fish" was taken from the stratum. The ancient name "Dian" from Yunnan Province and the common genus name of lungfish are suffixed with "bi-wing fish (named for having two dorsal fins)", and the species name is named after the place where the fossil was found, Huize.
The holotype fossil specimen of Huizedian bipterus is a head specimen with nearly complete cranial carapace, tooth plate, vomer bone, parasphenoid bone and part of the brain.
The research team used high-precision computed tomography (CT) equipment and three-dimensional reconstruction technology to establish a three-dimensional model of the internal sensory canal system and bone fragment structure of the fossil specimen. The fossil layers of the bipedia are dominated by gray-white and purple-red quartz sandstone intercalated with argillaceous siltstone and mudstone of the same color, mixed with gray limestone and argillaceous limestone, representing a sedimentary environment dominated by bays.
The Silurian and Devonian fish fossils produced in Qujing, Yunnan are rich in species, beautifully preserved, and have many primitive types, filling a large number of "missing links" in the early fish evolution tree.
Academician Zhu Min, the corresponding author of the paper, said that the Huizedian bipterus is the ninth Devonian lungfish discovered in China so far, and it is also a new member of Qujing's "ancient fish kingdom".
This study not only fills the gap in the fossil record of Devonian fish in the Huize area, but the discovery of this new genus of lungfish also provides new materials for clarifying the phylogenetic relationship of early lungfish, and for understanding the Devonian fins Early evolution and radiation of fish 'opened a new window'.
Ecological restoration map of Huize Dianbi-winged fish.
Photo by Luo Yanchao and Ma Meng
The new type of tooth plate leads to "eating soft but not hard" in Huizedian biplaneta
The author of the paper and associate researcher Qiao Tuo of the Institute of Ancient Spine of the Chinese Academy of Sciences pointed out that the tooth plate of the lungfish is formed by the specialization of the inner pterygoid and the anterior joint bone, which is the iconic structure of the lungfish. have an important role.
In order to eliminate the loss caused by the tooth plate grinding the prey, the lungfish has a unique mechanism to "recycle" the old teeth: as the lungfish grows, the old teeth on the tooth plate disappear due to reabsorption and wear, while the old teeth on the tooth plate disappear. New teeth grow on the edge of the tooth plate.
She said that in 2006, international colleagues in paleontological research classified the dental plates into four categories according to the teeth of the lungfish dental plate and whether the dentin had reabsorption: one is that there is no resorption, and the teeth form the main body; the other is that the teeth appear on the edge of the dental plate. , the middle is the reabsorbed part; the third is no tooth and its reabsorption, and the dentin layer is used for grinding; the fourth is no tooth proliferation, the main body is composed of reabsorbed dentine, and the edge has a bite ridge.
The tooth plate of Huizedian bipterus is different from these four types that have been found, and it represents a completely new type of tooth plate.
This special structure allows its upper and lower jaws to only engage in a looser bite. Therefore, Huizedian Diptera may not be able to eat hard shelled food like other lungfish, and cannot "eat hard".
The research team speculates that the Huizedian Diptera may use methods such as sucking to eat aquatic mollusks and even other fish, and can only "eat soft".
Giotto said it has long been debated whether the bone fragments at the front of the upper jaw of lungfish are the vomer or the membranous palatine.
This study also explored the homology of the upper jaw bone fragments of the lungfish. The research team supported the hypothesis that the bone fragments at the front of the upper jaw of the lungfish are vomer bones rather than membranous palatine bones through the discovery of Dipteridae from Huizedian.
The 3D virtual model of the sensory tube system and its membranous bone, vomer, pterygoid and parasphenoid bone.
Photo courtesy of Luo Yanchao
Quadruped ancestors and lungfish "parted ways" 420 million years ago
What is the relationship between lungfish and ordinary fish?
Luo Yanchao said that fish generally live in water and breathe with gills, but lungfish can not only breathe with gills, but also breathe directly through the swim bladder, which is similar to the lung.
With this special skill, lungfish can break free from water, burrow into the soil during the dry season, and survive for months or more in a cocoon of secretions, before returning to the water to swim in the rainy season.
Although lungfish and tetrapods constitute a "sister group" and are more closely related than other fish, as early as 420 million years ago in the Early Devonian, the ancestors of tetrapods, including humans, were "relative" with lungfish. "Parted ways", about 360 million years ago, quadrupeds evolved lungs and conquered land, while lungfish, which continue to live in water, got rid of the shackles of water in another way.
Chotuo concluded that the lungfish originated in the early Early Devonian, and then rapidly differentiated, and its diversity peaked in the Late Devonian, but after the Devonian, the diversity and evolution rate of lungfish gradually decreased, and the current life There are only three genera of lungfish left: African lungfish, South American lungfish and Barramundi.
Therefore, lungfish is also an important "living fossil", and its fossil records are well preserved throughout the geohistorical period. The changes in the body structure of lungfish continuously demonstrate their adaptation process from ocean to terrestrial freshwater environment.
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