Fossil specimens of Young's fish (two on the right) used in this study. Photo by Sun Zifa, a reporter from China News Service
Beijing, May 6 (Xinhua) -- Following the recent discovery in Qujing, Yunnan Province, a special fossil of a new genus of lungfish that "eats soft but not hard" about 390 million years ago, "Huize Dian Biplank", the team of academician Zhu Min of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (Institute of Paleovertebrates of the Chinese Academy of Sciences) has recently revealed the mystery of the origin of the feeding habit of lungfish "gnawing hard bones" through in-depth research on the fossils of "pioneer Yang's fish" (Yang's fish) about 410 million years ago.
This important research paper on the origin and rapid evolution of crustivivity in lungfish of paleovertebrates was recently published in the international academic journal Nature Communications. Zhu Min said that this not only provides key fossil evidence for revealing the initial changes in the structure of lung fish and feeding habits, but also proposes a new hypothesis for the study of the origin of crustivity in lung fish.
China News Service reporter Sun Zifa photographed ">
Dr. Cui Xindong presented and introduced the fossil specimens and research results of Yang's fish. Photo by Sun Zifa, a reporter from China News Service
Lungfish are fish that can "gnaw hard bones"
The first author of the paper, Dr. Cui Xindong of the Institute of Ancient Spine of the Chinese Academy of Sciences, said in an exclusive interview with a reporter from the China News Agency in Beijing on May 6 that lungfish are a type of meat fin fish that can breathe with "lungs" (that is, specialized swim bladders, which can absorb air), a special skill that allows lungfish to get rid of the shackles of water and dive into caves to hide and survive when the river dries up.
Lungfish are also a fish that can "gnaw hard bones": their palate inner wing bones and the anterior joint bone of the lower jaw have long grinding tooth plates; the lower jaw is short and thick, directly connected to the skull; and the adductor muscles of the jaw are very developed.
These features give lungfish a strong bite force and are able to prey on invertebrates with hard shells, a particular feeding method known as "shell-eating" (also known as "nail-eating").
The rate of evolution of lung fish traits. Courtesy of Cui Xindong
Two Young's fish fossils preserve the structure of food habits
Cui Xindong pointed out that the oldest lungfish stem group member Yang's fish is one of the typical representatives of the primitive meatfin fish in the Qujing Xitun vertebrate fauna of the early Devonian (about 410 million years ago), which has been named by academician Zhang Miman since 1981, which has aroused continuous attention from the international academic community, and follow-up related studies have gradually proved that Yang's fish is the original representative of lungfish, and all lung fish, including strange fish, constitute a "sister group", and Yang's fish discovery also provides a well-constrained minimum estimation time for the divergence point of lungfish-tetrapods.
However, in addition to the jaw arch, other anatomical structures related to food habits of Young's fish, such as tongue arch, gill arch and palate structure, are not clear due to the lack of fossils, which also makes the origin time and order of occurrence of the characteristics related to the crustivity of lung fish have not been clarified. In recent years, in the fossil excavation work, the research team has collected two fossil specimens of Yang's fish that have fortunately preserved the tongue arch, gill arch and palate structure, thus laying an important foundation for the research on the "shell-eating" of lungfish.
Where does lungfish's "shell-eating" ability come from?
Cui Xindong said that the "hope strange fish" in the early Devonian period (about 410 million years ago) is considered to be the most primitive lungfish, which already has typical lungfish "shell-eating" characteristics, such as developed tooth plates and short and thick jaws. The phylogenetic location of Young's fish lies between the foraminiferous fish (another important branch of the lungfish) and the chia fish, which is more primitive than the kiwi fish. Therefore, Young's fish is the key to studying the origin of lungfish "shell-eating".
Ecological restoration map of "Pioneer Yang's Fish". Brian Choo drawing
This study of fossil specimens of Young's fish that preserves the structure of the tongue arch, gill arch and palate shows that Young's fish has a strong bite force; its tongue and jaw are short and thick, similar to that of lungfish; the morphology and arrangement of the teeth on the inner wing bone have been very similar to that of the odd fish and other primitive lungfish, but it still retains the outer wing bone and membranous palate bone with large teeth, but the teeth are very thick and blunt.
Combining these anatomys, the team reconstructed the way youngfish eat: mainly using rough and blunt teeth to crush the prey, while the smaller teeth on the tooth plate played an auxiliary fixation role.
Further comparative studies found that the exotic fish and the more advanced lungfish had a stronger shell-eating ability, their palatal bone fused with the skull, the outer wing bone and the membranous palate were lost, and the inner wing bone thickened to form a strong tooth plate, which was able to vigorously grind the prey.
Three-dimensional reconstruction model of the specimen "Pioneer Young's Fish". Courtesy of Cui Xindong
Lung fish have rapidly radiated since their origin
Cui Xindong said that lungfish have shown a high degree of specificity from the beginning of their appearance, and the diversity is very high, and it is believed that they have undergone rapid evolution at the beginning of the evolutionary stage.
The research work on Young's fish fossils used Bayesian terminal dating method to quantitatively analyze the phylogenetic relationship, differentiation time and evolution rate of paleozoic lungfish, and the results supported the hypothesis of early rapid evolution of lungfish.
The results show that lungfish originated in a window of about 7 million years between about 420 million and 413 million years ago and underwent rapid evolution, especially the characteristics associated with feeding have a significantly higher rate of evolution than other characteristics.
The time of differentiation of lungfish and their close relatives, the rate of trait evolution, and the skull bones representing the genus species. Courtesy of Cui Xindong
According to Matt Friedman, a professor at the University of Michigan and one of the co-authors of the paper, lungfish have evolved rapidly since their origins, becoming the most diverse meat-finned fish in the Devonian period. In contrast, another major branch of lungfish, foraminiferous fish, had relatively conservative morphological characteristics and low diversity, eventually becoming extinct at the end of the Devonian period.
The team believes that the success of lungfish is likely to be due to the rapid evolution of feeding habits in the early stages of evolution, which opened up new ecological spaces, and the pioneer Yang's fish just recorded the initial state of this key innovation. (End)
Source: China News Network