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CAS researchers unveil primitive form&nb

时间:2006-05-16 22:40来源:Sibs.ac.cn 作者:admin 阅读:

With over 50,000 species, Osteichthyans, or bony fish, accounts for 98% of the present-day vertebrates. Bony fish falls into two groups: actinopterygians, meaning ray-finned bony fish, and sarcopterygians, meaning lobe-finned bony fish. The huge morphotype difference of the two catagories cast doubts on research into the origin and evolution of bony fish. The recent discovery of a primitive fish species by CAS researchers and colleagues provides a missing link between the two lineages, unveiling unique features for understanding primitive bony vertebrates.

    As reported in the in the May 4 issue of the journal Nature, a team led by ZHU Min, a paleichthyologist and director of the CAS Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) and YU Xiaobo from Kean University in US (a CAS Overseas Expert Assessor), has found a fossil fish that lived more than 400 million years ago in southwest China's Yunnan Province. The creature combines features of ray-finned bony fish, which include the majority of modern fish species, and lobe-finned fish, the group that spawned the ancestors of today's land vertebrates. The new fossil fish is believed to be closely related to the common ancestor of the two vertebrate lineages that went on to dominate the modern world.

    Named Meemannia eos gen. et sp. nov. after Prof. ZHANG Miman (Mee-mann Chang), a CAS member and a leading paleontologist in China, the primitive fossil fish, which is represented by chunks from four separate skulls, has a skull roof much like that of ray-finned bony fish, the group that includes most modern fish. But the fine features of its anatomy may also shed light on the evolutionary origin of cosmine -- a hard surface-tissue found in many fossil lobe-finned fish, such as coelacanths and lungfishes that later gave rise to land vertebrates. The new species provides important insight for studying the early evolution of bony vertebrates and indicates a possible morphotype in exploring the common ancestry of two lineages.

    The discovery of the new species Meemannia lends further support to the hypothesis proposed by Zhu and colleagues in 2001, stipulating that the ancient South China block was the center of origin of lobe-finned fish (sarcopterygians). With the support from the National Foundation for Natural Sciences of China, the National Key Basic Research Program and CAS, their findings on the origin of bony fish and tetrapod, have been published many times in prestigious journals, such as Nature, providing significant fossil data to calibrate the "molecular clock" for timing major evolutionary events.

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