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May 7, 2006

More fishy evolution stuff

Another clue to how early bony vertebrates evolved:

BEIJING, May 7 (Xinhua) – A Chinese research team has discovered four fossils of a new species of fish dating back 400 million years which may provide clues to the evolution of fish.
Dr. Zhu Min, the leading scientist from the Chinese Academy of Sciences (CAS) Institute of Vertebrate Paleontology and Pale anthropology, said Sunday that the newly discovered species may represent a bridge between two vertebrate lineages that ultimately went on to dominate the modern world.
The find made by Zhu and his colleagues was published in the latest issue of the British journal Nature.
The fossilized creature, found in southwest China’s Yunnan Province, combines features shown by ray-finned bony fishes, including the majority of modern fish species, and by lobe-finned bony fishes, the group that spawned the ancestors of today’s land vertebrates, Dr. Zhu said.
The ancient fish, represented by chunks from four separate skulls, has a skull roof much like that of actinopterygian, the group that includes most modern fish, Dr. Zhu said.
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 sarcopterygians, the fish that later gave rise to land vertebrates, he said.
Cosmine is characterized by a network of pores and canals in the tissue, overlaid by a single enamel-based layer, Zhu explained.
The 405 million-year-old fossil possessed several such layers over the pore-canal network, suggesting that the cosmine arose after all but one of these layers disappeared, he said.

Zhu named the ancient fish Meemannia eos after his mentor Chang Mee-mann, a respected vertebrate paleontologist and pioneer of early fish evolution (Eos is the Greek goddess of dawn).

You can read the opening paragraph of the (subscription-only) Nature piece here. The image is a ventral view of the posterior portion of Meemannia eos’s skull roof.

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