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418m-yr-old fish fossil holds key to human evolution

By Lin Shujuan (chinadaily.com.cn)
Updated: 2009-03-26 16:48

The recent discovery in China of an unusually intact and ancient fossil fish, the distant ancestor of about 99.7 percent of today’s living vertebrates including human beings, has provoked a rash of new fieldwork and a fresh look at the early evolution of vertebrates.

An artist's illustration of an ancient fish, called Guiyu. The recent discovery in China of an unusually intact and ancient fossil fish, the distant ancestor of about 99.7 percent of today's living vertebrates including human beings, has provoked a fresh look at the early evolution of vertebrates. [chinadaily.com.cn]

The fish, called Guiyu and described in detail in today's (May 26) journal Nature by Zhu Min and his colleagues from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) under the China Academy of Sciences, dates back to the Silurian period, more than 418 million years ago.

It is the earliest known representative of a very large vertebrate group, the "bony fishes" or Osteichthyes, the class of vertebrates that includes everything from humans to halibut.

There are more than 60,000 living species of Osteichthyes today, including almost all the fish that we eat (except sharks) and all land vertebrates, according to Zhu, the first author of the Nature report.

"Crucially, this piscine offshoot of our own distant past is both unusually intact and exceptionally old," says Professor Michael I. Coates from the University of Chicago, who wrote a review of the discovery of Guiyu also in today's Nature.

"Earlier stretches of Osteichthyan history are littered with fossil detritus, such as isolated teeth and scales," says Coates.

Guiyu, with an almost complete fossil specimen, is a valued addition to the "poorly resolved patch of vertebrate evolution", says Coates.

Zhu admits the discovery of Guiyu is "a lucky find", which allows people across the world to see for the first time what our distant ancestor looked like, and gives "a better idea of when, where and how the Osteichthyes evolved, and how they are related to other vertebrate groups such as sharks".

The discovery of Guiyu in Yunnan province has added to the increasing evidence that some of the key steps in early vertebrate evolution took place in southern China about 400-450 million years ago, at a time when that region was a small separate island continent near the equator, according to Swedish paleontologist Per Ahlberg from Uppsala University.

"It also help us to interpret the less complete fossils," says Ahleberg, who has arrived in China for a visit to its discovery site in Southwest China. "It will greatly increase our understanding of the earliest Osteichthyes.

"A specific point of interest for me is that rocks of similar age from Sweden and Estonia have yielded fossils of two other early Osteichthyes -- Andreolepis and Lophosteus -- that are known only from isolated bones and scales. My research group at Uppsala University is working on these fossils. Through comparisons with Guiyu and other early fossil fishes from China we hope to be able to make better and more detailed interpretations of our own material than would otherwise be possible."

Zhu says it is expected the discovery of Guiyu will revitalize the "long stagnant research tracing the very basal root of vertebrates". "More surprises are to be expected."