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."

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Editor:Yang Jie