Facing up to a backwards fossil.

Facing up to a backwards fossil

Fossils of primitive, jawless fish dating back 470 million yearsare the oldest known examples of vertebrates, a subphylum to which both human beings and salamanders belong. Because the evidence of these fish, called agnathans, is scant and fragmentary, scientists know little about the agnathans' appearance or about their evolutionary history. However, one scientist is discovering new information simply by turning around a "backwards' fossil.

This fossil is one of a handful of the earliest known agnathanfossils, all of which date back to the Ordovician period. In a reexamination of the fossil, David K. Elliott from Northern Arizona University in Flagstaff realized that "the person who had described it had somehow gotten it back to front.'

Because of this error, the fossil had been dismissed as aheadless, tailless mass of scales and plates. But in the July 10 SCIENCE, Elliott reports that both head and tail are well preserved, making this the most complete vertebrate known from the Ordovician, he says.

Because of new information discovered by the fossil turnaround,Elliott believes that this fossil and several similar ones had been inappropriately assigned to an order of fish, Heterostraci, whose members have only a single set of tube-like openings that run to the gills. Elliott, however, has found several sets of openings on the reexamined fossil.