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February 2007

Feature

 

Discovery of the oldest fossil lamprey in the world

Two images of the underside of the lamprey fossil, showing the complementary faces of the split slab of shale where it resided. Credit: Robert Gess/Nature Publishing Group

Scientists from the University of the Witwatersrand and the University of Chicago have discovered a 360 million-year-old lamprey, from Witteberg Group rocks near Grahamstown, in the Eastern Cape, demonstrating that modern lampreys are remarkable living fossils. The report is published in Nature.

This jawless fish fossil was discovered by Robert Gess, a PhD student at the Bernard Price Institute for Palaeontological Research at Wits, under the supervision of Prof. Bruce Rubidge of Wits and Dr Mike Coates of the University of Chicago.

Scientists from around the world are currently engaged in reconstructing the evolutionary tree of life, combining data from the structure of living organisms, the fossil record and the analysis of DNA. In ancient seas, jawless vertebrate fish predated and gave rise to jawed fish, from which all vertebrates, including humans, descended. The only surviving group of jawless vertebrates are the lampreys which, as a result, are attracting intense scientific interest. Only in living lampreys may jawless vertebrate embryology or DNA be studied, resulting in lampreys being increasingly used as surrogate ancestors in researching jawed vertebrates.

Lampreys are, however, highly specialised for a parasitic existence, sucking onto living fish, using a disc that surrounds their circular mouth, to feed on blood and tissue with the aid of a rasping tongue. Knowing when lampreys acquired this specialization, would suggest how representative they really are of ancient fish.

The boneless cartilagenous skeletons of lampreys have, however, left virtually no fossil record - only three fossil species having previously been described, in none of which is a sucker-disc visible.

The remarkably well-preserved new fossil, described in the prestigious scientific journal Nature, published today, is older than any previously discovered fossil lamprey by 35 million years. Only 42mm long it reveals details of its fin, gill basket and, most importantly, its mouth region. It’s circular mouth, situated at the center of a large sucker disk and encircled by small teeth, is remarkably like that of living lampreys, revealing that lamprey adaptations for a blood-sucking lifestyle were acquired in ancient seas, before modern fish faunas arose. Lampreys are therefore ‘living fossils’ that have remained largely unaltered through more than 360 million years and four major extinction events.

The fossil has been named Priscomyzon riniensis (from Latin prisco (ancient) myzon (a lamprey) and Rini, the Xhosa name for Grahamstown and surrounds).

It is one of a remarkably diverse fossil fish and invertebrate fauna revealed by Gess during more than a decade of excavations at a locality revealed by road building in 1985. Through the helpful co-operation of the South African National Roads Agency Limited (SANRAL), he has been able to preserve this locality through a number of subsequent roadworks and to prepare a large collection of unique fossils for scientific s study.

In 1999 SANRAL let a contract for the remedial works on a number of roads on the Grahamstown bypass. During the construction it was discovered that fossils had previously been found in a portion of the one cutting and the work was halted. The Albany Museum was invited to undertake some studies of the fossil bearing material, and the contractor was requested to work elsewhere until the palaeontological studies had been completed and the design of the remedial works was changed to incorporate safeguarding the fossil bearing material. Approximately 20 cubic meters of the fossil bearing material was transported to Bathurst where Gess was to continue studying the material, in the hope to find additional fossils.

The research was sponsored by the National Research Foundation, the Department of Science and Technology and the Palaeontological Scientific Trust (PAST). - WITS


More information:

  Witwatersrand University: www.wits.ac.za 

 

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