South Africa has again shown itself to be a unique archive on the dawn of animal life of our planet. Recently, its fossil treasury delivered yet another precious find: a 360-million-year-old fish.
The 4cm-long lamprey, discovered near Grahamstown in the Eastern Cape, is the oldest fish of its kind yet discovered.
Jawless fish are the oldest known fish in the fossil world, and the group still persists today in the form of lampreys and hagfish. For this reason lampreys have long been the focus of scientific attention. Living lampreys are known along all continents except, ironically, Africa.
According to South African palaeontologist Robert Gess, who made the discovery, the fossil may shed light on the evolutionary process, as the DNA of modern-day lampreys can be used in drawing up trees of life.
Only three ancient lampreys had previously been discovered. The ÂÂrarity of such finds arises from the fact that the ancient fish is made of cartilage, which does not fossilise as readily as bone.
The fossil fish discovery has been highlighted in an article written by a team from the universities of the Witwatersrand and Chicago published in the United States-based ÂÂscientific journal Nature this week.
According to Gess, the fish indicates that modern lampreys are living fossils in the mould of the coelacanth, which has remained unchanged for 360-million years.
The fossil is only one of a remarkably diverse fish and invertebrate fauna fossil find unearthed by Gess over more than a decade of painstaking excavations at a roadside quarry near Grahamstown.
Gess, who has worked at Waterloo farm, the site of the lamprey discovery, for 20 years, describes it as his own personal time machine in ÂÂdocumenting the history of primeval life forms. He attributes his successes to ”passion, a keen eye and pocket knife”.
The ancients fish’s locality was revealed by road-building activities when the bypass around Grahamstown was built in 1984. With the cooperation of the National Roads Agency Gess was able to rescue the site and preserve a very large collection of precious fossils.
”It is the only good site from the western half of Gondwana [the ÂÂprehistoric super-continent] that documents the life of early Earth,” said Gess, who is doing his doctorate on the fish fossils found at the site at Wits.
The anaerobic nature of the mud deposited in an estuary millions of years ago ensures that plants and fish that lived in there are often exceptionally well preserved. As a result, a perfect ”photo” of the lamprey had been taken.
The world inhabited by the ancient lamprey had no land vertebrates, plants having only recently colonised the land.
In the past 500-million years the Earth has experienced five major extinction events, which have removed up to 90% of species living at the time of each holocaust.
The latest discovery indicates that lampreys and coelacanths are the only vertebrate animals to have survived almost unchanged through four of these extinctions.
Gess said the lack of evolutionary changes that lampreys have undergone in 360-million years shows that they found a successful niche and stuck to it. While some other jawless fish evolved into the first fish with jaws and then into land-walking creatures, the lamprey has remained loyal to its original lifestyle.