Giant trilobite discovered

About twice the size of the previous record holder

By BBC News Online science editor Dr David Whitehouse

The largest trilobite yet discovered has been identified by Canadian palaeontologists.

Trilobites were very widely distributed

The creature, which dates from 445 million years ago, measures 72 centimetres in length. This is about twice the size of the previous record holder.

Trilobites are an extinct group of sea-dwelling arthropods (animals with an outer skeleton and jointed body and limbs) that are distantly related to crabs, scorpions and beetles.

They are probably the most common fossils of the Paleozoic Era (about 545-250 million years ago) and scientists use them to help date different layers of rock.

"A trilobite of this size really is an amazing discovery," said Dr Graham Young, a member of the team that discovered it.

Useful creatures

The specimen is an example of a previously unknown species, and was found by researchers studying ancient tropical coasts, of the Late Ordovician and Early Silurian geological periods (458-408 million years ago), in Manitoba, Canada.

The team found the specimen just outside their intended search area

When the fossil was unearthed, most of its segmented exoskeleton was missing and only the rear most portion of the tail shield was present.

Scientists realised just what a monster they had when they started to clean up the specimen. The fossil is now on display in the Manitoba Museum of Man and Nature in Winnipeg.

Most trilobites are between 3 and 10 cm (1 - 4 inches) in length. The creatures evolved quickly and were widely distributed, making them useful tools to compare the ages of rock strata in different parts of the world.

Colder climates

"There is nothing familiar about this particular specimen! It is an important and amazing find," says Manitoba Museum's Dr Bob Elias.

The fossil is now on display to the public

Dr Graham Young said: "We have found a very unusual specimen that illustrates some of the diversity and weirdness of ancient life. A trilobite of this size really is an amazing discovery."

In July 1998, a team of scientists set out for northern Manitoba hoping to find fossils similar to those uncovered by previous digs, like the 43-cm (17-inch) long trilobite excavated in the area a decade before.

The team struck lucky just outside their original search area. The trilobite's size contradicts the idea that larger animals are more commonly associated with colder climates.

Although northern Manitoba is now sub-arctic, hundreds of millions of years ago it would have been submerged in salty seawater located on the equator.

All images courtesy of the Manitoba Museum of Man and Nature