View Full Version : Arachnid's clue to dino wipeout

Thursday, May 19th, 2005, 02:54 AM
A spider relative called a harvestman trapped in amber could shed light on how arachnids were affected by the extinction that wiped out dinosaurs.
The 100-million-year-old arachnid, which looks like it might have died last year, wandered though a dinosaur-dominated world.

Though older fossils exist, hardly any are known from the Mesozoic Era (245 million-65 million years ago).

Details appear in Proceedings of the Royal Society B journal.

"This specimen came from the Mesozoic Era, so basically the same time as the dinosaurs and generally there are very few fossil arachnids from this period," said co-author Jason Dunlop, from Museum für Naturkunde in Berlin, Germany.

"If you go back to the period of about 300 to 400 million years ago, you actually have more arachnid fossils. So the fact that we have any harvestmen from this time period is really quite unusual."

Extinction mystery

Harvestmen are small arachnids with very long, thin legs and a small body.

One of the reasons this specimen is causing excitement is that it might help tackle the question of how many arachnid groups managed to survive the great extinction of around 65m years ago.

This is thought to have been caused by an asteroid strike at the end of the Cretaceous Period, throwing up dust that blocked sunlight and dragged down temperatures globally.

If a fossil from the Mesozoic Era belongs to a family that existed in more modern times, its lineage must have made it through the extinction.

Although this particular harvestman cannot be included in modern groups, it is pretty similar to later, post-extinction specimens. This could mean that its lineage survived the catastrophe - and if it did, then it is likely others did, too.

"You have a fossil of 100 million years ago and at the end of the Cretaceous Period, about 65 million years ago, you have the end of the dinosaurs and the supposed mass extinction of all these animals," said Dr Dunlop.

"So this amber specimen gives us the first chance to really ask, 'did this affect creepy-crawlies as well'?

"We can't put this in exactly a modern group but if you look at much younger ambers from maybe 40 million years ago, those are even more like modern ones."

Paul Seldon, an arachnid expert from the University of Manchester, UK, agrees the harvestman adds another brick in the wall of evidence.

"Whenever you find an arachnid from the Mesozoic Era, you can nearly always place it in a modern family," he told the BBC News website. "This means there may well have been extinctions of species, but overall the arachnids seem to have sailed through."

Good design

The leggy creature probably led life in quite a similar way to its modern successors.

Unlike true spiders, which are predators, harvestmen have broader tastes. They eat vegetable matter, dead insects and reportedly even enjoy dining on the odd bird dropping.

The harvestman hit on a successful evolutionary "design" fairly early on and has changed rather little over the past few hundred million years.

"We think they would have lived a similar life to modern harvestmen," said Dr Dunlop.

"If you go back to a very, very ancient fossils and look at the internal organs, you see it actually has reproductive organs just the same as a living one; it has a breathing system the same as a living one. So, it looks like there hasn't been any major change in the body plan."

Dr. Solar Wolff
Saturday, May 21st, 2005, 05:52 AM
Cockroaches survived several of these extinctions going back to Carboniferous times.