Findings: Downsizing in adversity

It was the most catastrophic episode in our planet's history and came close to wiping out all complex life. Now it seems that even the survivors of the Permian-Triassic mass extinction carried its mark for hundreds of thousands of years.

In the first systematic investigation into the fossilised remains of the creatures that lived in the immediate aftermath of the event 250 million years ago, palaeontologists have found that those creatures that did not perish shrank in size in the years that followed - dubbed the Lilliput effect by scientists.

Richard Twitchett, lecturer in palaeontology at Bristol University, and Nathan Price-Lloyd, a postgraduate student, studied the remains of hundreds of marine fossils found in the Dolomites in northern Italy to reveal the extent of the dwarfism.

The disaster was more extreme than the one that later wiped out the dinosaurs. It swept away 90 per cent of marine species and 70 per cent of land vertebrates - global biodiversity took 100 million years to recover its previous level.

The palaeontologists found that the average size of a species of brachiopod called Lingula , a shellfish still alive today, was 15mm before the event. Afterwards it shrank to 3mm. A now-extinct species of snail called Bellerophon shrank from 17mm to 5mm in size.

Both returned to their previous size within a few hundred thousand years.

The palaeontologists found a similar recovery pattern in two species of bivalve and with fossilised burrows left behind by a type of marine worm, which were up to 2cm in diameter before the event, but 2mm afterwards.

Dr Twitchett said it was likely that the catastrophe involved the collapse of the marine food chain, which took several hundred thousand years to recover.

In the face of this food shortage, creatures shrank over the generations to reduce the amount they needed to eat.

Other mass extinction events appear to have triggered similar, albeit shorter-lived, effects.

The findings will be presented to the Palaeontological Association's annual meeting at Cambridge University next week.