Early land creatures borrowed shells for protection around 500 mln yrs back

London, April 11 (ANI): In a new research, scientists have studied the fossilized tracks left by arthropods 490 to 510 million years to suggest that these creatures crawled out of the ocean onto land and borrowed shells to survive in an otherwise hostile world.

According to a report in New Scientist, the research was done by Palaeontologist James Hagadorn of Amherst College in Massachusetts, US.

The fossilised tracks were left in sandstone in central Wisconsin, 490 to 510 million years back by Protichnites, an arthropod with many pairs of legs crawling across the sand and dragging its tail behind. But, some of the tracks show odd markings along their left side, as if the animals had bent tails that dragged to one side.

Hagadorn and Adolf Seilacher of Yale University now report that these tracks are very similar to the distinctive ones left by a hermit crab carrying a coiled shell.

They conclude that the unusual tracks must belong to Protichnites that had partly inserted their tails into similar shells in order to carry them on land.

Hauling shells would have given the critters an advantage. Trapped moisture protected them from drying out and helped keep their gills moist.

The shells also shielded the animals from harsh ultraviolet light and protected them from changing temperatures.

Although the behaviour resembles that of a hermit crab, Hagadorn suspects these early explorers were the ancestors of a long-extinct group called sea scorpions, which had 6 to 13 pairs of legs.

The tracks suggest the shells probably came from coiled molluscs, but other sources are possible.

The hermit-like behaviour obviously had advantages, but the researchers say it is unclear how it came about.

"We have no idea how this originated or what led to it," Hagadorn said. (ANI)