In the first study to use trace fossils – which is the fossilisation of footprints, tracks and burrows – experts have revealed how animals colonised the land.
The seven year long study, which examined all known trace fossils across a 200 million year period, found that sea creatures made their way from the ocean, the shallow waters and eventually to spread across the world.
The research revealed that once the critters reached land, there was a rapid evolutionary process followed by long periods of calm.
Lead author Dr Nicholas Minter, from the University of Portsmouth’s School of Earth and Environmental Sciences, said: “When the first animals emerged from the oceans they had a blank canvas, there were no other animals there and so they diversified rapidly both in how they behaved and in the ecological roles, or the part they played, in the theatre of life.”
The population of the critters which went land-bound is small, but spiders emerged from crabs while slugs and snails came from the same families as squid and cuttlefish, according to the study published in the journey Nature Ecology and Evolution.
Dr Minter explained: “Not many from any one group, or Phylum, made the transition from sea to land or fresh water.
“What’s surprising is the leaps in evolution follow the same pattern – an early evolutionary burst of rapid diversification and a long period of relative calm – each time animals conquered new habitats, first the margins between sea and land, then floodplains, followed by rivers, deserts and lakes.
“Each burst was an evolutionary experiment, yet the results are very similar.
“As scientists, we know experiments tend to have different outcomes if you change the parameters, but in this case, there is a consistency which suggests a fundamental constraint on the behavioural and ecological roles fulfilled by animals on land.”