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Modern anthropod trackways. Photo: Nicholas Minter

From the waters of the Earth, creatures like arthropods and worms emerged, crawling and slithering, onto land. After these first evolutionary steps were taken, the diversity exploded quickly and in countless directions, resulting in the planet’s staggering diversity.

The first steps of marine life colonizing land are explored and discussed in the latest Nature Ecology and Evolution.

The seven-year analysis of previous fossil and track finds by the team from the University of Portsmouth concludes that animals began to take the first steps, and then quickly use their drier environment for better chances at survival.

“Trace-fossil evidence for the colonization of new environments shows repeated early-burst patterns of maximal ichnodisparity (the degree of difference among basic trace-fossil architectural designs), ecospace occupation, and level of ecosystem engineering prior to maximal ichnodiversity,” they write. “The results… are based on an exhaustive search of published accounts of Palaeozoic trace fossils worldwide.”

The small critters like trilobites began to walk onto land more than 500 million years ago, according to the records. They and similar arthropods like aglaspidids, chasmataspidids and marellamorphs left trackways and scratch imprints in the shallow waters and sands of the coast.

Then mollusks left oval imprints and trails with furrows. Worms and crustaceans produced burrows and other trails.

The fossil record then spreads out into other specialized creatures, including deposit-eating animals and predators to eat various other diversifying life forms.

The explosive evolutionary pattern repeats itself across the world, on various continents, they write.

“Despite differing environmental contexts, the results of each colonization event are largely similar, characterized by initial rapid realization of maximal ichnodisparity and a later increase in ichnodiversity,” they write. “This pattern conforms to an early-burst model.”

The reason for the bold new paths onto the shores were various – but came down to survival, they add.

“The search for food and lack of competition for terrestrial organic matter may have spurred the earliest stages in the colonization of land,” they write. “Another likely initial driver of terrestrialization was predator avoidance.”

Life continued to diversify, in both flora and fauna, on land and in the oceans for tens of millions of years – until the first mass extinction. New research published earlier this month proposes that the first of five such huge events was caused by massive volcanic activity. 

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