A new study published in the journal Geology suggests extinct arthropods known as trilobites were likely able to venture into very shallow water of the upper portion of ancient tidal flats.

“Discoveries like this are so important because they are at the core of our understanding of early evolutionary breakthroughs,” said study lead author Prof Gabriela Mángano from the University of Saskatchewan.

Prof Mángano and her colleagues discovered a huge number of fossilized trilobite tracks in rocks from the Appalachian Mountains.

The fossils reveal trilobites moved closer to the land during the Cambrian explosion some 540 million years ago

The Cambrian explosion is when almost all modern groups of animals appeared for the first time in the fossil record and the tidal flats likely served as a rich area for the creatures to forage food and for nesting activities.

The rocks also showed signs of cracks from periodic drying, suggesting prolonged exposure to subaerial conditions.

“Trilobites are distantly related to crabs, scorpions and beetles and were once widely distributed,” Prof Mángano said.

“This makes them useful tools to compare the ages of rock strata in different parts of the world.”

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M. Gabriela Mángano et al. Trilobites in early Cambrian tidal flats and the landward expansion of the Cambrian explosion. Geology, published online December 13, 2013; doi: 10.1130/G34980.1