If you spawn in The Footpaw (selecting West Zone 2, or sometimes South Zone 1 in The Island map) you can easily find them in early game. Just look for the narrow peninsula in the East (a very safe place with almost no predators, literally none in the South area). You will frequently find trilobites on the southwestern coast.

Trilobites are very usefull, because they're passive and weak: that makes them probably the easiest source of chitin, a convenient source of meat and a source of oil and silica pearls, two important resources you'll need late in the game.