The explained dinosaur-egg route is a complete fossil set taken to Dr. Ivy, followed by incubation. The game also names sea reptile eggs as a Sunken Grotto objective, but does not explain their full use.
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Fossil-to-dinosaur route
Complete the set, bring it to Dr. Ivy’s DNA Lab, then warm the egg in the incubator. After hatching, feeding above half belly fullness is the stated condition for dinosaur growth.
Sea reptile eggs are a separate objective
The Explore section names sneaking into the Sunken Grotto to take sea reptile eggs. It does not confirm their pickup controls, respawn rules or whether they follow the same incubator process.
Choosing the next guide
Use the fossil route for the documented hatch-and-raise loop. Use the Grotto objective as a separate exploration lead, with its exact route still to be established.
Your next task
Choose the guide that matches the step you are working on next.