The First Land Animals
Since autotrophs are the basis of a food web, plants had to exist on land before self-sustaining ecosystems with animals were possible.
Cambrian sand dunes show a few tracks made by aquatic arthropods and gastropods.
The oldest known air-breathing land animal was an arthropod, a tiny millipede that lived 428 mya.
Arthropod footprints and remains become more common in the Late Silurian.
Arthropods were well-suited to be first on land:
Slim, strong legs.
A modern millipede,
Image in the public domain.