Animals live on land

The first animals to live permanently on land were small arthropods, relatives of today's millipedes, centipedes, spiders and insects. The oldest well-dated example is Pneumodesmus newmani, a millipede about 428 million years old from Stonehaven, Scotland, whose body shows pores called spiracles for breathing air. Millipedes such as Kampecaris, around 425 million years old, are almost as early. Some trackways in even older rock may record earlier visitors, but they are harder to interpret.

Land was a hard place to live. An animal out of water risks drying out, must hold up its own weight, and needs a way to take in oxygen from air. Arthropods already had a waterproof exoskeleton and jointed legs, which gave them a head start. They also arrived after plants had colonized land, so there were things to eat: living plants, fungi and the litter of dead material. Small predators such as early arachnids soon followed their prey. Vertebrates did not reach land until some 30 to 50 million years later, in the Devonian, when four-legged forms evolved from lobe-finned fish.