Life › Seas, forests & the move to land › Plants colonize land
Arthropods walk onto land
by c. 425 million years ago (millipede fossils); tracks earlier· Event· Animals
Strong evidenceGood evidence; dates or details still being refined.
Millipedes, early arachnids and other arthropods became the first animals to live on land, by about 425 million years ago.
See it on the Life map →What happened
Arthropods, with jointed legs and a tough outer skeleton that slows drying out, were well suited to land. Trackways suggest some ventured onto tidal flats in the Cambrian. The oldest body fossils of land animals are millipedes from Scotland, roughly 425 million years old (exact dates debated); one, Pneumodesmus, has breathing holes (spiracles) for air. Arachnids and wingless hexapods followed by about 410 million years ago. Arthropods made the move several separate times.
Why it matters
They were the first animal residents of land, forming food webs with plants and fungi and later becoming prey for the first four-legged vertebrates.
The evidence (fossils, genes, rocks)
Scottish millipede fossils, mites, arachnids and springtails in the Rhynie chert, and fossil trackways in Cambrian and Ordovician rocks.
Still debated
Whether animals first lived on land in the Cambrian, as some tracks and molecular clocks suggest, or only in the Silurian, as body fossils suggest.
Connections (3)
▸Plants colonize land provided food and shelter for Arthropods walk onto landStrong evidence
The connection
Plants turned bare ground into habitat. Their living and dead tissue fed early millipedes and mites, many of which ate decaying plant matter, while low plant mats kept the ground moist and shaded. Predators such as early arachnids followed the plant-eaters.
When and how
Silurian and early Devonian, about 430–400 million years ago; best seen in the Rhynie chert, Scotland, about 407 million years ago.
How sure are we?
The Rhynie chert preserves arthropods among plant stems, plant tissue damaged by feeding, and fossil droppings full of plant material.
Debates and open questions
Whether some arthropods reached land before plants, feeding on microbial crusts, as Cambrian trackways may hint.
▸Arthropods walk onto land provided prey for Vertebrates move onto land (tetrapods)Strong evidence
The connection
When vertebrates came onto land, millipedes, arachnids and insects were already there, a ready food supply. Early tetrapods were meat-eaters: in water they ate fish, and on land many fed on arthropods. Plant-eating tetrapods appeared only late in the Carboniferous.
When and how
Coastal and swamp habitats, about 370–330 million years ago, as tetrapods spent more time out of water.
How sure are we?
Inferred from teeth and jaw shapes and from sites where tetrapods and land arthropods occur together; direct stomach contents are rare.
Debates and open questions
How important insect prey was in drawing tetrapods onto land, compared with escaping predators or finding new places to breed.
▸Arthropods walk onto land included the ancestors of Insects: the first animals to flyStrong evidence
The connection
Arthropods moved onto land several separate times. Millipedes and arachnids were among the pioneers; another line, crustacean-like animals related to today's shrimp, became six-legged hexapods. Wingless hexapods such as springtails lived among plants by about 410 million years ago, and insects arose from this land-living branch.
When and how
Molecular clocks suggest the Ordovician, about 480 million years ago; the oldest fossils, early hexapods in the Rhynie chert, Scotland, are about 407 million years old.
How sure are we?
DNA shows insects nest within the crustaceans (together called Pancrustacea), and early hexapod fossils appear alongside other land arthropods.
Debates and open questions
Which crustaceans are insects' closest relatives (remipedes are a leading candidate) and exactly when their ancestors left the water.