Life › Seas, forests & the move to land
Vertebrates move onto land (tetrapods)
c. 395–360 million years ago· Event· Animals
Strong evidenceGood evidence; dates or details still being refined.
Lobe-finned fish evolved limbs with toes and gradually moved from shallow water onto land, about 395–360 million years ago.
See it on the Life map →What happened
The shift took tens of millions of years. Fish such as Tiktaalik had sturdy fins, a neck and lungs. Early tetrapods such as Acanthostega and Ichthyostega from Greenland, about 365 million years old, had legs with up to eight toes but kept gills or lived mostly in water. Limbs seem to have evolved first for moving through shallow, plant-choked water; fully land-based life came later, in the Carboniferous.
Why it matters
This is the origin of every four-limbed vertebrate: amphibians, reptiles, birds and mammals, including humans. Our arms, hands and lungs trace back to it.
The evidence (fossils, genes, rocks)
Fossils from Greenland, Canada, Latvia and elsewhere; footprints at Zachełmie, Poland, about 395 million years old (published 2010); and shared genes controlling fin and limb growth.
Still debated
The Polish footprints predate the best fish–tetrapod fossils, so where and when limbs first appeared is debated; a few researchers question whether tetrapods made them.
Inside this (4)
Connections (4)
▸Tiktaalik is a transitional step toward Vertebrates move onto land (tetrapods)Well established
The connection
Tiktaalik combined fish features (scales, fins, gills) with traits of four-legged animals: a neck, sturdy ribs, lungs and fin bones forming shoulder, elbow and wrist. It could probably prop itself up in shallow water. It shows the tetrapod body being assembled in stages, before true legs with toes.
When and how
Ellesmere Island, Nunavut, Canada, about 375 million years ago; found in 2004 by Neil Shubin, Ted Daeschler and Farish Jenkins.
The evidence
Its mix of features fits between fish like Panderichthys and early tetrapods like Acanthostega, both in anatomy and in age.
Debates and open questions
Whether Tiktaalik ever left the water, even briefly, or only propped itself up in the shallows is still argued from its bones.
▸Vertebrates move onto land (tetrapods) led to The amniotic eggWell established
The connection
Early tetrapods, like amphibians today, had to return to water to lay eggs. In one group of these four-limbed animals, eggs gained protective membranes and a shell, letting embryos develop on dry ground. That step, by about 318 million years ago, split the amniotes off from the amphibian line.
When and how
Carboniferous coal-swamp forests; the earliest amniotes, such as Hylonomus, were found inside fossil tree stumps at Joggins, Nova Scotia, about 318–312 million years ago.
The evidence
Family trees based on skeletons and genes place amniotes inside the tetrapods, descended from amphibian-like ancestors. All living amniotes share the same egg membranes.
Debates and open questions
Which early tetrapod group gave rise to amniotes is debated, as is whether the egg evolved before or after these animals moved onto drier ground.
▸Late Devonian extinction set back Vertebrates move onto land (tetrapods)Strong evidence
The connection
Early tetrapods lived in shallow coastal and river waters hit by the Hangenberg event, about 359 million years ago, and most Devonian tetrapod lineages disappeared. Afterward comes 'Romer's Gap', some 15 million years with few tetrapod fossils, before survivors spread across land in the Carboniferous.
When and how
End of the Devonian, about 359 million years ago; studied by Jennifer Clack, Lauren Sallan and colleagues.
How sure are we?
Fossil counts show many tetrapod and fish lineages vanishing at the boundary; recent finds in Scotland partly fill Romer's Gap.
Debates and open questions
Whether Romer's Gap reflects a real collapse or a shortage of fossil-bearing rock; recent Scottish finds suggest the record is partly to blame.
▸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.