EVOLUTION

Vertebrates Walk onto Land

~390 million years ago

Phanerozoic · Paleozoic · Devonian

Before any skeleton records it, footprints do. A quarry in Poland preserves trackways of four-legged vertebrates crossing a tidal flat eighteen million years before the oldest bones of such an animal, and ten million years before the fish that are supposed to have preceded them. Those fish are known too. Tiktaalik had a shortened skull, a neck that turned, and a front fin holding a wrist that could bend and take weight.

Why it matters

Everything that walks on land descends from one crossing: amphibians, reptiles, birds, mammals, us. The fin became a limb, and that limb has been rebuilt a thousand times since without ever being replaced. Tracks now push the whole transition earlier and make it faster, which means the Devonian record of it is far more incomplete than anyone assumed.

Dating & uncertainty

The origin sits anywhere from the Early to the Late Devonian depending on which evidence is weighted: tracks come first, bodies much later, and a track without its maker cannot be assigned to a species. Australian footprints described in 2025 push the first fully land-adapted vertebrates back further still, which shortens the whole transition.

Sources

1. Niedźwiedzki et al. (2010), Nature · Tetrapod trackways from the early Middle Devonian period of Poland
2. Daeschler et al. (2006), Nature · A Devonian tetrapod-like fish and the evolution of the tetrapod body plan
3. Shubin et al. (2006), Nature · The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb
4. Long et al. (2025), Nature · Earliest amniote tracks recalibrate the timeline of tetrapod evolution

Earth history as one day

21:56:172 h 4 min before midnight

if Earth’s 4.54 billion years were compressed into a single day