Menu

Ancient life · Life in the sea

Graptolites

Floating colonies that look like pencil marks on rock.

Enlarged

Didymograptus, a “tuning fork” graptolite from south Wales, was about 2 cm long. Beside a person 1.75 m tall; ticks every metre.Body shape drawn for this site

When
About 520 to 350 million years ago; floating from the start of the Ordovician
Where
Seas worldwide; in Britain, in Scotland, Wales and north-west England
Size
Didymograptus, a “tuning fork” graptolite from south Wales, was about 2 cm long
Dark, branching graptolite fossils on pale rock, with a red scale bar of half a centimetre.
Tetragraptus, a graptolite with four branches, from Victoria, Australia. Each saw-tooth along a branch was the tube of one animal.TetragraptusfruticosusBendigonian by Wilson44691, Public domain, via Wikimedia Commons. Resized.

Fossil graptolites are thin, often shiny marks on rock that look as if someone drew them in pencil. Their name means “writing in the rocks”. Each one is the remains of a colony: a branching system of tubes, made of collagen like our fingernails, with one small animal living in each tube. Some colonies held up to 5,000 of them.

The first graptolites lived fixed to the sea bed. At the start of the Ordovician they began to float, and became some of the first animals to live in the open sea, feeding on single-celled life near the surface. New species evolved so fast that geologists use them to date rocks, in slices of time as short as a few hundred thousand years.

They died out long ago, but small sea animals called pterobranchs, alive today, seem to be their close relatives.

Graptolites640 Manow
Graptolites: 520 to 350 million years ago. That is 11% of the way back to the Earth’s birth.Periods from the ICS chart

Found in Britain. See where Britain was at the time in Britain’s journey.

Also in life in the sea

Sources