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Lobe-finned fish
c. 425 million years ago (Guiyu) to today· Organism or group· Animals
Well establishedStrong fossil, genetic or geological evidence.
Bony fish with fleshy, limb-like fins built around a single upper bone, the group that later produced four-legged animals.
See it on the Life map →What happened
Ray-finned fish such as trout have fins made of thin, fanned rays. Lobe-finned fish have a muscular fin base with a chain of bones: one bone, then two, then smaller ones, the same pattern as the human arm. The oldest well-preserved example is Guiyu, about 425 million years old, from Yunnan, China. Living members are two coelacanth species and six lungfish species, plus, by descent, all tetrapods.
Why it matters
Their sturdy fins were the starting point for legs; in family-tree terms, humans are a highly modified branch of the lobe-finned fish.
The evidence (fossils, genes, rocks)
Fossils such as Guiyu and Eusthenopteron, the 1938 discovery of a living coelacanth off South Africa, and DNA showing lungfish are tetrapods' closest living fish relatives.
Still debated
Why lobe-finned fish, diverse in the Devonian, dwindled to eight living fish species while ray-finned fish grew to over 30,000.
Connections (2)
▸Jawed fish include Lobe-finned fishWell established
The connection
Lobe-finned fish belong to the bony fish, the branch of jawed fish that built skeletons of bone. Bony fish then split into ray-finned fish, which are most fish today, and lobe-finned fish, whose fleshy, bone-filled fins later became legs.
When and how
Split by about 425 million years ago, in Silurian seas; early forms such as Guiyu from Yunnan, China, described by Zhu Min and colleagues in 2009.
The evidence
Fossils showing a sequence of jaw, fin and skull changes, and DNA linking coelacanths and lungfish with tetrapods.
Debates and open questions
Some early bony fish mix ray-finned and lobe-finned features, making the exact split hard to place.
▸Lobe-finned fish include the tetrapod-like TiktaalikWell established
The connection
Within the lobe-finned fish, one branch (the tetrapodomorphs) lived in shallow, often oxygen-poor waters. Over some 30 million years their fins grew sturdier, their heads flatter and their lungs more important. Eusthenopteron and Panderichthys show the trend; Tiktaalik is one of the most limb-like forms that is still technically a fish.
When and how
Devonian rivers and deltas, about 400–375 million years ago, on the old continent of Euramerica; Tiktaalik was found in Arctic Canada in 2004.
The evidence
A series of fossils in dated rocks shows stepwise changes in fins, skulls and shoulders, matching predictions from comparative anatomy.
Debates and open questions
Which environments drove these changes, whether rivers, swamps or tidal flats, is debated.