Nature study reclassifies the Scottish fossil Westlothiana as a stem tetrapod with aquatic adaptations

30 September 2026

Nature published on 30 September 2026 a study that reclassifies Westlothiana lizziae, one of the best known fossils from East Kirkton in West Lothian, Scotland.
The specimen dates to the Early Carboniferous, in the Visean stage.
It had been widely cited as the earliest terrestrially adapted stem amniote, that is a land-adapted close relative of the amniotes; the new phylogenetic analyses return it instead as a stem tetrapod.
The evidence includes unexpected plesiomorphies of the skull roof, palate, braincase and mandible, together with aquatic adaptations such as an ossified internal gill skeleton and extensive denticles on the palate and mandible.
The authors conclude that terrestrial adaptations, including an amniote-like pedal formula, the loss of fin-like forelimb function and superficially claw-like terminal phalanges, evolved in a mosaic fashion in a transitional, amphibious context before the origin of the tetrapod crown group.