Acanthostega

Acanthostega is an extinct Late Devonian vertebrate among the earliest known tetrapods. Its limbs had digits, but its anatomy indicates it lived primarily in water.

Tetrapod: A vertebrate with four limbs or descended from a four-limbed ancestor. Acanthostega is an early member of the tetrapod lineage, despite its aquatic life.
Acanthostega gunnari: The type and best-known species of the extinct Devonian genus Acanthostega. This species supplies the principal anatomical evidence associated with the genus.
Late Devonian: The final epoch of the Devonian Period, spanning about 383 to 359 million years ago. Acanthostega lived during this interval, when early tetrapods diversified.
Ichthyostegalia: An extinct group of early tetrapods from the Devonian and earliest Carboniferous. Acanthostega is commonly placed among these early tetrapods, whose habits varied.
Tiktaalik: An extinct Devonian vertebrate with both fishlike traits and features associated with tetrapods. Its fossils illuminate nearby stages in the fish-to-tetrapod transition.
Acanthostega hand: The forelimb extremity of Acanthostega, notable for having eight digits. Its digit count shows that early tetrapod hands differed from the five-digit pattern common today.
Greenland: The world’s largest island, located between the Arctic and Atlantic oceans. Acanthostega fossils were discovered in East Greenland’s Devonian deposits.
Walking: A terrestrial form of locomotion in which limbs support and propel the body across a surface. Acanthostega’s limbs had digits but were not suited to routine terrestrial walking.
Lobe-finned fish: A group of bony fishes with fleshy paired fins supported by internal bones. Acanthostega belongs to the evolutionary lineage that arose among lobe-finned vertebrates.
Acanthostega skull: The skull of Acanthostega, preserving features of an aquatic Devonian vertebrate. Its structures help reconstruct how Acanthostega fed and sensed its surroundings.

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