Knowra Tetrapod Tetrapod A vertebrate with four limbs, or descended from a four-limbed ancestor. Tetrapods include amphibians, reptiles, birds, and mammals, including lineages whose limbs were later reduced or lost.
Vertebrate : An animal with a backbone or an embryonic precursor called a notochord. Tetrapods are one major branch of vertebrates.
Tiktaalik : An extinct Devonian lobe-finned fish with a flattened skull, neck, and robust fin bones. Its anatomy documents features near the fish-to-tetrapod transition.
Vertebrate limb evolution : The evolutionary history of paired vertebrate appendages, from fins to limbs and their many modified forms. Tetrapod limbs arose through changes to paired fins and later diversified.
Amniota : The clade of vertebrates whose embryos develop with an amnion, comprising reptiles, birds, and mammals. Amniotes radiated into many terrestrial forms and account for most living tetrapod diversity.
Limb : An appendage attached to an animal's body, especially an arm, leg, wing, or flipper. Tetrapod ancestry is defined by the presence of paired limbs.
Acanthostega : An extinct Devonian vertebrate with limbs and digits that was primarily aquatic. It shows that digits evolved before fully terrestrial locomotion.
Lung : An internal organ for gas exchange between air and blood in many vertebrates. Air breathing helped some ancestral lineages function in oxygen-poor waters and on land.
Reptile : A vertebrate in the reptile lineage, including turtles, lizards, snakes, crocodilians, and birds. Reptiles are one major living radiation within the tetrapod tree.
Pentadactyl limb : A limb with five digits or a structure derived from that five-digit pattern. The familiar five-digit arrangement underlies many tetrapod limbs, despite extensive variation.
Ichthyostega : An extinct Devonian tetrapod with limbs and a body adapted to both aquatic and terrestrial movement. Its fossils preserve an early tetrapod anatomy beyond the fin-to-limb transition.
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