![]() ![]() One essential adaptation in the evolution of tetrapods was the ability to locomote on land, a trait that required significant morphological and functional changes in the appendicular system. The ability to move in a variety of terrestrial and semiterrestrial environments opened up a range of new ecosystems for colonization and led to the diversity of tetrapod clades we see today. The vertebrate water-to-land transition initiated in the Devonian was a key event in the history of life. It follows that the attribution of some of the nondigited Devonian fossil trackways to limbed tetrapods may need to be revisited. Our findings suggest that some fundamental features of tetrapod locomotion, including pelvic limb gait patterns and substrate association, probably arose in sarcopterygians before the origin of digited limbs or terrestriality. annectens also lifts its body clear of the substrate using its pelvic fins, an ability thought to be a tetrapod innovation. Surprisingly, given these morphological traits, P. ![]() We found that a species of African lungfish ( Protopterus annectens) uses a range of pelvic fin-driven, tetrapod-like gaits, including walking and bounding, in an aquatic environment, despite having a derived limb endoskeleton and primitively small, muscularly supported pelvis. ![]() As the sister group to tetrapods, lungfish are a morphologically and phylogenetically relevant sarcopterygian taxon for understanding the order in which these events occurred. The locomotor component of this transition can be divided into four major events: terrestriality, the origins of digited limbs, solid substrate-based locomotion, and alternating gaits that use pelvic appendages as major propulsors. Tetrapods evolved from sarcopterygian fishes in the Devonian and were the first vertebrates to colonize land. ![]()
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