Fig. 1

Fin-to-limb transition involved a suite of anatomical changes including loss of dermal fin rays and the acquisition of digits. a Pectoral fin skeleton of Tiktaalik roseae, an elpistostegid fish. The fin contains both dermal skeleton (lepidotrichia) and endochondral skeleton. Illustration modified from Shubin et al. [64]. b Forelimb skeleton of Acanthostega gunnari, a stem tetrapod. The limb exhibits a polydactylous pattern, which is characteristic of the earliest limbs. Illustration modified from Coates et al. [65] follows that labeling scheme, although other labeling schemes have been proposed for autopodial elements (e.g., [66]). c Forelimb skeleton of human (Homo sapiens). This limb shows a pentadactyl pattern and also mesopodial (wrist) elements; these features characterize the crown-group tetrapod condition. Illustration modified from Owen [67]. For each illustration, anterior is oriented to the left. Extinct taxa are noted with a dagger (†)