Tetrapodien

Tetrapodien is a term used in comparative anatomy and paleontology to refer to the ancestral limb structure of tetrapods, the group of vertebrates that includes amphibians, reptiles, birds, and mammals. This basic five-fingered (or pentadactyl) limb plan, consisting of a single upper bone (humerus or femur), two lower bones (radius and ulna, or tibia and fibula), a set of wrist or ankle bones (carpals or tarsals), and then digits (fingers or toes), is a fundamental characteristic that unites these diverse animal groups.

The evolution of the tetrapod limb from the paired fins of lobe-finned fishes is a significant event in vertebrate history, marking the transition from aquatic to terrestrial life. While the basic tetrapodien blueprint remains recognizable, it has been extensively modified throughout evolutionary history to adapt to a vast array of lifestyles and environments. For example, the limbs of a whale are adapted for swimming, those of a bat for flight, and those of a human for bipedal locomotion, yet the underlying skeletal structure can still be traced back to the tetrapodien. Fossil evidence, such as Tiktaalik, provides crucial insights into the intermediate stages of this evolutionary transformation, showcasing features that bridge the gap between fish fins and tetrapod limbs. The study of tetrapodien variations helps scientists understand evolutionary relationships and the adaptive radiation of vertebrates.