Multiple lines of tetrapods show reduced limbs or their loss. Such patterns are in diverse lines associated with multiple other characteristics. Only bodily elongation represents a common denominator. Analysis suggests that elongation for traverse of crevices in a sheltering environment and for the utilization of undulatory locomotion may have provided the initial selective advantage to the system. Limb reduction would then have been secondary. This hypothesis leads to several interesting implications about the process of diversification in tetrapods.