AN EARLY JURASSIC JUMPING FROG

WITH nearly 4,000 living species(1), frogs are numerically the most su ccessful of modern amphibian groups, Their distinctive anatomy, which exhibits numerous unique features in both the axial and appendicular s keletons(2-6), represents a major departure from the body plan of Pala eozoic amphibians, We report here the discovery of the earliest known frog, associated with caecilians that retained limbs(7), that exhibits primitive characters but shares with later anurans such features as f usion of the caudal vertebrae (urostyle), a rod-like ilium, and elonga te hind limbs. The evolution of saltation in anurans entailed transloc ation of the ilium below the sacral rib, recruitment of the primitive tail musculature to transmit force from the hind limb to the axial ske leton during a jump, and development of iliosacral mobility, We reinte rpret the caudopelvic transition from Palaeozoic amphibians to modern frogs with reference to Triadobatrachus massinoti, an Early Triassic a mphibian that possesses some frog-like features(8). The Early Jurassic age and Laurasian provenance of the new frog support the hypothesis(4 ) that the widespread occurrence of primitive extant anurans reflects an ancient Pangaean distribution.