Pipid frogs from the Early Cretaceous of Israel and pipid evolution

The discovery of a horizon rich in frogs in the lower early Cretaceous of Makhtesh Ramon, Israel, is recorded, and the geology, age, paleoecology, fauna, flora, and climate are discussed. Articulated frog skeletons comprise most of the fauna. They are described as two new pipid genera including three species: Thomcilioctis rostriceps, 800 specimens; Cordicephalus gracilis, 49 specimens; and Cordicephalus longicostatus, 14 specimens. All species are aquatic, variable, and represent a melange of 21 primitive and 16 specialized characters. In all, the pelvis, skull, and pectoral girdle are highly variable, the limbs less so. The skull, pelvis, and limbs are essentially specialized, the column and pectoral girdle primitive. Thoraciliacus is more aquatic, variable, and specialized than Cordicephahis, yet both are the most primitive and earliest sure pipids known. The thoraciliacid line is related to South American and African Cretaceous pipoids; it flourished in the Cretaceous, and became extinct in the Tertiary,
while Cordiccpludus is on the ancestral line of Tertiary xenopids. Reevaluation of pipid classification does not support a separate family for Cretaceous pipoids which may be referred to Recent Pipidae. Ramon pipids suggest that pipids pursue a progressive primary aquatic adaptation, this operating as the main evolutionary selective factor since their probable Triassic origin from proanurans. Pipids have probably never been taxonomically prolific, but their record suggests a rapid basic diversification, extinctions, and slower later evolution. Evolutionary trends since early Cretaceous times involve a series of structural changes, explicable as progressive improvements in aquatic adaptations. Pipids had an almost worldwide distribution in Cretaceous and probably Upper Jurassic times,
but their center of origin is still obscure.