Doleserpeton, Xerodromeus and Apateon

Doleserpeton annectus (Sigurdsen and Bolt 2010) Early Permian~290 mya, ~8 cm in length. Derived from a sister to Utegenia and Amphibamus, Doleserpeton phylogenetically preceded Gerobatrachus and other proto frogs.

Distinct from Amphibamus, the skull of Doleserpeton had a rounder profile and a much deeper otic notch. The palatines were tiny and directed medially. The pterygoids lost their medial connections to the vomers and were broadly separated and diagonally directed toward the base of the orbit. The parasphenoid and basipterygoid were much enlarged. The teeth were tiny and bicuspid (pedicellate), as in frogs.

The presacral number decreased to 24. Two sacral vertebrae were present. The dorsal ribs were more gracile. The caudal ribs were reduced in number and size.

The clavicles were reduced. The scapulocoracoid was shorter. The forelimb was more shorter and more gracile. Manual digit 5 may have been absent here because no succeeding taxa have it. The hand was more robust than the foot.

The dorsal process of the ilium was angled posteriorly. The hind limb was shorter and more gracile.

Xerodromeus gracilis (originally Melanerpeton (Apteon) gracilie, Schoch and Werneburg 2023) has more robust premaxillary teeth, is larger overall and lacks a fenestra between the nares. These taxa are basal toGerobatrachus, frogs and salamanders.

Apateon pedestris (von Meyer 1844, Early Permian, 295mya; 12 cm in length) was long considered a temnospondyl in the family Branchiosauridae. Here Apateon nests between Doleserpeton and Gerobatrachus in the lepospondyl lineage of frogs, like Rana.

Resembling a small salamander with a long, laterally flattened tail, Apateon had a shorter rostrum and large orbits than Doleserpeton. The pineal opening was larger. The ilium was more erect. The pubis was missing. The ectopterygoid did not contact the maxilla and the palatine did so only with a narrow process.

Small scales covered the body. Three pairs of external gills were present for underwater respiration. Many species are known, as well as a good ontogenetic series.

The evolution of the frog skull. From left to right: Utegenia, Doleserpeton, Gerobatrachus and Rana, a living bull frog. The reduction, fusion and loss of the skull bones is apparent here.

Frog evolution. From left to right: Utegenia, Doleserpeton, Gerobatrachus and Rana, a living bull frog. The reduction of the spine and enlargement of the hind limbs is apparent here.

Sigurdsen T and Bolt JR 2010. The Lower Permian amphibamid Doleserpeton (Temnospondyli: Dissorophoidea), the interrelationships of amphibamids, and the origin of modern amphibians. Journal of Vertebrate Paleontology 30(5): 1360-1377.

von Meyer H 1844. Briefliche Mittheilung an Prof. Bronn gerichtet. Neues Jahrbuch für Geognosie, Geologie und Petrefakten-Kunde 1844: 329-340.

Schoch RR and Werneburg R 2023. Adult branchiosaurid temnospondyls: the life cycle of
Xerodromeus gracilis. Papers in Palaeontology, 2023, e1513.

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Lissamphibia

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Salamanders and Frogs