Characters of the jaws and frontals are often used to differentiate albanerpetontid genera and species, yet the reliability of these characters has rarely been examined. Frontals are diagnostic for the genera Albanerpeton and Celtedens and for species in the latter genus. The value of frontals at the specific level in Celtedens may be inflated by lack of information about variation in jaw structure. Characters of the frontals, jaws, and body size differentiate species of Albanerpeton. Differential diagnoses are presented for the Albanerpetontidae based on cranial and vertebral characters and for the two named genera based on frontal characters. Each genus is characterized by one autapomorphy: fused frontals triangular in Albanerpeton and internasal process bulbous in Celtedens. An enigmatic albanerpetontid from the Middle Jurassic (upper Bathonian) of England has a unique mixture of frontal and premaxillary character states that precludes it from being included in either Celtedens or Albanerpeton. This leaves the oldest occurrences of the two genera in, respectively, the Late Jurassic (Kimmeridgian) and Early Cretaceous (latest Aptian/ earliest Albian).

Key words: Albanerpeton, Albanerpetontidae, Allocaudata, Amphibia, Celtedens, Lissamphibia, taxonomy.

James D. Gardner [jgardner@ualberta.ca], Laboratory for Vertebrate Paleontology and Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9 Canada.