ABSTRACT The recent discovery of a plethodontid salamander,Karsenia koreana, in Korea challenged ourunderstanding of the biogeographic history of the familyPlethodontidae, by far the largest family of salamanders,which otherwise is distributed in the New World with afew European species. Molecular studies suggest thatKarsenia forms a clade with Hydromantes (sensu lato),which includes among its species the only other OldWorld plethodontids. We studied the skull of K. koreanaand compared it with that of other plethodontid genera,especially members of the subfamily Plethodontinae,which it resembles most closely in general anatomy. Theanatomy of its skull corresponds to the most generalizedand apparently ancestral condition for plethodontids. Noclearly autapomorphic states were detected, and no synapomorphiescan be found that would link it to othergenera. The Karsenia skull is cylindrical and well ossified,giving an impression of strength. In contrast, theskull of Hydromantes is highly derived; the skull is flattenedand the bones are weakly ossified and articulated.Hydromantes and Karsenia share no unique anatomicalfeatures; differences between them are especially evidentin the hyobranchial skeleton, which is generalizedin Karsenia but highly modified in Hydromantes, whichis well known for its highly projectile tongue. Plethodonand Plethodon-like species, including Karsenia and to alesser degree Ensatina, represent the more generalizedand apparently ancestral plethodontid morphology. Specializedmorphologies have evolved along only a fewmorphological axes within the Plethodontidae, resultingin a pattern of rampant homoplasy. Our analysis of theanatomy of the new Asiatic lineage illuminates somepotential mechanisms underlying adaptive morphologicalevolution within the Plethodontidae. J. Morphol.271:533–558, 2010.