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A new genus of giant salamander (Urodela, Cryptobranchidae) from the Pliocene of Japan

paleontology
taxonomy
zoology

Abstract

The family Cryptobranchidae, commonly known as giant salamanders, originated at least by the Paleocene and has persisted to the present day. However, its fossil record is extremely fragmentary, with few occurrences known from East Asia after the Miocene. Here we report three vertebral specimens of a cryptobranchid salamander from the Upper Pliocene Tsubusagawa Formation (around 3.5 Ma) of Oita Prefecture, Japan. These specimens were previously identified as Andrias sp., including extant species, but their taxonomic status remained unresolved. In this study, we re-examine the material and provide a more detailed description and attempt to resolve its taxonomic status. Our study demonstrates that it is a new taxon, Limnospondylus ajimuensis gen. et sp. nov., because it shows a unique combination of characters in the mid-trunk vertebra. This new giant salamander inhabited freshwater lacustrine environments and may have reached a total length of approximately 110 cm by around 18 years of age. The discovery of this new taxon helps to fill a significant gap in the Asian fossil record of this group. It also highlights the morphological and ecological diversity of Cryptobranchidae and provides essential implications for understanding their evolutionary history.
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