Taxonomic overview of Neogene crocodylians in Myanmar

Although Neogene crocodylians were well documented from Indo-Pakistan, few fossils were known from Southeast Asia, precluding the understanding of their evolutionary and biogeographic history. Here, we describe crocodylians from the Neogene Irrawaddy Formation of central Myanmar and evaluate their taxonomic status. Tebingan, SE of Magway (lower Upper Miocene) yields Gavialis and Crocodylus that differ from the previously known species of each genus, and the Gwebin area, SW of Bagan (Upper Pliocene) produces Crocodylus cf. palaeindicus. Taking into account the materials without provenance data, Neogene crocodylians from Myanmar include at least three gavialids and two Crocodylus that are characterized by different craniomandibular and postcranial features. The body length estimates for the gavialines from Tebingan and an unknown locality in central Myanmar are 7.5 m and 8.6 m, respectively, which exceed the maximum size limit of extant Gavialis gangeticus. Together with the previously reported large taxa, gavialids repeatedly evolved large body sizes in the Neogene of Asia. Gavialis from the Miocene of Myanmar is one of the oldest records of the genus, and its unraised orbital rim suggests that the “telescoped” eyes derived later during the genus evolution. Crocodylus cf. palaeindicus from the Pliocene of Myanmar indicates the species range was extended from western India to Myanmar during the Neogene. The absence of Crocodylus siamensis in the Neogene of India and central Myanmar implies the species originated east of central Myanmar.