Lost in synonymy: Integrative species delimitation reveals two unrecognized species of Southern Asian tree squirrels (Rodentia: Sciuridae: Callosciurinae)

Abstract We present a comprehensive integrative taxonomic review of Callosciurus caniceps and Tamiops mcclellandii as they are currently defined. This review combines published molecular evidence, craniodental morphometrics, pelage and bacular variation, evaluations of potential hybrid zones using museum specimens and citizen science photographs, and, for C. caniceps , bioacoustic evidence. Our findings lead to the recognition of two species that had been lost in synonymy and highlight future perspectives on species delimitation in Sciuridae. By comparing phenotypic differentiation across climatic and vegetation transitions and contextualizing our results with the evolutionary history of our study systems, we provide insights into distribution, ecogeographical patterns, and speciation drivers in Southeast Asian vertebrates.