Cranial Morphology and Taxonomic Distinctions Among South Asian Treeshrews: Who is the larger treeshrew?

South Asian treeshrews include the Madras Treeshrew, Anathana ellioti (Waterhouse, 1850), the Northern Treeshrew Tupaia belangeri (Wagner, 1841), and the Nicobar Treeshrew Tupaia nicobarica (Zelebor, 1869), each occupying distinct and non-overlapping geographical areas in South Asia. In this study, we investigated the morphological relationships among these species using museum specimens collected over a wide spatial and temporal range of India and Myanmar. We analysed 20 cranial measurements and four external traits to evaluate inter- and intraspecific morphological differentiation, employing distance-based morphometric approaches validated by multivariate analyses. Our findings revealed considerable heterogeneity in cranial morphology with three species exhibiting clear differentiation, despite slight overlaps in morphometric space. Additionally, our research established that T. nicobarica is the largest of the three South Asian treeshrews and ranks as the second largest treeshrew globally following T. tana- a previously unrecognized distinction. Furthermore, our results support the non-recognition of the five traditionally allopatric subspecies of T. belangeri and the two subspecies of A. ellioti . The additional diagnostic characteristics identified in this study enhance the understanding of morphological distinctions among the South Asian treeshrews and contribute to broader taxonomic knowledge of treeshrew diversity.