The vertebral column forms the central axis of the vertebrate body and has a crucial role in body support and locomotion. It is composed of a number of repetitive, serially homologous skeletal elementsthe vertebrae. The homeobox (Hox) genes are known to be directly involved in somite and vertebrae formation and play a key role in the attainment of vertebral identity (Krumlauf, 1994;Mallo et al., 2010;Woltering, 2012). It has been proposed that different vertebral morphologies are governed by unique combinations of Hox genes expressed in the somites (Kessel & Gruss, 1991;Wellik, 2007) with the corollary that few Hox genes expression boundaries can be used as markers for regional differentiation of the axial skeleton (Böhmer et al., 2015;Burke et al., 1995;Narita & Kuratani, 2005). For example, the cervico-thoracic transition in amniotes is determined by Hox-5 and Hox-6 genes and the formation of the lumbo-sacral boundary is under control of the Hox-10 and Hox-11 genes (Wellik & Capecchi, 2003). Recent morphometric studies have provided new insight into presacral vertebral regionalization in amniotes (Head &

Serially homologous structures may have complex patterns of regionalization and morphological integration, influenced by developmental Hox gene expression and functional constraints. The vertebral column, consisting of a number of repeated, developmentally constrained, and highly integrated units—vertebrae—is such a complex serially homologous structure. Functional diversification increases regionalization and modularity of the vertebral column, particularly in mammals. For salamanders, three concepts of regionalization of the vertebral column have been proposed, recognizing one, two, or three presacral regions. Using three‐dimensional geometric morphometrics on vertebra models acquired with microcomputerized tomography scanning, we explored the covariation of vertebrae in four closely related taxa of small‐bodied newts in the genus Lissotriton. The data were analyzed by segmented linear regression to explore patterns of vertebral regionalization and by a two‐block partial least squares method to test for morphological integration. All taxa show a morphological shift posterior to the fifth trunk vertebra, which corresponds to the two‐region concept. However, morphological integration is found to be strongest in the mid‐trunk. Taken jointly, these results indicate a highly integrated presacral vertebral column with a subtle two‐region differentiation. The results are discussed in relation to specific functional requirements, developmental and phylogenetic constraints, and specific requirements posed by a biphasic life cycle and different locomotor modes (swimming vs. walking). Further research should be conducted on different ontogenetic stages and closely related but ecologically differentiated species.