Microendemism can be the rule in the Brazilian Caatinga: evidence from flat lizards of the <i>Tropidurus semitaeniatus</i> group (Squamata: Tropiduridae)

Microendemism remains a poorly studied phenomenon within Brazil’s Caatinga biome, yet recent research has revealed a number of species complexes with diverging lineages confined to narrow geographic ranges. These lineages often inhabit remote and undersampled regions lacking conservation efforts. Notable examples include the flat lizards from the <i>Tropidurus semitaeniatus</i> group, which comprises the broadly distributed <i>T. semitaeniatus</i> species complex plus <i>T. helenae</i>, <i>T. jaguaribanus</i>, and <i>T. pinima</i>, all endemic to the Caatinga biome. Incomplete knowledge of their taxonomic boundaries, phylogenetic relationships, and geographic distribution hinders both the formal description of new microendemic taxa and their conservation assessment. To address these gaps, we conducted a phylogenomic analysis of the <i>T. semitaeniatus</i> group employing ultra-conserved elements (UCEs) and investigated its microendemic diversity. Our analysis revealed that <i>T. semitaeniatus</i> is paraphyletic, with <i>T. helenae</i> emerging as sister to a clade formed by microendemic lineages of <i>T. semitaeniatus</i> (<i>sensu lato</i>), within which <i>T. jaguaribanus</i> is embedded. Additionally, the discovery of a new microendemic species, <i>Tropidurus galileii</i> sp. nov., from calcareous formations of Itaguaçu da Bahia, Brazil, exposed <i>T. pinima</i> as paraphyletic, revealing a novel species complex composed of multiple microendemic lineages. This finding led us to produce the first illustrated morphological guide for the <i>T. semitaeniatus</i> group, aimed at facilitating future comparative studies. Most species requiring taxonomic treatment in the <i>T. semitaeniatus</i> group exhibit morphological distinctiveness, and the number of microendemic taxa is significantly higher than previously estimated. Our findings suggest that range expansion followed by allopatric speciation is unlikely to be the sole driver of microendemism in this group. However, the specific biogeographic processes underlying the origin of microendemic lineages remain elusive. This study sheds light on the microendemic lizard diversity of the Caatinga, emphasizing the urgent need for enhanced systematic and conservation efforts. http://zoobank.org/urn:lsid:zoobank.org:pub:062DCEAA-67D9-41B9-B155-EC538BFE8182