We used a combined analysis of one nuclear (28S rDNA) and three mitochondrial markers (COI, 12S
rDNA, 16S rDNA) to infer the molecular phylogeny of the Notostraca, represented by samples from the
six continents that are inhabited by this group of branchiopod crustaceans. Our results confirm the
monophyly of both extant notostracan genera Triops and Lepidurus with good support in model based
and maximum parsimony analyses. We used branchiopod fossils as a calibration to infer divergence
times among notostracan lineages and accounted for rate heterogeneity among lineages by applying
relaxed-clock models. Our divergence date estimates indicate an initial diversification into the genera Triops
and Lepidurus in the Mesozoic, most likely at a minimum age of 152.3–233.5 Ma, i.e., in the Triassic or
Jurassic. Implications for the interpretation of fossils and the evolution of notostracan morphology are
discussed. We further use the divergence date estimates to formulate a biogeographic hypothesis that
explains distributions of extant lineages predominantly by overland dispersal routes. We identified an
additional hitherto unrecognised highly diverged lineage within Lepidurus apus lubbocki and three additional
previously unknown major lineages within Triops. Within T. granarius we found deep differentiation,
with representatives distributed among three major phylogenetic lineages. One of these major
lineages comprises T. cancriformis, the T. mauritanicus species group and two hitherto unrecognised T. granarius
lineages. Samples that were morphologically identified as T. granarius diverged from the most
basal nodes within this major lineage, and divergence dates suggested an approximate age of 23.7–
49.6 Ma for T. cancriformis, indicating the need for a taxonomic revision of Triassic and Permian fossils
that are currently attributed to the extant T. cancriformis.We thus elevate T. cancriformis minor to full species
status as Triops minor Trusheim, 1938 and include in this species the additional Upper Triassic samples
that were attributed to T. cancriformis. We further elevate T. cancriformis permiensis to full species
status as Triops permiensis Gand et al., 1997
