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Abstract We report here the discovery of a remarkable new monotypic mygalomorph spider genus, known only from one geographical location along the central coast of California. The single relict species comprising Cryptocteniza kawtakn. gen. n. sp., is morphologically distinct and geographically isolated from other related genera, with its closest phylogenetic relatives found much further to the east in New Mexico and Arizona. Using a phylogenomic approach employing anchored hybrid enrichment, we reconstruct the evolutionary history of the family Euctenizidae Raven, 1985 to explore relationships among genera, affirmatively place previously undescribed taxa, explore rates of diversification, and reconstruct the group’s biogeography. A biogeographic analysis shows that extinction likely played a significant role in shaping the observed disjunct modern-day distribution of Cryptocteniza and its sister taxa. Our extinction hypothesis is further bolstered by a diversification rate analysis identifying considerably higher rates of speciation in other euctenizid lineages like AptostichusSimon, 1891. Consequently, changes in environmental conditions (or other related biotic and/or abiotic factors) may have spurred an adaptive radiation in related genera now widely distributed across the California Floristic Province biodiversity hotspot, with concomitant extinction in Cryptocteniza following the Miocene and establishment of a Mediterranean climate. Owing to its phylogenetic distinctiveness, incredibly narrow distribution and age, we show that Cryptocteniza meets all the criteria of an ‘Endangered Living Fossil’ and is consequently of grave conservation concern. 

Spiders (Order Araneae) are massively abundant generalist arthropod predators that are found in nearly every ecosystem on the planet and have persisted for over 380 million years. Spiders have long served as evolutionary models for studying complex mating and web spinning behaviors, key innovation and adaptive radiation hypotheses, and have been inspiration for important theories like sexual selection by female choice. Unfortunately, past major attempts to reconstruct spider phylogeny typically employing the “usual suspect” genes have been unable to produce a well-supported phylogenetic framework for the entire order. To further resolve spider evolutionary relationships we have assembled a transcriptome-based data set comprising 70 ingroup spider taxa. Using maximum likelihood and shortcut coalescence-based approaches, we analyze eight data sets, the largest of which contains 3,398 gene regions and 696,652 amino acid sites forming the largest phylogenomic analysis of spider relationships produced to date. Contrary to long held beliefs that the orb web is the crowning achievement of spider evolution, ancestral state reconstructions of web type support a phylogenetically ancient origin of the orb web, and diversification analyses show that the mostly ground-dwelling, web-less RTA clade diversified faster than orb weavers. Consistent with molecular dating estimates we report herein, this may reflect a major increase in biomass of non-flying insects during the Cretaceous Terrestrial Revolution 125–90 million years ago favoring diversification of spiders that feed on cursorial rather than flying prey. Our results also have major implications for our understanding of spider systematics. Phylogenomic analyses corroborate several well-accepted high level groupings: Opisthothele, Mygalomorphae, Atypoidina, Avicularoidea, Theraphosoidina, Araneomorphae, Entelegynae, Araneoidea, the RTA clade, Dionycha and the Lycosoidea. Alternatively, our results challenge the monophyly of Eresoidea, Orbiculariae, and Deinopoidea. The composition of the major paleocribellate and neocribellate clades, the basal divisions of Araneomorphae, appear to be falsified. Traditional Haplogynae is in need of revision, as our findings appear to support the newly conceived concept of Synspermiata. The sister pairing of filistatids with hypochilids implies that some peculiar features of each family may in fact be synapomorphic for the pair. Leptonetids now are seen as a possible sister group to the Entelegynae, illustrating possible intermediates in the evolution of the more complex entelegyne genitalic condition, spinning organs and respiratory organs.