First global phylogeny of whip spiders (Amblypygi)

Asymmetrical rates of cladogenesis and extinction abound in the Tree of
Life, resulting in numerous minute clades that are dwarfed by larger
sister groups. Such taxa are commonly regarded as phylogenetic relicts or
“living fossils” when they exhibit an ancient first appearance in the
fossil record and prolonged external morphological stasis, particularly in
comparison to their more diversified sister groups. Due to their special
status, various phylogenetic relicts tend to be well-studied and
prioritized for conservation. A notable exception to this trend is found
within Amblypygi (“whip spiders”), a visually striking order of
functionally hexapodous arachnids that are notable for their antenniform
first walking leg pair (the eponymous “whips”). Paleoamblypygi, the
putative sister group to the remaining Amblypygi, is known from Late
Carboniferous and Eocene deposits but is survived by a single living
species, Paracharon caecus Hansen, 1921, that was last collected in 1899.
Due to the absence of genomic sequence-grade tissue for this vital taxon,
there is no global molecular phylogeny for Amblypygi to date, nor a
fossil-calibrated estimation of divergences within the group. Here, we
report several individuals of a previously unknown species of
Paleoamblypygi from a cave site in Colombia. Capitalizing upon this
discovery, we generated the first molecular phylogeny of Amblypygi,
integrating ultraconserved element sequencing with legacy Sanger datasets
and including described extant genera. To quantify the impact of sampling
Paleoamblypygi on divergence time estimation, we performed in silico
experiments with pruning of Paracharon. We demonstrate that the omission
of relicts has a significant impact on the accuracy of node dating
approaches that outweighs the impact of excluding ingroup fossils. Our
results underscore the imperative for biodiversity discovery efforts in
elucidating the phylogenetic relationships of “dark taxa”, and especially
phylogenetic relicts in tropical and subtropical habitats. The lack of
reciprocal monophyly for Charontidae and Charinidae leads us to subsume
them into one family, Charontidae (new synonymy).