Treating Fossils as Terminal Taxa in Divergence Time Estimation Reveals Ancient Vicariance Patterns in the Palpimanoid Spiders

Abstract

Incorporation of fossils into biogeographic studies can have a profound effect on the conclusions that result, particularly when fossil ranges are nonoverlapping with extant ranges. This is the case in archaeid spiders, where there are known fossils from the Northern Hemisphere, yet all living members are restricted to the Southern Hemisphere. To better understand the biogeographic patterns of archaeid spiders and their palpimanoid relatives, we estimate a dated phylogeny using a relaxed clock on a combined molecular and morphological data set. Dating information is compared with treating the archaeid fossil taxa as both node calibrations and as noncontemporaneous terminal tips, both with and without additional calibration points. Estimation of ancestral biogeographic ranges is then performed, using likelihood and Bayesian methods to take into account uncertainty in phylogeny and in dating. We find that treating the fossils as terminal tips within a Bayesian framework, as opposed to dating the phylogeny based only on molecular data with the dates coming from node calibrations, removes the subjectivity involved in assigning priors, which has not been possible with previous methods. Our analyses suggest that the diversification of the northern and southern archaeid lineages was congruent with the breakup of Pangaea into Laurasia and Gondwanaland. This analysis provides a rare example, and perhaps the most strongly supported, where a dated phylogeny confirms a biogeographical hypothesis based on vicariance due to the breakup of the ancient continental plates.

The fossil history of pseudoscorpions (Arachnida: Pseudoscorpiones)

“…Feaella groehni would extend the known range of this family into former Laurasian land masses in Europe and at the same time indicate past extinction in the Northern Hemisphere. The same pattern that has been inferred for other arachnid groups, such as archaeid spiders, which only occur today on Gondwanan land masses but are known as fossils in Baltic amber and compression fossils from China (Wood et al, 2012). Secondly, the pseudoscorpion data may indicate former sympatry of two sister families that exclude each other today because of differences in climatic preferences.…”

“…the appearance of the first forests in the Devonian for onychophorans; Murienne et al, 2013) or mixed sets of morphology and DNA sequence data with the inclusion of stemgroup fossils (e.g. archaeid spiders, see Wood et al, 2012). …”

Ancient dates or accelerated rates? Morphological clocks and the antiquity of placental mammals

“…These methods simultaneously consider both character and temporal information in terminal taxa to co-estimate phylogeny, divergence dates and evolutionary rates. To date, such 'morphological clock' models have been used mainly in the context of total evidence (TE) analyses that combine morphological and molecular data [27][28][29][30][31]. However, they can also be applied to purely morphological datasets [32,33].…”

A living fossil tale of Pangaean biogeography

“…In those cases, the inferred dispersal scenario is simply a consequence of the group not being old enough to be influenced by tectonic movement in the first place. In fact, a few examples of global distributions rooted to the continental break-up still exist, with prominent cases in old lineages of animals [7][8][9] and plants [6,10]. Another issue emerges from the previous statement: in many old groups that could be good models for historical biogeography, vagility often blurs the biogeographic signal and inferring historical scenarios might simply be impossible.…”