Shifting speciation mode and biogeographic patterns during the Late Ordovician (Sandbian-Katian) in Laurentian brachiopods (Atrypida, Anazygidae)

The Late Ordovician was a period of substantial environmental change. The
co-evolution of Earth systems changes involving tectonic uplift, eustasy,
and biotic changes are recorded in the Late Ordovician in Laurentia. In
this study, species of the brachiopod family Anazygidae within the genera
Zygospira and Catazyga were analyzed to assess dispersal pathways among
eight sedimentary basins. Stochastic analysis applied to a Bayesian
phylogeny (Anazygidae_tree.tre) through BioGeoBEARS facilitated estimation
of speciation events including episodes of vicariance and basin-to-basin
dispersal events (Anazygidae_geoareas.data) within the clade. Three
algorithms were implemented and compared (BioGeoBEARS_code.R).
Dispersal-extinction-cladogenesis (DEC) + jump dispersal parameter was the
best supported model. For suggestions, advice, or requests related to the
code and how to re-run our results, please contact the author. 
Results (b_AICc_table.csv) indicate that Anazygidae originated from an
ancestral vicariance event, and most subsequent speciation events occurred
via dispersal (total of 14 distinct episodes). Vicariance events are
constrained to Mohawkian (Sandbian 2 to Katian 1) time and correlate to
tectonic events. Dispersal events dominated during Cincinnatian (Katian
1–4) time and promoted increased diversification of anazygid species.
Dispersal events are related to epicontinental circulation patterns and
regional sea level changes and can be linked to connectivity and isolation
pulses between the mid-continent and southern basins. Dispersal events
exhibit a directional trend from the mid-continent toward the
southern-most basins in Laurentia. Long-distance dispersal can be
explained by jump dispersal events, with marginal-Laurentian islands
acting as “stepping-stones” for intracratonic species. Anazygid speciation
declined in the Richmondian (Katian 4). Zygospira and Catazyga became
extinct in Laurentia as the epicontinental seas drained and climate cooled
during the late Katian.