A revised dated phylogeny of the arachnid order Opiliones

Area of Science:

• Evolutionary Biology
• Arthropod Phylogenetics
• Molecular Dating

Background:

• Dating the Opiliones (harvestman) tree of life is crucial for understanding their ancient origins and biogeography.
• Previous studies have been limited by methodological constraints and incomplete diversity data.

Purpose of the Study:

• To reconstruct the evolutionary history and divergence times of Opiliones using updated molecular dating methods and diverse datasets.
• To test the placement of fossil and newly discovered lineages within the Opiliones phylogeny.
• To assess the congruence of divergence time estimates using different dating approaches.

Main Methods:

• Total evidence dating integrating morphological and molecular sequence data for 47 Opiliones species, including Palaeozoic fossils.
• Node dating using a phylogenomic dataset of 24,202 amino acid sites for 14 Opiliones species across all extant suborders.
• Utilized fossil calibrations to constrain divergence time estimates.

Main Results:

• Congruent age estimates for basal Opiliones nodes (e.g., Opiliones, Palpatores) across different analyses when constrained by fossil calibrations.
• High uncertainty intervals for derived nodes (e.g., Cyphophthalmi, Laniatores) lacking fossil calibrations and undersampled lineages.
• Total evidence dating yielded older median ages for ingroup nodes compared to node dating, influenced by Palaeozoic fossil placements.
• Basal diversification of Opiliones is supported in the Ordovician-Devonian period.

Conclusions:

• Opiliones originated in the ancient Ordovician-Devonian period, confirming their deep evolutionary history.
• Molecular dating, especially total evidence dating, provides robust estimates for basal divergences but requires careful calibration for derived lineages.
• Continued discovery of both fossil and extant Opiliones diversity is essential for refining evolutionary inference.