page_title: Tetrophthalmi
section_title: Phylogeny
hierarchical_section_title: Tetrophthalmi / Phylogeny
caption_attribution_description: English: Total evidence phylogeny incorporating morphology and molecules for extinct and extant species. Colored branches correspond to suborders. Numbers on nodes are posterior probabilities. Yellow icons indicate branch attachment frequencies for Tetraophthalmi.
context_page_description: Tetrophthalmi is an extinct suborder of Opiliones that had both median and lateral eyes. First described in 2014, it is known from two extinct species. Phylogenetic analysis suggests that this eye arrangement is the ancestral condition for harvestmen, placing Tetrophthalmi and Cyphophthalmi in a basal position within Opiliones.
context_section_description: In Garwood et al.'s phylogenetic tree, the basal Opiliones split into the "Phalangida" and stem Cyphophthalmi.  The Cyphophthalmi stem then diversified into Cyphophthalmi proper and Tetrophthalmi, while the Phalangida split into Laniatores and the "Palpatores".  Finally, the Palpatores diversified into Eupnoi and Dyspnoi.  The analysis moves the divergence of the extant suborders from the Devonian Period to the Carboniferous. The opiliones' own divergence is dated to 414 million years ago, and arachnids are estimated to have originated during the late Cambrian to early Ordivician.
  Genetic analysis performed on a modern Phalangium opilio specimen found a suppressed gene that, if active, would generate a second pair of eyes at the lateral location, providing independent evidence that four eyes is the ancestral condition.  Garwood et al. also argue that a Carboniferous harvestmen diversification is more consistent with changes observed in other terrestrial arthropods, which have been linked to high oxygen levels during that period.
  Another recent phylogeny recovered Hastocularis as an early banching opilionid in the harvestman tree, along with the Cyphophthalmi. Eophalangium, the other genus in Garwood et al.'s Tetrophthalmi was recovered in a polytomy with the remaining oplionids, however.
caption: Phylogenetic analysis of Opiliones
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