Evolution of Spiders - Early Spider-like Arachnids

Early Spider-like Arachnids

Among the oldest known land arthropods are Trigonotarbids, members of an extinct order of spider-like arachnids.

Sharing many superficial characteristics with spiders, Trigonotarbida were terrestrial, respired through book lungs, and walked on eight legs with two additional legs adapted to use around their mouth. Arguments still remain open as to whether they possessed the ability to create silk. This had been popular thought for quite some time, until an unpublished fossil was described with distinct microtubercles on its hind legs, akin to those used by spiders to direct and manipulate their silk.

Regardless, Trigonotarbida are not considered true-spiders. They are generally accepted as an independent early offshoot within the Arachnida clade, and not directly ancestral to modern spiders.