Prehistoric arachnid genera

Chimerarachne is a genus of extinct arachnids, containing five known species. Fossils of Chimerarachne were discovered in Burmese amber from Myanmar which dates to the mid-Cretaceous, about 100 million years ago. It is thought to be closely related to spiders, but outside any living spider clade. The earliest spider fossils are from the Carboniferous, requiring at least a 170 myr ghost lineage with no fossil record. The size of the animal is quite small, being only in body length, with the tail being about in length. These fossils resemble spiders in having two of their key defining features:

Arthrolycosa (meaning wolf [spider] with joints) is an extinct genus of arachnids, possibly spiders, that lived about 300-250 million years ago.