Two teams of Chinese scientists have begun study of a species of spider with a long tail, which is found in amber at least 100 million years old.
The Chimerarachne found in Myanmar fills a gap in the evolution of the spiders.
The spiders found are tiny, from less than 2 mm to 2.8 mm long excluding the tail, which is at least twice the body length.
Chimerarachne is either the most primitive spider known, or else belongs to a group of extinct arachnids which were very close to spider origins, the researchers said.
The studies by researchers at the Nanjing Institute of Geology and Paleontology under the Chinese Academy of Sciences were published side-by-side in Nature Ecology and Evolution.