GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 38-29
Presentation Time: 9:00 AM-5:30 PM


DOWNEN, Matthew R., Department of Geology, University of Kansas, Lawrence, KS 66045 and SELDEN, Paul A., Geology Dept., University of Kansas, Lawrence, KS 66045

The Crato Formation of Brazil is an early Cretaceous (115 Ma) Fossil-Lagerstatte well known for exceptionally preserved arthropods. Insects dominate the fossil assemblage, but spiders (Arachnida: Araneae) are relatively abundant. A fossil spider belonging to family Palpimanidae, relatively rare ground dwelling spiders with distinctly englarged front legs, is preserved only in part, with the ventral side visible. The fossil is preserved in 3D as a goethite replacement. Micro-computed tomography (micro-CT) was used to image the dorsal side of the spider. The dorsal view of the specimen reveals the eye arrangement, a useful taxonomic character in most spiders, and an abdomen that is deflated, likely the result of taphonomic processes.

This fossil spider possesses the typical characteristics of Palpimanidae including a robust front pair of legs with greatly inflated femora and a reduced number of spinnerets (2) surrounded by a sclerotized ring. The spider has 8 eyes with the lateral pairs of eyes almost touching, a trait suggestive of the subfamily Chediminae. The specimen is unusual in that patellae are excavated retrolaterally with a thorn-like projection. These thorn-like projections are observed in some extant male palpimanids belonging to subfamily Palpimaninae. A phylogenetic analysis including the fossil and extant species from all of the subfamilies within Palpimanidae places the fossil nested within Chediminae. This specimen is likely a subadult male, suggested by the thorns on the legs and the unmodified pedipalps.

Today, palpimanids are dispersed throughout the tropics and subtropics (excluding Australia). This is the first reported fossil palpimanid and first chedimine from South America. A fossil chedimine in South America is not surprising, as South America and Africa were still relatively close during the Cretaceous. It is possible that Chediminae is still present in South America, but no living specimens have been found. Palpimanids are primarily araneophageous (eating other spiders) and have been observed invading the retreats and nests of other spiders in addition to eating spider eggs.