The earliest palpimanid spider (Araneae: Palpimanidae), from the Crato Fossil-Lagerstatte (Cretaceous, Brazil)

摘要

The Crato Formation (Lower Cretaceous) of Brazil is well known for an exceptionally preserved terrestrial arthropod fossil assemblage. Spiders are relatively abundant, but few have been formally described. A fossil spider belonging to the family Palpimanidae, araneophageous ground-dwelling spiders with distinctly robust front legs, is preserved with the dorsal side hidden within the rock matrix. For the first time, micro-computed tomography (micro-CT) was used to image a fossil spider preserved in a rock matrix, to reveal the dorsal side of this specimen, revealing the eye arrangement, a useful taxonomic character in most spiders, and a deflated abdomen, likely the result of taphonomic processes. The specimen possesses other distinguishing characteristics of Palpimanidae, including an inflated first leg femur, a heavily sclerotized scutum, and a reduced number of spinnerets (2) surrounded by a sclerotized ring. The spider has eight eyes with the lateral pairs extremely close together, a trait suggestive of the subfamily Chediminae. The specimen also possesses an unusual first leg patella with a retrolateral excavation and a thorn-like projection. A new genus is erected, and the spider is named Cretapalpus vittari gen. et sp. nov. A phylogenetic analysis including extant species from each of the subfamilies within Palpimanidae places the fossil at the base of Chediminae + Otiothopinae. This is the earliest reported fossil palpimanid and first chedimine from South America. A fossil chedimine in South America is not surprising because the South American and African plates were still relatively close during the Early Cretaceous.