The taxonomy and taphonomy of fossil spiders from the Crato Formation of Brazil

Abstract

In order to develop a clearer picture of the paleoenvironment of the Crato Formation, an early Cretaceous Fossil-Lagerstätte, the taphonomy and taxonomy of fossil spiders were examined. The Crato Formation is represented by deposits of thinly laminated limestones with abundant terrestrial invertebrate fossils. One aspect of the Crato Formation depositional environment that has been debated is the salinity of the ancient lake in which this unit was deposited. To investigate the paleosalinity, the leg orientations of fossil spiders from the Crato, Green River, and Florissant formations were examined as well as the leg orientations of modern spiders drowned in varying salinities. The leg orientations of drowned modern spiders suggest hypersalinity produces a tightly curled leg orientation and fresh water produces an extended leg orientation. The results of drowned modern spiders are comparable to the fossil spiders preserved in lacustrine deposits of similar salinity, and thus, suggest the Crato Formation was deposited in hypersaline water. In addition, the taxonomy of the fossil spiders from the Crato Formation was elucidated. The abundant araneoids previously named Cretaraneus martinsnetoi Mesquita, 1996 have been redescribed and placed in a new genus, Olindarachne, within Araneidae. Two other families of spider have been described, Nephilidae and Palpimanidae. The age range of Palpimanidae is extended back nearly 90 million years from a previous specimen from Dominican amber (Neogene), and the geographic range for Araneidae, Nephilidae, and Palpimanidae has been expanded to the South American continent during the Early Cretaceous.