EFFECTS OF SLOPE AND TEMPERATURE ON THE MORPHOLOGY OF EXPERIMENTAL SPIDER AND SCORPION TRACKWAYS

Terrestrial trackways of arthropods are common in certain strata, such as the Permian Coconino Sandstone of Arizona, and are often the only evidence of the animals that once traversed the area. Some of the more common ichnogenera of these strata are Paleohelcura and Octopodichnus, attributed to scorpions and spiders respectively. Several studies have attempted to reproduce these trackways in the laboratory but none systematically investigated the effects of temperature, slope and moisture content on the locomotion of the trackmakers and the trackways produced. Experimental trackways were created using an African Emperor scorpion, Pandinus imperator, and a Pink-Toed tarantula, Avicularia avicularia. The trackmakers were videotaped in order to accurately document their stepping patterns. Speed of the animal, slope, and temperature affected the placement of the feet, which led to differences between trackways. Drag created by the tarantula's legs established direction of travel for both uphill and downhill movements when experiments were created with a 20^o angle. When running, both arthropods created similar elongate tracks. At temperatures above 21^oC, scorpion tracks tend to remain elongated while tarantula tracks become more oblong. These experiments show similarities with previous studies such as a wide variety of track morphologies for scorpions with impressions that varied from two to four tracks on each side and that tarantula tracks are consistent with four tracks on each side. However, with experiments in damp or slightly moist sand, tracks were not created with either species because the animals were too light to leave impressions. These experiments support earlier hypotheses that spiders are the possible track makers for Octopodichnus raymondi. Only at temperatures of 21^oC and a slope of approximately 20^o do scorpion tracks show similarities to Paleohelcura trackways.