| Description |
The presence of both active sand dunes and lithified Pleistocene dunes in the area surrounding Puerto Penasco, Sonora, Mexico, offers and opportunity to study the formation and preservation of arthropod burrows in a coastal dune environment. The modern dunes in this area host abundant and diverse terrestrial arthropods. The majority of these organisms are formicids (ants), Coleopterans (beetles), and arachnids (spiders, solifugids, and scorpions). Most of these organisms interact with the soil in some manner, which often produces traces (trails, trackways, and burrows). In many cases, such traces are distinct enough to be associated with a particular organism. Identification and association of modern arthropods and their burrows creates a basis for comparison between the modern burrows and those found in nearby Pleistocene eolianites. The recognizable Pleistocene trace fossils includes the ichnogenera Planolites, Skolithos, Taenidium, and Gyrolithes. Ichnologic evidence from this study demonstrates that through the analysis of modern and fossil burrow morphologies, some important conclusions can be drawn regarding the faunal assemblage present at the time of ancient dune formation. The assemblage of arthropod traces found in the Pleistocene dunes is represented mainly by burrows of coleopterans and arachnids. These traces are very similar, if not identical, to burrows of the modern representatives of those groups. However, some types of burrows were very rare, including especially those of ants and scorpions, which are quite prevalent in the modern dunes. The low occurrence of these kinds of burrows may be due to reduced populations of the producing organisms present at the time of dune formation, or it may be a function of burrow taphonomy (i.e., poor preservation potential of ant and scorpion burrows). Ichnologic evidence suggests that climate in the region has changed little since the Pleistocene. Sedimentologic analysis of both modern and Pleistocene dune material supports this hypothesis. Arthropods have been present in terrestrial habitats since at least the middle Paleozoic. Because of their sensitivity to climatic and habitat conditions and their pervasive distribution throughout virtually every terrestrial environment, the identification and correlation of arthropod burrow systems can provide a valuable tool for paleoecologic interpretation and paleoenviornmental reconstruction on continental settings. |
