PANDURALIMULUS BABCOCKI N. GEN. AND SP., A NEW LIMULACEAN HORSESHOE CRAB FROM THE PERMIAN OF TEXAS

Abstract

Fossil horseshoe crabs are rare, and new discoveries have the potential for providing important taxonomic and biostratigraphic information. The superfamily Limulacea Zittel, 1885, embraces the lineal ancestors of the modern genera, including Limulus Muller, 1785, within the Limulidae Zittel, 1885. The geologically oldest of the limulaceans are arrayed within the late Paleozoic Paleolimulidae Raymond, 1944. The first discovery, as well as all authentic specimens, of fossil paleolimulids have been from the Late Paleozoic rocks of Kansas and Illinois. This paper not only describes a new genus and species of horseshoe crab but also records the first occurrence of the family in north-central Texas, and clarifies placement of taxa within the Paleolimulidae. Specimens were collected in Baylor County aproximately 15 km northeast of Seymour, Texas, from a layer of clastic sediment within the Lower Permian (Leonardian) Maybelle Limestone, the member comprising the lower part of the Lueders Formation (National Museum of Natural History site USNM 41884) (Fig. 1). The Lueders Formation ranges from 50 to 275 ft (15–82 m) thick and is comprised of alternating shale and limestone (Stafford, 1960). The limestones of the Maybelle Member are thick, massive, fossiliferous, and resistant (Beede and Waite, 1918). The paleoenvironment in which these rocks were deposited was most likely deltaic; gymnosperms, pteridosperms, horseshoe crabs, bivalves, and other fossil fragments occur together in a fine-grained, blue-gray matrix suggesting a marginal marine setting. Babcock and Merriam (2000) suggested that xiphosurans might be preserved in tidally influenced coastal settings like this because high depositional rates would favor preservation of the delicate cuticle. Figure 1 —Generalized stratigraphic section showing the position from which the xiphosurans were collected ### Subclass XiphosuraLatreille, 1802 Order Xiphosurida Latreille, 1802 Suborder Limulina Richter and Richter, 1929 Superfamily Limulacea Zittel, 1885 Family Paleolimulidae Raymond, 1944 #### Diagnosis Ophthalmic ridges meeting anterior to cardiac lobe; …