MAPPING SPATIAL AND STRATIGRAPHIC DISTRIBUTION OF DECAPODS IN THE LUOPING BIOTA (MIDDLE TRIASSIC) OF CHINA: REFINING FAUNAL ASSOCIATIONS

The Middle Triassic Luoping Biota within the Guanling Formation has been documented by over 20000 specimens of vertebrates and invertebrates preserved in a sequence of calcareous mudstones. Diversity is high, with fish, reptiles, arthropods (mysids, thylacocephalans, isopods, horseshoe crabs, and decapods), echinoderms, and brachiopods dominating the assemblage. Among the decapods, three species of lobsters and four species of shrimp have been documented by several hundred specimens. The objective of the present study is to determine the distribution of the decapods both stratigraphically and spatially (on the bedding surfaces), and to plot their positions relative to other fossils occurring with them. In the process, we mapped the position of all fossils we could identify in over 1000 quadrats, each measuring 0.5 meters on a side. One of the surfaces was large enough that we were able to map 762 quadrats (190.5 square meters). Although the Luoping Biota is extremely diverse, the decapods occur predominantly with only a few other common fossils. One notable association is with thylacocephalan crustaceans that were extremely abundant ion some surfaces. Another association is with small fish, most of which can be assigned to just a couple of species. The distribution of fossils on the bedding surfaces is patchy, and no particular orientation has yet been noted. It is interesting that both benthic and pelagic organisms occur on the same bedding surfaces. Although the Luoping Biota also yields an array of large fish as well as reptiles, none were noted on the bedding surfaces that were mapped. Thus, the initial impression is that the Guanling Formation consists of layers representing different environments and that the characterization of the unit as containing a vast array of taxa, although true, may give the false impression that all the organisms lived and interacted with one another. Research supported by National Geographic Society 9128-12 and NSF OISE 1126137 to Feldmann and Schweitzer and Chinese Geological Survey 1212011140051 and 1212011120621 to Hu.