THE RISE AND FALL OF JINOGONDOLELLA: THE EVOLUTION AND PALEOGEOGRAPHY OF A GUADALUPIAN CONODONT GENUS

The genus Jinogondolella defines the Guadalupian (Middle Permian) in West Texas and the first occurrence of three species defines the bases of the three stages of the Guadalupian in the GSSP stratotype sections in the Guadalupe Mountains. The first species of the genus, Jinogondolella nankingensis, defines the base of the Guadalupian and the last species probably evolved into Clarkina, a subspecies of which defines the basal boundary of the succeeding series, the Lopingian (Upper Permian). Detailed recent studies have yielded a wealth of information on the morphologic and geographic variation of the genus and the number of species described steadily rises. The genus is currently interpreted to have a 15 element apparatus that has been reconstructed from some excellent material from West Texas. Sixteen species are currently recognized from the Delaware basin area and several key species including morphotypes of J. nankingensis and J. aserrata also are found in the Phosphoria basin allowing for accurate correlation of the Roadian and Wordian to the Phosphoria and other areas of northern Pangaea. Both of these species occur in the Meade Peak Phosphatic Shale, J. nankingensis throughout much of the unit and J. aserrata in the uppermost part in southeast Idaho where the section is the thickest. Morphotypes of J. nankingensis vary in abundance from the Delaware and Phosphoria basins and reflect the change from a warm to cooler water mass. Jinogondolella occurs with Mesogondolella in the Phosphoria and at least in the upper part of the Meade Peak seems to alternate in dominance from bed to bed suggesting warming and cooling cycles of the water with Mesogondolella dominating cooler and Jinogondolella dominating warmer water masses.