PRELIMINARY APPARATUS RECONSTRUCTION OF JINOGONDOLELLA ALTUDAENSIS, AND ITS BEARING ON THE ORIGIN OF CLARKINA

The Reef Trail Member of the Bell Canyon Formation is the uppermost basinal unit in type Guadalupian strata, international reference for the Middle Permian Series. These strata are characterized by species of the conodont genus Jinogondolella. Conodonts from the Reef Trail Member represent the zone of Jinogondolella altudaensis. These are the youngest species of Jinogondolella, which was replaced by Clarkina—the genus that characterizes the Lopingian (Upper Permian) Series. The basal Lopingian GSSP is defined on the transition from Clarkina postbitteri hongshuiensis to Clarkina postbitteri postbitteri. Clarkina postbitteri hongshuiensis most likely evolved directly from advanced forms of Jinogondolella altudaensis in west Texas, although some workers support derivation from different ancestral species. Advances in our understanding of both the Reef Trail Member and apparatus reconstructions for Jinogondolella now allow us to more rigorously approach this important lineage question.

The zone of Jinogondolella altudaensis is comprised of several species of Jinogondolella, so it has been difficult to secure monospecific faunas for multi-element study. We currently have several faunas from the Reef Trail Member in which Jinogondolella altudaensis, the predominant species in terms of richness, co-occurs with only one other Jinogondolella species. By a process of elimination, we can reconstruct a partial apparatus of Jinogondolella altudaensis for preliminary comparison with Clarkina. Jinogondolella altudaensis had dimorphic P₂ elements that are sometimes difficult to differentiate because the posterior process tends to break a few denticles away from the cusp. This process is twisted and in one form at a significant angle to the anterior process, so careful sieving is necessary for recovery. The M and S₀ elements do not appear to be particularly distinctive from other Jinogondolella species, although some M elements commonly have an almost crescent-shaped cusp. The S₁ elements can have a similar cusp, and all the S₁s have a reduced posterior process. The S₃ elements are bipennate with an anterior process that bifurcates near the cusp. These apparatus features support Jinogondolella altudaensis as the immediate ancestor of Clarkina.