Geographical clines in Permian and lower Triassic gondolellids and its role in taxonomy

Continuous and gradational geographic variation within a species, a geographic cline, is a concept familiar to biologists describing modern species and subspecies. In contrast, true geographic clines are rarely described by palaeontologists because it is extremely difficult to determine the divergence of samples from a time plane. Palaeontologists usually describe morphoclines or chronomorphoclines that represent anagenetic evolution within lineages. This paper examines geographic clines within Permian gondolellids as a possible solution to correlating between distinct provinces that became established during the Kungurian. These clines are distinguished by the gradual geographic variation of the carinal configuration and size of the cusp in P1 elements for a given time-slice. It is not certain what is controlling this morphologic response, but since the P1 element was used for food processing it is possible that it relates to variations in potential prey affected by some environmental gradient like temperature. Furthermore, the recognition of clines affects systematics as temporal subspecies should be distinguished across their geographic range. The evolutionary development of taxa with distinct morphology that become restricted to certain provinces, as in the serrated Jinogondolella, is fundamental to the concept of clines. In addition, the recognition of character changes in other elements within the gondolellid apparatus will affect the identification of distinct clades and as a result several gondolellid genera are treated cladistically. The taxonomy of gondolellid taxa including Mesogondolella, Jinogondolella, Clarkina, Neogondolella, and Neospathodus are discussed and a new genus, Neoclarkina, is described.