The Late Permian araxoceratid ammonoids: a case of repetitive temporal and spatial unfolding of homoplastic conch characters

摘要

The Wuchiapingian (early Late Permian) ammonoid family Araxoceratidae shows a morphological spectrum that is recurring in the three genera Araxoceras (early Wuchiapingian; Transcaucasus-Iran), Vedioceras (late Wuchiapingian; Transcaucasus-Iran) and Konglingites plus Kiangsiceras (late Wuchiapingian; South China). All three display a range of conch morphology from millstone-shaped to reel-shaped; they also repeatedly show the formation of a tricarinate venter. When the suture line is regarded as the main character for phylogenetic relationships in this group, these conch characters must be seen homoplastic because they iteratively formed in time and space. From the Wuchiapingian sedimentary rocks of NW Iran, three new species of araxoceratid ammonoids are described herein: Araxoceras truncatum n. sp. and Araxoceras insolens n. sp. (both early Wuchiapingian) as well as Vedioceras fusiforme n. sp. (late Wuchiapingian). With these new taxa, the taxonomic diversity and particularly the morphological disparity of the Late Permian ammonoids from the Transcaucasus-NW Iran region is extended.