ALMATIUM SP. FROM THE MIDDLE TO LATE TRIASSIC MADYGEN FORMATION, SW KYRGYZSTAN AND THE PHYLOGENETIC STRUCTURE OF THE CALMANOSTRACA

The Madygen Formation is a noted terrestrial and aquatic lagerstätten found in SW Kyrgyzstan. Among the notable animals that it contains is a provisional new species of branchiopod crustacean belonging to the genus Almatium. The main differences between the Madygen Almatium specimens and specimens of Almatium from elsewhere lie in discontinuous proportional differences in the shape of the carapace. Larger samples may eventually demonstrate that these proportional differences are allometric and that the Madygen Almatium specimens are part of a single, highly variable species of Almatium across the Triassic of Asia.

Traditionally, Almatium has been placed in the Kazacharthra—a clade of unique notostracan-like branchiopod crustaceans. Together with the notostracans, they form the clade called the Calmanostraca. However, owing to the morphological heterogeneity of the purported kazacharthrans, there is very little morphological support for the monophyly of Kazacharthra. A phylogenetic analysis (parsimony and Bayesian) of the Calmanostracans demonstrates this by finding essentially no structure to the kazacharthrans, and failing to recover their monophyly in the Bayesian analysis. Even so, many kazacharthrans remain very poorly known—it is possible that as they become better known, their phylogenetic resolution will increase.