Kimiltei Is a New Late Cambrian Lagerstätte with the Faunistic Complex of Arthropods (Euthycarcinoidae, Synziphosurina, and Chasmataspidida) in the Irkutsk Region

Abstract

Abstract: A new locality Kimiltei, Irkutsk oblast, where unmineralized remains of arthropods were buried en masse, is described. The U–Pb zircon dating yielded a Cambrian age with the youngest values of 492 ± 4 Ma. Kimiltei arthropods are represented by Chasmataspidida, Synziphosurina, and Euthycarcinoidea. The last two groups have not been known in the Siberian Platform, and the first one has been described in this area only from Devonian rocks. The Irkutsk findings are the most ancient representatives of their groups, and their distribution areas turn out to be wider than previously known. Their co-burial is noteworthy, because the representatives of these groups have never been found together before. Taking into account the fact that the descendants of all three groups gave rise to the terrestrial lines of chelicerates and insects, the Kimiltei assemblage is the entire fauna of the land arthropod ancestors. Their cohabitation is indicative of the fact that they started their expansion on land from some close ecological niches in the intertidal zone.