Early post-embryonic polyxenidan millipedes from Saxonian amber (Eocene)

Abstract

Early post-embryonic stages of arthropods are rarely found in the fossil record. They seem even more rarely reported in literature, possibly as it is more difficult to establish new species based on these specimens. Here we report two immature specimens of polyxenidan myriapods (Diplopoda, Polyxenida) preserved in Saxonian amber (Eocene). Specimen 1 represents a stage I individual with only three pairs of trunk appendages, the collum and three additional tergites. It is interpreted as a representative of the polyxenidan ingroup Polyxenidae. Specimen 2 represents a stage II individual with four pairs of trunk appendages, the collum and three well-sclerotised tergites. It is interpreted as a representative of the polyxenidan ingroup Synxenidae. We additionally discuss the challenges of further systematically interpreting immatures and fossil polyxenidans in general. We also discuss how the further exploration of data of immature polyxenidans, extant and fossil, has the potential to improve our understanding of their evolution and biology.