The ‘Alum Shale Window’—Contribution of ‘Orsten’ Arthropods to the Phylogeny of Crustacea

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Abstract
Exceptional three‐dimensional preservation of phosphatized Upper Cambrian arthropods of different groups from southern Sweden permits not only description of their morphology in full detail but also assumptions on functional morphology and life habits. Ontogenetic stages, in some cases in complete sequences, give additional information about habitual changes in the life cycle. Altogether this provides a wide data basis for phylogenetic considerations, particularly for the crustacean branch of the Arthropoda. Among the ‘Orsten’ fossils, a number could be recognized as representatives of crown‐group crustacean taxa, such as the Skaracarida and Bredocaris as members of each of the two different lineages of Maxillopoda, or Rehbachiella as a member of the Branchiopoda. Another set of forms shares some characters with the crowngroup crustaceans but lacks a large number of others. These fossils, identified as representatives of the stem line of Crustacea, provide a hitherto unknown data set for the interpretation of morphological and functional changes in the evolution towards the crown‐group of this taxon.