Original Article

Development Genes and Evolution

, Volume 222, Issue 5, pp 253-268

A holomorph approach to xiphosuran evolution—a case study on the ontogeny of Euproops

  • Carolin HaugAffiliated withZoological Institute and Museum, Department of Cytology and Evolutionary Biology, University of Greifswald Email author 
  • , Peter Van RoyAffiliated withDepartment of Geology and Geophysics, Kline Geology Laboratory, Yale UniversityResearch Unit Palaeontology, Department of Geology and Soil Science, Ghent University
  • , Angelika LeipnerAffiliated withMuseum am Schölerberg
  • , Peter FunchAffiliated withDepartment of Bioscience, Aarhus University
  • , David M. RudkinAffiliated withDepartment of Natural History (Palaeobiology), Royal Ontario Museum
  • , Lothar SchöllmannAffiliated withLWL-Museum für Naturkunde
  • , Joachim T. HaugAffiliated withZoological Institute and Museum, Department of Cytology and Evolutionary Biology, University of Greifswald

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Abstract

Specimens of Euproops sp. (Xiphosura, Chelicerata) from the Carboniferous Piesberg quarry near Osnabrück, Germany, represent a relatively complete growth series of 10 stages. Based on this growth sequence, morphological changes throughout the ontogeny can be identified. The major change affects the shape of the epimera of the opisthosoma. In earlier stages, they appear very spine-like, whereas in later stages the bases of these spine-like structures become broader; the broadened bases are then successively drawn out distally. In the most mature stage known, the epimera are of trapezoidal shape and approach each other closely to form a complete flange around the thoracetron (=fused tergites of the opisthosoma). These ontogenetic changes question the taxonomic status of different species of Euproops, as the latter appear to correspond to different stages of the ontogenetic series reconstructed from the Piesberg specimens. This means that supposed separate species could, in fact, represent different growth stages of a single species. It could alternatively indicate that heterochrony (=evolutionary change of developmental timing) plays an important role in the evolution of Xiphosura. We propose a holomorph approach, i.e., reconstructing ontogenetic sequences for fossil and extant species as a sound basis for a taxonomic, phylogenetic, and evolutionary discussion of Xiphosura.

Keywords

Euproops danae Euproops rotundatus Fossilized ontogeny Tagmatisation Hapantotype