HU research team investigates the evolutionary relationship of 400 million year-old fossils on the basis of their eyes
Trilobites had eyes like insects and crustaceans.
Trilobites are probably the most successful and best-known fossil arthropods. More than 20,000 species inhabited Paleozoic seas for 300 million years. Nevertheless it remained unclear until now whether trilobites were more closely related to chelicerates or to insects, crustaceans and myriapods. A research team from Humboldt-Universität zu Berlin (HU), the Zuse Institute Berlin and the Natural History Museum, Berlin has been able to demonstrate that trilobites had eyes like insects and crustaceans and not like chelicerates. The team investigated the fine structure of trilobite eyes using 400 million year-old fossils. With the results of the investigation it is now possible to determine the evolutionary relationship of trilobites more precisely. The study has been published in Nature Communications.
Despite numerous studies on the biology of trilobites, their phylogenetic position in the stem lineage of arthropods was unresolved and the subject of controversial debates. On the one hand, trilobites are counted as chelicerates on the basis of their body shape and their extremities, which resemble those of modern horseshoe crab. On the other hand, they have antennae on their heads like insects, crustaceans and myriapods. The fine structure of compound eyes constitutes another important characteristic that distinguishes the major groups of living arthropods. The Berlin research team directed by Professor Gerhard Scholtz (HU) together with Andreas Staude of the Zuse Institute und Jason Dunlop of the Natural History Museum used modern methods such as synchrotron X-rays and micro-computed tomography to reconstruct in detail the internal anatomy of trilobite eyes using the well-preserved fossil remains of two species. They were able to show that trilobites had so-called crystalline cones underneath the lenses of their compound eyes. These structures, made of transparent cells, collect light and guide it to the underlying receptor cells, whose light-perceiving structures were shown in trilobites for the first time in this study. Thus the entire anatomy of trilobite eyes resembles the eyes of crustaceans, insects and myriapods and points to a close relationship between trilobites and these groups, since the compound eyes of chelicerates have no crystalline cones.
Professor Gerhard Scholtz, Humboldt-Universität zu Berlin, Institut für Biologie, phone: (030) 2093-6005, email: firstname.lastname@example.org
Scholtz, G., Staude, A. and Dunlop, J. A. 2019. Trilobite compound eyes with crystalline cones and rhabdoms show mandibulate affinities. Nature Communications. https://doi.org/10.1038/s41467-019-10459-8