Palaeobiology of Silurian trilobites from North Greenland

Abstract

The Telychian (Llandovery, Silurian) reefs of North Greenland yield extensive collections of diverse and remarkably well preserved trilobites. The collections comprise 36 named trilobite species (32 new), and 30 under open nomenclature. These are assigned to 32 genera (six new). Members of the Scutelluidae (10 new species, four new genera), Illaenidae (one new species), Proetidae (10 new species, two new genera), Aulacopleuridae, Scharyiidae (three new species), Brachymetopidae, Harpetidae, Cheiruridae (three new species), Encrinuridae (two new species), Calymenidae, Phacopidae, Lichidae (two new species), and Odontopleuridae (one new species) are represented. Aspects of phylogenetic relationships within the Scutelluidae and Illaenidae are problematical because of the high number of effaced taxa. Selected effaced genera are analysed using cladistics, confirming the polyphyletic nature of effacement. Counts of trilobite sclerites from thirteen reef localities are analysed using cluster and correspondence analyses to identify trilobite associations, and taphonomic signatures. Seven trilobite associations are identified: Scutelluid-Illaenimorph; Scutelluid; Scutelluid-Cheirurid; Scutelluid-Harpetid; Proetid; Encrinurid; Illaenimorph. These can be encompassed within the previously defined Illaenid-Cheirurid ‘Community’. Trilobites are predominantly associated with a cement-rich microbial lithofacies deposited between storm- and fair-weather wave base. The variable distribution of taxa within the reefs is partly a reflection of intense hydrodynamic sorting in reef environments