Summary of a revision of New York State Ordovician eurypterids: implications for eurypterid palaeoecology, diversity and evolution

Abstract

The record of Ordovician Eurypterida from New York State, USA, is shown to be largely false. Twenty-nine species in 17 genera are here recognised as pseudofossils, reducing by more than 75% the total number of named Ordovician eurypterid taxa. Consequently, 10 families now have their first occurrence either later in the Ordovician or in the Early Silurian. The implications for eurypterid palaeoecology, diversity and evolution are not as straightforward as would be expected from such a drastic taxonomic revision. All Ordovician eurypterids are now known to occur in shallow-water, near-shore shales or fine-grained carbonates. Diversity measures indicate that the end-Ordovician extinction event appears to have had less effect on eurypterids than previously known, and their turnover is level in the Ordovician.

Two new Silurian species ofEurypterus(Chelicerata: Eurypterida) from Norway and Canada and the phylogeny of the genus

“…Morphological terminology follows Tollerton (1989) and taxonomy follows Novojilov (1962). Morphological terminology follows Tollerton (1989) and taxonomy follows Novojilov (1962).…”

“…Can be separated from E. lacustris by the position of the eyes (Tollerton 1993). Can be separated from E. lacustris by the position of the eyes (Tollerton 1993).…”

“…4A) Carapace 20.0 mm long, 25.8 mm wide, L/W ratio 0.78, lateral angle approximately 95•, on the border between the subquadrate and trapezoid carapace shapes (Tollerton 1989). 4A) Carapace 20.0 mm long, 25.8 mm wide, L/W ratio 0.78, lateral angle approximately 95•, on the border between the subquadrate and trapezoid carapace shapes (Tollerton 1989).…”

“…In these two taxa, the genal facets of the carapace therefore articulates towards the second tergite, not the first. The telson shape is styliform (Tollerton 1989: fig. 1) and Jones & Kjellesvig-Waering (1985: figs 3.1, 3.2 and 3.4).…”

A new Ordovician eurypterid (Arthropoda: Chelicerata) from southeast Turkey: Evidence for a cryptic Ordovician record of Eurypterida

“…Since Tollerton (2004) recognized that the majority of Ordovician eurypterids from New York State (accounting for approximately 75% of Ordovician eurypterid diversity at the time) were either pseudofossils or, in one case, a phyllocarid carapace, Ordovician eurypterids have been considered rare, with the majority of familylevel clades originating in the early Silurian. The recent discovery of as yet undescribed eurypterids from the late Ordovician Manitoba biotas (Young et al, 2007) and the Middle Ordovician St Peter Formation in Iowa (Liu et al, 2006) suggests, however, that Ordovician eurypterids are not as rare as has been assumed, and the discovery of Paraeurypterus serves to strengthen this possibility.…”