EARLY CHELICERATE PALEOBIOLOGY - NEW INSIGHTS FROM LATE ORDOVICIAN KONSERVAT-LAGERSTÄTTEN

Two recently discovered Konservat-Lagerstätte deposits in central and northern Manitoba, Canada, are yielding important new fossils. Some of these provide a compelling (and often confounding) record of emerging chelicerate arthropod diversity in Late Ordovician (Richmondian) restricted shallow marine environments of central Laurentia.

Biotic assemblages from the William Lake (Grand Rapids Uplands; Williston Basin) and Airport Cove (Churchill area; Hudson Bay Basin) sites both contain representatives of the early xiphosurid horseshoe crab Lunataspis aurora, as well as moderately abundant eurypterid remains. Recently recovered juvenile individuals of L. aurora reveal allometric growth of the prosomal shield and telson. Elements of two unusual new eurypterid taxa have so far been distinguished, one at each locality, and distinctive taphonomic signatures at the widely separated sites provide a range of paleobiological data, from sub-millimetric surface detail on discrete organic cuticle fragments to near-complete articulated molt configurations approaching 20 cm in length. The eurypterid from William Lake possesses a puzzling chimera-like combination of exoskeletal characters, including a novel swimming paddle morphology and pretelson segment, setting it apart from all other described forms.

A single specimen from the William Lake section is the first Ordovician record of a sea spider, and the only known fossil occurrence of the rare and bizarre Pycnogonida in rocks of demonstrable shallow-water origin. Fragmentary remains of other non-biomineralizing arthropods found at both sites hint that additional chelicerate groups, such as the ‘synziphosurines’ and chasmataspidids, may also be present. All of the evidence suggests that Ordovician marginal marine habitats may have been prime targets for early chelicerate exploitation.