Bivalved arthropods from the Middle Ordovician Winneshiek Lagerstätte, Iowa, USA

Abstract

The Middle Ordovician (Darriwilian) Winneshiek Lagerstätte of northeast Iowa is preserved in a meteorite crater. Besides conodonts, the fossils are dominated by arthropods, particularly eurypterids and phyllocarids. Here we describe the bivalved forms, which include at least seven different taxa. The small phyllocaridCeratiocaris winneshiekensis, new species, is the most abundant; it is the oldest representative of the Ceratiocarididae. A single incomplete abdomen and telson bearing furcal rami is reminiscent of notostracan branchiopods but its affinities are unknown.Decoracaris hildebrandi, new genus and species, is a rare form with a shield that extends anteriorly into a swollen horn and reaches lengths of 9 cm: it may represent a thylacocephalan crustacean but this cannot be confirmed without soft parts.Iosuperstes collisionis, new genus and species, is represented by suboval valves 10–25 mm long: its affinities are unknown. A probable leperditicopid, which ranges in length from 8 to 18 mm, is commonly preserved in a ‘butterflied’ configuration. It does not preserve the scars and sinuses characteristic of three-dimensionally preserved leperditicopids from elsewhere. Finally the fauna includes at least three ostracods, including a palaeocope with a granular surface and relief similar toLomatopisthia, and a smooth ?podocope. The Winneshiek fauna differs from those of other Ordovician Lagerstätten from restricted settings such as Airport Cove and William Lake in Manitoba (Katian) where, apart from ostracods, bivalved arthropods are absent, and Silurian examples such as Brandon Bridge (Telychian), which lacks eurypterids, and the Williamsville Member of the Bertie Formation (Pridoli) where conodont assemblages are absent.

Exceptionally preserved arthropodan microfossils from the Middle Ordovician Winneshiek Lagerstätte, Iowa, USA

“…; Briggs et al . ). Ostracods can possess one or two pairs of sequential, arcuate filter‐like structures (e.g.…”

“…Our material raises the possibility that by the Middle Ordovician, small-bodied, filter-feeding branchiopods had spread to restricted, marginal marine environments, or even freshwater habitats (from which the remains may have been transported). However, more material is needed to rule out alternative affinities for the Winneshiek SCFs, especially because both ostracods and phyllocarids have been documented from the biota (Liu et al 2006;Briggs et al 2016). Ostracods can possess one or two pairs of sequential, arcuate filter-like structures (e.g.…”

“…The Winneshiek Shale in Iowa, USA, is a Darriwilian (Middle Ordovician) Konservat-Lagerst€ atte (site with exceptionally well-preserved fossils; see Seilacher 1970) that is notable not least for its arthropod fossils. It has yielded the currently oldest described eurypterids (Lamsdell et al 2015a), phyllocarids with softtissue preservation (Liu et al 2006;Briggs et al 2016), ostracods and other bivalved arthropods (Briggs et al 2016), and a dekatriatan-like euchelicerate (Lamsdell et al 2015b). Apart from this, unusually large conodonts (elements up to 16 mm in length) with complete apparatuses (Liu et al 2017), possible jawless fishes, linguloid brachiopods, molluscs, algae and acritarchs have been found (Liu et al 2006;P.A.…”

“…; Briggs et al . ), ostracods and other bivalved arthropods (Briggs et al . ), and a dekatriatan‐like euchelicerate (Lamsdell et al .…”

Exceptionally preserved conodont apparatuses with giant elements from the Middle Ordovician Winneshiek Konservat-Lagerstätte, Iowa, USA

“…The Winneshiek fossil fauna includes a variety of new forms, and the invertebrate fossils are dominated by arthropods (Lamsdell et al, 2015a;Nowak et al, 2015;Briggs et al, 2015Briggs et al, [2016), including the oldest eurypterid Pentacopterus (Lamsdell et al, 2015b). Possible algae and jawless fish also occur in the fauna.…”