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They were the dominant predators in certain nearshore and peritidal settings
(Kluessendorf
1994
). Eurypterids are considered to be the sister group of Arachnida
(Weygoldt and Paulus
1979
).
The organic nature of eurypterid cuticles has long been known, and early studies
of the detailed morphology of these arthropods were based on material from the
Silurian of Oesel (Saaremaa), Estonia, prepared by dissolving the enclosing matrix
(Holm
1898
; Wills
1965
; Selden
1981
). The fossil record of eurypterids is primarily
the result of organic preservation of the cuticle, mainly representing molts (Selden
1984
), although the Ordovician Soom Shale of South Africa preserves evidence of
such internal structures as muscle tissue, as a result of very early authigenic miner-
alization (Braddy et al.
1995
,
1999
).
Most work on eurypterid cuticle has dealt with its ultrastructure (e.g.,
Dalingwater
1973
). An early analysis of the chemistry of cuticle from Saaremaa
tested its resistance to weak acids and bases, and suggested that it is composed of
chitin (Rosenheim
1905
), although other long-chain polymers are also resistant to
such treatment. A preliminary study of the composition of the cuticle of a
Carboniferous eurypterid,
Adelophthalmus
sp., showed that it lacked traces of
chitin and the cuticle had been altered to an aliphatic geopolymer (Stankiewicz
et al.
1998a
). The original composition of eurypterid cuticle was presumably sim-
ilar to that of
Limulus
and scorpions, as inferred from the extant phylogenetic
bracket (Witmer
1995
).
Material
A number of settings preserve eurypterid cuticles in a manner that allows them to be
peeled or scraped off the rock surface. Fossil cuticles were analysed from six different
localities and fi ve different horizons in Ontario and Nova Scotia (Canada), Kansas,
Indiana and New York (USA); three of the horizons are Silurian, whereas two are
Carboniferous in age (Table
7.1
). The oldest is the Kokomo Member of the Wabash
Formation of Indiana, interpreted as Ludlow (ca 420 MA) based on conodonts
(Kleffner and Rexroad
1999
). The Kokomo Member is a fi nely laminated, argilla-
ceous limestone with alternating dark and light bands. The other Silurian horizons
sampled are in New York and Ontario, Canada, and their stratigraphic relationships
are well known. The Pittsford Member of the Vernon Formation in New York is
Late Ludlow, and slightly younger (ca 419 MA) than Kokomo, and is composed of
dark grey to black shales and olive calcareous mudstones. The youngest Silurian
horizon is the Williamsville A Member (ca 417 MA), represented by the fossils
from Ridgemount Quarry and Fort Erie town, both in Ontario, Canada. The
Williamsville A Member of the Williamsville Formation is a dolomite with high
magnesium content. The Carboniferous sequence at Joggins, Nova Scotia, is
Bashkirian in age (ca 312-313 MA) and consists of alluvial and lacustrine deposits
in the Cumberland Group; the sample analyzed here came from a greenish grey
shale horizon from within a red mudrock and sandstone sequence close to the
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