Climacograptus
wilsoni
Graptolites are an extinct group of hemichordates that
are most commonly preserved as carbonized compressions on shale bedding
planes. They are typically not glamorous fossils, but they are critically
important guide fossils and are widely used in biostratigraphy and for
international correlation.
The most abundant group of graptolites in the fossil
record is the graptoloids. Graptoloid graptolites typically resemble
small hacksaw blades. Each “tooth” of the hacksaw blades housed a
tentaculate, filter-feeding organism. The entire hacksaw blade is the
graptolite skeleton, known as a rhabdosome - a nonmineralized colonial
skeleton. Most graptolites were planktonic.
Shown below is a basinal black shale from Scotland
with Climacograptus wilsoni Lapworth, 1876 fossils on it (Animalia,
Hemichordata, Graptolithina, Graptoloidea, Diplograptidae). It comes from
the lower part of the Lower Hartfell Shale (Moffat Shale Group, Climacograptus
wilsoni Zone, Soudleyan Stage, ~mid-Caradocian, upper Middle Ordovician).
Locality:
Main Cliff at Dob’s Linn (~36.1-43.1 meters below the Ordovician-Silurian
boundary GSSP), north side of A708 Road, just west of the small village of
Burkhill, ~20 km northeast of Moffat, far-northern Dumfries County, Southern
Uplands, southern Scotland, UK.
Climacograptus wilsoni Lapworth, 1876 rhabdosomes on black shale (2.6 x 2.5
cm) from the Lower Hartfell Shale (upper Middle Ordovician) at Dob’s Linn,
southern Scotland.