Many groups of invertebrates are represented in the fossils of D.A.R.
State Park. Plate 1 will help you to identify these fossils. The name,
phylum (major group) and age of each fossil are provided in the
explanation of the plate. The following paragraphs describe each phylum
represented in the Park rocks.
[Illustration: Plate 1. Typical fossils found in the Glens Falls
Limestone.]
_Arthropods._ D.A.R. State Park rocks contain trilobites with the
following imposing names: _Cryptolithus tesselatus_ (crip-toe-LITH-us
tessell-AH-tus[5]), _Isotelus gigas_ (ice-so-TELL-us GIG-us) and
_Flexicalymene senaria_ (flex-eye-cal-ah-Mean-ee sen-AREA). These
fossils are figured on Plate 1, 1-A, B, C, D; 2; 3. Within the Park
_Cryptolithus tesselatus_ is very common wherever fossils occur.
Generally only the cephalon or head portion of this trilobite is
preserved. The cephalon is easily recognized by three concentric rows of
pits arranged around the brim. _Cryptolithus_ is an excellent _index
fossil_[6] for the Park rocks. The arthropod phylum is characterized by
animals with jointed legs, segmented bodies and a jointed outer armour
of _chitin_.[7] For examples, the crabs, lobsters, spiders, scorpions
and insects are arthropods. Trilobites appear early in the fossil record
but they did not survive beyond the Paleozoic Era.
_Explanation for Plate 1_
(_all drawings are X1 unless otherwise indicated_)
1-A. _Cryptolithus tesselatus_, Arthropod (Trilobite), Middle Ordovician
(Trenton Stage). Front view of the Cephalon or head. (X2)
1-B. _Cryptolithus tesselatus_, Arthropod (Trilobite), Middle Ordovician
(Trenton Stage). Oblique front-lateral view of the Cephalon. (X2)
1-C. _Cryptolithus tesselatus_, Arthropod (Trilobite), Middle Ordovician
(Trenton Stage). Top view of the Cephalon. (X2)
1-D. _Cryptolithus tesselatus_, Arthropod (Trilobite), Middle Ordovician
(Trenton Stage). Side view of the Cephalon. (X2)
2. _Isotelus gigas_, Arthropod (Trilobite), Middle Ordovician. Top view
of specimen.
3. _Flexicalymene_, Arthropod (Trilobite), Ordovician to Silurian. Top
view of an enrolled specimen.
4-A. _Dinorthis pectinella_, Brachiopod, Middle Ordovician (Trenton
Stage). Exterior view of the brachial valve.
4-B. _Dinorthis pectinella_, Brachiopod, Middle Ordovician (Trenton
Stage). Exterior view of the pedicle valve.
5. _Reuschella edsoni_, Brachiopod, Middle Ordovician. Exterior view of
the pedicle valve.