NEW YORK FOSSILS

Fossil Section Introduction

FOSSIL GROUPS

The major groups of invertebrate animals most commonly represented in the local fossil record are described below.

PORIFERA - the sponges. Body with two cell layers, between which a skeleton (organic, calcareous, or siliceous) is secreted as fibers, needle-like spicules, or (in the stromatoporoids) calcite laminae. Usually poorly preserved and difficult to recognize.

CNIDARIA (formerly Coelenterata) - corals, hydroids, jellyfish. Sac-like body with opening surrounded by stinging tentacles. May occur as polyp (as in corals) or medusa (jellyfish). The coral animal resides in a corallite of calcium carbonate strengthened by longitudinal (septa) and transverse (tabulae) partitions. May be solitary or colonial. Two major Paleozoic groups: rugose ("horn") corals and tabulate ("honeycomb") corals.

BRYOZOA - the "moss animals." Very tiny colonial animals that usually construct a calcareous skeleton. Each tiny opening was home to an individual zooid. Colonies come in varied forms: branches, massive mounds, crusts on shells, delicate lace-like fans.

BRACHIOPODA - animals with a bivalved shell but most closely related to bryozoans. Distinguished from clams (pelecypods) by the symmetry: each brachiopod valve has bilateral symmetry (sides mirror images of each other) - this is never true for clams.

PELECYPODA (also called "Bivalvia") - clams, mussels, oysters. Mollusks with calcareous bivalved shell; each valve lop-sided (never bilaterally symmetrical) with the beak (earliest part) pointing toward the front. Articulated specimens of many species when viewed edge-on show bilateral symmetry.

GASTROPODA - snails. Mollusks with single coiled shell, usually in a right-handed (dextral) spiral, but may be left-handed (sinistral) or planispiral.

CEPHALOPODA - nautiloids, ammonoids, squid, octopus. Many fossil types with external shell, but only two modern genera have one. Shell may be straight or coiled (usually planispiral), divided internally by partitions (septa) into chambers connected by tube (siphuncle) that was used to regulate buoyancy.

TRILOBITA - Extinct marine arthropods with a head (cephalon) followed by a segmented thorax and a tail (pygidium). The name is actually from their three-part longitudinal division into an axial lobe bordered on either side by a pleural lobe. Each thoracic segment protected a pair of branched legs beneath. Several types found in this area, including:


Dalmanites limulurus
Silurian


Phacops rana
Devonian


and Greenops boothi
Devonian


EURYPTERIDA - Extinct arthropods most closely related to the horseshoe crab, with a prosoma (head and thorax region with appendages) followed by an abdomen (twelve segments and a telson). Not very common, but included here because one genus (Eurypterus) represents the official New York State fossil.

Eurypterus lacustris
Silurian




CRINOIDEA - crinoids or "sea lilies" - a group of echinoderms (starfish, sea urchins, and relatives). Usually includes a crown (main body or calyx with arms surrounding the mouth) attached to a long stem (column) that in many was anchored to the bottom by holdfasts or root-stocks. Body protected by calcite plates that usually separate after death; column composed of many plates (columnals) stacked together. At times crinoids were so abundant that their skeletal remains make up a major part of the rock in some formations.

GRAPTOLITES - members of the phylum Hemichordata common in some Paleozoic rocks. Colonial, with rod-like, branching, or lace-like colonies that because they are organic are usually preserved as carbonized films in black or dark gray shales.