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UPPER PENNSYLVANIAN PERIOD INVERTEBRATES OF NEW MEXICO
As the geologic column below illustrates, New Mexico
offers paleontology enthusiasts a long natural history, from the Precambrian
Period to the Late Pleistocene Epoch.
More specifically, North-central New Mexico offers a diverse selection
of vertebrates and invertebrate fossils within the most prolific portion of the
Pennsylvanian Period. From the
Mississippian through the Pennsylvanian Period, a shallow sea covered most of
New Mexico leaving sandstone and fossil evidence of fish, amphibians, and
eurypterids. Carboniferous plants, such
as ferns, were deposited and preserved as fossil impressions in the shale, their
trunks, limbs, and twigs left as fossilized bark and petrified wood. Further out from the primeval marshes, into
the depths of the ancient sea, a thick layer of limestone was deposited,
leaving the greatest assortment of fossils.
The most abundant, which I can attest to by the weight of my samples,
were the brachiopods, explained below.
In many ways the Upper Pennsylvanian, as witnessed in New Mexico’s
Madera Formation, was an age of brachiopods.
But as the following photos illustrate there was also an abundance of
bryozoans, crinoids, fusulinids, mollusks, and other invertebrates, whose
descendents still fill the seas today.
Fossil Wood From The Sandia Formation, New Mexico
The Carboniferous forest, so typical of the
Pennsylvanian Period of New Mexico, is represented by wood and bark samples
collected in the Sandia Mountains (outcrops of the Sandia Formation), New
Mexico, shown in the photo below. In
the Pennsylvanian Period plants took hold, expanding, and setting the stage for
the Permian Age of Amphibians. The
lowlands that bordered the shallow sea of New Mexico were covered with lush,
green, and tropical foliage. The stable climate of this period supported
lepidodendron and calamite trees, some of which grew up to one hundred feet
tall. In the primeval forests were also
thrushes, ferns, and the ancestors of conifer trees. (A more detailed discussion of this period is given in this link.)
Note: To zoom in and out , click on the photo
below:
An Assortment of Marine Fossils from the Madera Formation, New Mexico
The
Upper Pennsylvanian Madera Formation contains several orders, families and species of
marine invertebrates. My
specimens came from Battleship Rock, near Jemez Springs in Sandoval County and
outcrops near Albuquerque in Bernalillo County, New Mexico. The most fossiliferous strata in New Mexico
is, in fact, near the town of Jemez Springs.
Crynoids, bryozoans, fusilinids, pelecypods, and gastropods, as well as
the numerous brachiopods species explained below, swam in a shallow sea. The most numerous member of the echinoderm
order were the crinoids. Less common
were the nautiloids, ammoids, and trilobites.
The numerous fish swimming in the primeval sea included bony fishes,
sharks, and lung fish. On land early
amphibians, giant insects, and a myriad plant species formed a canopy of
greenery —the first jungles of earth.
(For an in depth discussion of New Mexico’s most fossil rich zone in the
Upper Pennsylvanian Period, refer to this link.)
Note:
To zoom in and out, click on the photo below:
Brachiopods from the Madera Formation, New Mexico
Though the Upper Pennsylvanian Period of New Mexico
offers the collector a diverse range of species, from the Lower Mississippian
Period to the Late Pleistocene Epoch, the most abundant marine invertebrates in
the Madera Formation of North-central Mexico are the brachiopods, which I
collected near the US Park Service Ranger Station in Tijeras, New Mexico. For many fossil hunters brachiopods are
often confused with pelecypods. Pelecypods,
or bivalves, in addition to having a different biological makeup than
brachiopods, have different lines of symmetry.
In what biologist call bilateral symmetry, their top valve mirrors the
bottom valve, along the hinge line of the shell. Brachiopods symmetry, however,
runs along along the transverse plane, perpendicular to the hinge line. Seen from the side, their two halves are
actually asymmetrical, whereas clams and their kin are often almost identical.
The left side of the shell mirrors the right side of the shell. (A graphic description is given in this link.)
Note: To zoom in and out, click on the photo below:
