Return to Paleontologoy Archives
UPPER PENNSYLVANIAN PERIOD INVERTEBRATES OF NEW MEXICO
As the geologic demonstrates 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.
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 photos
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 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 photos below:
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 in Sandoval and Bernalillo Counties. 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 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 photos below: