Bruce L. Stinchcomb, Ph.D.,
St. Louis Community College at Florissant Valley
St. Louis, Missouri 63135
Missouri's diversity in its fossils reflects the great diversity in its geology.
Strata ranging from the Precambrian to Pleistocene crop out within the state
(Branson 1944), and many of these yield fossils. The fossils are discussed
below, proceeding from the geologically oldest to youngest.
The oldest rocks in Missouri, which crop out extensively, are of Precambrian
(Proterozoic) age (Unklesbay and Vineyard 1992). These form the geological
center of the Ozark uplift and are primarily of igneous origin. Many of these
igneous rocks formed from cooling within the earth's crust and do not contain
fossils. More than half of Missouri's outcropping Precambrian rocks were
formed at the earth's surface, most originating from massive outbursts of hot
volcanic ash that welded itself into a very hard rock upon falling to the surface.
Interbedded within a thick mass of these welded tuffs are beds of water-laid
bedded tuffs and dirty sandstones.
Structures known as stromatolites, produced by blue-green algae (also called
blue-green bacteria or cyanobacteria), are found in these bedded tuffs in Iron
County. These stromatolites may have formed in a lake of volcanic origin. They
have a distinctive laminated morphology and have been given the form-genus
name Ozarkcollenia (fig. 1R). Ozarkcollenia occurs in limited areas of the
Ozarks and appears similar to Alcheringa, a type of stromatolite found in
Stromatolites, which represent the earliest record of life on Earth, were
produced by the life activities of communities of monerans. This usually
involved photosynthesis. But some stromatolites were formed by
nonphotosynthetic, chemotrophic bacteria. Some nonstromatolitic objects
that may be of biogenic origin also occur in these 1.5-billion-year-old rocks
in Missouri. Such fossil-like objects, frequently found in Precambrian rocks,
are known as dubiofossils. A dubiofossil is an object that may or may not be
of organic origin. A pseudofossil, on the other hand, is something that looks
like a fossil but has been determined not to be of biogenic origin. Precambrian
fossil-like dubiofossils occur worldwide, and the process of sorting out and
evaluating them is ongoing (Hofmann 1992).
Rock strata representing what would be some 800 million years of geologic
time are missing between Missouri's Precambrian rocks and the earliest
strata of the Paleozoic Era. In Iron, Madison, and St. Francois counties,
Middle Cambrian strata (Lamotte Sandstone) contain fossils of primitive
inarticulate brachiopods (fig. 1P) as well as mystery trackways that resemble
the tracks made by a motorcycle. These tracks, given the trace fossil name
Climactichnites (fig. 4E), represent one of the Cambrian paleontological
mysteries (Yochelson 1990).
The unit above the Lamotte Sandstone, the Bonneterre Formation, contains
typical Cambrian fossils such as trilobites (Lochman 1968), hyolithes,
brachiopods, and small snail-like fossils called Pelagiella (fig. 4D). Larger
mollusks called monoplacophorans also occur in dolomites of the
Bonneterre Formation (Stinchcomb 1975). Above the Bonneterre Formation,
slabby beds contain totally different trilobites from those of the Bonneterre,
including small perfect specimens (Stitt 1983) and horseshoe-crab-like
arthropods called aglaspids. Two trilobite genera from the Davis Formation
are named from the Old Lead Belt town of Elvins, Missouri: Elvinia sp. and
Elvinella sp. Elvinia gives its name to a biostratigraphic horizon, the Elvinia
Zone, found in many Upper Cambrian sequences throughout North America.
The names of these trilobites now serve as a kind of "memorial" to the town,
as "Elvins" has been incorporated into the city of Park Hills and officially
exists no more.
Massive cherty dolomites, the Potosi and Eminence formations of younger
Cambrian age, occur above the slabby beds of the Davis Formation. They
yield numerous snail-like fossils and monoplacophorans and a number of
trilobites (fig. 4F, G). MonopIacophorans reached their maximum diversity
toward the end of the Upper Cambrian. Cone-shaped monoplacophorans
(hypseloconids), spoon-shaped ones (proplinids), and even septate forms
(shelbyocerids) are present (fig. 1F-J, L).
The youngest Cambrian strata in Missouri are cherty dolomites of the
Eminence Formation, the cherts of which can be, locally, chock-full of
fossils (Bridge 1931). Among these are hemithecellids, a group of
mollusks that belongs to what are generally known as plated mollusks
(fig. 1D, E, K, M, N, Q). Paleontologists currently interpret these in
different ways, and like many fossils from the Cambrian Period, they
are puzzling and peculiar. One interpretation regards them as the plates
of primitive chitons. Another considers them representatives of an
extinct group of mollusks, possibly an extinct molluscan class. Many
other peculiar mollusks also occur in cherts of the Eminence, the
fauna of which is still being discovered. Above the Eminence Formation
is a series of strata that has, at various times during the past seventy years,
been placed in either the Cambrian or the Ordovician Period. Currently,
it is placed at the beginning of the Ordovician, but many of the fossils
have strong Cambrian affinities. In addition, spectacular stromatolite
reefs occur in these strata through out the Ozark region.
The Ozark region exposes an extensive sequence of strata representing the
earliest part of the Ordovician Period. These strata contain, among their
many fossils, one of the earliest cephalopod faunas; these mollusks had a
chambered shell like the pearly nautilus (fig. 1A-C). Although the earliest
cephalopods have shells that are small and slightly curved, suggestive of
the monoplacophoran genus Hypseloconus, unlike monoplacophorans
they have a large number of chambers and, most significant, a tube called
a siphuncle, which connected the chambers (fig. 1C). Cherts of the
Gasconade and Roubidoux formations are locally highly fossiliferous
and contain numerous mollusks such as gastropods, monoplacophorans,
and cephalopods (Heller 1954).
In the southernmost parts of the Missouri Ozarks, strata contain some of
the youngest Lower Ordovician fossils. Fossils of the lower third of the
Ordovician System are quite distinctive, compared with those of the middle
and upper parts of the Ordovician. Because of this, there was during the
1920s a proposal to establish another geologic system between the
Cambrian and the middle and upper parts of the Ordovician. This new
geologic unit, to be called the Ozarkian System, never was accepted by
the international geologic community.
Some of the youngest of Lower Ordovician fossils, like those from the
Smithville Formation, are found free in red residual clays, as perfect quartz
casts that weathered from the dolomites. These attractive fossils, because
they require no extraction from rock, are quite popular with collectors.
They include trilobites, which are rarely found complete in Missouri. One
of these, Lutesvillia bispinosa, like Elvinia, celebrates another small
Missouri town that no longer exists; Lutesville has been incorporated into
Marble Hill, Missouri.
A thick sequence of poorly fossiliferous strata occurs above the Lower
Ordovician. In a few areas in southeastern Missouri, these strata have
yielded the teeth of conodonts, chordatelike animals once considered
to represent some of the oldest vertebrates. Above these normally
unfossiliferous beds are the Plattin, Decorah, and Kimmswick formations,
limestones often full of fossils. These Middle Ordovician fossils have a
more "modern" look than do the fossils, from the older strata. The Middle
Ordovician yields the first abundant corals, bryozoans, and echinoderms
such as crinoids, paracrinoids, and starfish (Unklesbay 1978).
Paracrinoids, one of a number of, extinct echinoderm classes established
during the past fifteen years, resemble morel mushrooms. Representatives
of a number of these echinoderm classes are found in deeply weathered
limestones south of St. Louis (fig. 2I) and are restricted to the Middle
Ordovician limestones of the midwestern states.
Other extinct echinoderm classes found in Middle Ordovician rocks of
Missouri include the coinlike edrioasteroids (fig. 2H), edrioblastoids, and
cystoids (fig. 2E, F).
The cystoid Pleurocystites lacks the five-sided symmetry characteristic
of most echinoderms; it has bilaterial symmetry and somewhat resembles
some forms of early vertebrates. The Middle Ordovician Kimmswick
Limestone yields most of these strange echinoderms; they are exposed
by natural etching on deeply weathered surfaces of limestone under red
Middle and Upper Ordovician strata in northeastern Missouri produce a
number of spectacular trilobites such as Isotelus and Ceraurus, both genera
prized by collectors. The sunflower "coral," Receptaculites, is not a coral at
all. This paleontological puzzle is a common fossil in northeastern Missouri
(fig. 2B). Receptaculites has been considered a sponge, an alga, or part of
an extinct kingdom of multicellular animal-plant-like organisms.
The Upper Ordovician Maquoketa Formation of northeastern Missouri is
famous for producing large numbers of small, eyeless trilobites of the species
Ampyxina bellutula (fig. 2J). Other larger trilobites, such as Isoletus and
Bumastus, can occur with graptolites and conularids (fig. 2G). Graptolites are
primitive forms of the phylum chordata, the same phylum to which vertebrates
belong. Conularids are thin, phosphatic, cone-shaped shells whose taxonomic
affinities, like those of the receptaculitids, remain totally problematic.
The Silurian, compared with the Cambrian and Ordovician, has limited outcrops
in Missouri. Graceful, delicate crinoids and starfish are probably the most
desirable Silurian fossils known from the state. Both taxa have been found in
the vicinity of Cape Girardeau. Trilobites occur in two areas: (1) in red
iron-bearing limestone, the Bainbridge Formation, along the Mississippi River
near Cape Girardeau, and (2) in slabby Silurian dolomites of northeastern
Missouri. Some nondescript plantlike compressions, from shales interbedded
with these trilobite-bearing strata, appear to be fragments of primitive, leafless
land plants. They represent part of the earth's first "coat" of green plants that
covered the land areas of the Ozark region during the Silurian Period.
The slabby dolomite layers of the Edgewood Formation in northeastern Missouri
yield trilobites (Dalmanites sp.) and delicate crinoids as well as fossil tetracorals.
Here also, in slabby siltstone layers, are fragments of early fossil vegetation,
primitive leafless plants called psilophytes.
Devonian strata, like those of the Silurian, have a somewhat limited distribution
in Missouri. Rocks of Early Devonian age occur in southeastern Missouri, where
the most spectacular fossil is the huge crinoid Scyphocrinus sp. (Bassler 1914).
This crinoid lived as floating colonies in Lower Devonian seas (fig. 2K). The
bulblike floats of this large crinoid are sometimes found along with the giant
calyx, usually in slabs forming the bed of the Mississippi River, accessible
only when the water level is particularly low.
Fossil vertebrates appear with some regularity for the first time in Middle
Devonian strata of northeastern and central Missouri. These are, primarily,
the teeth and spines of shell-crushing, sharklike animals and the teeth of
bony armored fish called placoderms. However, invertebrate fossils are
much more common than vertebrate fossils in Missouri's Devonian strata.
Corals, abundant in Devonian rocks of central Missouri, include well-known
types such as Hexagonaria and Favosites, particularly abundant along
Cedar Creek in Callaway County. Other fossils from Missouri's Devonian
rocks include brachiopods, trilobites, pelecypods, cephalopods, and
Isolated occurrences of fossiliferous Devonian rocks are also found in parts
of the Ozark region. These fossils, preserved in a gray quartzite, include
trilobites and a variety of mollusks. These isolated Devonian outcrops
represent small remnants of strata that have been removed by erosion in
most parts of the Ozarks. These remnants were usually preserved in ancient
sinkholes. Some of the fossils found in these Paleozoic outliers are
different from those found around the edge of the Ozarks. The outliers
have a higher proportion of mollusks than do Devonian outcrops beyond
or at the edge of the Ozarks.
Large parts of Missouri were covered by warm shallow seas during the
Mississippian Period, and extensive limestone beds were deposited. These
limestone beds yield a great many invertebrate fossils, including various
crinoids. Some of the largest Paleozoic crinoid faunas in the world are found
in the limestones and cherts of Mississippian age in Missouri and surrounding
states (fig. 3J, L). The large, primitive sea urchins (echinoids) are legendary.
Around 1910, zinc mines of southwestern Missouri produced beautiful
specimens of these echinoids, some the size of oranges, and each exquisitely
covered with a fine sphalerite druse (fig. 3N). The melonlike echinoid
Melonechinus, found in the St. Louis area, is also very desirable in the eyes
of collectors (fig. 3M).
Colonial and solitary rugose and tabulate corals are common fossils in
Mississippian strata (fig. 2D). Paleozoic corals are really different from
corals living in warm parts of today's ocean. Modern corals (hexacorals or
scleractiniarians) probably did not originate directly from Paleozoic types.
They may have evolved from some nonskeletonized common ancestor that
existed in the Paleozoic but left no fossil record. Mass extinctions at the
end of the Paleozoic Era (Permian Period) wiped out rugose and tabulate
Other fossils that occur in Mississippian strata, often in great abundance,
are brachiopods (fig. 3H), bryozoans, blastoids (fig: 3C), mollusks, and the
teeth and spines of sharklike fishes (fig. 3D, E; fig. 4A-C).
Most of the invertebrates that lived in Mississippian seas were a food source
for sharks and sharklike fishes. The crushed or punctured tests of crinoids
and other invertebrates show the efficiency of these predators (fig. 3G). The
flat, crushing teeth and serrated dorsal spines of these fishes are relics from
Mississippian seaways (fig. 3A, B).
Rocks and fossils of the Pennsylvanian System in Missouri are quite different
from those of the Mississippian. Invertebrate fossils in Pennsylvanian strata
are dominated by brachiopods, particularly large productids. Crinoids are
less abundant than they were during the Mississippian; however, some superb
crinoids have been found in the Kansas City area. Other common fossils in the
Pennsylvanian rocks of Missouri are fusulinids. These are the "shells" or tests
of protists, single-celled organisms, that reached almost an inch in size; these
were giants among single-celled life forms.
Pennsylvanian strata in the northern part of the St. Louis area produce a
variety of mollusks (Knight 1930). Here a sequence of thin limestones,
partly of algal origin, produces a rich fauna of mollusks, particularly
gastropods, scaphopods, and cephalopods (fig. 3F). These Pennsylvanian
beds differ both in the appearance of strata and in contained fossils from
those of nearby Illinois or western Missouri; however, out-crops are limited,
and urbanization of the St. Louis metropolitan area has covered many of
the fossil sites.
The presence of abundant, diversified land plants sets the Pennsylvanian
strata apart from earlier systems. A variety of fossil land plants such as true
and seed ferns, tree and herbaceous ferns, horsetail-scouringrush-Iike trees
(Calamites sp., fig. 4N), scale trees (fig. 4K), and Cordaites (primitive conifers?)
occur locally in abundance in Missouri's Pennsylvanian rocks. These plants were
the source of plant carbon that produced the relatively thin coal beds of western
and northern Missouri.
Attractive and well-preserved compressions of Pennsylvanian vegetation are
found in abundance at Knob Knoster near Warrensberg, Missouri, in buff
shales of the upper Middle Pennsylvanian Pleasanton Group. Fourteen miles
south, near Windsor, old spoil piles have yielded ironstone concretions
containing fossils similar to those of the famous Braidwood (Mazon Creek),
Another Pennsylvanian fossil group that is widely dispersed in collections
from Missouri consists of clams (pelecypods) preserved on the surface of
slabs of hematite. Of interest both as mineral and fossil specimens, these
hematite slabs are found scattered over fields in parts of Platte and Clay
Silicified logs of tree ferns, some quite large, occur in parts of the Ozarks.
These trees were probably buried in silica-rich clays that were preserved
from erosion because they were deposited in sinkholes; such ancient sinkhole
surfaces are known as paleokarsts. Paleokarst is a unique feature of the
geology of the Ozarks that covers almost half of Missouri. Some of the
plant fossils in these paleokarsts represent the flora of a drier, more upland
environment; and many of the plants differ from the more common ones
associated with coal seams (Bassom 1968).
Upper Pennsylvanian strata in the Kansas City area have yielded trackways
and bones of amphibians and, possibly, also those of early reptiles. In the
Winterset Limestone, large, coiled nautiloid cephalopods (fig. 2C) and other
well-preserved marine invertebrates are found. The Pennsylvanian is the time
of the appearance of the first reptiles, a harbinger of what was to come later
in the Mesozoic Era---the age of reptiles. Occasionally, jaw fragments and
bones of rare amphibians are found in sediments, sometimes deposited
Jurassic rocks may occur in Missouri. Some clays, associated with paleokarsts
in the southeastern Ozarks (Bollinger and Butler counties) may have been
deposited during the Jurassic. A peculiar fossil turtle, Namocheyles sp., in
which the shell was covered with little beadlike knobs, occurs in clays in one
of these paleokarsts. Beaded turtles are more representative of the Jurassic
than they are of any other part of geologic time.
Cretaceous rocks and fossils are found in southeastern Missouri. Marine
Cretaceous fossils occur on Crowley's Ridge, a hilly area southeast of the
Ozarks, which exhibits an entirely different geology from that of the nearby
Ozarks. Molds of various mollusks, including ammonites and nautiloids,
have been found near Bell City in Stoddard County (fig. 4I, J). Bones of
mosasaurs, one of the large marine reptiles of the Mesozoic, have also
been found in the Bell City area. Cretaceous rocks of southeastern Missouri
also yield leaves of some of the first flowering plants, the angiosperms
(fig. 4L, M). During the Cretaceous, broad-leafed, seed-producing plants
became abundant for the first time; these plants included such tropical
forms as fig, cinnamon, and magnolia.
One of Missouri's paleontological enigmas are the bones, teeth, scutes,
and gastroliths of dinosaurs and other reptiles found in clays deposited
in ancient sinkholes in the southeastern part of the Ozarks. The only
known dinosaur from Missouri was found in Bollinger County while a
cistern was being dug on the Chronister farm in 1941. The bone-bearing
clay was apparently deposited in a solution structure in what is a geologically
complex area. Most dinosaur bones found at the Chronister site are now
thought to be those of hadrosaurs (duckbilled dinosaurs); however, originally
they were thought to be those of one of the last of the sauropods and were
given the name Neosaurus missourensis.
Strata of the Cenozoic Era, like those of the Mesozoic, have limited
occurrence in Missouri. Strata representative of the early part of the
Cenozoic occur on Crowley's Ridge in the southeastern part of the state.
The Cenozoic Era, the age of mammals, is the time of the appearance of
many life forms that dominate and characterize the modern world. Marine
mollusks of the Cenozoic are similar to those found in modern seas.
Impressions of the leaves of such flowering plants as Magnolia (fig. 4H)
and oak are locally common in clays on Crowley's Ridge.
Peculiar fossil mosses (bryophytes) have been reported in Eocene shales
of Crowley's Ridge in Arkansas, and similar fossils occur near Dexter,
Missouri. Bryophytes are primitive land plants that appear, from their
primitive nature, to be like fossils in ancient strata of the lower Paleozoic.
However, the fossil mosses of Crowley's Ridge are much like mosses
living today (fig. 4,0).
Strata of the later part of the Cenozoic Era, the Quaternary Period,
usually consist of sand, gravel, or clay that cover large parts of Missouri
as well as other parts of the Midwest. LocalIy, these sediments contain
fossil bones, teeth, and land vegetation of kinds characteristic of cold
climates. Most of the Quaternary consisted of the "ice age," or the
Pleistocene Epoch. Some of the largest of the fossil bones found in
Pleistocene sediments belonged to such extinct animals as the mammoth,
mastodon, giant beaver, and ground sloth (Mehl 1962). Sediments that
form the beds of the Missouri and Mississippi rivers were deposited during
both the Pleistocene and Holocene epochs of the Quaternary Period and
can yield a variety of ice-age bones on gravel bars, particularly when the
rivers are low.
During periods when the glaciers diminished and melted---the interglacial
stages of the Pleistocene--the climate of Missouri and the rest of the
Midwest was warmer at times than it is today. During these interglacial
stages an ecosystem characteristic of lower latitudes shifted northward,
and Missouri became the home of such animals as the peccary, tapir, and
even giant turtles. When the climate turned cooler with the onslaught of
another glacial advance, Missouri's Pleistocene ecosystem shifted to that
characteristic of a colder climate and a higher latitude.
Missouri is famous for occurrences of ice-age mammals associated with
swamps and bogs (Mehl 1962). Occurrences of mastodons in swamps
along the Pomme de Terre River of the western Ozarks, along the lower
Gasconade River, and at Barnhart, south of St. Louis, were all worked by
German emigrant Albrecht Koch during the mid-nineteenth century. Koch's
mastodon site south of St. Louis, now a state park, focuses on these animals,
which may have been killed by some of the earliest humans, the paleo-Indians.
It was in the late Pleistocene that the geologic record joined that of man and
set the stage for the last epoch of the Quaternary, the Holocene Epoch. The
Holocene comprises the past twelve thousand years of more than 4.6 billion
years of Earth's history.
Bassler, R. S. 1913. Notes on an unusually fine slab of fossil crinoids.
Proceedings U.S. National Museum 46(2009):57-59.
Basson, P. W. 1968. The fossil flora of the Drywood Formation of southwestern
Missouri. Vol. 44 of University of Missouri Studies. Columbia, Mo.
Branson, E. B. 1944. The geology of Missouri. Vol. 19 of University of Missouri
Studies. Columbia, Mo.
Bridge,J. 1931. Geology of the Eminence and Cardareva quadrangles, 1930.
Missouri Bureau of Geology and Mines. Vol. 24.
Heller, R. L. 1954. Stratigraphy and paleontology of the Roubidoux Formation
of Missouri. Missouri Geological Survey and Water Resources. Vol. 35.
Hofmann, H. J. 1992. Megascopic dubiofossils. In The Proterozoic biosphere:
A multidisciplinary study, ed. by J. W. Schopf and C. Klein, 413-19. New York:
Cambridge University Press.
Howe, W. B. 1966. Digitate algal stromatolite structures from the Cambrian
and Ordovician of Missouri. Journal of Paleontology 40(1):64-77.
Knight, J. B. 1930. The gastropods of the St. Louis, Missouri, Pennsylvanian
outlier. Journal of Paleontology 4:1-88.
Lochman, C. 1968. Crepicephalus faunule from the Bonneterre Dolomite
(upper Cambrian) of Missouri. Journal of Paleontology 42(5):1153-62.
Mebl, M. G. 1962. Missouri's ice-age animals. Missouri Geological Survey
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Stinchcomb, B. L. 1975. Paleoecology of two new species of Late
Cambrian Hypseloconus (monoplacophora) from Missouri. Journal of
Paleontology 49(2):416-21. ---. 1986. New monoplacophora (Mollusca)
from Late Cambrian and Early Ordovician of Missouri. Journal of
Stinchcomb, B. L., and G. Darrough. 1995. Some molluscan problematica
from the Upper Cambrian-Lower Ordovician of the Ozark uplift. Journal of
Stitt, J. H. 1983. Enrolled Late Cambrian trilobites from the Davis Formation,
southeast Missouri. Journal of Paleontology, 57:93-105.
Unklesbay, A. G. 1978. Common fossils of Missouri. Columbia: University
of Missouri Press.
Unklesbay, A. G., and J. D. Vmeyard. 1992. Missouri geology: Three billion
years of volcanoes, seas, sediments, and erosion. Columbia: University of
Wittlake, E. B. 1968. Fossil mosses from the Upper Wllcox (Lower Eocene)
of Arkansas. The American Midland Naturalist 80(2):543-47.
Yochelson, E. L., and M. A. Fedonkin. 1993. Paleobiology of Clilmactichnites,
an enigmatic Late Cambrian fossil. Smithsonian contributions to
paleobiology 74. Washington, D.C.: Smithsonian Institution Press.
Bruce L. Stinchcomb, Ph.D.,
Publication: Rocks & Minerals Vol. 72, No. 6 (11/01/97)
This web publication authorized by: Dr. Bruce L. Stinchcomb