PAGE 1 -- MONERA AND PROTISTA
MONERA
The Kingdom Monera includes those organisms that have prokaryotic cells. Among other things this means that there is no nucleus. Monerans that cannot photosynthesize are known as "bacteria" and those that can are "cyanobacteria". Bacteria are important as fossils only because they are the only form of life known for the earlier part of the Precambrian (the Archaean). Colonial Cyanobacteria create mats that trap sediment, forming a sort of hybrid fossil/sedimentary structure called a "stromatolite" (Greek = "layered rock"). These are most common in later Precambrian (Proterozoic) and Cambrian rocks, though they do occur in younger rocks deposited in unusual or stressful environments as well.
The first photograph is of some Late Pennsylvanian (Stephanian) spherical stromatolites from near Morgantown, WV. Notice that the large one on the left is broken open, revealing the thin laminae that give the fossil its name. The bar is 1 cm. (Photo by B. Carter)
PROTISTA
The Kingdom Protista includes most unicellular organisms with eukaryotic
cells. These cells differ from prokaryotic ones in having a nucleus, among
other things. Protists that photosynthesize are called "algae",
those that cannot are "Protozoa". Algae are important in geology
for a couple of reasons. First, some planktonic forms make good guide
fossils for determining the ages of rocks and making stratigraphic
correlations. Second, many colonial forms produce copious amounts of
carbonate sediment. By some estimates, most of the fine-grained limestone
in the rock record was produced by such algae. The
photograph at right shows a type of colonial algal skeleton called a "rhodolith".
These specimens, created by a species of Archaeolithothamnium, are roughly spherical, though flattened and other shapes also
occur. The name "rhodolith" comes from the Greek "red rock" in reference to
the red-pigmented algae that form the nodules, giving them a reddish color when
alive. As with the stromatolite shown above, the round shape comes from
the growth of the nodule by accretion of laminations, but in this case the
laminations are actually calcium carbonate secreted by the algae, not simply
trapped sediment. Once again the bar scale is 1 cm long. (Photo by
B. Carter)
Fossil protozoa are very common and useful to geologists because some make excellent guide fossils for stratigraphic correlation and others make good environmental indicators. There are some (called Radiolaria) that make their shells of silica, and produce "siliceous oozes" in deep water. These oozes can later become chert. Most protozoans make their shells of calcite, and these are called "Foraminifera" or "forams". The next three pictures are of Foraminifera of various types. The first is a large member of a common family called "nummulitids" (Latin = "coin-like") which are very common in Paleogene rocks. This specific one (Nummulites gizehensis) came from Middle Eocene rocks near El Fashn, Egypt. These are very useful guide fossils in the Paleogene of the Mediterranean region, where the Eocene and Oligocene were once known as the "Nummulitic" epoch. The scale is 1cm, suggesting a VERY large unicellular organism. (Photo by B. Carter)
The next photograph is of several specimens of "fusulinid" forams (Latin = "football-shaped"). These are also good guide fossils, but for Pennsylvanian and Permian rocks. This particular species is Triticites osagensis from Late Pennsylvanian rocks near Brownwood, TX. The scale is 1 cm. (Photo by B. Carter)
Both nummulitids and fusulinids are somewhat larger than might be expected of single cells. Some Middle Eastern nummulitids reached about 20 cm (8 inches or so) in diameter. Most forams are much smaller, typically the size of those barely visible on the microscope slide in the final picture. The scale is once again 1 cm. (B. Carter)
