I've devoted a number of pages in Arizonabc.com to invertebrates, because these are the ones you will come across most of the time. First the itty bitty things that you might at first overlook when hitting the outcr op. Once you discover the world of fossils best seen under magnification, you might be hooked. These minions are everywhere, if you know how to look for them.

PHYLUM PROTOZOA Protozoa are single celled and are the simplest and most primitive of animals preserved as fossils. Some are colonial but most are single, free living forms which perform all life functions independently.

Permian fusulinid

Living example of diatoms

Protozoans often secrete hard shells called a "test" which offer them protection. These hard parts become fossilized and provide the only record of the history of the group from their early beginnings. The group is composed of a large and variable number of animals of every size, shape and habitat, from aquatic to parasitic. Certain fossil protozoans are valuable as fossils because of their use in correlating rocks in the oil industry.
Although most are small and microscopic, a group in the past called the foraminifera grew to large size, large enough to be seen with the unaided eye in many Arizona formations. These forams, ranging from .01 to 190 mm., are common in many of Arizona's Pennsylvanian through Mississippian limestones. Unless weathered out in three dimensions like the fusulinds shown above, when limestone is broken with your rock hammer, you see these rice-size protozoa in cross section, as photographed at the right.
You love fossils but have a space or spousal problem? Regardless, you can collect, study and enjoy tiny specimens. In fact, if you collect microfossils, you'll be able to store some 200,000 average sized foraminifer in the average matchbox and over one and a half million in the larger household- sized matchbox, or millions in a cigar box.
Try that with trilobites or ammonites! Apart from the saving in storage space what are the other advantages in collecting small fossils? They are easier to collect because you just collect a sample of the sediment and don't have to spend hours in the cold winter rain, or hot desert sun looking for them. To study microfossils you will need a few special pieces of equipment - a binocular microscope and some good quality sieves. Some tiny fossil critters can be clearly looked at with just a magnifying glass.
 I recommend that you forget about these because the processes of collection and preparation are both difficult and often dangerous because they require some pretty strong acids. The conodonts ("worm") jaws on the pin-head on the left would be considered monsters to a microfossil collector. Really, if you're an avocational fossil collector, size really doesn't matter. You'll find a way.
"Microfossils" are roughly 0.05 to 2mm in size are most often remains of the complete hard parts of organisms, the common ones are foraminifer and ostracods." Nanos", that is nanofosils, are truly microscopic and might be such things as coccoliths, dinofiagellate cysts and pollen.

Big for a microfossils

Microfossils are almost always present to one degree or another, but its best to look in rocks that are poorly cemented, so that you can dis-agregate (break down) the grains to have a clear look at the fossils. In many Paleozoic rocks you will probably have to be content with looking at fossil cross sections or microfossils that that are seen in relief on the surface of weathered limestone. You'll also notice that sedimentary rocks that have formed lots of tiny things are compromised by the crystal growth and are either gone or distorted. Sediments laced with iron sulfides (marcasite not pyrite) often have the fossils rotted by the marcasite and sulfuric acid or dissolved away completely.
Nanofossils, or fossils too small to be observed in the field without having a high-powered microscope, are usually collected blind, and brought back to the laboratory in chunks of matrix to be examined later. Often, if unsure of a sample, a collector can guess the content of his sample by feel: microfossils are infrequently found in clastic rocks (composed of sediments coarser than silt), and most frequently found in clayey rocks (clay and many shales) which feel soapy or talc-like, a phenomenon caused by the millions of spherical specimens rolling upon one another.
Micro fossils as seen under high magnification. A whole 'nother world.

Larger microfossils, such as foraminifera ranging in size from one millimeter to more than ten centimeters, can be collected much in the same manner as other macro, or readily visible, fossils. An absolute necessity for collecting such specimens is the lOX or more powerful hand lens. Often obscure, foraminifera are best observed on weathered surfaces or on freshly broken surfaces moistened with the tongue.

Forams are best observed in the direct sunlight, and as a collector should remember, nothing helps more than knowing what you are looking for. Study the literature and learn to recognize the many shapes of microfossils and small macrofossils as they are easily, and often, overlooked even by the professionals. Rick Hill, an astronomer in Tucson who normally looks at the big picture, likes really tiny fossils. He's developed new techniques for
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