CLASSIFICATION AND COLLECTING TECHNIQUES

PHYLUM CHORDATA:
A SPINAL CHORD AND VERTEBRA

This group is comprised of the highest forms of life on earth, and since man is part of this group, it is perhaps the most familiar. The term chordate simply means having a spinal or notochord which acts to interconnect the animals complicated nervous system. The vertebrates are members of the chordata which have developed a bony, jointed support for the notochord. The classification of the vertebrates is as follows:

VERTEBRATE FOSSIL CHARACTERISTICS

The following table consists of the general characteristics of vertebrate fossils which have been found in Arizona deposits. It is designed to aid in the identification of fragmentary specimens, and the collector should rely on specific publications concerning vertebrate paleontology or the advice of professionals for more detailed identification.

FISH: There exists a general misconception that all fish, because they have fins and live in water, should be grouped under the single biological class Pices (Lat. picis, fish). This would be no more true than lumping all terrestrial animals under the heading mammal.
Fossil Fish Characteristics:

CLASS AGNATHA

The jawless, sucking fish ranging from the Devonian (?) to the present. Modern examples of these primitive fish are the lamprey-eels, and the hag-fish. The living agnathous fish, the lamprey, is semiparasitic, attaching itself to other fish with a rasping sucker, and living off their flesh and blood. These are very rare as fossils, and non to my knowledge have been found so far in Arizona.

CLASS
CHONDRICHTHYES

The class Chondrichthyes contains approximately 850 species of skates, rays, and sharks. They have jaws, lots of teeth, paired fins, and a cartilage endoskeleton.
Cretaceous shark tooth Lamna
Paleozoic shark tooth Cladodus.
Cretaceous stingray tooth Ptycodus
Cartilaginous fish first appeared during the Devonian period and expanded in diversity during the Carboniferous and Permian before nearly disappearing during the great extinction that occurred near the end of the Permian. Some fragmentary evidence suggests cartilaginous fish were present during the Ordovician, although the best skeletal evidence is from the Devonian. Despite scanty skeletal presence (cartilage not preserving nearly so well as bone), shark teeth are common fossils in some deposits.
CLASS OSTEIOHTHYES
Osteichthyes are bony fish such as trout, flounder and bass and a whole lot of strange, extinct bony fish that are in the fossil record from Middle Devonian to present.The large extinct bony fish (right) Xiphactinus audax, along with the aquatic lizards called mosasaurs, was a major predator of the Cretaceous seas. This giant extinct "bulldog fish" was clearly a predator using its its long conical teeth to catch other fish as prey. The specimen was found by Michael Triebold in Lane County, Kansas, but fossils of this bony fish species have been found in the Cretaceous Mancos Shale of northeastern Arizona. Specimens are known ranging in size from a few feet up to 18 feet (6 meters). One fossil even contains a one meter long fossil of another fish Gallicus. From Triebold Paleontology, Inc.

CLASS PLACODERMI

Placoderms were the armored bottom-feeders of the early Paleozoic. Usually in Arizona a fossil collector will find the bony plates of the placoderm's head shield, isolated and difficult to identify. Complete placoderm fish like the one shown on the right are rare fossil specimens in any Arizona collection.
CLASS OSTEICHTHYES

The bony fish (Osteon = "bone"; "icthys" = "fish") are today the most diverse and numerous of all vertebrates. Bony fish (Class Osteichthyes) are first seen in fossils from the Devonian (about 395 million years before present). They differ from most of the cartilaginous fish in many ways. Importantly for the fossil record, the skeleton of most forms are composed of true bone which can preserve well. Most of the specimens you will find as fossils belong to the superorder Teleostei. Teleosts are the most successful of the fishes (they make up 95% of all fish species).

A herring, Kinghtia alta
Bony fish are also the most modern of the fishes (they evolved about 65 million years ago). The other common fish fossil in Arizona are the holosteans. Holosteans survive today as the garpikes (Lepisoste) which are also found as fossils in Arizona in rocks 225 million years old. The gar's scales are really tough being covered with a thick enameloid called ganoine which lies on a thick support of lamellar bone with a layer of dentine sandwiched between the two. In some Cretaceous deposits, like the Fort Crittenden Formation of Adobe Canyon in the Santa Rita Mountains, well preserved gar scales are abundant.
Fossil Garfish scales similar to these are very common in Arizona's Cretaceous Fort Crittenden Formation(Paleo Direct)
A modern Garfish, not much different from their fossil counterparts, only these start to stink after a while in your collection.
Teeth: Usually needle-like bony fish, or convex-concave blades in sharks. Skate teeth are rounded and nipple-like for use in mollusk crushing.
Bone: Usually thin, often preserved in complete skeletons, associated with flesh impressions or carbon. Vertebra concave on both ends. Scales are common fossils. These features are what make collecting fish. Like plants, smaller fish (which are easier to collect by the the avocational fossil hunter) are often found complete, and,well, look like fish. Shark teeth often make up a big part of a fossil hunter's collection because they can be so common in some places, they are easy to find because the shiny enamel catches your eye, and there is a certain charisma because the very word "shark" is intriguing to many people.
COLLECTING OF FOSSIL FISH
Well-preserved fossil fish are perhaps the most highly prized of specimens, with the possible exception of trilobite, in any fossil collection. Their remains occur most commonly in shales, with fragmentary fossils such as teeth and vertebra found in unconsolidated silts, mans, and conglomerates. 

With few exceptions, fossil fish are compressed, with bones well preserved, though distorted by pressure of rock and by current action prior to burial. The flesh of fish is often preserved by distillation or carbonization, though a great many complete fossil fish are merely impressions.

Although fossil fish are more common than most other types of vertebrate remains, they are by no means easy to find, especially in Arizona. Even if fossil fish are known to occur in a particular rock unit, prospecting blind for specimens can take up much of a collector's day or weekend. Since fish fossils are infrequently evenly distributed throughout a particular formation, a collector should always check the paleontological literature of an area before he goes out, especially with the intention of collecting fossil fish. 

Fossil fish are collected in much the same manner as plant remains. Overburden should first be removed from above a known fish bed allowing the collector to lift large slabs of shale. In this way, when the slabs of shale are split with a flat chisel, a good possibility exists that specimens obtained will be complete.

Specimens in shale or mudstone usually need little if any stabilization in the field, and can be easily transported to the laboratory. Large specimens, several feet in length, require methods of collecting beyond the scope of this book. It is advisable to call for professional help if such discoveries are made.

CLASS AMPHIBIA

Amphibians are tetrapod amphibious vertebrates which must return to water to reproduce. Their geologic range is from Devonian to present. Thank goodness the amphibians liked to get up on land and tramps across mudflats to get from one watering hole (and breeding ponds) to the next. In doing so they left a huge number of their footprints and trackways in Arizona rocks in the late Paleozoic (Permian) and the Early Mesozoic (Triassic). Fossil amphibian bones in Arizona are generally restricted to the Chinle Formation, and it is an odd geological imponderable that when you find tracks, bones are nowhere in sight, and visa versa. But don't give up on bones, they are there.

CLASS REPTILIA 

These are tetrapod vertebrates which do not need water for reproduction, because of the development of the amniot, or self-contained egg, housed in a hard, semi-porous shell. Reptiles are generally cold-blooded with scales or armor present. Their geologic range is from the Pennsylvanian to present. Arising from Paleozoic amphibian stock, reptiles became dominant in Arizona during the early Mesozoic. Many kinds of fossil reptiles can be found in Arizona, from the smallest lizards to the mighty archosaurs, the dinosaurs. Reptiles in Arizona have a geologic range from the Permian to the present.

CLASS AVES

The birds are thought to be glorified reptiles as they have many characteristics in common with the reptiles. Entirely warmblooded and feathered, the birds have a geologic range from the Jurassic to the present. Rare in Arizona, fossil bird bones have been found in Pliocene to late Pleistocene deposits. Giant Ice Age condor bones are found in caves of the Grand Canyon.

CLASS MAMMALIA

The warmblooded vertebrates which are characterized by having hair, and mammary glands on which young nurse. Mammals have a questionable geologic range because the earliest members of the class share a great many anatomical characteristics with the reptiles. Generally, the range is thought to be Triassic to present.
Gomphothere, a proboscidian found in the San Pedro badlands near Benson and St. David.
A well-preserved gomphothere molar
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