Geology Lab: Introduction to Paleontology

In order for an organism to be preserved it must meet two criteria:

1.) Possession of hard parts such as bones, teeth, or exoskeleton. These remains are more likely to be preserved than organisms with only soft part. 2.) Rapid burial in a medium capable of retarding decomposition such as fine-grained sediments on shallow sea bottoms, clays, and sometimes volcanic ash. If the organism is not buried, it can be destroyed by: Biological means (predators, scavengers, and bacteria) Mechanical activity (wave action or crushing) Chemical (atmosphere or dissolution)

Ancient peoples

Ancient peoples thought that fossils were placed in rocks by supernatural beings as a prank. Around 450 B.C., Herodotus, a Greek historian, first suggested that these remains were from sea creatures that lived when the ocean covered the land, but this hypothesis was abandoned by Aristotle who argued that the shapes grew within the rocks. Some people even argued that fossil shells formed when seeds dropped by clouds washed down into the cracks and grew inside rocks. The concept of inorganic growth remained firmly entrenched until the Renaissance.

Phylum Arthropoda

Arthropods represent over 80% of all living animal species (both invertebrate and vertebrate) and have adapted to all habitats. Arthropods have a chitinous exoskeleton, and were some of the first organisms to appear in the fossil record during the Cambrian. Because their exoskeleton does not lend itself to preservation, only a few groups have left a significant fossil record.

Because

Because not all organisms have hard parts and undergo rapid burial, the fossil record is not a completely accurate representation of the history of life on Earth. Only a small percentage of the Earth's living organisms have been preserved as fossils; as such the fossil record is very incomplete because of surface processes that destroy organic remains, tectonic events, deep burial and metamorphism, but in spite of all these things, fossils are quite common.

Phylum Brachiopoda

Brachiopods are sessile benthonic organisms which live on shallow sea bottoms. Their fossil remains are very useful in stratigraphic correlation as age indicators, depth indicators, and in their evolutionary development.

Phylum Bryzoa

Bryzoans are small marine animals that live in colonies. They occupy a variety of habitats, and can be found on rocky bottoms in clear, shallow seas and deep water environments.

Burrows and Borings

Burrows and Borings form when animals dig into soft sediment in search of food or shelter and produce a burrow. Often burrows are filled with fine sediment which preserves them. Borings are holes usually made into wood or shells because the animal is in search of food or shelter.

William Smith

By the early 1800's, work by William Smith and others had found that different fossils occur in different layers of rock within a sequence of sedimentary layers, and the layer at which the species disappeared from the rock record represents the time it went extinct, the premise of the Principle of Biological Succession. Work by Charles Darwin and Alfred Russell Wallace on organic evolution and natural selection, aided by the geologic time revolution, led the way to a greater understanding of the fossil record, and what we know today about Earth history.

Carbonization

Carbonization is the most common method of preserving soft parts. After an organism is buried in sediment, the remains are subjected to higher pressures and temperatures which drive off the volatile substances such as hydrogen, nitrogen, and oxygen. The more stable substances, primarily carbon, are left behind as a film, often preserving very detailed structures.

Carl Linnaeus

Carl Linnaeus (1707-1778), a Swedish botanist, physician, and zoologist, was the father of modern taxonomy. He laid the foundation for binomial nomenclature, the systematic means of classifying animals and plants, providing an orderly approach to studying and identifying organisms that is still used today. Carl Linnaeus, a pioneer in the systematic study of previous life forms.

Phylum Cnidaria

Cnidarians include modern day representatives such as jellyfish, corals, and others; as well as those of paleontological importance. Cnidarians are important environmentally as their presence can give some indication of water temperature, salinity, turbidity, and available nutrients in paleoenvironments. They are also important as a part of the fossil record; their rapid evolutionary development allows many species to serve as index fossils.

Concretions

Concretions are large concentrations of cementing material and they are found in a wide variety of shapes and sizes. Weathering often reshapes them into forms which resemble organic structures. In Nacogdoches, ironstone concretions are commonly observed as they are more resistant than the surrouding material. As weathering and erosion occurs, these concentrations are left behind as erosional remnants.

Cone-in-Cone

Cone-in-Cone structures appear to be a series of cones packed one inside the other. Their origin has been the subject of much discussion, but many believe them to be the result of pressure. They have been confused with organic structures because they exhibit transverse ridges and longitudinal striations.

Coprolites

Coprolites are fossilized fecal pellets or excrement from animals. These traces provide clues as to the animal's eating habits and anatomical structure. These can be particularly important when the organism is extinct.

Dendrites

Dendrites are branching patterns of a mineral substance which resemble a fern or a tree in silhouette. The mineral substance is usually manganese dioxide or pyrolusite and appears as an encrustation in cracks, crevices or joints from precipitating waters.

Fossil Groups

During the next few labs on fossil identification, we will primarily learn to identify invertebrate fossils (organisms that do not have a backbone or spinal cord) based on their morphological characteristics. These characteristics are the result of the evolutionary path these particular species took, the habitat in which they lived, and the mode of life practiced by these organisms. Some of the various phyla we will study:

Phylum Echinodermata

Echinoderms are composed of calcareous plates that knit together to give these organisms a spiny outer skin. They live along sea bottoms and can be attached or free-moving. Attached echinoderms are mostly known from fossil remains. Both attached and unattached echinoderms have representatives living today.

Index Fossilsl

Fossils can be excellent indicators of geologic time. Many fossils have a relatively short life span and can be used as time equivalent "guides" for the purpose of correlating rock units. Based on the Principle of Biological Succession, these fossils also help geologists assign a relative age to these units. Fossils that appear within a limited geologic time range are called index fossils and should possess four characteristics: Easily identified, Abundant, Have a wide geographic distribution, Have a short (limited) geologic range. These index fossils are used by stratigraphers to correlate rock units at the surface and in the subsurface, using well logs and cuttings. Microfossils are particularly important in the subsurface, as many smaller samples can remain intact during drilling activity and help geologists to trace specific rock units.

Modes of Fossil Preservation

Fossils may be preserved as direct evidence in either an altered or unaltered state, or as indirect evidence in the form of molds, casts, or trace fossils. Types of direct evidence include: Unaltered preservation, carbonization, permineralization, and replacement.

Gastroliths

Gastroliths are well-rounded, polished stones believed to aid in the digestion of food in an animal's stomach. Some birds that live today, and their Mesozoic relatives, the dinosaurs, swallowed these stones to help digest the large amount of vegetation needed to sustain their bodies. The stones became pitted and rounded due to gastric acids and grinding in the animal's stomach.

Georges Cuvier

Georges Cuvier (1769-1832) expanded upon the work by Linnaeus, incorporating both fossils and living species into the classification. He is also well known for establishing extinction as a fact, a controversial speculation at the time. His study of the rock units of the Paris basin established the basic principles of biostratigraphy.

Habitats of Marine Life

Habitat is the natural environment of an animal or plant and the study of the relationship between the organism and its environment is called ecology. Paleoecology deals with ancient organisms and their relationship to their natural habitat. By studying present day organisms and the environments in which they live, we can make inferences about ancient organisms and their environments. If an animal assemblage today is found to be living in a shallow marine environment, then a similar fossil assemblage in a rock layer probably was deposited in a similar shallow marine environment sometime in the geologic past. Fossils are excellent indicators of the environment or habitat in which they lived.

The systematic nomenclature for horse and man

Horse: Animalia, Chordata, Mammalia, Perissodactyla, Equidae, Equis caballus Man: Animalia, Chordata, Mammalia, Primata, Homindae, Homo sapiens Oyster: Animalia, Mollusca, Bivalvia, Pterioda, Ostreidae, Crassostrea virginica Red Oak Tree: Plantae, Anthophyta, Magnoliopsida, Fagales, Fagaceae, Quercus rubra

Curiosity

In spite of theological resistance, many people expressed curiosity about the world and the possibility that these remains were in fact ancient organisms that had inhabited our world in the past. Nicolas Steno, James Hutton and their contemporaries were attempting to comprehend geologic time; their work set the stage for the acceptance of previous life forms and their preserved remains as a catalog of the Earth's biological evolution.

Indirect Evidence

Indirect evidence of organisms occurs when the actual organism is not preserved, but evidence of the existence of the organism is preserved as a trace fossil. Trace fossils are valuable to geologists because they provide us with information of water depth, food supply, rates of sedimentation, and feeding habits. They are sometimes the only indicators we have to reconstruct the organisms' habits, because skeletal remains have not been preserved. The study of traces is called ichnology.

Habitats can be subdivided based upon water depth

Littoral: this zone is between high and low tide and contains those animals and plants which can withstand periodic episodes of wetting and drying as well as wave activity. Neritic: Neritic is the area between low tide and 600 feet (around 200 meters). There is usually good sunlight penetration of the water column in this zone as well as a plentiful food supply. For this reason, a large variety and number of organisms can be found in this environment. Bathyal: From600 feet to 6000 feet (around 2000 meters) below the water surface is referred to as the bathyal zone. It is characterized by cold temperatures and great pressure. Numerous organisms have adapted to these conditions and occupy habitats in this region. Marine habitats are areas within the ocean defined by water depth and sunlight penetration. Many organisms, particularly those that are attached to some substrate and filter their nutrients from seawater, depend on photosynthesis to produce micro-nutrients.

Mary Anning

Mary Anning (1799-1847) was a British fossil collector and paleontologist who became known around the world for her important finds in Jurassic marine beds in the cliffs along the English Channel. She discovered the first ichthyosaur skeleton that was correctly identified; the first two plesiosaur skeletons, the first pterosaur skeleton located outside of Germany; and important fish fossils. Her observations also played a key role in the eventual understanding that coprolites, known as bezoar stones at the time, were in fact fossilized feces and that belemnite fossils contained fossilized inc sacs similar to those in modern cephalopods. Her work contributed to fundamental changes in scientific thinking about prehistoric life and the history of the Earth. Mary Anning, one of the first female paleontologists, was instrumental in helping define Mesozoic life in Great Britain. Although she was denied admittance to the Geological Society of London, she was later recognized as one of the leading scientists of her time.

Mode of Life of Marine Organisms

Mode of life refers to how marine organisms live today or lived in the past. Often, even though the animal is extinct, we can determine the mode of life based on certain features found on a fossil.

Molds and Casts

Molds and Casts are formed when buried shell material is progressively dissolved, leaving a void in the rock which represents superficial features of the organism. If an "impression" in mud is made representing the outside of the shell, an external mold is formed. Sediment may fill the interior of the shell preserving the internal anatomy of the organism and thus form an internal mold. Internal molds are sometimes referred to as "steinkerns" (stone kernel). Because a mold forms by the dissolution of original shell material, a void is created. When the void space is filled by a mineral substance, a cast forms and is a replica of the original shell.

Phylum Mollusca

Mollusks are generally soft-bodied, un-segmented creatures with an external shell or an internal shell (although some have no hard parts such as slugs). This phyla is divided into five classes, but only three are important as fossils.

The Fossil Record

Most fossils are found in sedimentary rocks, where they are unequally distributed both horizontally and vertically. As environments change, so do the organisms that live there; thus fossils are indicators of environmental conditions and evolutionary trends. They are also useful for determining the relative ages of rock units and a record of organisms that have lived in the past that are now extinct. Fossils may be preserved as direct evidence in either an altered or unaltered state, or as indirect evidence in the form of molds, casts, or trace fossils.

Morphological Characteristics

Most organisms have a specific set of characteristics that help identify those species. One of the easiest ways to identify fossils is to first identify the symmetry. Symmetry refers to the orderly arrangement of parts of an object in relation to lines, planes, or points. Some organisms have radial symmetry, bilateral symmetry, pentameous (five-sided) symmetry, or no apparent symmetry at all. Radial symmetry is the symmetrical repetition of parts around an axis. Any vertical section through the center of the object will divide the objects into symmetrical halves. Common examples of this would be the division of a pizza, or any circular object. Bilateral symmetry is the symmetrical duplication of parts on either side of a plane. The plane divides the object into two halves that are mirror images of each other. Pentameous symmetry is common in Phylum Echinodermata, both in the fossil record and living species. Symmetry is one of the morphological characteristics used to classify fossil species. Radial symmetry divides a circular object into symmetrical halves. Many fossil shells exhibit bilateral symmetry and Phylum Echinodermata often exhibits pentamerous symmetry.

Robert Hooke

Robert Hooke, an English naturalist philosopher, published a book in 1665 called Micrographia. One of the observations in his book was a comparison of the microscopic structure of ordinary wood to fossil wood, leading him to conclude that fossilized objects like petrified wood and fossil shells were the remains of living things "soaked in petrifying water laden with minerals", one of the first scientific references to fossil preservation. Hooke was also one of the early proponents of organic evolution and believed that fossils provided reliable clues to the past history of life on Earth, and that in some cases they might represent species that had become extinct through some geological disaster. Robert Hooke's microscope used to identify fossilized wood.

Fossils

Rocks throughout the world contain remains of previous and existing life forms, commonly known as fossils. Fossils, from the Latin derivative fossilis, means "dug out" and originally referred to any object that had been dug out of the ground. As the field of paleontology, the study of fossils, evolved, the definition of a fossil was revised to mean "a naturally preserved remain or trace of an organism which has lived in the geologic past." Therefore, tools and implements devised by man would be artifacts, not an actual fossil.

Septarian Nodules

Septarian Nodules are structures normally made of mudstone and are characterized by cracks which widen toward the center and die out near the margins. The crack system is usually polygonal and filled with a crystalline substance, most commonly calcite. It is thought that the formation of these structures begins with fine-grained, water saturated sediment which dehydrates and produces shrinkage-crack pattern. Filling of the cracks occurs with precipitated mineral matter. When many septarian nodules are weathered, the interior vein system appears to be "turtle backs" and is classified as a pseudofossil.

Phylum Porifera

Sponges are the primary member of Phylum Porifera. These organisms are multi-cellular animals that lack organization into definite tissue.

The fossil record

The fossil record is biased and it continues to be analyzed and interpreted as new information becomes available. Organisms with hard parts are more likely to be preserved than soft bodied organisms, and shallow marine shelled organisms are more likely to be preserved than land organisms. Organisms that live on the sea bottom are more likely to be preserved than swimmers; and smaller organisms are more likely to be preserved intact than larger organisms.

Tracks and Trails

Tracks and Trails form as animals move across a soft substrate. They provide clues as to the size and shape of prehistoric animals. Trails are impressions made by appendages or tails of animals as they drag along the soft sediment surface. Interpretations of anatomy or habits can be made from such markings.

Unaltered Preservation

Unaltered Preservation occurs when the original material is preserved, including soft parts such as insects in amber or woolly mammoths frozen in ice. Sometimes that original hard shells of marine organisms may be preserved intact. The process of drying out (desiccation), can sometimes preserve unaltered remains in desert areas.

Altered Remains

When the original material of an organism is changed, the mode of preservation is classified as altered. There are three common ways of producing altered remains: Carbonization, Permineralization, and Replacement.

Replacement

Replacement occurs in environments as groundwater may dissolve the original material atom by atom and replace it with another mineral. In this manner, the original structure of the organism may be preserved. Calcite and aragonite shells are commonly replaced by quartz or pyrite.

Fossil Identification

Paleontologists classify fossils using the Linnean system. This system utilizes morphologic structure as the basis for categorizing groups and determining evolutionary relationships. In the Linnean system, the further down the category, the more closely related are its members. The kingdom is the broadest category which includes the largest number of diverse organisms. Fossils may be members of the animal, plant, protistan (simple single or multi-celled organisms with a nucleus), or moneran (simple single cell organisms without a nucleus) kingdom. The second broadest category is the phylum, then the class, order, family, genus, the generic name, and species, the name of the species. The names are usually derived from Greek or Latin and may describe something about the organism being named. When writing the genus species name for a particular organism, both the genus and species names are underlined or italicized, and the genus name is capitalized. For this class, we will identify most fossils by their phylum, class, and order. Some fossils, known as index fossils, we will identify by their genus name.

Permineralization

Permineralization, also called petrification, is a style of fossil preservation in which mineral bearing waters flow through porous material such as bones and shells and precipitate calcite or silica in void spaces. This means of alteration adds density to the bone or shell while preserving it.

Marine organisms can be classified into three categories according to their mode of life:

Planktonic: These organisms are floaters that drift in the surface waters with waves and currents. They are very small, single-celled organisms which make up the ultimate food source in the ocean. They are commonly carried great distances by oceanic currents. Nektonic: Nektonic animals are swimmers which occupy regions of the sea below the surface of the water and above the ocean floor. This group includes fishes, whales, a few mollusks, and some arthropods. Benthonic: Bottom dwellers are benthonic organisms which may be attached or mobile. If they are attached, the organisms are referred to as "sessile"; organisms that are free to move are referred to as "vagrant". Benthic organisms are often categorized whether they live in the sediments (infaunal), or on top of the sediments (epifaunal). The mode of life of marine organisms refers to how the animal interacts with its environment; whether it is attached or vagrant, if it lives in the water column as a swimmer, or if it is a floater, circulated by ocean currents.

Phylum Protozoa

Protozoans are microscopic, single-celled organisms that form the bottom of the food chain. They are paleontologically significant and used often in subsurface correlation.

Pseudofossils

Pseudofossils are naturally occurring inorganic minerals or rocks which sometimes resemble fossil forms of organic origin. Most of them are found in sedimentary rocks.