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Main Text What is paleontology? Paleontology is more than just dinosaurs! Paleontology is the study of the history of life on Earth, as reflected in the fossil record. Fossils are the remains or traces of organisms (plants, animals, fungi, bacteria and other single-celled living things) that lived in the geological past and are preserved in the crust of the Earth. There are many subdivisions of the field of paleontology, including vertebrate paleontology (the study of fossils of animals with backbones), invertebrate paleontology (the study of fossils of animals without backbones), micropaleontology (the study of fossils of single-celled organisms), paleobotany (the study of plant fossils), taphonomy (the study of how fossils form and are preserved), biostratigraphy (the study of the vertical distribution of fossils in rocks), and paleoecology (the study of ancient ecosystems and how they developed). Paleontologists also frequently are involved in studies of evolutionary biology. Fossils of the Burgess Shale - Cambrian Paleontology - The Ancient Life History of the Earth, e- book Author: Henry Alleyne Nicholson Paleo Carbon PALAEOS: The Trace of Life on Earth The Cambrian Period http://www.ucmp.berkeley.edu/cambrian/camb.html The Cambrian Period marks an important point in the history of life on earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion", because of the relatively short time over which this diversity of forms appears. It was once thought that the Cambrian rocks contained the first and oldest fossil animals, but these are now to be found in the earlier Vendian strata. Introduction to the Vendian Period http://www.ucmp.berkeley.edu/vendian/vendian.html When Charles Darwin wrote On the Origin of Species, he and most paleontologists believed that the oldest animal fossils were the trilobites and brachiopods of the Cambrian Period, now known to be about 540 million years old. Many paleontologists believed that simpler forms of life must have existed before this but that they left no fossils. A few believed that the Cambrian fossils represented the moment of God''s creation of animals, or the first deposits laid down by the biblical Flood. Darwin wrote, "the difficulty of assigning any good reason for the absence of vast piles of strata rich in fossils beneath the Cambrian system is very great," yet he expressed hope that such fossils would be found, noting that "only a small portion of the world is known with accuracy." Since Darwin''s time, the fossil history of life on Earth has been pushed back to 3.5 billion years before the present. Most of these fossils are microscopic bacteria and algae. However, in the latest Proterozoic — a time period now called the Vendian, or the Ediacaran, and lasting from about 650 to 540 million years ago — macroscopic fossils of soft-bodied organisms can be found in a few localities around the world, confirming Darwin''s expectations. The Vendian, sometimes called the Ediacaran, is the latest portion of the Proterozoic Era. It began about 650 million years ago, and ended about 543 million years ago with the beginning of the Cambrian Period. Unlike later portions of the geologic time scale, the Vendian has no formal subdivisions nor distinct early boundary. This is in large part due to the fact that it has only recently become a subject of interest to paleontologists. For many decades, paleontologists believed that life began in the Cambrian, or that if simpler life had existed in the Precambrian, that it left no fossil evidence for us to find. A few believed that the Cambrian fossils represented the moment of God''s creation of animals, or the first deposits laid down by the biblical Flood. Darwin wrote, "the difficulty of assigning any good reason for the absence of vast piles of strata rich in fossils beneath the Cambrian system is very great," yet he expressed hope that such fossils would be found, noting that "only a small portion of the world is known with accuracy." Many paleontologists held little hope that fossils would ever be found in rocks so ancient as the Vendian. It is now known that rock layers may be deeply buried, twisted, folded and melted by geologic forces. It is easy to see that such changes to rock would destroy any fossils that might otherwise have been preserved. Older layers of rock, which have been around for a longer time, are more likely to have undergone such changes, and are thus less likely to preserve fossils. With no known fossils from the Vendian little more could be said, but in the 20th century macroscopic fossils of soft-bodied animals, algae, and fossil bacteria have been found in these older rocks in a few localities around the world. With the discovery of these earliest fossils came a surge of interest in the Vendian and the Proterozoic Era that continues today. What was life like 560 million years ago? Bacteria and green algae were common in the seas, as were the enigmatic acritarchs, planktonic single-celled algae of uncertain affinity. But the Vendian also marks the first appearance of a group of large fossils collectively known as the "Vendian biota" or "Ediacara fauna." The question of what these fossils are is still not settled to everyone''s satisfaction; at various times they have been considered algae, lichens, giant protozoans, or even a separate kingdom of life unrelated to anything living today. Some of these fossils are simple blobs that are hard to interpret and could represent almost anything. Some are most like cnidarians, worms, or soft-bodied relatives of the arthropods. Others are less easy to interpret and may belong to extinct phyla. But besides the fossils of soft bodies, Vendian rocks contain trace fossils, probably made by wormlike animals slithering over mud. The Vendian rocks thus give us, and YOU through our virtual museum, a good look at the first animals to live on Earth. Introduction to the Proterozoic Era http://www.ucmp.berkeley.edu/precambrian/proterozoic.html The period of Earth''s history that began 2.5 billion years ago and ended 543 million years ago is known as the Proterozoic. Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic -- stable continents first appeared and began to accrete, a long process taking about a billion years. Also coming from this time are the first abundant fossils of living organisms, mostly bacteria and archaeans, but by about 1.8 billion years ago eukaryotic cells appear as fossils too. With the beginning of the Middle Proterozoic comes the first evidence of oxygen build-up in the atmosphere. This global catastrophe spelled doom for many bacterial groups, but made possible the explosion of eukaryotic forms. These include multicellular algae, and toward the end of the Proterozoic, the first animals. The period of Earth''s history that began 2.5 billion years ago and ended 544 million years ago is known as the Proterozoic; it is divided up, rather arbitrarily, into the Paleoproterozoic (2.5 to 1.6 billion years ago), Mesoproterozoic (1.6 billion to 900 million years ago) and Neoproterozoic (900 to 543 million years ago). Near the beginning of the Proterozoic, stable continents first appeared and began to accrete, a long process taking about a billion years. Ancient Global Pollution The first "pollution crisis" hit the Earth about 2.2 billion years ago. Several pieces of evidence -- the presence of iron oxides in paleosols (fossil soils), the appearance of "red beds" containing metal oxides, and others -- point to a fairly rapid increase in levels of oxygen in the atmosphere at about this time. Oxygen levels in the Archaean had been less that 1% of present levels in the atmosphere, but by about 1.8 billion years ago, oxygen levels were greater than 15% of present levels and rising. (Holland, 1994) It may seem strange to call this a "pollution crisis," since most of the organisms that we are familiar with not only tolerate but require oxygen to live. However, oxygen is a powerful degrader of organic compounds. Even today, many bacteria and protists are killed by oxygen. Organisms had to evolve biochemical methods for rendering oxygen harmless; one of these methods, oxidative respiration, had the advantage of producing large amounts of energy for the cell, and is now found in most eukaryotes. Where was this oxygen coming from? Cyanobacteria, photosynthetic organisms that produce oxygen as a byproduct, had first appeared 3.5 billion years ago, but became common and widespread in the Proterozoic. Their photosynthetic activity was primarily responsible for the rise in atmospheric oxygen. The first traces of life appear nearly 3.5 billion years ago, in the early Archaean. However, clearly identifiable fossils remain rare until the late Archaean, when stromatolites, layered mounds produced by the growth of microbial mats, become common in the rock record. Stromatolite diversity continued to increase through most of the Proterozoic. Until about 1 billion years ago, they flourished in shallow waters throughout the world. Their importance for understanding Proterozoic life is tremendous; stromatolites that have been silicified (forming a type of rock known as stromatolitic chert) often preserve exquisite microfossils of the microbes that made them. Shown here is a sample of stromatolitic chert from the Bitter Springs Formation of central Australia, about 850 million years old. Note the typical fine banding patterns. Stromatolites began to decline in abundance and diversity about 700 million years ago. A popular theory for their decline (though certainly not the only possible explanation) is that herbivorous eukaryotes, perhaps including the first animals, evolved at about this time and began feeding extensively on growing stromatolites. Stromatolites are rare fossils after about 450 million years ago. Today, they are found only in restricted habitats with low levels of grazing, such as the shallow, saline waters of Shark Bay, Australia. The oldest fossil that may represent a macroscopic organism is about 2.1 billion years old. Several types of fossil that appear to represent simple multicellular forms of life are found by the end of the Paleoproterozoic. These fossils, known as carbon films, are just that: small, dark compressions, most resembling circles, ribbons, or leaves; they are most common and widespread in the Neoproterozoic (Hofmann, 1994). Some resemble seaweeds and may represent eukaryotic algae; we know from independent evidence that red algae and green algae appeared in the Proterozoic, probably over 1 billion years ago. There are tantalizing hints from trace fossils and molecular biology that animals may have appeared as much as 1 billion years ago. However, the oldest relatively non-controversial, well-studied animal fossils appear in the last hundred million years of the Proterozoic, just before the Cambrian radiation of taxa. The time from 600-650 million years ago to 543 million years ago, known as the Vendian period, saw the origin and first diversification of soft-bodied organisms known collectively as the "Vendian fauna" or "Ediacara fauna" (after the Ediacara Hills of southern Australia, where the first abundant and diverse fossils of this kind were found). Precambrian Time http://www.ucmp.berkeley.edu/precambrian/precambrian.html 4.5 billion years ago, the Earth was born. Comprehending that vastness in time is no easy task. John McPhee, in his book Basin and Range, recounts a nice illustration of what this sort of time means. Stand with your arms held out to each side and let the extent of the earth''s history be represented by the distance from the tips of your fingers on your left hand to the tips of the fingers on your right. Now, if someone were to run a file across the fingernail of your right middle finger, then the time that humans have been on the earth would be erased. Nearly 4 thousand million years passed after the Earth''s inception before the first animals left their traces. This stretch of time is called the Precambrian. To speak of "the Precambrian" as a single unified time period is misleading, for it makes up roughly seven-eighths of the Earth''s history. During the Precambrian, the most important events in biological history took place. Consider that the Earth formed, life arose, the first tectonic plates arose and began to move, eukaryotic cells evolved, the atmosphere became enriched in oxygen -- and just before the end of the Precambrian, complex multicellular organisms, including the first animals, evolved. Metazoa: Life History and Ecology http://www.ucmp.berkeley.edu/phyla/metazoalh.html Animals have a diploid life cycle. Animals have a diploid life cycle, in which the organism is diploid, and the only haploid cells are the gametes. There are male and female organisms, and the male provides sperm which fertilizes the female`s egg cell. The fertilized egg is called a zygote, and develops into a multicellular embryo which eventually becomes a new diploid organism. While this general scheme holds for many animals, there are numerous exceptions. Some insects, notably social insects such as bees, may produce haploid offspring, and animals such as Hydra may reproduce by asexual budding. There is also a great deal of variation among organisms that do follow the general scheme. For example, the two sexes may be found on the same organism, so that each organism may contribute sperm to the other`s eggs (a condition known as hermaphroditism). The sperm may be transferred to the eggs while still within the female, or be shed over the eggs after their release from the female`s body. The zygote may develop within the female (as in mammals), outside the female`s body (as in frogs), or even within the male`s body (as in certain fish). We suggest that you go deeper into our exhibits on animals to learn more about the many ways that animals go and have gone about their lives, or you can look at the alternation of generations page to find out more on how animals differ from other organisms. Animals are heterotrophic. One feature common to all animals is their ecological role as consumers, that is, they cannot manufacture their own food, and so must eat other organisms, or from other organisms, to obtain nourishment. There are three basic categories of consumers: predator - A predator devours other organisms, or parts of other organisms. This includes both carnivores such as wolves, which eat other animals, and herbivores such as cows, which eat plants. parasite - A parasite lives on or within another organism (the host), and obtains nourishment from the host without killing or swallowing it. These organisms range from ticks to tapeworms, and may be relatively harmless or may cause disease. detrivore - Detrivores feed on dead organisms, or on organic nutients in the soil or water. These organisms are vital to the food web because they recycle nutrients which would otherwise become unavailable. Earthworms and vultures are both examples of detrivores. Many animals specialize in their roles as consumers, they may feed exclusively on one food or one kind of food. Certain bats, for instance, are frugivores, and eat only fruits. These specialists often play important roles in the lives of the species with which they interact. In the case of the fruit bats, the bats are crucial for dispersing the seeds contained within the fruits. For more information on the many and diverse roles of animals, explore further into the animal exhibit. http://www.ucmp.berkeley.edu/phyla/metazoamm.html When you look across all animals and try to determine what features they all share, you may think of multicellularity. But multicellularity has been independently developed in at least seventeen different groups of organisms, including plants, chromists, fungi, and slime molds. If you think more deeply about the characters that all animals possess, you are left with small things, i.e., molecules. At the cellular level, animals begin to all look alike. But, animals also resemble many other groups of organisms at that level. If you separate out all of the things that only animals possess, what are you left with? The short answer is: an extracellular matrix (ECM) composed of collagen, proteoglycans, adhesive glycoproteins, and integrin. These four types of molecules are created inside, but exist outside, the cells of animals. These molecules fill up the spaces between cells and serve as structural elements. Most collagens are made of long proteins that wind around each other to form a triple helix, and the resulting fibers have a high tensile strength. Glycoproteins are large molecules which branch. These molecules have the property of resisting compressive forces. That is, they are kind of like springs; they can be squished and then return to their old shape. Integrin is the molecule that connects the outside of the cells to the extracellular matrix. The mechanical properties of these molecules are extremely important; for instance, they often form a scaffolding that becomes mineralized and so forms bones, shells, or spicules of various animals. However, the extracellular matrix also plays a key role in the development of animals, from sponges to sea otters. In the early development of animals, some cells are immobile and form sheets called epithelia. Other cells are motile, i.e., they move inside the animal. Cell motility is necessary for animals to develop from single cells into working individuals composed of many many cells. Extracellular matrix not only facilitates not only the mobility of motile cells and guides their movements within the developing embryo, but also helps to control the transition of cells from one type to another. It appears that all animals share this complex system of development mediated by extracellular matrix, whereas all other multicellular organisms do not. This character is common to all animals as the result of their being descended from a common multicellular ancestor that also possessed this character. http://www.ucmp.berkeley.edu/phyla/metazoasy.html Scientists care because phylogeny is the fundamental product of evolution. Therefore, a phylogenetic hypothesis is essential if you want to understand biological phenomena, most of which have an evolutionary explanation. Since many scientists would like to know how animal diversity and animal body plans came to be, presently there is a great deal of work on resolving the evolutionary relationships among the major groups of animals. Much of this research has relied upon morphological characters, especially those expressed in early development (e.g. embryological characters). More recently, a significant advance in our understanding of animal phylogeny has been brought about by the study of molecules (in particular genes and their protein products) contained within animal cells. The phylogeny presented here is a relatively conservative guess based upon various published studies of 18S ribosomal RNA sequence data. As you can see, there are quite a few unresolved branches, and therefore a great deal of work to be done in this area. Note that the phylum Porifera (the sponges) is paraphyletic. A few lines of independent evidence suggest that one group of sponges is actually more closely related to non-sponge animals than it is to the other sponges. This is an important finding for it implies that the lineage leading to all other animals (including ourseleves!) was directly descended from an animal with a sponge body and a sponge life style. Animals have a diploid life cycle. Animals have a diploid life cycle, in which the organism is diploid, and the only haploid cells are the gametes. There are male and female organisms, and the male provides sperm which fertilizes the female`s egg cell. The fertilized egg is called a zygote, and develops into a multicellular embryo which eventually becomes a new diploid organism. While this general scheme holds for many animals, there are numerous exceptions. Some insects, notably social insects such as bees, may produce haploid offspring, and animals such as Hydra may reproduce by asexual budding. There is also a great deal of variation among organisms that do follow the general scheme. For example, the two sexes may be found on the same organism, so that each organism may contribute sperm to the other`s eggs (a condition known as hermaphroditism). The sperm may be transferred to the eggs while still within the female, or be shed over the eggs after their release from the female`s body. The zygote may develop within the female (as in mammals), outside the female`s body (as in frogs), or even within the male`s body (as in certain fish). We suggest that you go deeper into our exhibits on animals to learn more about the many ways that animals go and have gone about their lives, or you can look at the alternation of generations page to find out more on how animals differ from other organisms. THE HAPLOID-DIPLOID LIFE Cycle http://www.ucmp.berkeley.edu/glossary/gloss6/altergen.html The haploid-diploid life cycle is the most complex life cycle and thus has lots of variation. It is also the most common life cycle among plants since all land plants, the vascular plants and the bryophytes, are haploid-diploid. An alternation of generations defines the haploid-diploid, or 1n-2n, life cycle. This occurs when a multicellular 2n sporophyte (SPT) phase alternates with a multicellular 1n gametophyte(GPT) phase The Fossil Bacteria Record http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookDiversity_2.html Fossil evidence supports the origins of life on earth earlier than 3.5 billion years ago. Specimens from the North Pole region of Western Australia are of such diversity and apparent complexity that even more primitive cells must have existed earlier. Rocks of the Ishua Super Group in Greenland yield possibly the fossil remains of the earliest cells, 3.8 billion years old. The oldest known rocks on earth are 3.96 Ga and are from Arctic Canada. Thus, life appears to have begun soon after the cooling of the earth and formation of the atmosphere and oceans. These ancient fossils occur in marine rocks, such as limestones and sandstones, that formed in ancient oceans. The organisms living today that are most similar to ancient life forms are the archaebacteria (the archaea in modern usage). This group is today restricted to marginal environments. Recent discoveries of bacteria at mid-ocean ridges add yet another possible origin for life: at these mid-ocean ridges where heat and molten rock rise to the earth''s surface. Many of the ancient phototrophs and heterotrophic bacteria lived in colonial associations known as stromatolites. Cyanobacteria are on the outer surface, with other photosynjthetic bacteria (anoxic) below them. Below these phottrophs are layers of heterotrophic bacteria. The layers in the stromatolites are alternating biogenic and sedimentologic in origin. A modern day stromatolite is shown in Figure 20. Figure 20. Image of Sharks Bay, Australia stromatolites, a cross section of one of these structures, and a closeup of the cyanobacteria that make up the bulk of the feature | |||
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