Glossary

Acritarch Any small, roughly spherical fossil with a wall composed of an organic material such as sporopollenin usually removed from enclosing sediments by maceration (dissolving the rocks with hydrofluoric acid). Animalia The kingdom to which animals belong. anoxic Depleted in oxygen, as are deep marine waters with poor circulation. aragonite A mineral, composed of calcium carbonate, which forms needle-shaped or fibrous crystals. arthropod A member of the phylum Arthropoda, animals with...

Info

A comparison of the major features of the Garden of Ediacara-style of ecosystem with those of the familiar Heterotrophic Pyramid ecosystem which has dominated the earth since the Cambrian. FIGURE 8.10. A comparison of the major features of the Garden of Ediacara-style of ecosystem with those of the familiar Heterotrophic Pyramid ecosystem which has dominated the earth since the Cambrian. burrow in a geometrically regular pattern to avoid excavating the same sediment over again....

Small Shelly Fossils

As discussed in the first chapter, the appearance of abundant shelly fossils has long been recognized as a puzzling discontinuity in the geologic record. What are these earliest shelly fossils Were all of them formed by animals This section will provide an introduction to some of the earliest shelly fossils. Although by no means exhaustive, the thumbnail sketches below will introduce all the major shelly animal groups that appear in the Early Cambrian. The first and last appearances of many...

Selected Specimens

This appendix lists locality and stratigraphic positions plus repository information for specimens which are illustrated in this book but which have not been published elsewhere see also figure 4.30 and M. McMenamin (1984) for information on the specimens from Sonora, Mexico. Specimens deposited in the Institute of Geology Museum (address Departmento de Paleontologia, Instituto de Geologia, Cuidad Universitaria, Delegacion de Coyoacan, 04510, Mexico, D. F.) are assigned four-digit Institute of...

Precambrian Oxygen

Oxygen is a very unusual gas to find in a planetary atmosphere. Perhaps the most astute scientific prediction made in the second half of the twentieth century is f. E. Lovelock's surmise that the surface of Mars is currently lifeless because its atmosphere is at chemical equilibrium (Brand, Sagan, and Margulis 1977). The air on Mars is chemically stable and does not show chemical anomalies such as the presence of highly reactive free oxygen. The presence of large amounts of a corrosive gas such...

The Cambrian Explosion

The history of life is not a continuum but rather is punctuated by episodes of great change. Many of these episodes of change are marked by the appearances and disappearances of unique life forms. The greatest appearance episode in earth history occurred at the beginning of the Cambrian Period (sometime between 500 and 600 million years ago), when abundant shelled animals began to fossilize and to become part of the rock record. Compared to the vastness of geologic time, the appearance of...

Ecological Chaos and Innovation

THROUGHOUT this book we have referred to the Cambrian radiation of animals as an explosion, a term which implies that the appearance of these animals was a geologically sudden event. Not all paleontologists agree with this, and some prefer to see the Cambrian radiation as the moment in geologic time when animals first appear as shelly fossils, not necessarily when these types of animals first came into being. Therefore, there are two ways of viewing the Cambrian explosion either it was the...

Trilobites

The best known and most typical Cambrian fossils are trilobites. The familar Cambrian species Elrathia kingii figure 4.12 has been quarried in great quantities from the Wheeler Shale of western Utah and can be found all over the United States in rock shops and museum stores, often fashioned into bolo ties and earrings. The Ute Indians of Utah made specimens of Elrathia into amulets, calling them by the Ute name timpe khanitza pachavee, which roughly translates to little water bug that likes to...

Brachiopods

Brachiopods are important constituents of Early Cambrian shelly faunas. Brachiopods are bivalved, exclusively marine, organisms. They survive today but are not as common as they have been in the geologic past. All brachiopods past and present have been filter feeders, with the exception of a few that are thought to have had photo-symbionts. The two valves of a brachiopod shell enclose the body of the brachiopod in much the same way that a clamshell encloses the body of a clam. Filter feeding is...

Other Small Shelly Fossils

Hyolith Fossil

In addition to anabaritids, numerous other conoidal fossils are known from earliest Cambrian limestone. One small fossil, Tiksi-theca, can only be distinguished from anabaritids by the lack of the three furrows. A group related to anabaritids has six symmetric furrows instead of just three. Not all of the early shelly fossils are cone-shaped with pointed ends. Some are cylindrical to very weakly tapering tubes. Coleoloides is such a tube with a calcium carbonate originally aragonitic shell....

Changes In The Vendian Sea Floor

As noted above, abundant burrowers appear slightly before the great wave of biomineralization. Probing deposit feeders, such as the tracemaker of Phycodes pedum, began to excavate sediments to depths of several centimeters at the beginning of the Cambrian. Dwelling burrows several centimeters in length, such as Skolithos, first appeared in the Cambrian, and provided protection for filterfeeding animals. If a skeleton is broadly defined as a rigid body support, a burrow is in essence a skeleton...

Marine Chemistry Of Mirovia

Soft Path Hard Photoautotroph Mcmenamin

In addition to increases in the ecological dimensionality of the sea floor in upward and downward directions , marine chemistry and nutrient levels underwent significant changes during the Vendian-Cambrian transition. Brasier 1986 and Conway Morris 1987a discuss the geochemical clues indicating major oceanic chemistry perturbations that may have had a direct bearing on the biological evolution near the Vendian-Cambrian boundary. Marine sulphur is a participant in these fluctuations....

Mollusks

The final major group of Cambrian shelly fossils are the mollusks. Mollusks are the most familiar and successful phylum of shelled invertebrate animals in modern seas, including clams bivalves , snails gastropods , squids and octopuses cephalopods , chitons and a number of less important groups. Several major mollusk groups make their debut in the Early Cambrian, and most of the groups that appear subsequently can be thought of as descendants of the first Cambrian mollusks. The Early Cambrian...

Echinoderms

Echinoderms are a phylum of spiny-skinned, exclusively marine animals that first appear in the Early Cambrian. Modern examples include starfish, sea urchins, crinoids sea lillies , and sea cucumbers. All modern examples have five-fold or pentameral radial symmetry like a five-pointed star , but this is not the case for many fossil echinoderm groups. Echinoderms are most easily recognized as fossils by their distinctive skeleton composed of plates. Echino-derm plates qualify as sclerites, but...

Archaeocyathans

Perhaps the most distinctive and yet puzzling of Cambrian shelly fossils are the archaeocyathans, also called archaeocyathids. Ar-chaeocyathans have a cup-shaped, originally calcareous, skeleton with porous, double walls connected by partitions called septa figure 4.11 . The walls and septa are a meshwork of connecting rods FIGURE 4.11. Cut away diagram showing the structure of a typical Lower Cambrian archaeocyathan. Diameter of cup 2 cm. After Dcbrenne 1964 FIGURE 4.11. Cut away diagram...

Vendian Extinctions

Onuphionella

The extinction events of the Vendian tend to be overshadowed by the fact that the Vendian-Cambrian transition experienced the great est radiation of multicellular life known. A mass extinction occurs when large numbers of organisms in different habitats die out at the same time, as occurred near the end of the Cretaceous, with the extinction of dinosaurs and all other large terrestrial animals, as well as many types of marine organisms. The earliest known, reasonably well documented, mass...

Precambrian Cambrian Boundary Problem In India

Trace fossils and the basal Cambrian boundary. Geological ournal Special Issue 9 1-8. Alpert, S. P. and J. N. Moore. 1975. Lower Cambrian trace fossil evidence for predation on trilobites. Lethaia 8 223-230. Anderson, M. and S. Conway Morris. 1982. A review, with descriptions of four unusual forms, of the soft-bodied fauna of the Conception and St. John's Groups late Precambrian , Avalon Peninsula, Newfoundland. Third North American Paleontological Convention, Proceedings 1...

The Rifting of Rodinia

Terre Ere Glaciation Varanger

Natomically modern humans first appeared on earth some time during the Ice Age or Pleistocene Epoch of the Ceno-zoic Period. There is no good reason to believe that this episode of glaciation is over, and it is entirely plausible that the great North American ice sheet could return in another ninety thousand years or so and grind New York City into the Atlantic seafloor. There is an interesting parallel between the origin of modern humans and the emergence of animals both events are associated...

Decade

Number of spurious Precambrian animal fossil descriptions plotted against year. The three highest peaks in the data primarily result from the work of Dawson 1860-1870 , Walcott 1890-1900 , and various overenthusiastic recent workers 1960-1970 . stone, contained four elongate lobe-shaped objects, each with concentric U-shaped ridges at the end of the lobe. The U-shaped ridges looked a lot like the concentric layers of sediment that form in many types of animal-built burrows. I...

Symmetry Eyes And Brains

Animal body plans can be lumped into two categories radially symmetric and bilaterally symmetric. Cnidarians and echinoderms are well-known examples of radial body plans. Radial animals are s jmmetric about a central axis, and may have three-fold radial symmetry as in Tribrachidium figure 2.4 , fourfold as in a jellyfish or fivefold as in the five arms of a starfish . Radial animals may also be tubular, as in sea cucumbers and predatory priapulid worms. First known from the Burgess Shale Conway...

The Golden Spike

In geological parlance, the word Cambrian can have two meanings. The first, and most commonly used, designates an interval of geologic time spanning from the second in which the first Cambrian sand grain was deposited until the instant that the first sediments of the Ordovician were laid down. No one was there with a stopwatch to mark these events, so these moments must remain theoretical instants of the geological past. Their importance is that they mark the beginning and ending of the sum...

Scleritomes

Lapworthella Meaning

Most of the fossils just discussed are fairly simple and nondescript, at least compared to the broad spectrum of shell groups among modern marine organisms. This simple shell form makes classification difficult. Just as numerous types of animals can make a simple tubular burrow, many types of animals can create a simple tubular or conical shell. But the classification problems with tubular and conical shells are not nearly as daunting as are those for a group of Early Cambrian fossils known as...

The Garden of Ediacara

Less simply put, all living things require energy-rich molecules that can be broken down by organisms to provide energy. As mentioned in the introductory chapter, some autotrophic organisms are able to create these molecules by using energy sources and chemical building blocks taken from the nonliving environment that surrounds them. The bodies of heterotrophs are dependent on autotrophs to fabricate these energy-rich molecules for them. Because photosynthesis is by far...

Aliens Here on Earth

Cambrian Explosion

For every complex problem there is a solution that is Before discussing the Ediacaran fauna, a distinction needs to be made between the two major types of animal fossils body fossils and trace fossils. Body fossils are either actual parts of the organism s body such as a shell or a bone , or impressions of body parts even if the parts themselves have been dissolved away or otherwise destroyed . The imprint of a feather or leaf or the external surface of a shell are examples of body fossils....