Death Decay and Disarticulation Death

The taphonomic history of most organisms generally begins with their death, although in arthropods, including trilobites, molted exuviae also become a part of the preserved record. Death of organisms may involve gradual normal mortality. However, many of the spectacular Lagerstatten occurrences involve mass mortality of many individuals and species due to environmental crises (Brett and Seilacher 1991). These crises may include storm and seismic shock events, volcanic eruptions such as those at...

Abrasion Corrosion and Encrustation

It is often difficult to distinguish between trilobite skeletons that have been physically abraded and those that have been corroded by biogeochemical processes. As a generalization most trilobite remains are too fragile to withstand prolonged abrasion, and this fragility may account for the rarity of trilobite skeletons in some nearshore, sandy environments in which trace fossils indicate that trilobites were common. It is well known that clay-sized sediment is ineffective as an abrasive...

Soft Tissue Decay

The most destructive process to affect the bodies of organisms is the decay of soft parts. The most volatile parts are tissues, such as internal organs and muscle, and as a result such tissues are very rarely encountered as fossils. Where they are preserved, it is usually (but not always Butterfield 1990) the result of early dia-genetic mineralization (Allison 1988b). Anoxia historically has been viewed as a prerequisite for the preservation of such tissues (e.g., Whittington 1971b). However,...

Historical Notes

Lhwyd provided the first record of trilobites in the literature in 1698, with the publication of plates depicting two Welch trilobites, identified as fish. In 1771, J. I. Walch originated the use of the name trilobite as a distinct class of animal. L. D. Herrmann, however, used the term triJobus as part of the name for a trilobite fossil, as early as 1711. (For the very early trilobite references, see the publications by H. Burmeister (1843, 1846).) In 1822, C. Stokes was the first to...

Trilobites Above Earth May Have

Scientists estimate that life on Earth may have begun as early as three billion years ago. For much of its history, however, life was confined to single-celled bacteria. Stromatolites, layered mounds of sediment trapped by mats of blue-green cyanobacteria, are the predominant fossils for nearly two billion years of geologic history. Finally, in the late Precambrian Ediacarian Period, about 570 million years ago, enigmatic soft-bodied forms of multicellular life first appeared as impressions in...

Asaphoides Florentinensis Trilobite

New York in the Cambrian. A. New York in the Upper Cambrian, showing the carbonate bank over much of the state. B. Cross section of the plate movement during the Upper Cambrian. C. Stratigraphic chart of the Cambrian exposures in New York. From Isachsen et al. (1991). Printed with permission of the New York State Museum, Albany, N.Y. FIGURE 4.8. Close-up of Upper Cambrian Potsdam Sandstone showing sets of cross-bedded quartz-rich sandstone. Cut along Street, Whitehall, Washington...

Articulated Remains

Skeletons of organisms in which the skeleton is composed of multiple elements weakly bound together by ligaments or musculature, such as trilobites, are only rarely preserved intact. Modern experimental studies indicate that the degradation of soft tissues in arthropods occurs within a period of a few hours after death, while destruction of ligaments ensues in weeks to months. As such, skeletons may be completely disarticulated within a period of a few months or less Plotnick 1986, Allison...

Foreword

Tom Whiteley, an accomplished amateur paleontologist, has taken the lead in compiling a much-needed popular account of the trilobites of New York. Sumptuously illustrated with generous photographs of complete specimens of New York trilobites, this book is more than a regional field guide. It also testifies to Gerry Kloc's expertise in preparation and Carlton Brett's keen insight about the rocks and complex facies of the state. In essence, the book reprises the work of Charles Walcott, another...

Transport and Reorientation

Trilobite skeletons can be sensitive indicators of hydrody-namic conditions in the depositional environment. Under low-energy environments, typical of mudrocks, organism remains may be buried in situ. One might use the argument that well-articulated fossils such as trilobites must not have been transported and that their occurrence therefore indicates quiet water environments, but this inference must be made cautiously. Aside from obvious cases where this is not so e.g., in which these...

Info

Simplified stratigraphy of the Cambrian-Ordovician rocks in the Taconic allochthon. Adapted from Landing 1988 , with permission. nant or when productivity in the surface waters was increased, allowing the accumulation of organic matter. These intervals also contain beds of limestone breccia or angular conglomerates that represent debris flows broken from the edge of the continental shelf that avalanched down into deeper water. Actually, a rather diverse fauna of trilobites has been...

Prelude to the Paleozoic Late Proterozoic Collisions and the Grenville Orogeny

The oldest rocks in New York, exposed in the Adirondack Mountains and the Hudson Highlands, are somewhat more than 1 billion years old. These are crystalline rocks that were metamorphosed or altered from older rocks by enormous heat and pressure Figure 4.2 . Some were originally igneous rocks, formed from the cooling and crystallization of magmas, and others are sedimentary deposits, such as quartz sandstones, limestones, and shales. These were transformed metamorphosed by recrystallization and...

Lipp Alian

Laurentia Mid Proterozoic Reconstruction

Grenville mountain belt, fully formed by a billion years ago, was exposed in a life-less continental interior to the forces of weathering and erosion. We know that by about 550 million years ago, an entire thickness of continental crust had been removed and erosion had exposed the roots of the ancient Grenville Mountains. Laurentia is the term geologists apply to the ancestral Paleozoic core of North America, lacking certain areas such as the present eastern seaboard region eastern...

Fossil Diagenesis Geochemical Processing of Potential Fossils

Early diagenetic phenomena comprise the physicochemical processes that act on organism remains primarily after burial. Diagenetic features of fossils may provide information regarding the geochemistry of bottom waters and the upper taphonomi-cally active zone TAZ of the sediment column. Diagenetic features of note include evidence for early dissolution, compaction, and mineralization of fossils. The relative timing of dissolution is commonly recorded in skeletons. Trilobite exoskeletons were...

Trilobite Taphofacies

Various aspects of fossil preservation can be combined into the recognition and description of taphonomic facies or tapho-facies Speyer and Brett 1986, 1991 . Together with lithofacies, biofacies, and ichnofacies, taphofacies tend to vary predictably with sedimentary environments, as shown by studies in modern marine settings Parsons and Brett 1991 . The modes of preservation of fossils can provide important insights into a number of features of mudrock deposition, including 1 the sedimentary...

Trilobite Lagerstatten

Lagerstatten derived from the German mining term translated loosely as mother lodes are extraordinary fossil assemblages. Trilobite Lagerstatten include obrution deposits, reflecting a rapid smothering of benthic faunas by sediment, yielding fully articulated remains and Konservat-Lagerstatten, in which even soft parts are preserved by a combination of rapid burial, anaerobic decay, and early diagenetic mineralization Seilacher et al. 1985 . In this section we describe examples of trilobite...

Evolution and Cladistics

Fortey and Owens 1997 reviewed the evolutionary history of trilobites. This review should be considered the latest in what will be an ongoing series of arguments. The phylogeny or evolution of trilobites is known from the first calcified remains in the Lower Cambrian rocks to the last trilobites in the Late Permian. It is generally believed that trilo-bites as a class are monophyletic that is they are from a common ancestor Ramskold and Edgecombe 1991 . The earliest known trilobites are from...

Ontogeny

Arthropod Ontogeny

Ontogeny is the biological life cycle of an animal for the trilo-bite this would be from the presumed egg to the smallest larvae and the various intermediate stages, to the end of its life cycle. Considerably more is known about the adult phase of the trilo-bite life cycle because the vast preponderance of the fossil record is composed of the pieces of the exoskeleton representing late growth stages. Careful workers have found, however, a significant amount of information related to trilobites'...

Pagetia Clytioides

Olenoidcs stockportensis Pagetia erratica Ptychagnostus punctuosus UPPER CAMBRIAN Prosaukia briarcliffcnsis Pagetia clytioides Ptychagnostus gibbus Unlike the Cambrian, the Ordovician Period was a relatively long interval, spanning about from 489 to 438 million years ago. During this long span, North America continued to straddle the paleoequator, and New York lay in the southern subtropics Figure 4.5 . Early Ordovician saw a continuation of the passive Great American Tidal Flat environment....

Soft Body Parts

The unmineralized or soft parts of the trilobite body are very rarely preserved in the fossil record. Allison and Briggs 1993 made a listing of sites of exceptional fossil preservation, called by the German name Konservat-Lagerstatten. They recognized 19 marine sites worldwide in the Paleozoic, where soft body fossils are preserved. Nine of these sites are in the United States, and six of them yield trilobites. Only one site in the United States in their listing has significant trilobite...

Exoskeleton

The word trilobite, freely translated from Latin, means having the nature of three lobes. The name refers to the three lengthwise, lateral parts or lobes of the trilobite body Figure 2.1 A , not the three parts making up the body the cephalon or head Figure 2.1 D , thorax Figure 2.1E , and pygidium or tail Figure 2.IF . The central of the three lobes is referred to as the axial lobe Figure 2.IB and the side lobes of the thorax and pygidium, as the pleural lobes Figure 2.2C . Trilobites and...

Life Mode

Cryptolithus Tessellatus Appendage

The following discussion of life-mode is based almost exclusively on circumstantial evidence. As such, it is highly interpretive. Fortey 1985 pointed out that using the same body of knowledge, trilobites in the family Agnostidae have been hypothesized to be pelagic, benthic, parasitic, and epifaunal, possibly attached to algal strands. The fossil record does not often permit clear, unambiguous conclusions. However, one might assume that form follows function and that a trilobite's morphology is...

Text Figures

2.1 Trilobite structure using Eldredgeops rami 5 2.2 Trilobite structure using Kettneraspis tubercidata 6 2.3 The structure of the trilobite cephalon using Calymene species 8 2.6 Hxoskeletal pits or circular perforations 11 2.7 Ventral anatomy of the exoskeleton 12 2.8 Ontogeny of the trilobite 14 2.9 Trilobite exoskeletons with attached fauna or injury 18 2.10 Trilobite appendage reconstruction and nomenclature 19 2.11 Ventral anatomy and appendages 20 2.12 Internal anatomy of the trilobite 22...