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samenvatting paleontologie fauna (PT. 1) - UU
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- Universiteit Utrecht (UU)
smaenvatting voor paleontologie fauna, deel 1 van de cursus
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Paleontologie Fauna (PR. I)CHAPTER 1, PALEONTOLOGY AS A SCIENCE
Sir Francis Bacon established the methods of induction in science only through the patient
accumulation of accurate observations of natural phenomena that the explanation would emerge
common patterns among observations common patterns point to an explanation, or law of
nature. The other approach to understanding the natural world is a form of deduction, where a
series of observations point to an inevitable outcome. Karl Popper (1902–1994) explained the way
science works as the hypothetico-deductive method. What most natural scientists do is called
hypothesis testing; they seek to refute, or disprove, hypotheses. Scientific revolutions, or paradigm
shifts, are when a whole new idea invades an area of science. Speculation is constrained within the
hypothetico-deductive framework. Hypotheses are narrowed down quickly to those that fit the
framework of current observations and that may be tested. Hypotheses should be sensible and
testable. The word “speculation” can be misleading; perhaps “informed deduction” should make
biological sense. Leonardo da Vinci (1452–1519) explained the fossil seashells found high in the
Italian mountains interpreted them as the remains of ancient shells argued that the sea had
once covered these areas. Nicolaus Steno gave detailed descriptions of fossils. Robert Hooke was one
of the first to hint at the idea of extinction. The reality of extinction was demonstrated by the great
French natural scientist Georges Cuvier. Cuvier is sometimes called the father of comparative
anatomy; he realized that all organisms share common structures. He claimed to be able to identify
and reconstruct an animal from just one tooth or bone, and he was usually successful. After 1800,
Cuvier had established the reality of extinction. The geological periods and eras were named
through the 1820s and 1830s, and geologists realized they could use fossils to recognize all major
sedimentary rock units, and that these rock units ran in a predictable sequence everywhere in the
world. These were the key steps in the foundations of stratigraphy, an understanding of geologic
time. Some remarked there was a progression from simple organisms in the most ancient rocks to
more complex forms later. Charles Lyell (1797–1875), was an anti-progressionist the fossil record
showed no evidence of long-term, one way change, but rather cycles of change. Progressionism was
linked to the idea of evolution. Lamarck explained the phenomenon of progressionism by a large-
scale evolutionary model termed the “Great Chain of Being” or the Scala naturae all organisms
were linked in time by a unidirectional ladder leading from simplest at the bottom to most complex
at the top, indeed, running from rocks to angels. Charles Darwin (1809–1882) developed the theory
of evolution by natural selection in the 1830s by abandoning the usual belief that species were fixed
and unchanging. He also emphasized the idea of evolution by common descent, namely that all
species today had evolved from other species in the past. Only the stronger can survive
adaptation would be inherited. 19th Century palaeontology dominated by remarkable new
discoveries Burgess Shale in Canada in 1909 showed the extraordinary diversity of soft-bodied
animals. Similar but slightly older faunas from Sirius Passett and Chengjiang have confirmed that the
Cambrian was truly a remarkable time in the history of life. The first soft-bodied Ediacaran (older
than Cambrian) fossils were found in Australia.
,CHAPTER 2, FOSSILS IN TIME AND SPACE
Fossils store information on the finite strain and thermal maturation of rocks located in the planet’s
mountain belts, allowing the tectonic history of these ranges to be reconstructed; thermal
maturation information is important in identifying the levels of thermal maturity of rocks and the
gas and oil windows. In some cases, fossil shells also contain isotopes and other geochemical
information that can identify changes in global climate. A rock stratigraphy is the essential
framework that geologists and particularly palaeontologists use to accurately locate fossil collections
in both temporal and spatial frameworks. Nicolaus Steno law of superposition of strata,
fundamental to all stratigraphic studies. In addition, Steno established in experiments that
sediments are deposited horizontally, and rock units can be traced laterally, often for considerable
distances; remarkably simple concepts to us now, but earth shattering at the time. There is now a
range of different types of stratigraphies based on, for example, lithology ( lithostratigraphy), fossils
(biostratigraphy), tectonic units, such as thrust sheets (tectonostratigraphy), magnetic polarity
(magnetostratigraphy), chemical composition (chemostratigraphy), discontinuities
(allostratigraphy), seismic data (seismic stratigraphy) and depositional trends (cyclo- and sequence
stratigraphies). All aspects of stratigraphy start from the rocks themselves. Their order and
succession, or lithostratigraphy, are the building blocks for any study of biological and geological
change through time. Lithostratigraphic units are recognized on the basis of rock type. The
formation, a rock unit that can be mapped and recognized across country, irrespective of thickness,
is the basic lithostratigraphic category. A formation may comprise one or several related lithologies,
different from units above and below, and usually given a local geographic term. A member is a
more local lithologic development, usually part of a formation, whereas a succession of contiguous
formations, with some common characteristics is often defined as a group; groups themselves may
comprise a supergroup. All stratigraphic units must be defined at a reference or type section in a
specified area. Instead of defining the whole formation, the bases of units are defined routinely in
basal stratotype sections at a type locality and the entire succession is then pieced together later
act as the definitive section for the respective stratigraphic units, only basal stratotypes need ever be
defined. Successions of rock are often divided by gaps or unconformities. James Hutton (1726–1797)
noted the great cyclic process of mountain uplift, followed by erosion, sediment transport by rivers,
deposition in the sea, and then uplift again, and argued that such processes had been going on all
through Earth’s history. William Smith realized that different rocks units were characterized by
distinctive groups or assemblages of fossils. These early studies set the scene for biostratigraphic
correlation.
In very broad terms, the marine Paleozoic is dominated by brachiopods, trilobites, and graptolites,
whereas the Mesozoic assemblages have ammonites, belemnites, marine reptiles and dinosaurs as
important components, and the Cenozoic is dominated by mammals and molluskan groups, such as
the bivalves and the gastropods. This concept was later expanded by John Phillips (1800–1874), who
formally defined these three great eras. Very accurate correlation is now possible using a wide
variety of fossil organisms. Biostratigraphy is the establishment of fossil-based successions and their
use in stratigraphic correlation. Measurements of the stratigraphic ranges of fossils, or assemblages
of fossils, form the basis for the definition of biozones, the main operational units of a
biostratigraphy. Critics have argued that there can be difficulties with the identifications of some
organisms flagged as zone fossils; and, moreover, it may be impossible to determine the entire
global range of a fossil or a fossil assemblage, so long as fossils can be reworked into younger strata
by erosion and redeposition. Nonetheless, to date, the use of fossils in biostratigraphy is still the
best and usually the most accurate routine means of correlating and establishing the relative ages of
strata. In order to correlate strata, fossils are normally organized into assemblage or range zones.
, The known range of a zone fossil is the time between its first appearance datum (FAD) and last
appearance datum (LAD) in a specific rock section. This range, measured against the
lithostratigraphy, is termed a biozone. It is the basic biostratigraphic unit, analogous to the
lithostratigraphic formation. Only a small percentage of potential fossils are ever preserved.
Stratigraphic ranges can also be influenced by the Signor–Lipps effect the observation that
stratigraphic ranges are always shorter than the true range of a species, i.e. you never find the last
fossil of a species. The Signor–Lipps effect is particularly relevant to mass extinctions, when this back
smearing can make relatively sudden extinction events appear gradual.
A problem with many of the original definitions of the geological systems was that they were
separated from each other by unconformities bases of most systems then were represented by
stratigraphic gaps, and gaps provide a poor basis for the global correlation of systemic boundaries.
Chronostratigraphy or global standard stratigraphy is one of the most fundamental of all
stratigraphic concepts. The base of a chronostratigraphic interval is defined in a unique stratotype
section, in a type area using the concept of a “golden spike” or marker point. In practice the spike is
usually adjusted to coincide with the first appearance (FAD) of a distinctive, recognizable fossil
within a well-documented lineage. When discussing geological time, we generally use the adjectives
early, mid and late, but when dealing with rock the use of lower, middle and upper is more
appropriate.
North American oil geologists developed a whole new system in the 1960s called sequence
stratigraphy, an approach that emphasizes the importance of unconformities. Six main cycles
separated by unconformities large-scale cycles describing the major changes in sea level across an
entire continent. More minor sequences could be recognized within these major cycles. The fact that
sedimentary rocks can be described as packets of strata, presumably deposited during transgressive
events (when the sea floods the land), divided by periods of non-deposition during regressions
(when the sea withdraws from the land), forms the basis for sequence stratigraphy. The dividing
lines between transgressive and regressive system tracts are marked by various types and degrees of
unconformities that may be recognized on seismic profiles. Whereas most major sequence
boundaries are probably due to global eustatic changes in sea level associated with climatic change
or fluctuations in sea-floor spreading processes, sequences can also be generated by more local
tectonic controls. The architecture of sequences is controlled by changes in sea level, whether
eustatically or tectonically driven, or perhaps a mixture of both, and the room available for
sediment, termed accommodation space. Normal regressions, driven by increased sediment supply,
and forced regressions, driven by base level fall, will both generate falls in sea level, where base
level is the level above which deposition is temporary and prone to erosion. Transgressions are
prompted by base level rise, when this of course exceeds sedimentation rates. There are also six
main types of surface: subaerial unconformity, basal surface of forced regression, regressive
surface of marine erosion, maximum regressive surface, maximum flooding surface and
ravinement surface; the first three are associated with base level fall and the last three with base
level rise. Finally, there is a variety of systems tracts: lowstand, transgressive, highstand, falling
stage and regressive systems tracts. Changes in sea level seem to have had major effects on the
planet’s marine biotas. For example, shell concentrations may be associated with stratigraphic
condensation at maximum flooding surfaces, i.e. the deepest water facies where deposition is very
slow or they may lie near the top of highstand system tracts. Firm grounds and their biotas, that
usually include burrowers and encrusters, favour major flooding surfaces. Moreover, diversity
increases are often associated with marine transgressions as more shallow-water habitats are
created when continents are flooded. On the other hand, marked regressive events have been
associated with major extinctions through habitat loss. Transgressive units are generally more
widespread across continental areas, so increasing the chance to collect fossils = preservation
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