Examples of transitional fossil in the following topics:
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- Because not all animals have bodies which fossilize easily, the fossil record is considered incomplete.
- Because of the specialized and rare conditions required for a biological structure to fossilize, many important species or groups may never leave fossils at all.
- The fossil record is very uneven and is mostly comprised of fossils of organisms with hard body parts, leaving most groups of soft-bodied organisms with little to no fossil record.
- Groups considered to have a good fossil record, including transitional fossils between these groups, are the vertebrates, the echinoderms, the brachiopods, and some groups of arthropods.
- Some scientists have suggested that the geochemistry of the time period caused bad conditions for fossil formation, so few organisms were fossilized.
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- The detailed fossil record of horses has provided insight into their evolutionary progress.
- The fossil record of horses in North America
is especially rich and contains transition fossils: fossils that show intermediate stages between earlier and later forms.
- The
first equid fossil was found in the gypsum quarries in Montmartre,
Paris in the 1820s.
- The sequence of
transitional fossils was assembled by the American Museum of Natural
History into an exhibit that emphasized the gradual, "straight-line"
evolution of the horse.
- Although some transitions were indeed gradual progressions, a number of others
were relatively abrupt in geologic time, taking place over only a few
million years.
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- The fossil record of the mass extinctions was the basis for defining periods of geological history, so they typically occur at the transition point between geological periods.
- The transition in fossils from one period to another reflects the dramatic loss of species and the gradual origin of new species .
- The Cretaceous-Paleogene (K-Pg) boundary marked the disappearance of the dinosaurs in fossils, as well as many other taxa.
- The transitions between the five main mass extinctions can be seen in the rock strata.
- Extinction occurrences, as reflected in the fossil record, have fluctuated throughout earth's history.
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- Fossilized cells, cuticles, and spores of early land plants have been dated as far back as the Ordovician period in the early Paleozoic era.
- This field seeks to find transitional species that bridge gaps in the path to the development of modern organisms.
- Paleobotanists collect fossil specimens in the field and place them in the context of the geological sediments and other fossilized organisms surrounding them.
- Paleobotanists distinguish between extinct species, as fossils, and extant species, which are still living.
- This Rhynie chert contains fossilized material from vascular plants.
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- Fossils believed to represent the oldest animals with hard body parts were recently discovered in South Australia.
- These sponge-like fossils, named Coronacollina acula, date back as far as 560 million years.
- Another recent fossil discovery may represent the earliest animal species ever found.
- These fossils from South Australia date back 650 million years, actually placing the putative animal before the great ice age extinction event that marked the transition between the Cryogenian period and the Ediacaran period.
- Fossils of (a) Cyclomedusa and (b) Dickinsonia that evolved during the Ediacaran period.
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- Fossils range in age from 10,000 to 3.48 billion years old.
- These types of fossils are called trace fossils, or ichnofossils, as opposed to body fossils.
- The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata) is known as the fossil record.
- Fossils provide solid evidence that organisms from the past are not the same as those found today; fossils show a progression of evolution.
- Footprints are examples of trace fossils, which contribute to the fossil record.
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- The process of a once living organism becoming a fossil is called fossilization.
- Fossilization is a very rare process, and of all the organisms that have lived on Earth, only a tiny percentage of them ever become fossils.
- Fossilization can occur in many ways.
- Most fossils are preserved in one of five processes:
- Fossilized dinosaur bones, petrified wood, and many marine fossils were formed by permineralization.
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- A substantial hurdle is the difficulty of working out fossil ages.
- There are several different methods for estimating the ages of fossils, including:
- Paleontologists rely on stratigraphy to date fossils.
- If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.
- Misleading results can occur if the index fossils are incorrectly dated.
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- The evolution of viruses is speculative as they do not fossilize; biochemical and genetic information is used to create virus histories.
- When exploring the evolutionary history of most organisms, scientists can look at fossil records and similar historic evidence.
- However, viruses do not fossilize, so researchers must conjecture by investigating how today's viruses evolve and by using biochemical and genetic information to create speculative virus histories.
- Finding a common ancestor for viruses has proven to be far more difficult, especially since they do not fossilize.
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- Evidence from the fossil record and from a comparison of human and chimpanzee DNA suggests that humans and chimpanzees diverged from a common hominoid ancestor approximately 6 million years ago.
- In the past several years, however, many new fossils have been found.
- The fossil, informally called "Toumai," is a mosaic of primitive and evolved characteristics.
- To date, it is unclear how this fossil fits with the picture given by molecular data.
- The scientists who discovered the first fossil found that some other scientists did not believe the organism to be a biped (thus, it would not be considered a hominid).