Chapter 16- Biol 100

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A flat-headed animal between 4 and 9 feet long. In some ways it resembles giant fish (fins and scales) but also had traits that resembled those of land-dwelling amphibians- notably a neck, wrists,and finger like bones.


A vertebrate animal with four true limbs that is jointed, bony appendages with digits. Mammals,amphibians, birds, and reptiles are tetrapods.

Transitional Organisms

intermediate states between an ancestral form and that of its descendants are referred to as transitional forms. There are numerous examples of transitional forms in the fossil record, providing an abundance of evidence for change over time.

How are fossils made and dated?

They are formed in a number of ways: an animal or plant may be frozen in ice, trapped in amber, or buried in a thick layer of mud. The entombed organism is thereby protected from being eaten by scavengers or rapidly decomposed by bacteria. Over time, if conditions are right, the organism’s shape is preserved. Logically they are as old as the rocks that encase them, so if you know the age of the rocks, you then know the age of the fossil. Can also use radiometric dating and relative dating.


Anatomical, genetic, or developmental similarity among organisms due to common ancestry

Vestigial Traits

A structure inherited from an ancestor that no longer serves a clear function in the organism that possesses it.

Embryonic Development

We can identify homologous structures by tracing their embryological development. Some if our middle ear bones, for example, are homologous with jaw bones of reptiles and bones supporting gills in fish. We know this because all of these structures develop from the pharyngeal pouches that appear in all vertebrate embryos early in development. This development homology is strong evidence that all vertebrate animals are related by common ancestry. Genetic changes over time have introduced modifications in later stages that give rise to distinct species with vast physical differences.

DNA Evidence of Evolution

Related organisms share DNA sequences inherited from a common ancestor. Over time, the sequence in each species acquires independent mutations. The more time that has passed, the greater the number of sequence differences that will be present. Thus, the percentage of nucleotides that differ between two species gives an indication of the evolutionary distance between them.


Which of the following statements regarding The dating of fossils if FALSE? a) Fossils can be dated using a method called radiometric dating b) Fossils can be dated relative to other fossils found in layers of rock c) Fossils can be dated using a microscope to examine tissue d) Fossils can be dated using the rock in which they are discovered e) Fossils can be dated by dating the rock layers directly above and below the fossil


Which of the following scenarios would be LEAST likely to result in a fossil? a) A beetle that becomes trapped in tree sap b) A snake that dies and is quickly covered in soft mud c) humans who are quickly buried alive in volcanic ash d) A jellyfish that dies and floats to the bottom of the ocean e) A boar that is trapped in a tar pit and sinks quickly


Which of the following changes in the evolutionary history of horses is documented by the fossil record? a) A gradual decrease in body size b) A gradual increase in the number of toes c) A gradual decrease in the number of toes d) A direct path from the ancestor to modern- day horses


Why are fossils generally going to be more useful for studying animals that lived in or near water (e.g. streams, lakes, oceans, etc.)? a) Because all animals need water b) Because water is where most rocks form c) Because dead animals are more likely to be in conditions that all fossilizatioin d) Because no decomposers are living in water e) Because water prevents the organisms


Which of these characteristics would be expected to apply to a transitional fossil? a) It should completely be completely different from any other species b) It should have some similarity to the species before it c) It should have some similarity to the species after it d) It should be exactly the same as modern species e) Both B and C


The Tikataalik fossil, which dates back 375 million years, is considerewd a transitional fossil because____ a) The species lived while the earth was still forming b) It was discovered half in the water half on land c) The organism was swimming when it was crushed by a falling rick d) It shows the transition between two- and four- legged orhganisms e) It displays features found on both aquatic and land-dwelling species


Which of the following sequences places Tiktaalik in the correct evolutionary order? a) Ray-finned fish, lobe- finned fish, Tiktaalik b) Lobe- finned fish, Tiktaalik, tetrapods c) Tetrapods, ray- finned fish, Tiktaalik d) lobe-finned fish, tetrapods, Tiktaalik e) Tetrapods, lobe- finned fish, Tiktaalik


Which of the following features did TIktaalik possess that were not possessed by earlier vertebrates? a) Fingers and toes b) A flexible wrist c) Fins d) lungs e) Gills


What can we learn about vertebrate evolution from Tiktaalik that we did not know before? a) How vertebrates evolved vertebrates b) How vertebrates evolved jaws c) How vertebrates evolved lungs d) How vertebrates evolved tetrapod limbs e) B and D


The variation in shape and function of the forelimb in tetrapods is a result of_____. a) Evolutionary adaptation to different environments b) Unrelated ancestry c) Rapid evolution and land transition d) Tetrapod limb manipulation e) Environmental toxins


The forelimb of a chicken and a primate contain many of the same bones arranged in the same order. This is an example of_____. a) Tetrapodology b) Similarity c) Comparable limbs d) Limb sharing e) homology


Although all organisms share the same four nucleotides, it is the ________ of the nucleotides that makes each species unique. a) Quantitiy b) Shape c) Sequence d) Distance e) Growth


Organism XYZ has a DNA sequence of GGTATAGAGT. By examining the sequences of nucleotides below, determine which organism is most closely related to organism XYZ. a) GGTTGAGAGT b) GGTATATAGG c) GGTATAGAGG d) GTTATAAGGT e) It is impossible to tell which organism is most closely related based in this evidence


Which of the following can be used by scientists to understand evolution? a) Molecular data b) The study of anatomy c) Development homology d) Fossil records e) All of the above can be used to help scientist understand evolution


Why do some portions of DNA function as a kind of evolutionary clock when comparing two different species? a) Because portions of the DNA have no function b) Because mutations will accumulate over time c) Because changes to DNA always occur quickly and easily d) Because organisms change their anatomy at a constant rate e) Because mechanism is available for removing mutations that are harmful


How is it possible for homologous structures to look very different when comparing two different species? a) Because those species may have exposed to different environments during their evolution b) Because those species may use the structures for very different purposes c) Because those two species may be separated by millions of years of evolutionary history d) A and B e)All of the above

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