Lynn Wingard. Fossils can be used to recognize rocks of the same or different ages. The fossils in this figure are the remains of microscopic algae.
The pictures shown were made with a scanning electron microscope and have been magnified about times. In South Carolina, three species are found in a core of rock. In Virginia, only two of the species are found. We know from the species that do occur that the rock record from the early part of the middle Eocene is missing in Virginia.
Foot length increased, number of toes reduced from 4 to 1 toe, size of toes became larger in the horse over time Objective: Understand Evolution as Change of a Population Over Time Key words: fossils, adaptation, evolution, natural selection 7. How do you call the changes in foot length, number of toes, and size of toes in the horse over time? Evolution 8.
How would natural selection have caused changes in the size, feet, and teeth of the horse? Horse Teeth The earliest horses had teeth that were adapted to browsing on young shoots of trees and shrubs. The present-day horse is much larger and has larger teeth that are adapted to grazing on the tough leaves of grasses.
Size and Number of Toes Early horses were adapted to living in wooded, swampy areas where more toes where more toes were an advantage. The single-hoofed toes of the present-day horse allow it to travel fast in the plains. Related documents. Horse Idioms. Periodic Table Crossword Puzzle. Formal Speeches.
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For example, species of unrelated animals, such as the arctic fox and ptarmigan a bird , living in the arctic region have temporary white coverings during winter to blend with the snow and ice [Figure 3]. The similarity occurs not because of common ancestry, indeed one covering is of fur and the other of feathers, but because of similar selection pressures—the benefits of not being seen by predators.
Embryology, the study of the development of the anatomy of an organism to its adult form also provides evidence of relatedness between now widely divergent groups of organisms.
Structures that are absent in some groups often appear in their embryonic forms and disappear by the time the adult or juvenile form is reached. For example, all vertebrate embryos, including humans, exhibit gill slits at some point in their early development.
These disappear in the adults of terrestrial groups, but are maintained in adult forms of aquatic groups such as fish and some amphibians. Great ape embryos, including humans, have a tail structure during their development that is lost by the time of birth. The reason embryos of unrelated species are often similar is that mutational changes that affect the organism during embryonic development can cause amplified differences in the adult, even while the embryonic similarities are preserved.
The geographic distribution of organisms on the planet follows patterns that are best explained by evolution in conjunction with the movement of tectonic plates over geological time.
Broad groups that evolved before the breakup of the supercontinent Pangaea about million years ago are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, for example the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. Australia has an abundance of endemic species—species found nowhere else—which is typical of islands whose isolation by expanses of water prevents migration of species to other regions.
Over time, these species diverge evolutionarily into new species that look very different from their ancestors that may exist on the mainland. Like anatomical structures, the structures of the molecules of life reflect descent with modification. Evidence of a common ancestor for all of life is reflected in the universality of DNA as the genetic material and of the near universality of the genetic code and the machinery of DNA replication and expression.
Fundamental divisions in life between the three domains are reflected in major structural differences in otherwise conservative structures such as the components of ribosomes and the structures of membranes. In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences—exactly the pattern that would be expected from descent and diversification from a common ancestor.
DNA sequences have also shed light on some of the mechanisms of evolution. For example, it is clear that the evolution of new functions for proteins commonly occurs after gene duplication events. These duplications are a kind of mutation in which an entire gene is added as an extra copy or many copies in the genome.
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