Earth is the planet that rich of living things and they are biologically classified into Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. Mammal is one of the classes in Kingdom Animalia. Several studies have been conducted to visualize the evolution of mammals from their ancestors. Mammals have several descriptive characteristics which are their evolution trend, reproductive behavior, physical appearance, specific blood circulation system and their feeding behavior (refer to Figure 1 in Appendix 1). The first descriptive characteristic of mammals is the evolution. “Mammalian characteristics evolved gradually over a period of 200 million years” (Miller & Harley, 2007, p. 359). The beginning of Tertiary period is defined as the start of the “age of mammals” when extinction of many reptilian ancestries occurred and caused the adaptive radiation of mammals. They evolved during the Triassic period when dinosaurs appeared. This was the earliest mammals. They were tiny shrew-like mammals with delicate skeleton. According to Hickman, Robert, Keen, Larson, and Eisenhour (2011), the first placental mammals appeared at the beginning of the Cretaceous period and diverse rapidly. Most of the knowledge of early mammalian phylogeny study depends on the analysis of their fossilized teeth and skull fragments. There are several changes in the structure of sensory organs, bones, teeth and brain to become more adaptive to dynamic environment. The second characteristic of mammals is reproductive behavior. Most of them have explicit mating seasons, so that birth and the young occur at the most favorable time of the year (Villegas-Amtmann, Atkinson, & Costa, 2009). According to Hickman et al. (2011), any male mammals ca... ... middle of paper ... ...l diversity. New York, NY: The McGraw-Hill Companies Inc. Hickman, C. P., Roberts, L. S., Keen, S. L., Eisenhour, D. J., Larson, A., & I ‘Anson, H. (2011). Integrated principles of zoology. New York, NY: The McGraw-Hill Companies Inc. Hickman, C. P., Roberts, L. S., Keen, S. L., Larson, A., & Eisenhour, D. J. (2011). Animal diversity (6th ed.). New York, NY: The McGraw-Hill Companies Inc. Martin, R. E., Pine, R. H., & DeBlase, A. F. (2001). A Manual of Mammalogy: with Keys to Families of the World (3th ed.). New York, NY: The McGraw-Hill Companies Inc. Miller, S. A., & Harley, J. P. (2007). Zoology (7th ed.). New York, NY: The McGraw-Hill Companies Inc. Villegas-Amtmann, S., Atkinson, S., & Costa, D. P. (2009). Low synchrony in the breeding cycle of Galapagos sea lions revealed by seasonal progesterone concentration. Journal of Mammalogy, 90(5), 1232-1237.
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1These two populations are different species because they have different capabilities of performing in nature. For example there is behavioral isolation. My evidence for that is that in the data, it states that the average time spent in courtship display for the St. Kitts rodent is 12.6 seconds. While the courtship display for the Nevis Rodent is 21.3. You can see that there is a major difference in the way that they behave. Also there is another type of isolation which is gametic isolation. There is gametic isolation because the average gestation time for St. Kitts rodent is 29.3 days. The average gestation for the Nevis rodent is 42.7 days. Therefore a sperm from St. Kitts rodent wouldn’t survive in the reproductive tract of the Nevis rodent. It wouldn’t survive because it wouldn’t develop properly and is not accustomed to its environment. There is also another type of isolation happening with the rodents of St. Kitts. This type of isolation is called temporal isolation. There is temporal isolation because the article states, “the reproductive seasons are being delayed by up to one year.” This is talking about that the rodents are having a hard time finding mates therefore, their reproductive season is being delayed. Also in the article it states, “In the 240 attempts to bring a Nevis animal into the St. Kitts population, you are unable to observe a single successful reproductive event.” The rodents are mechanically isolated, because if you can’t have a reproductive event, there reproductive organs might not be matching with one another. Their appearance might look identical but they are genetically different.
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