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Annotated Bibliography 1.) Gol'din, Pavel. "Naming an Innominate: Pelvis and Hindlimbs of Miocene Whales Give an Insight into Evolution and Homology of Cetacean Pelvic Girdle." Springer Online Journals Complete 41 (2013): 473-79. Springer Link. Web. 14 Sept. 2014. . New findings of ancient whale species allow scientists to compare pelvic anatomy with four limbed, aquatic ancestors to the whale. The article describes how the ischium in modern whales is reduced and the potential genes that are responsible for reducing the size of this bone. The genes associated with the reduction in ischium size could shed light on the evolution of the pelvic girdle in whales. 2.) Tajima, Yuko, Yoshihiro Hayashi, and Tadasu Yamada. "Comparative Anatomical Study on the Relationships between the Vestigial Pelvic Bones and the Surrounding Structures of Finless Porpoises (Neophocaena Phocaenoides)." J-Stage 66.7 (2014): 761-66. The Journal of Veterinary Medicine. Web. 14 Sept. 2014. . In this article, Japanese researchers discuss possibilities of pelvic bone evolution in aquatic mammals. Along with the evolution of the pelvic bone, these researchers go on to discuss modern uses for the commonly referred “vestigial” hip bones in aquatic mammals. 3.) Dines, J.P., E. Otárola-Castillo, and P. Ralph. "Sexual Selection Targets Cetacean Pelvic Bones." Evolution: International Journal of Organic Evolution (2014). Wiley Online Library. Web. 14 Sept. 2014. . This article describes the importance of shape and size of pelvic bones for mating purposes in mammals, particularly aquatic mammals with “vestigial” hips. Current research describes that the hip bone in whales or other aquatic mammals may not be vestigial, and this opposes current theories made by modern scientists. Instead, the article states that aquatic, mammalian pelvic bones may play an important role in mating for males. 4.) Don, Emily, Peter Currie, and Nicholas Cole. "The Evolutionary History of the Development of the Pelvic Fin/hindlimb." Journal of Anatomy 222.1 (2012): 114-33. Journal of Anatomy. Web. 14 Sept. 2014. . Researchers from Sydney Australia discuss the history of hindlimbs in mammals and pelvic fins in fish to shed light on the possible evolutionary forces that caused these fins and limbs to take on certain characteristics. 5.) Boisserie, Jean-Renaud, Rebecca Fisher, and Fabrice Lihoreau. "Evolving between Land and Water: Key Questions on the Emergence and History of the Hippopotamidae (Hippopotamoidea, Cetancodonta, Cetartiodactyla)." Biological Reviews 86.3 (2011): 601-25. Wiley Online Library. Web. 14 Sept. 2014. . Researchers from Ethiopia and France discuss the evolution of the Hippopotamus. The Hippopotamus is a close relative to whales and dolphins, but the Hippo lives in a semi-aquatic habitat. The researchers hope that their findings will shed light on the ecological niche of the hippo and how this could potentially relate to the evolution of similar mammals.--Hegedus.13 (talk) 13:04, 15 September 2014 (UTC)

1. There is no explanation or theory as to the significance of whales losing their hind limbs to help them succeed in a marine environment. 2. There is no comparative anatomy of the cetacean skeletal structure with ancestral tetrapod mammals. 3. The pelvic like bones in modern male cetaceans tend to be larger than those of the female ones possibly due to mating purposes Hegedus.13 (talk) 04:46, 1 October 2014 (UTC)

https://en.wikipedia.org/wiki/Evolution_of_cetaceans

The reduced pelvic bone in the finless porpoise male act to support the male genitalia in a similar way to terrestrial mammals. Tajima, Yuko, Yoshihiro Hayashi, and Tadasu Yamada. "Comparative Anatomical Study on the Relationships between the Vestigial Pelvic Bones and the Surrounding Structures of Finless Porpoises.The Journal of Veterinary Medicine 66.7: 761-766

https://en.wikipedia.org/wiki/Evolution_of_cetaceans Modern cetaceans have rudimentary hind limbs, such as reduced femurs, fibulas, and tibias, and a pelvic girdle, consisting of an ilium, ischium, and pubis bone. Cetacean hind limbs and bones of the pelvic girdle can be compared to terrestrial mammals. Over the course of evolution, the cetacean skeletal structure went through many alterations that now make it very distinguishable from terrestrial mammals. Certain genes are believed to be responsible for the changes that occurred to the cetacean pelvic structure and hind limbs. Possible gene candidates for modifications made to the cetacean pelvic girdle include BMP7, PBX1, PBX2, Prrx1, and Prrx2. These genes all serve a purpose in pelvic girdle development in different animal species. Different genes are thought to be responsible for the evolution of cetacean hind limbs. One potential gene that could be involved in hind limb reduction is called the Shh gene. This gene is thought to be responsible for the reduction of distal portions of hind limbs. Another gene that could be involved in hind limb reduction is called the Tbx4 gene. The Tbx4 gene is responsible for hind limb development in humans and mice, and researchers compared the Tbx4 gene in cetacean development with the Tbx4 gene in human and mice development to determine if the gene acts differently in cetaceans. The pelvic girdle and reduced hind limbs in modern cetaceans were once thought to be vestigial structures that served no purpose at all. It is now believed that the pelvic girdle does serve a useful purpose. The pelvic girdle in male cetaceans is different in size compared to females, and the size is thought to be a result of sexual dimorphism. The pelvic bones of modern male cetaceans are more massive, longer, and larger than those of females. They are also involved in supporting male genitalia that remain hidden behind abdominal wales until sexual reproduction occurs.

FINAL DRAFT STARTS HERE Joseph Hegedus Tuesday 11:30 Evolution of Hind-Limbs and the Pelvic Girdle in Cetaceans The evolution of the pelvic girdle and hind-limbs in cetaceans, aquatic mammals such as dolphins and whales, is particularly interesting because it represents an event where four-legged terrestrial mammals evolved to live in an aquatic environment. Researchers believe that cetaceans evolved from land animals and not other aquatic animals because based on skeletal evidence the first mammals to walk the earth lived in terrestrial environments. After knowing that cetaceans evolved from terrestrial mammals, the question became how these mammals adapted to live in a marine environment. Ancestral cetacean skeletal remains display how evolution has slowly reduced or altered the size of their pelvic bones and hind limbs. Modern whales and dolphins have no external hind limbs and greatly altered pelvic bones compared to terrestrial tetrapods, suggesting that these body parts are now vestigial. A vestigial body part is one that is degenerated or rudimentary and has become functionless in the light of evolution. Although the previous theory was accepted for some time, new evidence and research suggest that the altered pelvic bones and hind limbs in cetaceans actually have a purpose. Through comparative anatomy and close observation, researchers came up of modes of evolution for the change in body structure for cetaceans, and potential purposes for these altered body plans. Based on phylogenetic trees and DNA comparisons, it is believed that cetaceans share a common ancestor with even-toed ungulates, which include deer, pig, camels, and hippopotamus. Excluding the cetaceans, all of the previously mentioned animals live in terrestrial or semi-terrestrial environments. This being the case, it makes most sense that the common ancestor among all of these relatives lived in a terrestrial habitat. Through several speciation events, semi-aquatic organisms arose, which eventually lead to fully aquatic marine mammals. Researchers do not fully know why a lineage of terrestrial mammals evolved only to move back to an aquatic environment, but fossil evidence and evolutionary concepts can attempt to explain how this happened. One of the ancestors of modern cetaceans is called the pakicetus, which were four-limbed mammals that lived in semi-aquatic habitats. These animals can be compared to hippopotamus because they live in similar habitats and hippopotamus are believed to belong to the sister group of cetaceans. Their dietary needs consisted of land mammals that lived near the water and some aquatic organisms. Researchers believe that pakicetus used its limbs for propulsion in shallow water, but they were not the best swimmers. The poor swimming attributes of these ancestors could explain the evolution of a tail fluke in cetaceans. A good explanation for the transition from hind-limbs to a tail fluke could be that the tail fluke allowed whales to better propel themselves through aquatic habits in order to hunt prey more efficiently. Competition for resources in a particular ecological niche can be challenging, so transitioning to the water could have lessened the competitive pressures for the cetaceans. In addition, some researchers believe that a global climate change, which increased the availability of nutrients in the upper layers of aquatic habitats, could have been a driving force for cetaceans to move to the water. With these environmental pressures acting upon cetacean ancestors, natural selection would be the evolutionary force to have acted on these mammals to continually reduce their external hind limbs in exchange for an elongated body with a tail fluke. The best suited aquatic members of the population would have the greatest chance for survival, and they would pass their genes on to future generations. Through evolutionary processes, certain phenotypes became more adequate than others and this allowed whale ancestors to give up their reliance to the land’s resources. Natural selection is a process that acts on organisms phenotypes, which eventually alters the genotypes of future generations. Through natural selection, the expression or turning off of certain genes can generate an evolutionary effect on populations through multiple generations. Evolution occurs because certain advantageous or deleterious alleles are selected for or against in populations, and certain phenotypes and genotypes become more advantageous than others. Researchers believe that there are particular genes in the evolutionary history of cetaceans that are responsible for their transition from four limbed tetrapods into long, slender, aquatic mammals with tail flukes and no external hind limbs. Pavel Gol’din, who performs research at Taurida National University in the Ukraine, describes in a research paper potential genes that could be responsible to the loss or reduction of hind-limbs, and alterations in pelvic girdle bones in cetaceans. Gol’din used remains of whales found near a lake in the Crimea region of the Ukraine dated between 20 million and 5 million years ago to make his consensus. There are a handful of genes that could have played a role in the alterations that occurred to the cetacean body plans over the years, but there are no definitive answers as to which genes were the most influential. Gol’din described how mutations or altered expression of some of these genes in laboratory mice provide significant insight into the function of these genes. For example, he mentions that the reduced signaling of genes called Shh genes leads to “gradual reduction of distal portions of the hind limb in the course of evolution”(Gol’din 2014). Based on Gol’din’s research, it is evident that altered gene expression of particular genes most likely played a role in shaping the cetacean body plan. Mutations, although a weak evolutionary force, could have also played a role in the evolution in cetaceans. Beneficial mutations can bring new alleles into populations that were once non-existent, and these alleles can become fixed in a population over many generations. A group of researchers from Japan studied the effects of mutation on a gene involved in hind limb development in humans, mice, and cetaceans, and their results were promising. According to the results, it is thought that a nonsynonymous mutation in one particular gene could be related to hind limb development in cetaceans. The mutation appears to alter the function of a protein associated with the gene. Evidence from these researchers suggests that mutation could have played an important role in the transition from land to water for ancestral cetaceans. Once cetaceans made it to the water, it is believed that they no longer needed hind-limbs or a pelvic girdle in order to survive in their new habitat. Furthermore, researchers and scientists once thought that the pelvic girdle and hind-limbs in modern cetaceans are just vestigial remnants from their ancestors who once roamed the land. However, recent evidence suggests that some of these “vestigial” bones actually serve a purpose in cetaceans. Anatomically, whales and dolphins have a pelvic girdle, which consists of an ilium, ischium, and pubis bone, all of which are bones associated with the pelvic girdle. Some whale species, but not all cetaceans, also have reduced hind-limbs such as femur bones or tibias. Research on the hind-limbs of whales has provided evidence as to how these bones became reduced, but it has not shown any significance as to why these mammals still possess these bones. However, there is evidence advocating that the pelvic girdle in whales is necessary for certain activities. Researchers from USC, the Natural History Museum in Los Angeles, and the University of Tokyo explain that the pelvic girdle in modern cetaceans is necessary for genital support and mating ceremonies in males. Researchers from Tokyo provide evidence that explains how the muscles and bony attachments of finless porpoises that reside in an eastern Asian river are critical for the support and function of male genitalia (Tajima 2004). Similar research conducted in Southern California shows that pelvic girdle size in several male, cetacean skeletal remnants were disproportionately large compared to the rest of the skeleton. With the knowledge of how pelvic girdle muscles support the male genitalia, the researchers proposed that the size of the pelvic girdle in their specimens was a result of sexual selection. Sexual selection implies that certain characteristics are associated with a greater reproductive success. It is a mode of natural selection where certain individuals are better at acquiring mates than others. The genes of the most successful individuals are passed on and these genes help shape the evolutionary pathway of the population. A common result of sexual selection is sexual dimorphism. Sexual dimorphism occurs when there is a phenotypic difference between opposing sexes of the same species in the light of sexual selection. A form of sexual dimorphism has occurred in male cetaceans that has brought about a variance in pelvic girdle sizes (Dines 2014). Sexual selection suggests certain pelvic girdle sizes are optimal for reproduction. There were no suggestions as to whether the selection and sexual dimorphism were results of interspecific or intraspecific competition, but it is most likely that females drove males to this sexual dimorphism because females are the ultimate deciders of mate choice. Whales are part of a small group of mammals that spend their entire lives in aquatic environments. Their presence in water is due to evolutionary forces that drove their ancestors from a life on land to a life in water. The transition was made due to the effects of natural selection, mutation, gene expression, and perhaps other entities that have not been identified yet. Certain genes are responsible for the altered body plans of these mammals, and these alterations were made possible by genetic inheritance. Advantageous alleles and new allele combinations came about in cetacean ancestors that eventually led to the disappearance of external hind-limbs and the appearance of a tail fluke. The pelvic girdle of modern cetaceans is comparatively different from its ancestors and other tetrapods, but it remains prominent. The prominence of an altered pelvic girdle suggests that cetacean pelvic bones are not vestigial and actually serve a purpose. Researchers believe the purpose of the pelvic girdle in modern cetaceans is to provide structure and support for males. However the cetacean body plan came to be, whales and dolphins will always be an evolutionary wonder. CITATIONS References 1.) Gol'din, Pavel. "Naming an Innominate: Pelvis and Hindlimbs of Miocene Whales Give an Insight into Evolution and Homology of Cetacean Pelvic Girdle." Evolutionary Biology 41: 473-479. 2.) Tajima, Yuko, Yoshihiro Hayashi, and Tadasu Yamada. "Comparative Anatomical Study on the Relationships between the Vestigial Pelvic Bones and the Surrounding Structures of Finless Porpoises (Neophocaena Phocaenoides)." The journal of Veterinary Medicine 66.7: 761-766. 3.) Dines, J.P., E. Otárola-Castillo, and P. Ralph. "Sexual Selection Targets Cetacean Pelvic Bones." Evolution: International Journal of Organic Evolution. 4.) Don, Emily, Peter Currie, and Nicholas Cole. "The Evolutionary History of the Development of the Pelvic Fin/hindlimb." Journal of Anatomy 222.1: 114-133. 5.) Boisserie, Jean-Renaud, Rebecca Fisher, and Fabrice Lihoreau. "Evolving between Land and Water: Key Questions on the Emergence and History of the Hippopotamidae (Hippopotamoidea, Cetancodonta, Cetartiodactyla)." Biological Reviews 86.3: 601-625. 6.) Bajpai, S, JG Thewissen, and A Sahni. "The Origin and Early Evolution of Whales: Macroevolution 	Documented on the Indian Subcontinent." Journal of Biosciences. 34.5: 673-686. 7.) Marx, FG, and MD Uhen. "Climate, Critters, and Cetaceans: Cenozoic Drivers of the Evolution of 	Modern Whales." Science 327.5968: 993-996. 8.) Onbe, Kaori, Shin Nishida, Emi Sone, Naohisa Kanda, Mutsuo Goto, Luis A. Pastene, Shinsuke Tanabe, and Hiroko Koike. "Sequence Variation in the Tbx4 Gene in Marine Mammals." Zoological Science 24.5: 449-464.