User:Cascioli.4/sandbox

Topic: Changes in the morphology of cetaceans as they moved to land.

Source 1 Demere, T.A., McGowen, M.R., Berta, A., Gatesy, J. 2008. Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales. Systematic Biology 57:15-37.

This journal entry is mainly about how whales developed their teeth. The article goes back to when whales first developed teeth and compares the morphological structure to that of other mammals. This is very important as it relates to early whale development as they transitioned form water to land animals. Overall the article tries to make the connection of how land mammals can be related to early cetaceans.

Source 2

Sheen, Judy P.. "Morphological Evolution in Whales." Animal Sciences. 2002. Encyclopedia.com. 15 Sep. 2014 .

This article focuses on the main body parts of the whale and their origins. Specifically it references the phalanges, skull, lungs and other parts of the whale. It also uses fossil evidence to compare against extinct versions of whales. This is very important as it lists many and talks about many parts of the whale that have evolved from earlier whales. Knowing this information is very important in knowing exactly how whales evolved and what exactly they evolved into.

Source 3

Suetra, Raymond. "The Origin of Whales and the Power of Independent Evidence." The Origin of Whales and the Power of Independent Evidence. TalkOrigins, 10 Aug. 2001. Web. 15 Sept. 2014. .

This article covers almost all the stages of evolution for the evolution of whales. It shows many different stages of evolution from morphological evolution to embryonic evolution. The article uses all of this evidence to try and prove the evolution of whales into other types of species. This is very helpful as it shows the evolution happen in many different aspects of whales. This amount of variety is important in finding out exactly which evolutionary steps were most important for whales.

Source 4

Bajpai, S., J. G. M. Thewissen, and A. Sahni. "The Origin and Early Evolution of Whales: Macroevolution Documented on the Indian Subcontinent." Journal of Biosciences 34.5 (2009): 673-86. Web. 15 Sept. 2014.

This article can be very helpful because it talks a lot about early whales and their morphology. It talks in depth about early whale diversity, movement, teeth, and other helpful topics. The topics will be very useful to figure out how early whales differ from current whales and what changed. Also, it will be helpful because it discusses several different structures of the whale to help make its arguments.

Source 5

Bejder, Lars, and Brian K. Hall. "Limbs in Whales and Limblessness in Other Vertebrates: Mechanisms of Evolutionary and Developmental Transformation and Loss." Evolution and Development 4.6 (2002): 445-58. Web. 15 Sept. 2014. .

This article will be helpful for several reasons. One of the main reasons is because it describes the morphology of the whales of limbs. Also, the article compares the limbs in whales to other mammals. This will help draw similarities and connection between whales and mammals. This would be very beneficial in proving that both come from a common ancestor a long time ago. This ties back to finding all of the specific evolutionary changes whales underwent to become land animals.

Assignment

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

Article addition: Filter feeding is very beneficial as it allows modern baleen whales to efficiently gain huge energy resources, which makes the large body size in modern baleen whales possible.

Talk Portion: A Few Ideas I believe this page could use a few additions in some areas Cascioli.4 (talk) 00:03, 2 October 2014 (UTC)
 * I believe the page should go into a little more detail about the loss of hind limbs and the causes or benefits that came from it.
 * Try to find information about what ecological reasons led to the change from teeth to filter-feeding.
 * Add a section about skull morphology on baleen whales as it is different from ancestral versions.

FINAL DRAFT STARTS HERE

Over the course of millions of years, cetaceans have undergone several morphological changes that have evolved them into the modern baleen whale that is seen all over the world today. Modern baleen whales now look very different from their ancestors because of some key morphological changes that have better adapted them for life under water. Many of the ancestors of baleen whales actually lived on land and this shows just how dramatic the changes were in baleen whales. Some of the changes range from changes to their teeth and the way they feed to entirely losing back limbs. Currently, baleen whales are the largest living animals on Earth (Sasaki et al., 2005). Overall, modern baleen whales have undergone severe changes to become the animal that they are today.

One of the biggest changes to the morphology in baleen whales is their teeth and method of feeding. Modern baleen whales utilize a process called filter-feeding, which was not seen in their ancestors. Filter-feeding was a very important step forward from an evolutionary standpoint for baleen whales as it gave them several large advantages. One of the biggest advantages that came from filter feeding is the ease of the process for baleen whales. They essentially swim as they normally would but with their mouth partially open. This allows them to trap the prey they want to consume and then they are able to expel only the water and keep all of the prey inside of their mouths in one simple step. This process is not only easy but it also greatly increased the amount of food that a whale was able to consume at one time. Using filter-feeding whales are able to consume incredible amounts of food leading to huge nutrient stores in their bodies. This is one of the key factors that allows baleen whales to achieve the massive size that they have today (Deméré et al., 2008). The key morphological change that made filter-feeding possible was the change from teeth in the earlier cetaceous species to baleen in the modern species. It is believed that the earliest whales to utilize filter-feeding are around 25 million years old (Milinkovitch et al., 1995). Modern baleen whales do still contain teeth during the growth phase but juvenile and adult baleen whales exclusively have baleen instead of teeth (Deméré et al., 2008). Although, filter-feeding is seen as more beneficial, it is believed that there was a very early mysticete species that still contained teeth instead of the baleen filter-feeding strategy. This species of mysticete known as Janjucetus is shown to be very morphologically similar to all other species of mystictes meaning that it evolved from a common ancestor. While it is believed that modern baleen whales and Janjucetus of mysticete share a branch on a phylogenetic tree, it is also believed that modern baleen whales went onto further evolutions while this distinct group remained its own separate species (Fitzgerald et al., 2006). The largest evolutionary difference between modern baleen whales and Janjucetus was the baleens ability to filter-feed while Janjucetus still had traditional teeth..

Another major difference between modern whales and their ancestors is the lack of rear limbs. As many of the ancestors to baleen whales were land animals, they had four legs to walk the earth on. At some point in time the rear legs were deemed unnecessary and they were lost forever. This process took place over a large amount of time as the back legs continued to become smaller and less useful than in previous generations. The main cause for legs to be lost was the change in motion that whales had to undergo to help with their lives underwater. Now baleen whales have no hind legs and live their life completely underwater which is a dramatic change from their ancestors (Sheen et al., 2002). One key change that is brought about by the loss of hind limbs is the method of movement. Previous species would combine the motion of the tail and a paddling of the legs to create motion underwater where modern whales utilize oscillatory locomotion. The loss of the rear legs was an important step forward because it greatly reduced the drag that a whale would face while swimming. It also gave rise to oscillatory motion which is able to produce much more thrust with less energy cost than previous methods for underwater locomotion (Bejder et al., 2002).

The process of losing the rear limbs in baleen whales was a long and gradual process that took place as the animals moved from predominantly land to predominantly sea animals. One feature that arose during this time was the body size of cetaceans began to grow longer as the hind limbs began to become smaller. The first portion of the hind limbs to be lost was the digits and after that the more proximal portions started to become irrelevant and eventually disappeared. The full time span that it took to complete the loss of the rear limbs was around 10-12 million years. During this time the species studied can be seen to move from land to sea because as the rear legs became less and less prominent, the animal was not able to sustain its body weight on land anymore and thus had to rely on an increasingly aquatic lifestyle. Eventually, the hind limbs were basically useless on land and the animals became exclusively aquatic (Bejder et al., 2002).

While adult baleen whales have visibly lost their hind limbs, the hind limbs are actually present in the life cycle for a short time. The embryos of whales actually form the rear limbs during the early stages of the life cycle. Whales form hind limb buds during growth but the development of these buds is cut off early in the life of a growing whale. In some species, like the humpback whale, it is seen that the buds will persist for a longer amount of time than in other species. In the hind limb of whales is a signaling center called the apical ectodermal ridge (AER) and this center signals for the outgrowth of limbs. Eventually, the AER goes away and this causes the hind limb to stop all growth. The cells from the hind limb do not go to waste however, as some of them join together to help form the body wall of a whale (Bejder et al., 2002). In the process of whales losing their hind limbs it is clear that selection is very strong against hind legs as cetaceans moved from land to sea (Thewissen et al., 2006).

Another important step for modern cetaceans was the evolution of the ear when transitioning from land to sea. Hearing in water is very different from hearing on land so cetaceans had to develop a new way to hear as they became aquatic animals. While still land mammals, whales ears had three components, the outer ear, middle ear, and inner ear, similar to humans ears. Modern whales now use a different mechanism to be able to hear underwater. First, there is no external auditory meatus for the sound to travel into so the sound enters through the mandible instead. The sound then travels to the tympanic bone and is received at the tympanic window which replaces the tympanic membrane that is seen in land mammals. From the tympanic window sound vibrations are passed onto the inner ear where the sound is interpreted. Whales were not able however, to completely make the jump from land mammal transmission to odontocete transmission. In between these two transmission sequences is inertial transmission and at one point inertial transmission was the main way that whales could hear underwater. Inertial transmission, which is present in all mammals, is where sound reaches the inner ear by passing through the bones and soft tissue of the skull (Bajpai et al., 2009). Eventually, inertial transmission was replaced by odontocete transmission as odontocete transmission allows for more clarity in sound when hearing underwater.

The ability to functionally hear underwater was a very large evolutionary step forward for modern baleen whales. Their ability to now hear and comprehend noise underwater was an important step in being able to live their lives completely underwater. The evolution of the inner ear and hearing underwater allows modern baleen whales to communicate successfully with each other without having to move onto land. This is important because it meant that whales could interact with other whales and mate while staying completely underwater.

All of these morphological evolutionary changes are very important and can be used to conduct research in many different ways. From these changes it has been shown that whales are very closely related to many animals that originally would have been overlooked. Also, the differences in morphologies can help further build as accurate a phylogenetic tree as possible. Whales are known to be in a clade together but there are some problems with the relationships between cetaceans and research into these morphologies may be able to help clear up some of these issues (Milinkovitch et al., 1995). If more research is done it may also be revealed that whales are closely related to even more species than previously thought because of similar morphological characteristics.

Cetaceans as a whole have changed so much throughout their existence and are an incredible phylogeny to track back to their ancestors. Their relationship to other animals that are very different to them is incredibly interesting and is something that should be further studied. The fact that these animals moved from land to becoming completely aquatic is something that is hard to imagine. To accomplish this, cetaceans needed the help from a few key morphological evolutions like the switch from teeth to baleen, loss of hind limbs, and the change in ear structure to sustain their gigantic size and new way of life. Overall, the evolution of cetaceans from their ancestral form to their modern baleen form is something that is incredible and can’t be ignored as it is not every day that a species completely changes its habitat so drastically from its ancestral state.

References

Demere, T.A., McGowen, M.R., Berta, A., Gatesy, J. 2008. Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales. Systematic Biology 57:15-37.

Sheen, Judy P.. "Morphological Evolution in Whales." Animal Sciences. 2002. Encyclopedia.com. 29 Oct. 2014 .

Bajpai, S., J. G. M. Thewissen, and A. Sahni. "The Origin and Early Evolution of Whales: Macroevolution Documented on the Indian Subcontinent." Journal of Biosciences 34.5 (2009): 673-86. Web. 29 Oct. 2014.

Bejder, Lars, and Brian K. Hall. "Limbs in Whales and Limblessness in Other Vertebrates: Mechanisms of Evolutionary and Developmental Transformation and Loss." Evolution & Development 4.6 (2002): 445-58. Web. 29 Oct. 2014.

Thewissen, J. G. M., M. J. Cohn, L. S. Stevens, S. Bajpai, J. Heyning, and W. E. Horton. "Developmental Basis for Hind-limb Loss in Dolphins and Origin of the Cetacean Bodyplan." Proceedings of the National Academy of Sciences 103.22 (2006): 8414-418. Web. 29 Oct. 2014.

Fitzgerald, Erich M. G. "A Bizarre New Toothed Mysticete (Cetacea) from Australia and the Early Evolution of Baleen Whales." Proceedings of the Royal Society B 273 (2006): 2955-963. 15 Aug. 2006. Web. 29 Oct. 2014.

Milinkovitch, Michel C. "Molecular Phylogeny of Cetaceans Prompts Revision of Morphological Transformations." TREE 10.8 (1995): 328-34. Elsevier Science Ltd. Web. 29 Oct. 2014.

Sasaki, Takeshi, Masato Nikaido, Healy Hamilton, Mutsuo Goto, Hidehiro Kato, Naohisa Kanda, Luis Pastene, Ying Cao, R. Fordyce, Masami Hasegawa, and Norihiro Okada. "Mitochondrial Phylogenetics and Evolution of Mysticete Whales." Systematic Biology 54.1 (2005): 77-90. Web. 29 Oct. 2014.