Austin Lee
austinklee7@gmail.com
Monday, March 28, 2011
Limb Development
Ch.2 of Neil Shubin's book discusses the evolution of limbs starting from prehistoric organisms to modern day animals. A diagram on page 31 shows an interesting diagram of the bone structures of limbs from different animals, shaded to show how they are similar to one another. This chapter explains how even fish fins are related to our own arms, using Tiktaalik as the bridge between the two. Describe the relationships between our limbs and those of other animals all around us, and explain how fish limbs developed into the limbs of terrestrial animals. Use specifics given by Your Inner Fish and class material, as well as outside sources if necessary.
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ReplyDeleteSir Richard Owen was one of the leading anatomists in the 1800s. He noticed a pattern among the limbs of tetrapods (animals with four limbs). In many different animals that he looked at, the general pattern among bones in the limbs were the same: one bone attached to the torso, followed by two bones, followed by a larger collection of smaller bones that connect the fingers. This pattern holds true for all the limbed animals that we are familiar with, of course with variation for each animal. For instance, human forearms follow the pattern by having two, adjacent bones, while dogs' forearm bones are sometimes fused together. Also, in humans, the femur in the legs is the largest bone in the body while the corresponding bone in dogs is the same length as the rest of the bones. These differences are a result of evolution in the same way that dog ears are different than human ears: dogs have split from humans from a similar ancestor, and natural selection factors have shaped their anatomy to have selective advantages in dogs' environments, which are different from humans.
ReplyDeleteThe whole book was based on Tiktaalik, the animal which showed the transition from fish to land animals. One of the most striking things to notice was its development of limbs like we see in modern-day tetrapods. These limbs developed from fish fins, and the environment of Tiktaalik can help us understand why this transformation took place. The streams and riverbeds where Tiktaalik lived were filled with dead plants and other organic material that combined with the mud to create a mucky surface. The development of fins and limbs that could support the animal's weight would provide a great advantage to moving around the mucky river floor. Also, the fact that these fin-limbs jutted out of the body at a 90-degree angle helped them support the animal's weight.
http://www.ehow.com/facts_6749261_difference-dog-bones-human-bones.html
http://www.msnbc.msn.com/id/4638587/ns/technology_and_science-science/
Jeremy Solomon
imabum14@gmail.com
As Jeremy mentioned, Sir Richard Owens was a scientific leader in finding "important patterns in the seeming chaos of life's diversity" (Shubin 30). One of his most important discoveries was that "our arms and legs, our hands and feet, fit into a larger scheme" (30). The general pattern that he discovered in the human arm was found in dinosaurs, birds, seals, lizrds, and even bats: one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Of course, as Jeremy pointed out, there are small differences between creatures' limbs, but the they "lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes...the underlying blueprint is always present" (Shubin 31). A bat wing has really long fingers in order to increase the surface area of its wings and make flying more efficient, but the pattern of its wing is the same as a human arm. The reason the wing of a bat and the arm of a human share a common skeletal pattern is because they share a common ancestor, but different environmental pressures forced each to develop different selective advantages that would result in completely different species.
ReplyDeleteThe discovery of Tiktaalik gave new insight to the movement of animals from water to land. They had discovered a fish with a wrist. This limb development that is similar to tetrapods today helped bridge the gap between fish and amphibian. Its environment was some sort of shallow stream, which "would require fish to have limblike fins to propel themselves along the surface of shallow waters, hold their position in a current, or lift their head to the water's surface to gulp air" (http://news.nationalgeographic.com/news/2004/04/0401_040401_tetrapodfossil.html). Although Tiktaalik is far, far away from humanity, the fact that most of the major bones humans use to walk, throw, or grasp first appear in animals tens to hundreds of millions of years before is crucial to evolution. It shows, in fact, our "inner fish," and that all species did evolve from a common ancestor.
(http://news.nationalgeographic.com/news/2004/04/0401_040401_tetrapodfossil.html)
Hannah Kay (hgkay@aol.com)