Homologous and Analogous

Homologous traits can be found in many tetrapods, and two of those tetrapods are the crocodile and the mouse. The crocodile has four limbs which gives the two front limbs of the crocodile each a humerus radius, ulna and scapula. The two rear limbs of the crocodile each have a fibula, tibia and femur. When we compare this to a mouse,  you will find that the structure of the limbs are similar giving the front two limbs of the mouse a humerus, radius, ulna and scapula. The two rear limbs of the mouse also have a tibia, fibula, femur. The limbs of each organism having the same bone structure in common and each organism has four limbs, meaning that they have a homologus trait. The difference between a mouse and crocodile is that the mouse is a mammal and the crocodile is a reptile. The crocodile has webbing in between each phalange,  giving it the ability to swim.  The phalanges of mice do not have any webbing in between. Generally speaking,  the most common ancestor between these two species would be the lobe-finned fish. If we look at the tetrapod fossil record, you can see that the early tetrapod branched off into four directions which lead to amphibians, mammals, reptiles and birds. The tetrapod was the first four legged vertebrate that carried the trait which was then passed on to mammals and retiles. (http://www.ucmp.berkeley.edu/vertebrates/tetrapods/tetrafr.html)

There are many types of analogous traits that we can find everyday if we look close enough at all the different organisms that exist today. Some of those analogous traits can be found in birds and insects, specifically the wings of a bird and the wings of an insect. The wings of a birds have a much different structure compared to insects , and is similar to a tetrapod. The wings of a bird are made up of a skeletal structure which includes the phalanges, metacarpals, ulna, radius, humerus and scapula. The wings of the bird give it the ability to fly, because the structure has hollow bones, in which the bird evolved to be lightweight and have the ability to fly. Like birds, butterflies also have the ability to fly but do not have the same wing structure. Butterflies wings are made up of two chitonous layers, and thousands of colorful scales,  and many hairs which cover the outside of the wings.  The scales are outgrowths of the body and are plate-like setae. The  butterfly's  wings do not have a skeletal bone structure like birds. The bird's  wings and insect wings are analogous, and share a common function,  but they do not have a common original ancestor that could have evolved or been modified through evolution. I would say that the most common ancestor between insecta and reptilia would be arthropoda. The arthropoda organisms lead to chordata, which then lead to vertebrata  and reptilia. I think the trait of flying or having wings was carried down, and then lead to birds which are considered reptilia.

(http://darwinc.wikispaces.com/Charles+Darwin)

(http://www.enchantedlearning.com/subjects/butterflies/anatomy/Wings.shtml)

(http://www.birdsinbackyards.net/birds/Bird-Anatomy-How-do-birds-fly)

(http://www.untamedscience.com/phylum/chordata/)

(http://evolution.berkeley.edu/evosite/evo101/IIC1Homologies.shtml)