A cladogram is a reconstruction of the evolutionary history of species and as analyzed in this paper, it is the evolution diagram of a group of animals based on the distribution of newly evolved features or advanced features. Cladograms are tree-like relationship diagrams with the advanced features noted at the appropriate branching points.Each group, or clade, is recognized by the set of advanced features inherited from a common ancestor and contains all the descendants of that common ancestor. The cladogram that is being analyzed here is based on what was seen at the American Museum of Natural History (AMNH).Physical characteristics are used to divide the major groups of vertebrates on the vertebrate cladogram shown at the AMNH. The physical characteristics are the following: relatively long arms, uneven covering of enamel on teeth, eye sockets near snout, three-fingered hand, inset tooth rows form cheeks, hoof, three-toed foot, backward-pointing extension of pubis bone, stirrup-shaped stapes, grasping hand, hole in hip socket, placenta, three middle ear bones, antorbital opening, synapsid opening, palatal opening, watertight egg, four limbs, jaws, vertebral column and braincase.Tetrapod limbs (Figure 1.
1) are composed of three sections: !) the humerus, which is a single heavy bone that articulates with the body and forms the foundation of the limb; 2) two bones, which could be either tibia and fibula or radius and ulna, that are lighter and combine support with a greater degree of maneuverability; and 3) the section farthest from the body that consists of many smaller bones, wrist, ankle and fingers, providing considerable flexibility for locomotion and food gathering. The limbs of the tetrapods are unique in having an internal bony skeleton with movable joints surrounded by muscles that are grouped for specific functions.Limbs were used mainly for locomotion such as running, climbing or walking, particularly for early animals.
Later on, they used their limbs to hunt for prey, grasp and manipulate objects.Where did the vertebrate limbs originate according to the theory of evolution? How did it evolve? Fossil records suggest that limbs first evolved in fully aquatic vertebrates. It seems that limbs evolved first than the skull and the backbone. The records also suggest that this feature that is indicated in the appearance of living tetrapods did not suddenly appear all at once but were acquired gradually by our aquatic ancestors – the fish. Limbs are the most obvious and fossils reveal how they evolved from structures in the fins of fishes such as Eusthenopteron (Figure 1.
2) and Sauripterus.The Eusthenopteron, particularly, has bones in both of its fins that are the same with the later tetrapod limbs. It has a single heavy bone, the humerus, which connects with the body and followed by two connected bones which represent the radius and the ulna. Limbs provided a vast potential for diversity in moving about on land and gathering various preys.
Various abilities such as running, swimming, climbing, digging, flying and catching preys all evolved as the tetrapods diversified into a multitude of diverse species, from frogs and birds, to humans and whales.