Analyse of Vertebrate Forelimbs

1. Gather information from secondary sources (including photos/diagrams/models) to observe, analyse and compare the structure of vertebrate forelimbs.

Comparative anatomy is the study of the differences and similarities in structure between different organisms. An example of comparative anatomy is the pentadactyl limb which is the basic five-digit bone structure of many vertebrate’s forelimbs. The vertebrate forelimb (or the pentadactyl limb) comprises of the humerus (upper arm), radius and ulna (forearm), carpals (wrist), metacarpals (palm of hand), and phalanges (fingers).

The pentadactyl limb is evidence that present-day vertebrates (which include fish, birds, amphibians, reptiles and mammals) are closely related. It is believed they inherited this structure from an ancient aquatic ancestor, the lobe-finned fish. Due to natural selection, all vertebrate forelimbs, although have the same structure, are modified for very different uses. Therefore vertebrate forelimbs are homologous structures. Homologous structures are structures in different species that are similar because of common ancestry. They have the same basic structure but may appear somewhat different depending on the degree of modification produced by evolution.

One use for the vertebrate forelimb is swimming. Whales, otters and penguins have forelimbs which are modified to allow them to swim efficiently. The bones in whales are relatively compact and do not move within the flipper. This provides them with a strong ‘paddle’ which allows the whale to control the direction of their swimming. However, Otters have more flexible arms which allow for more movement. The metacarpals and phalanges are connected by skin which provides a webbed appearance. Penguins bone arrangement is only slightly different from a whale, although penguins are birds and their forelimbs were first adapted for flight and then swimming. Running is another use for the vertebrate forelimb, which can be seen in organisms such as horses, wolves and deer. Flight is a movement which requires special adaptations. Even though bats and birds forelimbs are suited for flying, they are quite different.

Forelimb structures of different vertebrates

2. Analyse information from secondary sources to prepare a case study to show how an environmental change can lead to change in species.

Evolution is a process of development, as from a simple to complex form or of gradual, progressive change as in social and economic structure. Whales have undergone many evolutionary changes over millions of years. They are large, intelligent aquatic mammals which belong to the Kingdom - Animalia, Phylum - Chordata, Class - Mammalia, Order - Cetacea, Suborder - Odontoceti, Family - Monodontidae, Genus - Delphinapterus and Species - Leucas. They breathe air through a blowhole into their lungs and have sleek, streamlined bodies that move easily through the water and are the only mammal besides manatees that live their entire life in water. They belong to the order Cetacea which is divided into the following groups: Toothed whales and Baleen whales. Toothed whales are called Odontoceti while Baleen whales are called Mysticeti. Primitive whales evolved from hoofed land mammals and may have evolved from shore-dwelling hyena-life Mesonychid that evolved into water living mammals. Whales may also have evolved from otter-like creatures which were approximately 10ft. long and 650lbs. This mammal had limbs that allowed it to swim but could also walk on land.

Our perceptions of whales are that they are like fish but whales are only like fish in that they live in water and have fins. A whale’s body contains a bone structure like mammals; its flipper has bones like a mammal’s forelimb and it is interesting to note the pentadactyl five digit bone structure (pictured below):-

Evolution occurs when natural selection causes changes in relative frequencies of alleles (gene determination) in the gene pool. Three examples of evolution which whales have experienced are

1) The change in a whale’s inner ear, 2) changes in a whale’s bone structure, and 3) the transition from legs to flippers for swimming. Sound transmission mechanisms change was an early whale evolution as the whale could hear both in and out of the water. However, eventually, the whale could hear only in the water. This was discovered by finding remains of some fossils. When the land mammals evolved