Comparitive Dentition Patterns Among Primates

Lemurs(Prosimians/Strepsirhini): a. Lemurs can be found on the island of Madagascar (an island off the coast of Africa), and the neighboring Comores Islands. They are arboreal creatures and live most of their lives in trees.Lemurs live in a variety of habitats. Some live in moist, tropical rainforests, while others live in dry desert areas.

b. Lemur dentition is heterodent and derives from an ancestral primate permanent dentition of . In the toothcomb of most lemurs, the bottom incisors and canine teeth are procumbent (face forward rather than up) and finely spaced, thus providing a tool for either grooming or feeding. The toothcomb in lemurs normally consists of six teeth (four incisors and two canines), although indriids, monkey lemurs, and some sloth lemurs only have a four-tooth toothcomb due to the loss of either a canine or an incisor.

c. The toothcomb, which is specific to Lemurs is a direct expression of their environment and habitat. It is useful in grooming and can be a handy tool in the harsh and diverse climate of Madagascar.

 Spider Monkey (New World Monkey/Platyrrhini): a. Spider monkey's are found in the tropical rainforests of Central and South America. They thrive in evergreen, semi deciduous and mangrove forests and almost never come down to ground level. These monkeys live in the highest parts of the trees found in rain forests, known as the 'upper canopy'. They prefer undisturbed high forests.

b. Spider monkey dentition is similar to that of all New World monkeys. They have 2 incisors, 1 canine, 3 premolars and 3 molars in each quadrant.

c. Since these primates are found high in tree tops their dentition has developed to facilitate the easy consumption of whole fruit and leaves.

Baboon (Old World Monkey/Cercopithecidae): a. Baboons live in sub-saharan west and north Africa. This area is extremely dry and arrid.

b. Baboon dentition can be characterized by a more elongated arch form, prominent maxillary canine crowns, and second and third molar crowns of greater size than first molar crowns.

c. Baboons eat mostly vegetation consisting of grasses, roots, seeds, but are known to eat small sub-saharan mammals such as hares and birds. This diet along with the behavioral adaption of showing their teeth to demonstrate dominance, has allowed for the evolution of this specific dentition.
 

Gibbon (Lesser ape/Hylobatidae): a. Gibbons can be found in the tropical and subtropical rainforests of India on Indonesia, China, and the islands of Sumatra, Borneo, and Java. They are arborean primates and spend nearly all of their lives in treetops.

b. Gibbons possess noticeable characteristics of their dentition. They have large, dagger-like canines in both the upper and lower jaw. These canines are not sexually dimorphic.
c. Gibbon canines are adapted for eating meat and much like baboons, for showing dominance. 

 Chimpanzees (Great ape/Hominidae): a. Chimpanzees are divided into two subspecies within Africa. The common chimpanzee can be found in west and central Africa, while the Bonobo can be found in the Congo. The Congo River acts as the main dividing line between these two species, and they can be found in a diverse range of habitats from the rain forest to grasslands.
b. Chimpanzee dentition is similar to that of the Old World apes and human species. They are the most closely related to humans out of all the primates. They have 2 incisors, 1 canine, 2 premolars, and 3 molars in each quadrant.
c. Like many primates with pronounced canines, Chimpanzees most likely developed them due to the necessity for tearing and eating meat from flesh and to show dominance.

Summary: Through my findings I have found that dentition patterns in primates are mostly due to their diet. Behavioral patterns have played a key role in the development of prominent canines in some of the larger apes, and smaller, more predominantly herbivore primates developed more square flat teeth for grinding small leafs and fruits.

Homologous and Analogous Structures

1. a. Humans and horses share a common homologous structure respectively, however they are two entirely different species. They are both mammals but share many differences.
    b. The arm of a human and the forelimb of a horse are considered homologous structures. Each structure contains similar bones. A humerus, carpals, metacarpuls, and phalanges. These structures however serve different funtions. The human arm aids in lifting, climbing, use of tools, and countless other activities, while the horses forelimb is mainly used for running. This homologous trait represents a genetic similarity that is evident in all mammals.
    c. Generally all mammals derive from a similar ancestor, and this is evident in similarities in much of their bone structure.
   
    d.

2.  a. Birds and insects share an analogous structure in their wings. Birds are part of the avian family while insects belong to the family of arthropods.
    b. Both species have wings but are composed of completely different structures. Bird wings contain hollowed out bones which allow them to be light enough to fly, but still agile enough to fly at high speeds and altitudes. Insect wings don't contain bones and are mainly extensions of their own exoskeletons. Although the structure of each species' wings are different, they are still functionally similar in the aid of flight.
    c. Although the common ancestor of these two species (which is probably some sort of reptile or fish) did not share the similar analogous trait, they did most likely evolve this structure due to similar environmental necessities.
    d.

Jena Baptiste-Lamarck: Influences on Darwin

Perhaps one of the most influential thinkers and scientists to aid Darwin in his findings of the evolutionary theory was Jean Baptiste-Lamarck. Lamarck's landmark theory was known as the inheritance of acquired characteristics. This theory suggested a dynamic relationship between a species and its environment, and suggested that should a certain species' environment change, that species would change over time to acclimate to its surroundings. A common example of Lemarck's theory is hypothetically expressed through giraffes. As giraffes continually consume leaves at the bottom of trees, they try to reach leaves in higher branches. This straining force brings new tissues to the neck, elongating it and passing this new trait onto its offspring. This theory, which has since been disproved was influential to Darwin in accumulating his own theories. It helped Darwin to conclude that organisms that are better suited to their environment will benefit from its resources. Lamarck differed in that he believed organisms were constantly evolving upwards towards greater complexity and perfection, while Darwin's theory of natural selection held that natural selection acted on random variation, not a constant improvement.
Darwin's publication On the Origin of Species was and still is heavily opposed by the church. In Darwin's time the church held great precedence over all scientific and philosophical discovery, and to make any verbal or written opposition to the church could lead to ones imprisonment and or death. This heavy constraint by the church only invigorated Darwin more to publicize and educate the public of his findings.



Sources: 

Introduction to Physical Anthropology text

http://www.pbs.org/wgbh/evolution/library/02/3/l_023_01.html