DISCUSION OF THE CHARACTERISTICS WHICH IDENTIFY EACH ORDER OF THE PLACENTAL MAMMALS AND LIST OF ORGANISMS

Placental animals are organisms which maintain their young in the body of the ''mother until the end of the period of the gestation'' (Wund and Myers, 2006). There are several orders of organisms which are found under the placental mammals which also have different unique or diagnostic features. These orders include ''Chiroptera, Artiodactyla, Rodentia, Logomorpha, Carnivora, Insectivora, Cetacea, Tubulidentata, Pholidota, Primates, Dermoptera, Proboscidea, Sirena, Scandentia, Edentata, Perissodactyla, Xenarthra, Embrythopoda, Creodonta and Condylarthra'' (Wund and Myers, 2006) . Under each order there is an also different animals such as Pigs and Deer.

In the order artiodactyla variety of characteristics and animals are found. These unique characteristics include two or four toes. ''Pigs, Deer, Cattle and Goats'' are examples of the order artiodactyla (Wund and Byers, 2006). Pholidota, in this order diagnostic features such as ''long toque and imbricate scales which tend to overlapp'' (Byers, 2005). The examples of animals which are found in this order include only Pangolins. Primates, the diagnostic features which primates possess include ''brain with a posterior lobe, claviculate and unguiculate'' (Wund and Myers, 2006). The examples of animals in the order primates are Monkeys, Lemurs and Chimpazees.

The order cetacea include animals such as Dolphins, Whales and Porpoises. The organisms which belong to the order cetacean usually have the following unique characteristics which is their ''highly specialized aquatic lifestyle'' (Byers, 2005). In the other side Logomorpha have two pairs of the upper incisors and molars without roots. Examples of animals which are found in this order are Rabbits, Hares and Pikas. In the order Chiroptera, only one example of animal is found. The animal which is found is Bats. The unique characteristic which Chiroptera possess is their modified forelimbs.

The order Carnivora include examples of animals such Dogs, Cats and Bears. The diagnostic feature which distinguish this order from others is their adptation on eating meat. Insectivora have these unique features, ''small brain, unspecialzed teeth, poorly developed eyes, small ears and a long pointed snout'' (Wund and Myers, 2006). Examples of animals found in the order Insectivora include Moles and Shrews. In the order Rodentia, examples of animals such as Mice, Rats, Squirrels and Gophers are found. The distinguishing characteristics in which Rodentia possess are one pair of chisel-like incisors and they have no canine teeth. Tubulidentata is the order in which only one example of animal is found. This animal is Aardvark. Tubulidentata possess a unique structure of the teeth. In adults canines and incisors are absent. The only teeth which are found are at the back of the jaw.

Animals which belong in the order Dermoptera have the unique features such as ''incisors which are specialized for comb-like teeth'' (Murphy and Eizirik, 2001). The adaptive incisors are also used for grooming. Examples found in these order Dermoptera include only Flying lemurs. Proboscidea is the order which include animals such as Elephants, Mammoths and Mastodons. Wund and Myers (2006) say that the diagnostic features which are found in this order include horns which consist of parietal bones and manatees. Sirenia is the order which include only one animal which is Sea cow. The only unique feature in this order is the absent of the teeth. Scandentia is the order in which animals such Tree shrews.

In the order Edentata, unique characteristics such as ''large claws for digging and lack of teeth are found'' (Murphy and Eizirik, 2001). The examples which are found in the order Edentata are Sloths and Armadillos. Byers (2005) says that Perissodactyla is the order which possess the following unique characteristics, hoofed forms and odd toed. Examples of animals which are found in this order include Horses, Donkeys and Zebras. Xenarthra is the order which possess the following unique characteristics ''long sticky tongues, long claws on their front teeth and small brain'' (Wund and Myers, 2006).

In conclusion, it is easy to say that in all orders mentioned above some examples of animals are faced with extinction. This is because that in other order such as Chiroptera we only find one example which is that of Bats. On the other side, as opposed to Chiroptera, in certain orders such as Primates we find more than one examples of animals. It is also common that in each order there is one or more diagnostic or unique characteristics.


References:

Byers, R. 2005. Post-Flood Marsupial Migration Explained. [Online]. Available from:
http://www.rae.org/marsupials.html [19 October 2005, 12: 20]

Murphy, W. J.; Eizirik, E. 2001. Molecular Dating and Biogeography of the Early Placental Mammal Radiation. [Online]. Available from: http://jhered.oxfordjournals.org/cgi/content/full/92/2/212 [February 2001, 07; 12:42]

Wund, M. and Myers, P. 2006. Order Insectivora. [Online]. Available from:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Mammalia.html [cited 25

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