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The purpose of this study is to discover the relationship between the number of teeth and the postcanine occlusal area and postcanine mesiodistal length in select OWM and NWM species. New World monkeys (NWM) have 12 premolars, whereas Old World monkeys (OWM) have 8. Four species are studied: Cercopithecus albogularis and Colobus guereza (OWM), and Cebus capucinus and Alouatta palliata (NWM). Two pairs of species are chosen because they are classified as having the same general folivorous and omnivorous diet: Co. guereza and A. palliata, and Cer. albogularis and Ceb. capucinus, respectively. Adult, wild caught, female specimens from the Smithsonian, National Museum of Natural History are studied. Sample sizes are as follows: 20 Co. guereza, A. palliata and Ceb. capucinus, and 14 Cer. albogularis.
The null hypothesis is there will be no difference in the overall occlusal area of the premolar and molar rows between the compared species, and that the occlusal area on the premolar row will be distributed differently among OWMs and NWMs individual teeth. Results show that an extra premolar in the NWMs increases the postcanine occlusal area and postcanine mesiodistal length contributed by the premolar row to the overall postcanine row. In NWMs, premolars make up 40-50% of the postcanine mesiodistal length and occlusal area while in OWMs, the premolars make up only 30%. Each premolar is close to the same length of 33% of the premolar row for NWMs; whereas in OWMs, each premolar is about of 50% of the premolar row. Therefore, in terms of postcanine length, the loss of P2 in OWM species leads to a uniform increase in postcanine length of P3 and P4. Likewise, when P2 is present, there is the same mesiodistal postanine length of about 33% on each premolar. Therefore, retention or loss of P2 does not seem to affect proportionate size of premolars