Anthropology: From Paleocene to Miocene
A Study Guide
In the world of anthropology several epochs or time periods prove vital to the classifications of primate species. Four hugely important periods that occur are the Paleocene, Eocene, Oligocene, and the Miocene. All of these geologic time frames are important as they each tell a story about the evolutionary process in which primates changed and were shaped.
Starting with the Paleocene time period of 65-56 MYA this marked the beginning of the adaptive radiation of mammals. Up until this time mammals have been recorded not to have existed.
The next geological time frame of significance is the Eocene period, which occurred from 56-35 MYA. The most notable discovery would be the initial radiation of primates. These fossils, which have been found throughout Eurasia, China, North America and Africa mark the start for these primates. Two families that arose during the Eocene were the Omomyidae and the Adapidae. These two families shared similar traits with one another and this included features such as the post orbital bar, nails instead of claws, convergent orbits and a series of adaptations for an arboreal lifestyle with an emphasis in leaping. However, although these two families share traits there are many features that distinguish the two as different. The Adapidae exhibited a different dental formula of 2:1:4:3 to 2:1:3:3 and had small incisors and large canines. Their diet most likely consisted of being foliverous and frugivorous. Many of them were believed to have been larger bodied being around 500g. They had relatively long snouts with small orbits relative to the size of the skull. The mandibular symphysis occasionally fused and had grasping feet and an opposable hallux. These primates for the most part were diurnal or active during the day. The Omomyidae however, exhibited a dental formula of 2:1:4:3 and had large incisors and small canines. They were most likely frugivorous and insectivorous. They had smaller bodies than 500g. Short snouts with large orbits relative to the skull. An unfused mandibular symphysis with grasping feet and an opposable hallux and were most active during the night because they were nocturnal.
It is interesting to point out that the features that separate the two families later adapt into opposite suborders than we would think. As it turns out the family of Adapidae's turn into the suborder we know as strepsirrhines and the Omomyidae become Haplorrhines. This is unusual due to the fact that the suborder Haplorhini is based off of features found in the Adapidae and features of the Omomyidae are heavily found in common Strepsirhini. Overall this is an important time in someways because this can be thought of as the starting point for not only monkeys but humans as well.
Moving onwards into the time frame of the Oligocene 35-24 MYA we begin to see the a diverse adaptive radiation of anthropoids including the first catarrhines (New World Monkeys) and platyrrhines (Old World Monkeys, Apes, Humans). The first ancestor to the family of Platyrrhines would be the Parapithecidae, which was very much like a Lemur. These New World Monkeys (most of which resided in South America) had physical characteristics that were unique to the primate species from before the Oligocene. This included having a 2:1:3:3 dental pattern, a Zygomatic-Parietal Contact, and no ear tubes. The origins of the first playtrrhines also has sparked several theories as to why they are geographically located where they are today. Since back then New World primates were found only in Africa and South America and the only way for them to reach North America is if they had rafted on favorable currents to the New World.
Much like how the first ancestor of the platyrrhines was Parapithecidae, the first ancestor to the Catarrhines is the Propliopithecidae. Unlike platyrrhines, these catarrhines had a dental formula of 2:1:2:3, a frontal-sphenoid contact, and an ear tube. During this historic time in history two different superfamilies appeared: the cercopithecoidea (All Old World Monkeys) and Hominoids (Apes and Humans). The difference between the two can easily be described with their features. For Cercopithecoids they had Bilophodont molars, narrow nasal aperture, cranial capicity was smaller than the face, laterally placed scapula, narrow and deep thorax, long lumbar region, and a long tail. Hominoids on the other hand had these traits : Y-5 molars, broad nasal aperture, cranial capacity equal or greater than face, dorsally placed scapula, broad and shallow thorax, short lumbar region, and no tail. These hominoids would then come to evolve into several species of apes and the species of homo-sapiens.
The last long period of time that is significance is the Miocene, which lasted from 24-5 MYA. During this epoch their was a diverse range of both cercopithecoids and hominoids. However, since I already discussed cercopithecoids earlier, I will discuss the range of differences in the hominoids. Starting with the Proconsul, which is ancestral to all hominoids, this primate had Y-5 molars, a post cranium that was more monkey-like, weighed around 10-150lbs, terrestrial and arboreal quadruped movements, and had think enamel that suggests that it was frugivorous and possibly ate seeds and nuts. The Pilopithecoidea was another primate similar to the the Proconsul that had a robust mandible, suspensory motion, and was possibly the first cattarrhine to leave Africa towards Asia. Both of these primates fall under the family of the Pongidae and both are considered by anthropologists to be "Dental Apes".
"True Apes" on the other hand showed a Y-5 pattern and ape like post cranium. The first of the "True Apes" is believed to have been Kenyapithecus, which has been dated to have lived around 16 MYA. Another couple of Pongidae were the Dryopithecus and Oranopithecus, which lived in Europe. The Gigantopithecus is the crown jewel of this time frame as it is the first primate believed to have been bi-pedal or first "walking" primate. This is due to the fact that the Gigantopithecus has his magnum foreman right below where its brain is, which is a strong indicator that the primate used only his two feet to walk.
Overall these time periods have shaped the very fabric of not only primates, but the course of human history. The vast characteristics that have changed throughout several millennium are both interesting and important in understanding how primates evolve in different ways. Although I hope my article on this subject proves to be useful I hope that anyone interested continues to pursue the knowledge of the past because only then can we understand how being human makes us unique. As always I hope you enjoyed this article and please feel free to leave comments.
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