Pauline Awuor Sangoro

 Plesiadapis Extinction: Written Assignment First Second Name Institution Abstract Plesiadapis were primates that existed in Europe and North America whose road to extinction has garnered significant debates centering around the origin of primates and their destruction. They are primates that took the form of lemurs. They can be compared to present-day beavers with long bushy tails and possessed great agility. One of their distinguishing characteristics was the location of their eyes. Unlike most living primates, their eyes were placed on the side of the heads instead of the front. In addition, they had longer snouts and jaws similar to rodents, and they had a diastema which separated the incisors from the molars. The enlarged snout enabled them to smell what they could not capture visually. They appeared to adapt to an omnivorous diet which comprised mostly of fruit and nuts. They had teeth similar to those of living primates with much flatter chewing teeth than those of mammals at the time hence making them predisposed to feeding on vegetation and soft fruit. Interestingly, they did not have grasping hands but were well-adapted to their environment. They had claws that enabled them to scale trees with great ease. Current reports do not indicate whether Plesiadapis lived on the ground or in the trees. However, they reveal that the mammals climbed trees. By observing the skeletal structure of the Plesiadapis, scientists believe that they were strong and skilled enough to climb trees hence leading to the conclusion that they were arboreal mammals. A French paleontologist and entomologist named François Louis Paul Gervaise discovered Plesiadapis in 1877. His paleontological work paved the way for other works in the world history of fossils. The extinction of the Plesiadapis and other nonhuman primates is a significant cause of concern, which thus prompts studies to create awareness on the factors causing the problem and solutions. Introduction Primates play an integral role in human evolution, biology hence becoming critical contributors to the livelihoods, cultures, and religions of humankind. Research shows that unsustainable human activities are the leading cause of primate extinction in the world today (Estrada, 2013). However, primates that existed before human beings went extinct to pave the way for more developed species. The earlier hominids came into abundant existence after dinosaurs went extinct over 65 million years ago. The Plesiadapis continues to thrive in newly cleared territories where they rapidly developed into many new species which include the ancestors of current-day primates. The Plesiadapis lived during the Paleocene period, which was approximately five years from the time the dinosaurs went extinct. It, therefore, explains their small size since the earlier primates did not achieve the large size associated with primates that came during the Cenozoic Era. Apart from their dental formula, the Plesiadapis had nothing in common with current primates like the monkey and man. Some scientists report that these species lived on trees and it is only after tens of millions of years of evolution that their descendants stopped scaling trees and started roaming the land to eat insects and animals (Gingerich, 2011). The descendants also managed to develop a larger brain capacity with every evolutionary period. Discovery of the Plesiadapis François Louis Paul Gervaise discovered the remains of Plesiadapis in France. The piece he found was the left-side mandibular fragment of the mammal of the type specimen MNHN Crl-16 (Erickson & Erickson, 2019). It can be traced back to the early Eocene epoch. The Plesiadapis are grouped under Plesiadapiform primates. Their remains have been recovered from seven different regions of Canada. These regions are Paleocene sites. The presence of fossils in North America and Europe is an indication that they originated from one point and migrated to another. Fossil evidence reveals that the Plesiadapis species originated in North America then moved across to Western Europe through Greenland. Older fossils found in Northern parts of America show that the Plesiadapis genus was originally from that region. They then shifted to Western Europe through Greenland. They abruptly disappeared from areas in America and became abundant in Europe for millions of years. It is possible that they colonized the region and dominated over other species. An abundance of the genus and the rapid rate at which they evolved paved the way for Plesiadapis species to impact the zonation of Late Paleocene continental sediments (Wilson, 2014). It also affected the connection of faunas on different sides of the Atlantic Ocean. The Menat region of France produced two remarkable skeletons of Plesiadapis with one being almost complete. The preservation of these skeletons is rather weak, but they display evidence of skin and hair remains, which is a unique attribute of Paleocene mammals. They are better preserved in fossils from Cernay in France where Plesiadapis remain as some of the most ordinary mammals. The existence of the Plesiadapis escaped the attention of most paleontologists, and when they finally discovered their remains, it still took a long while to make sense of them. At the time they were finally understood, the matter of human beings evolving from apes and monkeys always struck a raw nerve. It was only fifteen years after Charles Darwin’s publications of evolution treaties that the Plesiadapis was discovered (Ciochon, 2017). Dentition and Dietary habits of the Plesiadapis Much of the available information on the anatomy of Plesiadapis relies on fragments of jaw and teeth fossils. For this reason, much of its definition is based on dentition. The remains of the mammals reveal that they had to adapt to grinding and crushing using teeth in the cheek region. It, therefore, appears that their diet leaned more towards herbivorous and omnivorous adaptation. Both their upper and lower jaws have a dental formula of 2.1.3.3 (Chester et al., 2019). To accommodate the teeth is the skull. The Plesiadapis had a relatively broad and flathead which displayed a long muzzle. They possessed jaws and teeth that resemble those of a rodent. Their incisors were separated from it molars by a diastema (Szlay, 2017). By today’s standards, the mammals had a smaller brainpan than its current descendants. However, their braincase was still more substantial than that of contemporary hoofed animals. The Plesiadapis had a long bushy tail which is conserved in the Menat skeletons. Habitation of the Plesiadapis Their living habits have been a topic of great debate. Most primates and their relatives are skilled climbers or at least have the ability to scale heights. However, studies indicate that the plesiadapis were in too high a number to be entirely living on trees. Using this as part of the evidence, some paleontologists conclude that these mammals were land dwellers, just like present-day ground squirrels (Goodenberger, 2015). Notably, scientists have continued to conduct further studies to find out more information about these primates. Recent studies thus found out that the skeleton of a Plesiadapis was more adapted to adept climbing. The animals come to close comparison with tree squirrels or marsupials that live in trees such as possums. Their long sideways flattened claws, short, stout limbs, and long bushy tail are an indication that the animals were arboreal quadruped. Their body mass is approximated at 4.6 pounds. The Brain of the Plesiadapis Primates have always been known to exhibit more intelligence than other animals. Research shows that the Plesiadapis had a more extended and relatively narrower brain. Scientists approximate that their brain measured about 42 mm in length and a maximum width of 22 mm which covered the piriform lobes of the cerebrum. The scientists do not provide a particular figure for the depth, but it is estimated at around 12-13 mm (Anemone & Nachman). The Plesiadapis had large bulbus olfactorius which measured about 10 mm from front to back and around 5mm across. Studies on the fossils of the Plesiadapis have led to the inference that they had a cerebrum which measured about 22 mm in length and 22 mm in width that had a smooth dorsal exterior (Gingerich, 2011). There is no record of preserved anterior sides of the Plesiadapis. Available records of the posterior of the brain show obvious swellings on the natural endocast for diagonal sinuses and the dorsal sagittal sinus. They have an indistinct depression that is adjacent to the dorsal sinus which scientists interpret as a marginal sulcus. The dorsolateral exterior of the cerebrum, however, displays a more distinct sulcus that is adjacent to the marginal sulcus. It seems to be the rhinal fissure which restricts the extension of the neopallium or the neocortex to the piriform lobe found in the cerebrum of the Plesiadapis. A correct interpretation of the rhinal crack the neopallium in both Plesiadapis and today’s Tenrec stretched to around the same degree. The back of the cerebrum, right behind the slanting sinuses lays the largely uncovered midbrain tectum with two tiny but clear-cut swellings that represent the auditory quadrigeminal colliculi (Orliac et al., 2014). Even though they had a relatively larger brain than other mammals during their time, the Plesiadapis brain is still more primitive than that of other primates. Body size of the Plesiadapis The brain size of a living thing usually sparks interests only when its relation to the body size is considered. Similarly, the size of the Plesiadapis’ brain is only a matter of concern based on its comparison to its body size. It is possible to estimate the weight of the Plesiadapis based on their skeleton. From scientific studies, Plesiadapis possessed a longer ulna, humerus, and femur. They also had a greater humerus midshaft diameter than the scientists anticipated. Contrastingly, they had a shorter longest metatarsal and shorter tibia too. In addition, they also had a lot of long bones with smaller midshaft diameters than anticipated. Plesiadapis had longer and lighter limbs than the average mammal (Nyakatura, 2019). Plesiadapis: Primates or not? Despite the similarities they have with modern-day primates, scientists still opine that the Plesiadapis cannot be classified as primates. They suggest that these archaic forms lean more towards a different order referred to as Plesiadapiformes. They thus believe that the Plesiadapis was a sister group to the ancestors of modern-day primates. However, this is still a topic of debate because some paleoanthropologists are confident that the Plesiadapis is a direct ancestor of modern primates. It is also worth noting that Plesiadapis as early mammal-like hominids did not play a significant role in the overall advancement of the life of terrestrial animals. Most of the dramatic transformation occurred as a result of the emergence of grazing mammals who possessed hooves, grinding teeth, and digestive systems that were adapted to the environmental conditions. The evolved animals were herbivorous due to the availability of grass, leaves, and fibrous material. Carnivorous animals subsequently evolved as part of maintaining the natural order of things. They evolved to eat the surplus herbivorous that were present in the ecosystem. The scavenging and hunting species were the ancestors of present-day dogs, cats, and bears. Plesiadapis were mostly hunted by tree cats. Conclusion Despite Plesiadapis possessing characteristics that are similar to modern-day primates, it would be preposterous to assume that they are within the same lineage. The Plesiadapis was on a lower evolutionary position and can only come to close comparison to rodent-like creatures. Contemporary primates are on a different evolutionary plane. They are exceptional among other mammals in their way of life both on land and in the trees. Evolution has made it possible for these primates to develop larger brain capacities which enable them to move around trees by grasping and leaping with ease rapidly. Studies have revealed that the Plesiadapis was adapted to surviving on trees. However, they do not possess the skills that primates have today. They do not have the quick agility of modern primates, nor were they capable of jumping quickly through trees. Additionally, they had a smaller brain capacity compared to today’s primates. In the evolution process, Plesiadapis developed qualities that lack in modern primates. One of the distinguishing elements was the development of protruding incisors akin to those of rodents. It thus goes to show that the Plesiadapis was not a direct ancestor of today’s primates. Instead, they appear to have been a group that drifted from the parent primate during evolution. Just like there are other mammals such as bats and tree-shrews which possess characteristics similar to those of primates, Plesiadapis also belong to a different order of animals which are almost identical to evolved primates. To which group they belong is still a subject of debate. Scientists have therefore opted to declassify them from primates and instead put them under the order Plesiadapiformes.no links to present primates. Monkeys, chimpanzees, orangutans and even human beings among other primates did not descend from Plesiadapis. Reports already show us that Plesiadapis do not have qualities that link them to primates. They seem to be more associated with rodents. Their small size and dentition indicates that they were less primate and more rodent. Available reports show us that they must have been of a different subgroup which initially originated from the primates but then split during the evolution period. 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