Paranthropus Chewing In-Class Activity

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Anthropology

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Feb 20, 2024

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Name: Nghi Luu Food Types, Dentition, and Jaw Musculature We have been discussing how food, teeth, and muscles interact on skeletal anatomy. Remember Wolff’s Law , which states that bones shapes can change over time due to certain stresses caused by particular activities. The movements of tendons, ligaments, and muscles put stress on bones, which cause bones to reinforce themselves by adding new bone material (Chapter 5). The two main muscles involved in chewing are the temporalis and the masseter muscles. Note the difference in size and muscle orientation between the human, the gorilla, and Paranthropus (the robust Australopith). As the temporalis grows, it inserts higher and higher on the temporal bone, and in some species, an additional insertion area is needed! Continued muscle growth produces electrical impulses that stimulate bone growth, resulting in the sagittal crest. 1. On the figure above, label the temporalis and masseter muscles on the human, gorilla, and Paranthropus (robust Australopith). Now that you know where the muscles are on each of these hominids, you will now compare the way your jaw muscles feel when you chew different types of foods to gain an appreciation for the way in which food types may provide selective pressure for the evolution of various forms of jaw musculature. As you chew each of the types of food, locate and feel your chewing muscles. The temporalis is felt on the sides of the head above the temples, and the masseter on the lateral (outer) sides of the mandible in the region between your molars and the gonial angle (the lower, back “corner” of your mandible). Answer the following questions as you eat each of the different foods:

2. How much can you feel the contractions of the two muscles? Describe! Soft food: Grapes When I chew grapes, I notice relatively subtle contractions of the temporalis and masseter muscles. This generally requires less force to break down, so the muscle contractions may feel gentler compared to harder foods. Medium food: Corn flakes When I chew cornflakes, they require a moderate amount of force to break down. I believe this leads to more distinct muscle contractions compared to softer foods, Hard food: Apples Chewing apples have strong contractions of both the temporalis and masseter muscles. There is an increased resistance of the hard texture that necessitates greater force to break down the food. I think this possibly more widespread muscle activity. 3. Briefly describe what happens while you are chewing. What do your anterior teeth (your incisors and canines) do versus your posterior (premolars and molars) teeth? Does this change depending on the food type? While chewing, my anterior teeth are primarily involved in biting and initial food breakdown. They cut into the food and start the chewing process. My posterior teeth play a more significant role in grinding and further breaking down the food into smaller, digestible pieces. This is when the posterior teeth are responsible for the final stages of mastication. I believe that the function of my anterior and posterior teeth does change depending on the food type. For example, my anterior teeth do most of the work in breaking grapes down while my posterior teeth take on a more dominant role as they need to grind the hard food like apples. Now look back at the lab powerpoint and put the appropriate measurement for the appropriate tooth and species in the table below. Incisor width (mm) 2 nd molar width (mm) Index Modern human 8.13 9.80 82.96 Gorilla 12.75 15.85 80.44 Paranthropus 9.01 15.65 57.57

Calculate the incisor-to-molar index using the following equation and record your values in the last column of the table. incisor width molar width x 100 This index provides a ratio of incisor-to-molar width, giving you an idea of the relative size of the anterior to the posterior teeth.  >100 indicates that the molars are smaller than the incisors.  100 indicates that the incisors and molars are evenly matched.  <100 indicates that the molars are larger than the incisors. 4. Based on the index values in the table, which of the hominids do you assume would have eaten the toughest foods? Paranthropus is assumed to have eaten the toughest foods 5. Where the measurements from only the upper jaws, the lower jaws, or a combination of both? Were all of your specimens of the same sex, or were they a mixture of males and females? Do you think this affected your measurements? The measurements were taken from a combination of both the upper jaws and the lower jaws. Specifically, the incisor width was measured from the upper jaw and the second molar width was measured from the lower jaw. All the specimens were of the same sex which were all male. Yes, male specimens may limit the generalizability of the measurements, as dental features can vary between males and females. 6. Look once again at the figure of the hominids and at your notes from class. Why is the temporalis muscle so large and extensive in the gorilla and Paranthropus (the robust Australopith) and not so in the human? The temporalis muscle is larger in gorillas and Paranthropus than in humans due to adaptations for processing tougher plant materials in their diets. This reflects the evolutionary development of a robust chewing apparatus in response to their specific dietary habits.

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7. Briefly describe the association between molar size and jaw muscle size, with particular reference to Paranthropus (the robust Australopith). In Paranthropus, the large and flat molars indicate a dietary adaptation to hard foods. This is associated with an increased size of jaw muscles, such as the temporalis muscle, reflecting an evolutionary response for efficient chewing and processing of hard foods. 8. Now look at the unknown primate specimen. Based on what you have learned from this lab, what types of food does this primate eat? How do you know this? Explain. I think they eat soft foods such as fruits, leaves, or possibly insects. The moderate molar width suggests an ability to process a variety of foods, while the smaller incisors may indicate less reliance on cutting or processing tough items. That’s why I think they have omnivorous or frugivorous diets.

Paranthropus Chewing In-Class Activity

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