What are the two main chewing muscles? What are the three components of the canine shearing complex? Are the following features associated with apes (A) or humans (H)? 10 rounded dental arcade femur with bicondylar angle non-opposable big toe ilium of pelvis oriented to the sides foramen magnum more posterior broader pelvis small anterior inferior iliac spine narrow sacrum prognathism postorbital constriction small calcaneus
The Correct Answer and Explanation is:
Correct Answers:
Two main chewing muscles:
- Masseter
- Temporalis
Three components of the canine shearing complex:
- Large upper canine
- Lower premolar (sectorial premolar)
- Diastema (gap between teeth to accommodate canines)
Features and their associations:
- Rounded dental arcade – H
- Femur with bicondylar angle – H
- Non-opposable big toe – H
- Ilium of pelvis oriented to the sides – A
- Foramen magnum more posterior – A
- Broader pelvis – H
- Small anterior inferior iliac spine – A
- Narrow sacrum – A
- Prognathism – A
- Postorbital constriction – A
- Small calcaneus – A
Explanation (300 words):
The human and ape skeletal and dental features reflect their evolutionary adaptations to different locomotion styles and diets. The masseter and temporalis muscles are the primary chewing muscles responsible for elevating the mandible during mastication. The masseter is located at the sides of the jaw and provides strong vertical force, while the temporalis arises from the side of the skull and assists in elevating and retracting the mandible.
The canine shearing complex, often found in non-human primates, plays a key role in social behavior and processing food. It consists of a large upper canine, a lower first premolar modified into a sectorial tooth for honing the upper canine, and a diastema (a gap) in the opposing dental arch to accommodate the large canine. This complex is typically reduced or absent in humans.
In skeletal traits, humans and apes differ significantly due to bipedalism in humans versus quadrupedalism or brachiation in apes. Humans have a rounded dental arcade, a bicondylar angle in the femur allowing efficient upright walking, and a non-opposable big toe for propulsion. Their broad pelvis, small anterior inferior iliac spine, and narrow sacrum aid in upright posture and childbirth.
Apes show traits related to arboreal or quadrupedal movement: a posterior foramen magnum (suggesting a forward-leaning head posture), ilium oriented to the sides, prognathism (forward-projecting face), and postorbital constriction due to larger temporalis muscles. They also tend to have a smaller calcaneus compared to humans, reflecting less emphasis on heel-strike during walking.
These distinctions help paleoanthropologists identify fossil remains and determine whether a species showed human-like or ape-like locomotion and behavior.
