Australopithecus and Paranthropus Lab Activity- Student_updated June 2023

1 YOUR NAME: Isabella Sanchez LAB SECTION: 3 AUSTRALOPITHECUS and PARANTHROPUS CRANIAL ANATOMY and DIET This lab is designed to introduce you to variation among and between species of Australopithecus and Paranthropus , some of which were possibly our ancestors while others were lineages that became extinct. Using your knowledge of osteology, you will work in a group to develop a list of character states that can be used to distinguish the species and think about what their diets may have been. Lab Objectives • Identify differences among skulls of Australopithecus and Paranthropus species • Compare the major bones and muscles involved with mastication Overview of the Masticatory System The skeletal system that operates the chewing system of the human and ape lineages acts as a lever that moves up and down to accomplish mastication (chewing). The two main muscles in this system are the temporalis muscle and the masseter muscle. The temporalis muscle originates on the lateral side of the cranial vault and marks the cranium with a temporal line in humans. In some apes and early hominins the muscle is so large (and the brain case so small) that this muscle extends onto the top of the skull and forms a sagittal crest . The temporalis muscle then passes through the temporal fossa (the large foramen behind the orbit on the side of the skull that is enclosed by the zygomatic arch), before inserting onto the coronoid process of the mandible. The temporalis muscle functions to elevate (close the mandible). The masseter muscle originates on the zygomatic arch and inserts on the outer mandible at the gonial angle . It elevates the mandible and makes some side-to-side movements. Directions Your task for this lab will be to describe and compare a number of masticatory and dental traits among apes, humans, and fossil hominins belonging to the genera Australopithecus and Paranthropus . BEFORE you answer any of the questions for this lab, review the definitions of the traits and fully complete the observation sheet. Take a few moments to look at the skulls before filling in your observations. This is a group activity so discuss the features among your group.

2 Descriptions of Cranial Traits Facial Prognathism : Hold the cranium with the teeth parallel to the table and then examine how far the incisors project anteriorly in front of the orbits. Character states: pronounced, intermediate, reduced Diastema : In osteological terminology, a diastema is a gap between teeth. The diastemata we are interested in here are the ones adjacent to the canines. In apes, which have large canines, there is a diastema between the maxillary canine and lateral incisor and between the mandibular canine and first premolar. The canine from the opposite arch fits into these gaps when the teeth are in occlusion. Articulate the mandible with the cranium and see for yourself. In species with small canines, like humans, there are no diastemata. Character states: large, small, absent Molar area : Molar area is measured as the product of mediodistal length of the molar (i.e., the length of the tooth from the front to the back of the mouth) and buccolingual width (i.e., the width of the tooth from the cheek to tongue side). In this case we are interested in the area of the mandibular (lower) first molar. This measurement has been provided for you. Canine area : This variable is measured in the same way as molar area, except measured on the mandibular canine. This measurement has been provided for you. Mandibular canine to molar area ratio : This variable is calculated as canine area divided by molar area. This measurement has been provided for you. Incisor area : This variable is measured in the same way as molar area, except measured on both of the maxillary incisors. This measurement has been provided for you. Foramen magnum position : You examined this last lab. An easy way to examine the position of the foramen magnum is to mentally draw a line between the external auditory meati (ear holes) and see if the foramen magnum is between the ears or not. You can also look at the tilt of the foramen magnum by placing a pencil over the foramen in the sagittal plane. If the pencil tilts, the spinal cord would exit the cranium at an angle. If the pencil is flat, the spinal column would be directly below the cranium. Character states: posterior, anterior, intermediate Browridge prominence : Extant apes have quite projecting browridges, while many hominins do not. You can also examine the prominence of the brows with a pencil. A true browridge has two parts, a supraorbital torus (=bar of bone) and a supraorbital sulcus (=groove). If you hold the cranium with the teeth parallel to the table and place a pencil behind the torus, it will rest in the sulcus if the browridge is prominent. If there’s no dip behind the torus, the species lacks a true browridge. Character states: present, absent Position of the zygomatics : This is best tested by placing a pencil transversely across the nasal aperture. If the zygomatics are in front of the nasal aperture, the pencil will rest on them. If the zygomatics are behind the nasal aperture, the pencil will rest on the nasal opening. Character states: forward of or behind the nasal aperture Sagittal crest : This is the crest that is formed by the convergence of the temporal lines. Character states: present, absent

3 OBSERVATION SHEET Species Facial Prognathism Diastema Mandibular First Molar Area Mandibular Canine Basal Area Canine/ Molar Area Ratio Maxillary Incisor Area Foramen Magnum Position Brow ridge prominence Position of Zygomatics Sagittal Crest Pan troglodytes Pronounced Large Species Avg. 103.5 mm 2 Male Avg. 154.8 mm 2 Female Avg. 104.6 mm 2 Male 1.50 Female 1.01 Species Avg. 114.8 mm 2 Intermediate Present Behind Present Gorilla gorilla Pronounced Large Species Avg. 210.5 mm 2 Male Avg. 266.4 mm 2 Female Avg. 142.5 mm 2 Male 1.27 Female 0.68 Species Avg. 153.0 mm 2 Intermediate present behind Present Australopithecus afarensis Intermediate Absent Species Avg. 165.1 mm 2 Species Avg. 94.5mm 2 0.57 Species Avg. 87.98 mm 2 Anterior present behind Absent Australopithecus africanus Intermediate Absent Species Avg. 183.5 mm 2 Species Avg. 96.0 mm 2 0.52 Species Avg. 83.8 mm 2 Anterior present behind Absent Paranthropus aethiopicus Intermediate Absent Species Avg. no data Species Avg. no data No data Species Avg. no data Anterior present forward Present Paranthropus robustus Intermediate Absent Species Avg. 201.4 mm 2 Species Avg. 66.3 mm 2 0.33 Species. Avg. 63.6 mm 2 Anterior present forward Present