Genus Homo Lab Activity- KEY_updated summer 2023(1)

pdf

School

University of Arkansas *

*We aren’t endorsed by this school

Course

1011L

Subject

Anthropology

Date

Dec 6, 2023

Type

pdf

Pages

Uploaded by isabellasanchez401

1 YOUR NAME:______ KEY ______________ LAB SECTION:__________________ HOMO CRANIAL ANATOMY Objectives: After completing this lab, you should understand: • The morphological differences between Australopithecus and early members of the genus Homo • The variation among specimens that represent early Homo , how this variation is patterned, and why it is difficult to explain • Different possibilities for (and the importance of) the relationships between early Homo and later members of the genus Homo. • General trends in the evolution of the genus Homo and the phylogenetic relationships among middle and later Pleistocene species of Homo . Directions: Throughout this lab are various tables that list various characteristics. It would be wise to go through and fill out the tables before you begin to answer all of the questions. Take your time when filling out the charts and talk over features with your group mates. Ultimately, it is the anatomy of these species that you will be quizzed on. Use the descriptions of cranial traits provided below to complete each of the stations. Descriptions of Cranial Traits Cranial capacity: This value represents the volume (in cm 3 ) of the interior of the cranium. It is a rough estimate of brain size. This measurement has been provided for you. 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. 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. PLACEMENT (not shape) 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

2 Sagittal crest : This is the crest that is formed by the convergence of the temporal lines. Character states: present, absent Supraorbital torus (browridge) development : Examine the area just superior to the orbit. In all of the hominoid taxa, you notice a swelling of bone that projects over the orbits. In the extant apes, the supraorbital torus is quite prominent; however, it is more subtle in humans. In humans, its prominence is obscured in part by our forehead. This feature is also sexually dimorphic, with males having a more prominent torus than females. Character states: you will want to carefully describe (for example: small, large, intermediate) this feature to adequately compare among taxa Presence of retromolar gap : Examine the region just behind the third molar. In most species you cannot place a pencil between the mandibular ramus (the upright portion of the mandible) and the third molar. In some species, you can. The gap between the third molar and the ramus is called a retromolar gap. Character states: present, absent Presence of an occipital bun : Examine the occipital bone in the region above the insertion of the nuchal muscles. When most species are viewed laterally, the cranial vault makes a smooth arc from the area of the nuchal crests towards the frontal bone. In Neandertals and a few other fossil hominins, there is often a prominent bump (i.e., bun) on the occipital bone near the most posterior point of the cranium. This bump is large and can be grasped with your hand. Character states: present, absent Presence of a chin : Examine the mandibular symphysis of each species. Does the inferior portion of the mandible jut anteriorly in front of the teeth? If it does, then a chin is present. Character states: present, absent Shape of forehead : Look at the region of the frontal bone just above the orbits. Does the frontal bone rise steeply from the orbits, or is there a dip behind the orbits and the forehead sweeps backwards? Character states: steep, sloping SHAPE (not placement) of the zygomatic bones : This is best assessed by looking at the cranium in superior view. Generally, if you follow the zygomatic arch from the temporal bone, you will observe an approximately 90° degree turn onto the zygomatic bone, which faces forward on the face. In Neandertals, you should observe that there is a smooth continuous arc from the zygomatic arch to the zygomatic bone. Instead of facing forward, the Neandertal zygomatics are angled on the face. The zygomatics of Neandertals are sometimes described as being “swept back.” Character states: swept back, angled

3 Station 1: Comparing early Homo to Australopithecus and Paranthropus In this station, you will compare Australopithecus to early Homo and Paranthropus; all three of these species lived around the same time. How are they different from one another? Australopithecus africanus Paranthropus boisei Homo habilis Cranial Capacity ~525 cm 3 ~525 cm 3 ~650 cm 3 Molar Area 183.5 mm 2 255.8 mm 2 121.0 mm 2 Incisor Area 83.8 mm 2 77.0 mm 2 90 mm 2 Canine Area 96.0 mm 2 67.9 mm 2 36 mm 2 Placement of the Zygomatics Behind Forward Behind Sagittal Crest Absent Present Absent 1) How does Homo habilis compare to A. africanus and P. boisei ? Describe the general similarities and differences. Homo habilis has very similar dentition and cranial capacity to A. africanus. Cranial capacity is the only variable where A. africanus is similar P. boisei. Otherwise, P. boisei has much larger dentition, a sagittal crest, and forwardly placed zygomatics. 2) Consider that Paranthropus and Homo coexisted in eastern and South Africa. If a species like A. africanus is ancestral to both Homo and Paranthropus , what do you think the divergent morphological features of the masticatory apparatus in each lineage imply about dietary differences between Homo and Paranthropus ? Given its large masticatory apparatus and sagittal crest, Paranthropus must have had a diet that required either a lot of oral processing or the generation of large masticatory forces. Traditionally, Paranthropus was thought to be a hard object feeder; however, new evidence has overturned that hypothesis for P. boisei . Homo , on the other hand, has smaller teeth than Paranthropus and no sagittal crest and therefore is likely to have retained the generalized diet of its ancestor, A. africanus , which did not require large masticatory forces. Homo is also associated with stone tools, which it used in part to process animal carcasses. In Homo , part of food processing occurs extraorally (outside of the mouth), while there is no evidence for meat consumption or extraoral processing by Paranthropus .

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

4 Station 2: Variation within early Homo (one species or two?) As a group, the earliest Homo fossil samples are extremely variable. In fact, most scholars believe that these fossils are too variable to be a single species. These scientists have split the material into two species; the larger-brained, larger-toothed specimens are called Homo rudolfensis and the smaller-brained, smaller-toothed specimens are called Homo habilis . However, other scientists believe the differences can be explained by sexual dimorphism (the larger specimens are males; the smaller specimens are females). In this station, you will observe differences between male and female gorillas, which are extreme, and chimpanzees and humans, which are less dimorphic. Though the degree of dimorphism differs between the three hominoids, the pattern is basically the same. Finally, you will compare the two early Homo specimens. For each feature below, indicate whether the feature differs between males and females of a species. If it differs, describe the nature of the difference ♀ Gorilla gorilla ♂ Gorilla gorilla ♀ Pan troglodytes ♂ Pan troglodytes ♀ Homo sapiens ♂ Homo Sapiens Cranial Capacity 466 cm 3 543 cm 3 366 cm 3 399 cm 3 1190 cm 3 1380 cm 3 Supraorbital torus development Dimorphically larger, but proportionally the same to ♀ Slightly larger, but same proportion as ♀ Only subtly larger than ♀ Placement of the Zygomatics Dimorphically larger, but placement does not differ between males and females. The zygomatics are both over the molars in males and females. Slightly larger, but, but placement does not differ between males and females. The zygomatics are both over the molars in males and females. Only subtly larger than ♀ . The placement does not differ between males and females. The zygomatics are both over the molars in males and females. 1) Does the placement of the zygomatics relative to the nasal aperture differ between males and females of any of the above species? No

5 2) Calculate the ratio of male to female cranial capacity for each species? How does brain size compare in males and females? Gorilla (M/F) = 543/466 ≈ 1.17 Pan troglodytes (M/F) = 399/366 ≈ 1.09 Homo sapiens (M/F) = 1380/1190 ≈ 1.16 Given that males tend to be larger in body size than females, their slightly larger brains reflect that difference in body size. 3) In terms of the prominence of the supraorbital torus, which sex has a larger or more developed supraorbital torus? Males. 4) If the two early Homo specimens in the table below are a male and female of the same species, KNM-ER 1470 would be a male (due its larger overall size) and KNM-ER 1813 would be a female (due to its smaller overall size). Do the differences you observed between these two specimens match the differences between male and female apes and humans? Why or why not? No, H. rudolfensis and H. habilis exhibit the opposite relationship of the differences expressed between male and female apes and humans. In other words, though KNM-ER 1813 is classified as a female due to its overall size, it has more pronounced brows than KNM-ER 1470, which indicate a male of the species in apes and humans. Also, the two early Homo specimens differ in the placement of the zygomatics, which is not a dimorphic feature in extant apes or Homo sapiens . Finally, the ratio of brain size in 1470 to 1813 is 1.37, which is far larger than the difference observed in even gorillas, which are the most dimorphic of extant apes. Station 3: Early Homo as ancestor (comparing early Homo to Homo erectus ) Homo habilis and Homo rudolfensis are the best known early members of genus Homo. One of those species likely gave rise to Homo erectus ; however, it is unclear which early Homo species is the ancestor of Homo erectus . Compare the skulls to find out why. Homo erectus is the ancestor of even younger species of the genus Homo . KNM-ER 1470 ( H. rudolfensis ) KNM-ER 1813 ( H. habilis ) Cranial Capacity 700 cm 3 510 cm 3 Supraorbital torus development Smaller Larger/more developed Placement of the zygomatics Slightly behind nasal aperture, over premolars Further behind nasal aperture, over molars

6 KNM-ER 1470 Homo rudolfensis KNM-ER 1813 Homo habilis KNM-ER 3733 Homo erectus Cranial capacity 700 cm 3 510 cm 3 1000 cm 3 Relative Posterior Tooth Size Largest Intermediate Smallest Supraorbital torus development Smallest Intermediate Largest 1) In which of these features is Homo habilis more like Homo erectus ? Supraorbital torus development AND Relative Posterior Tooth Size 2) In which of these features is Homo rudolfensis more like Homo erectus ? Cranial capacity 3) Use Australopithecus as an outgroup and make an argument that either Homo rudolfensis or Homo habilis is the ancestor of H. erectus . Think about which features are primitive and which are derived and try to figure out which of the early Homo species is the ancestor of H. erectus (Hint: Multiple interpretations are possible. Back your answer up with evidence (i.e., specific traits)). Homo rudolfensis could be argued as the ancestor of H. erectus because of its larger cranial capacity than Homo habilis . Conversely, all other cranial morphology of Homo rudolfensis makes it less likely to be the ancestor of H. erectus . In other words, other than brain capacity, Homo habilis shares more derived features with H. erectus (see 3.1 above).

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

7 Station 4. Cranial morphology of middle and late Pleistocene Homo Starting in the middle and late Pleistocene, the genus Homo diverges into multiple lineages, mostly based on geography. • Early in this time frame, around 2-1 million years ago, Homo erectus is present in Africa, Asia, and Europe • But starting around a bit less than 1 million years ago, there are separate lineages of hominins in Europe and the Middle East (leading to Homo neanderthalensis ) and Africa (leading to modern Homo sapiens ) Fill out the chart based on the features that you observe in these specimens, using the terms provided in parentheses as a guide (some features have already been provided where they not possible to see). Use this chart to answer the questions below. Homo erectus Homo neanderthalensis lineage Homo sapiens lineage Fossil Name KNM-WT 15000 DH3 Sima de Los Huesos Shanidar Kabwe Herto Cro- Magnon Geographic Location Kenya Georgia (Europe) Spain Iraq Zambia Ethiopia France Geological Age 1.6 million 1.85 million 430,000 65,000 300,000 160,000 30,000 Cranial capacity ~900 cm 3 600 cm 3 1,390 cm 3 1,600 cm 3 1,280 cm 3 1,450 cm 3 1,600 cm 3 Supraorbital torus (small/large/ intermediate) Intermed Intermed. Large Large Large Large Small Occipital bun (present/absent) Absent Absent Present Present Absent Absent Absent Forehead shape (sloping/upright) Sloping Sloping Sloping Sloping Sloping Intermed. Upright Zygomatic shape (swept back/ angled) Angled Angle Swept back Swept back Angled Angled Angled Retromolar gap (present/absent) Absent Absent Present Present absent absent absent Chin (present/absent) Absent Absent Absent Absent absent present present

8 1) What features make the members of the H. neanderthalensis lineage unique compared to Homo erectus and Homo sapiens ? The neanderthal lineage is distinct from Homo erectus and Homo sapiens in having an occipital bun, swept back zygomatics, and a retromolar gap 2) What features make the members of the H. sapiens lineage unique compared to Homo erectus and Homo neanderthalensis ? The H. sapiens lineage is distinct in having a chin and an upright forehead 3) Now compare the oldest and the youngest fossils from both the H. neanderthalensis and H. sapiens lineages. What patterns do you notice in each of these lineages? In both lineages characters change over time. In the neanderthal lineage, the older specimen (Sima de los Huesos) tends to have the same characteristics as the younger (Shanidar) but the features are more pronounced in Shanidar In the human lineage characters also change, where earlier specimens (Kabwe/Herto) lack one or both of the derived characteristics (chin, upright forehead) that are observed in later specimens (Cro-Magnon)

9 Station 5. Comparing the postcrania of apes, early hominins, and Homo Homo erectus was the first species to migrate out of Africa. The intermembral indices (as calculated in the Primate Adaptation Lab) for Pan troglodytes, A. afarensis, H. erectus, and H. sapiens are provided below. Pan troglodytes Australopithecus afarensis Homo erectus Homo sapiens Intermembral Index 102 ~100 73 68 1) How would you describe the length of the arm relative to the length of the leg in A. afarensis ? What about in H. erectus and H. sapiens ? A. afarensis has a much longer arm to leg ratio than H. erectus and H. sapiens . In both Homo species, the legs are much longer than the arms. 2) Australopithecus afarensis, H. erectus, and H. sapiens are all bipeds. What might explain why the limb proportions are so different in the 3.0+ million-year-old A. afarensis than in the younger species of Homo ? Develop your own hypothesis and provide specific examples to support it. The limb proportion trend is a decreasing arm to leg length ratio. The proportionately long arms and curved phalanges of A. afarensis suggest that, though it was bipedal, it was still spending at least some time in the trees (using arboreal locomotion, though not efficiently). Perhaps A. afarensis was using the trees to avoid predators. In terms of energy efficiency, the long legs of H. erectus and H. sapiens increase stride length and make them more efficient long distance travelers and runners. Some have argued that the increase in leg length reflects either larger home ranges in Homo , which incorporate meat into their diet, or that they were the first hominins capable of endurance running

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Genus Homo Lab Activity- KEY_updated summer 2023(1)

Related Documents