Lab Assignment: Human Evolution

7/28/2019 Lab Assignment: Human Evolution

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Introduction

The aim of this analysis is to describe the morphology of a hominin cranium; to record

measurements taken on it; and to compare the hominin skull with a modern one using these

morphological descriptions and measurements. This report starts off with some background

information on the hominin and modern skulls. The general preservation condition will be

assessed in the following section. Sex and age of the individual will then be inferred from the

cranial morphology. In the fourth section, morphological information of the hominin cranium

will be described and it will be compared to that of the modern skull. Lastly, measurements

will be listed and interpreted to allow numerical comparisons. This constitutes a less

subjective and perhaps more accurate way of comparing two crania.

Background Information

The hominin cranium examined in this paper is a Homo habilis skull (KNM-ER 1813).

Kamoya Kimeu discovered the skull at East Lake Turkana (previously known as East Lake

Rudolf), in northern Kenya (Leakey 1974:655). The site is known for its rich deposit of

hominin skeletons and archaeological material. The remains of over 130 hominins have been

recovered from there since excavations began in 1968 (Phenice and Sauer 1977:54).

Associated stone implements were also found at the location (Phenice and Sauer 1977:53).

KNM-ER 1813 was a very fractured cranium with a number of missing parts. The left side of

the cranium is also distorted, plausibly a consequence of pressure being exerted on the skull

during the fossilisation process (Smithsonian Institution n.d.). To contrast theH. habilis skull

with modern human crania, a modern European male skull was chosen at random.


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General Preservation Condition

KNM-ER 1813 is incomplete. The left zygomatic bone, together with the thin bone

connecting it with the supra-auricular bone, is missing (Figure 1). Although what is

presumably most of the right cheekbone is present, the thin bone connecting that and the

supra-auricular bone is again not present (Figure 2). Thus the actual breadth of the cheeks is

unknown and the measurement of bizygomatic breadth shown in this analysis would just be

estimation. The left side of the skull behind the face has a couple of missing fragments

(Figure 2). Moreover, a rather large area of the bottom of the skull is missing (Figure 3).

Hence, the location of the foramen magnum is uncertain. Upon inspecting the teeth, it is

found that the left incisors are missing and the teeth on the right side are eroded (Figure 4).

Figure 1. KNM-ER1813 (left) Figure 2. KNM-ER 1813 (right)

Figure 3. KNM-ER 1813 (bottom) Figure 4. The teeth of KNM-ER 1813.


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The cranium in general is very fractured. Some bone fragments of the reconstructed model do

not match perfectly (Figure 5), therefore the cranial measurements may not be entirely

accurate. Also, because of the fragmented nature of the skull, some sutures are ill-defined.

The left side of the face of the cranium is deformed (Figure 6). The top outer corner of the left

orbit is crushed, affecting the assessment of the actual shape of the orbits. (With the left

cheekbone missing, the actual shape of the orbit is hard to tell.)

Inferred Sex and Age of the individual

The cranium is classified as a male. The general robusticity of the skull, its relatively large

nuchal chest, pronounced temporal lines and prominent glabella, supra-orbital margin and

ridges all support this classification. The only feature that suggests the identification as a

female is the small mastoid processes. Despite the fact that the individual possesses small

mastoid processes, the hominin skull is still identified as a male because it is highly probable

that the mastoid processes might have been worn down, as suggested by missing parts near

the mastoid processes and the difference in size of the left mastoid process and the right

mastoid process.

Figure 5. KNM-ER 1813 (Top) Figure 6. KNM-ER 1813 (front)


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KNM-ER 1813 belongs to an adult (20-35) as the third molar has erupted. The tooth shows

moderate tooth wear, suggesting that the individual is around 25-30 years old. The fact that

the cranial sutures are all fused also indicates that the individual is an adult.

Cranial Morphological Description: Description

The vault of the hominin skull is relatively large in terms of skull proportions. The rather

robust vault is also long, narrow and round other than the somewhat protruding occipital area.

The cranial sutures are evidently fused, yet their complexity cannot be deduced as the

cranium is too fragmented for all sutures to be presented clearly. The glabella is large and

prominent. The brows are large in the center (in terms of facial proportions) and gradually get

smaller towards the sides. They are also continuous, arched and protruding. The frontal is

high and rounded. There is no sagittal keel. The parietal is also quite round with distinct

temporal lines. Parietal torus is absent. The temporals are relatively high considering the skull

proportions. The occipital is angular and somewhat projecting with an occipital torus present.

The mastoid processes are small, short and robust. However, it should be noted that the short

and small-sized mastoid processes could have been a result of weathering and erosion. There

is a large part missing at the bottom of the skull at the area of the foramen magnum, therefore

the shape of the foramen magnum is uncertain. But judging from the right side, the almost

intact side, of the foramen magnum and the estimated locations of the basion and opisthion,

the foramen magnum is likely to be circular.

The face of the hominin skull is relatively small and short, although it is fairly broad

considering the size of the skull. A rather pronounced projection below the nose is observed.

Having examined the non-skewed right orbit, it is reasoned that the orbits of KNM-ER 1813

should be round as they are in the shape of deformed circles. This distortion might be


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attributed to the high degree of fragmentation. The orbits are relatively small, taking up about

one quarter of the face. The borders of the orbits appear to be sharp, although this again might

be due to the fact that the skull is highly fractured. The nasal aperture is large and rather

round. The nasal bones are flat and indistinct. The malars are robust. With reference to the

fact that the left cheekbone is missing and that the right zygomatic bone may have broken off,

the broadness of the cheeks of the individual cannot be asserted.

The teeth are quite large. Upon inspection, it is found that the teeth on the left side are well

preserved except the two missing upper left incisors; while the teeth on the right side are

barely observable, with most parts of the teeth eroded away, only the roots and the complete

crown of the second molar remain. After examining the teeth on the left side, it is found that

the teeth show moderate wear.

There are five discernible foramina on the skull: the supra-orbital foramina directly under the

brows, incisive foramen (located behind the incisors), the greater palatine foramen near the

third molar on the right side and the foramen magnum.

Cranial Morphological Description: Comparison

When compared with the modern European male skull, the vault of the H. habilis skull is

relatively smaller. The vaults of the two crania are of similar relative length in terms of skull

proportions, but the hominin cranium is narrower. It is also more robust than the modern

cranium. While both vaults are quite round (Figures 1 and 7), the angle of curvature of the

modern skull is more like a 90 curve (Figure 7) whereas the curve of the vault of the hominin

skull is much smoother (Figure 1). The sutures of the modern European male skull are also

fused. However, due to the obscurity of the sutures of KNM-ER 1813, the complexity of the


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sutures cannot be compared. The glabellas of the two skulls are of similar size, but the

glabella of the hominin skull is more prominent (Figures 6 and 8). The brows are larger (with

facial proportions taken into account). The brows of both skulls are arched. Although instead

of being non-continuous like those of the modern cranium, the brows of the hominin cranium

are continuous. The frontal of KNM-ER 1813 is lower, flatter than that of theH. sapiens skull

(Figures 1 and 7). Both frontals are not keeled (Figures 1 and 7). No parietal torus is found on

either skull, yet it is also noted that the modern parietal is slightly more angled than the

hominin one (Figures 1 and 7). In spite of the fact that both skulls belong to male individuals,

the temporal lines on KNM-ER 1813 are longer and more distinct (Figures 1 and 7). The

temporals of the hominin cranium are higher (Figures 1 and 7). The occipital of the hominin

skull has a marked torus and is therefore angled and somewhat protruding; there is no torus

on the occipital of the modern cranium and it is round and non-projecting (Figures 1 and 7).

Apparently, the modern skull has larger mastoid processes despite the fact that both skulls are

identified as male. Nevertheless, the small mastoid processes of the hominin cranium might

have resulted from weathering and erosion. The shape of the foramen magnum of the modern

skull is a vertical oval (Figure 9), whereas the deduced shape of the foramen magnum of

KNM-ER 1813 is round.

Figure 7. Modern European Male skull (left) Figure 8. Modern European Male skull (front)


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TheH. habilis skull has a relatively larger, longer and broader face when compared with the

modern European male skull (Figures 1 and 7). It is also more projecting below the nose

(Figures 1 and 7). The orbits of the modern skull are square instead of circles like those of

KNM-ER 1813 (Figures 6 and 8). They are also bigger and smoother-bordered. The nasal

aperture of the hominin cranium is comparatively larger and more round (Figures 6 and 8).

While the nasal bones of the modern human skull are keeled and quite prominent; those of the

hominin skull are flat and rather indistinct (Figures 6 and 8). The malars of the hominin

cranium are less gracile than those of the modern cranium (Figures 6 and 8). The broadness of

the two crania cannot be compared as the left cheekbone of KNM-ER 1813 is missing and the

right cheekbone may have been eroded.

Comparing the teeth on the left side of the skulls (as the teeth on the right side of KNM-ER

1813 have been worn away), it is clearly visible that the actual teeth of the two crania are of

similar size, which implies that the relative tooth size of the H. habilis skull is larger (Figures

1 and 7).

Figure 9. Modern European Male skull (bottom)


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KNM-ER 1813 has much less foramina than the modern European male skull. Yet this might

be because the hominin cranium was too fragmented and damaged that it would be hard to

distinguish whether the dents are actually foramina.


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Cranial Measurements

Measurement KNM-ER 1813Modern European

Male

Glabella-occipital length 136 166Maximum cranial breadth 96.5 133

Basion-bregma height 89 136

Basion-nasion length 73.5 98

Nasion-prosthion height 54.5 62.7

Basion-prosthion length 91.9 95

Bizygomatic breadth 95-110* 122

Nasal height 36.5 48.5

Nasal breadth 23.4 25.4

Orbit height (right) 28.8 32.2

Orbit breadth (right) 32 38.9

Palate length 58.5 47.3Palate breadth (external) 58.4 61

Palate breadth (internal) 31.6 36.7

Nasion-occipital length 131.8 165

Nasion-bregma chord (Frontal chord) 75.9 116.5

Nasion-bregma arc (Frontal arc) 89 128

Bregma-lambda chord (Parietal chord) 83.3 105.1

Bregma-lambda arc (Parietal arc) 90.5 116

Lambda-opisthion chord (Occipital

chord)64.2 93.1

Lambda-opisthion arc (Occipital arc) 86 108Table 1. Cranial measurements of KNM-ER 1813 and the modern European male skull.

NOTE: All values are corrected to one decimal place.

* Because both cheeks are incomplete, hence an estimated range of bizygomatic breadth is

given.

Cranial Measurements: Interpretation and Comparison

The maximum cranial length (glabella-occipital length) and the maximum cranial breadth of

KNM-ER 1813 are both significantly shorter than the values of the modern European male

skull. When these values are substituted into the equation of the Cephalic Index:

Maximum cranial breadth*100

Maximum cranial length


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The indices for the hominin skull and the modern cranium are 71.0 and 80.1 respectively.

According this index, the hominin skull is categorised as a dolichocephalic (80). This means KNM-ER 1813 and

modern humans are significantly different as KNM-ER 1813 is long-headed, whereas modern

humans are broad-headed.

The basion-bregma height represents the cranial height. Comparing the basi-bregmatic height

of the two skulls, the cranial height of the modern cranium is much taller than that of KNM-

ER 1813. But when the maximum cranial length of the two crania are divided by their

respective cranial heights, the resulting value of the hominin cranium is larger, meaning that it

is in fact taller.

The basion-nasion length reflects the facial height regardless of face projection. KNM-ER

1813 has a much shorter face than H. sapiens. When the basion-nasion length is divided by

the upper facial height, nasion-prosthion height, it is discovered that the upper face takes up a

larger portion of the face (in terms of height) in both skulls than the lower face, and that the

upper face of the modern skull takes a larger portion of the face than the hominin skull.

The basion-prosthion length measures the facial projection. Although the value of the basion-

prosthion length of KNM-ER 1813 is slightly shorter than that of the modern human skull, its

degree of facial projection is actually much higher considering how small the hominin

cranium is.

The nasal height of KNM-ER 1813 is shorter than that of the modern cranium. Yet, when the

nasal heights of the two skulls are divided by their respective basion-nasion lengths (the facial


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height), two similar values are achieved, suggesting that the hominin individual possesses a

relatively bigger nose than modern human beings. When we divide nasal height using nasal

breadth, a bigger value is attained for the modern cranium, indicating that modern human

nose is more elongated than that ofH. habilis.

The right orbit of KNM-ER 1813 is used for measurement since the left orbit is crooked. The

height of the orbits of KNM-ER 1813 is slightly shorter than that of the modern cranium.

However, taking into account the facial height of both skulls, the orbits of the hominin

cranium are taller than those ofH. sapiens.

The palate length of the hominin skull is significantly longer than the modern one; whereas

the palate breadths of the two crania are similar.

Table 2 shows the results of frontal chord and parietal chord divided by the sum of the length

of both chords of respective crania. Despite the huge difference in the actual values of the

chords, the proportion of frontal and parietal of both skulls is quite similar.

Chords KNM-ER 1813Modern European

Male

Nasion-bregma chord (Frontal chord) 0.51 0.50

Bregma-lambda chord (Parietal chord) 0.49 0.50

Table 2. Results of frontal chord and parietal chord divided by the sum of the length of both

chords of respective crania.

Comparing the difference between the arcs and chords can give the degree of projection of

frontal, parietal and occipital areas. A larger difference is noted for the frontal of KNM-ER

1813. This implies that the frontal of the H. habilis skull is more protuberant than the frontal

of the modern European male cranium. The difference between the parietal arc and the


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parietal chord of the modern skull is bigger than that of the hominin cranium, suggesting that

the parietal of the modern skull is more projecting. The occipital area of KNM-ER 1813 is

more protruding, as indicated by the significantly larger difference between the occipital arc

and the occipital chord.

Conclusion

In spite of being in the same genus Homo, the two skulls are different in a lot of aspects. It is

through time that evolutionary changes develop gradually, turning us from H. habilis into

what we are today. Due to the poor preservation of KNM-ER 1813, many parts of the skull

cannot be compared with modern skulls and quite a few measurements taken on it may not be

fully accurate. It is hoped that later on some relatively more complete H. habilis skulls will be

excavated to help identify what the changes that took place during our evolution from H.

habilis toH. sapiens are.

Reference:

Leakey, R.E.F.

1974 Further evidence of Lower Pleistocene hominids from East Rudolf, North Kenya, 1973.

Nature 248:653-656.

Phenice, T.W. and N.J. Sauer

1977Hominid Fossils: An Illustrated Key. 2nd edn. Dubuque, Iowa: W. C. Brown Co.

Smithsonian Institution

n.d. KNM-ER 1813 [on-line]. Available from: http://humanorigins.si.edu/evidence/human-

fossils/fossils/knm-er-1813[Accessed 9 January 2012].
http://humanorigins.si.edu/evidence/human-fossils/fossils/knm-er-1813http://humanorigins.si.edu/evidence/human-fossils/fossils/knm-er-1813http://humanorigins.si.edu/evidence/human-fossils/fossils/knm-er-1813http://humanorigins.si.edu/evidence/human-fossils/fossils/knm-er-1813http://humanorigins.si.edu/evidence/human-fossils/fossils/knm-er-1813

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Lab Assignment: Human Evolution

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