CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
VALIDITY OF THE SPECIES:
Australopithecus afarensis
A thesis submitted in partial satisfaction of the
requirements for the degree of Master of Arts in
Anthropology
by
James Braxton
May, 1983
The Thesis of James Braxton is approved:
California State University, Northridge
ii
ACKNOWLEDGEMENTS
I wish to thank the following people for their support and
guidance.
First, the members of my committee.
Second, my
family for their generous support, ideas, and allowing
me the time to complete my endless obsession.
Finally, to
Nancy Murray who generously donated her time, her computer
expertise, and for solving my constant program errors.
iii
TABLE OF CONTENTS
Acknowledgements •
iii
List of Tables
vi
List of Figures
vii
Abstract •
viii
CHAPTER
I.
II.
INTRODUCTION
1
LITERATURE REVIEW •
4
Biostratigraphical and Geochronological
Evidence
4
Osteological Remains
7
Morphological Characteristics •
10
Jaw and Dental Characteristics
10
Cranial Characteristics •
14
Postcranial Morphology
15
Biological Species Concept
17
The International Code of Zoological
Nomenclature and the Taxonomic Status
of Hadar-Laetoli Fossils
.•
17
Summary •
20
iv
Table of Contents (continued)
II I.
IV.
v.
VI.
MATERIALS AND METHODS
22
Materials--Fossil Hominid Sample •
22
Comparative Sample •
25
Measurement Data •
28
Methods
28
Univariate Analysis
31
Multivariate Analysis
31
Fossil Hominid Sample
32
RESULTS •
34
Univariate Analysis Histograms: Fossil
Hominid Sample Variation
34
Multivariate Analysis: Fossil Hominid Sample
41
Canonical Variate Analysis
48
Summary of Results
50
DISCUSSION
55
Morphological Characteristics •
55
International Code of Zoological Nomenclature •
56
Geographic Isolation
57
Statistical Implication •
58
CONCLUSION
61
Literature Cited •
64
v
LIST OF TABLES
Table
1.
2.
3.
Page
Comparison Between A.afarensis and later
Australopithecus and Early Homo • • • • • • • •
Fossil Hominid Specimens Included in the Analysis
and their Geologic Origin • • • •
11
...
Taxonomic Assignments of the Fossil Hominid
Specimens • • • • • • • • • • • • • • • •
23
26
30
6.
....
Fossil Hominid Sample Data - Mandibular Dentition . . .
Fossil Hominid Sample Data • . . . . . . . . . . . . . .
7.
Principal Component Analysis -Maxillary Dentition •
42
8.
Principal Component Analysis - Mandibular Dentition
43
9.
Principal Component Scores - Maxillary Dentition • •
44
10.
Principal Component Scores - Mandibular Dentition
46
11.
F Test of Mahalanobis D2 -Maxillary and Mandibular
Dentitions • • • • • •
4.
5.
12.
Fossil Hominid Sample Data - Maxillary Dentition
......
......
Jackknifed Classification - Maxillary and
Mandibular Dentitions • • • • • • • • • . . . . . . .
vi
29
33
49
53
LIST OF FIGURES
Figure
Page
1.
Geological Column of the Hadar Formation Histograms
2.
Maxillary Dentition - Canine
3.
Maxillary Dentition - p3
4.
Maxillary Dentition - Ml
37
5.
Mandibular Dentition - Canine
38
6.
Mandibular Dentition - P3
39
7.
Mandibular Dentition - M1
40
8.
Bivariate Plot of Principal Component Scores Maxillary Dentition • • • • • • • • • • • •
9.
10.
11.
....
.....
35
...
Bivariate Plot of Principal Component Scores Mandibular Dentition • • • • • • • • • • • •
Bivariate Plot of Canonical Variate Analysis Maxillary Dentition • • • • • • • • • • • •
Bivariate Plot of Canonical Variate Analysis Mandibular Dentition • • • • • • • • • • • •
vii
6
.....
.....
.....
.....
36
45
47
51
52
ABSTRACT
VALIDITY OF THE SPECIES:
Australopithecus afarensis
by
James Braxton
Master of Arts in Anthropology
This thesis is an attempt to test the hypothesis that Australopithecus afarensis is not significantly different from any other
Plio-Pleistocene hominid.
This problem is of interest to anthro-
pologists because corroborating the hypothesis of the proposed taxon
A.afarensis has important implications for interpretations of early
hominid phylogeny.
Analyses of fossil material from Hadar and Laetoli
suggest the following:
1) A.afarensis is the earliest known bipedal
hominid, 2) the extreme degree of morphological variation exhibited
by A.afarensis can most likely be attributed to sexual dimorphism
(rather than the Hadar-Laetoli fossils representing more than one
species), and 3) controversy over the taxon A.afarensis has caused
a reinterpretation of early hominid evolution.
The validity of the
proposed species, A.afarensis, was evaluated by a critical review of
viii
the literature and statistical analyses of dental measurements of a
representative sample of Pliocene and Pleistocene hominids.
Uni-
variate and multivariate statistical methods were utilized to compare
the variability exhibited by A.afarensis with that of the Fossil
Hominid sample.
The results of these analyses suggest that A.
afarensis is a valid taxon.
ix
CHAPTER I
INTRODUCTION
Fossil remains of the Pliocene and Pleistocene hominids that
represent the genus Australopithecus show considerable geographical,
temporal, and morphological variation.
Interpretation of these vari-
ations has led to many hypotheses, such as those proposed by:
1)
Wolpoff (1973) and Brace (1979), who state that sexual dimorphism
within one species can account for the known morphological variation
exhibited by the genus Australopithecus, 2) Walker and Leakey (1978)
who hypothesized that more than one species evolved, such that different australopithecene species may have been contemporaneous both
in time and space, and 3) Robinson (1963), whose dietary hypothesis
suggests that several genera may have co-existed simultaneously.
Plio-Pleistocene sites from Eastern and Southern Africa have
yielded fossil material for many hominids and among these remains,
several australopithecine forms have been discovered.
Australopithe-
cus africanus remains may be represented at Lake Turkana, Kenya, and
Omo, Ethiopia, as well as the South African sites of Makapansgat and
Sterkfontein (Howell, 1969; Leakey, 1978; Wolpoff (1971).
However,
Cronin et al. (1981) doubt the existence of A.africanus in the East
African geographic area.
Fossil material for A.boisei comes from
Olduvai Gorge, Tanzania, and Omo, Ethiopia.
Fossil remains for Aus-
tralopithecus robustus come from Lake Turkana, Kenya, as well as the
1
2
South African sites of Kromdraai and Swartkrans (Leakey, 1978;
Wolpoff, 1971).
These East and South African deposits represent time
spans of 3.0 million to 1.5 million years for hominids finds (Howell,
1969; Leakey, 1966; Leakey, 1972; Tobias, 1976).
Fossil remains of the proposed hominid Australopithecus afarensis
were found at two Pliocene sites in East Africa (subsequent use of the
name A.afarensis is for descriptive purposes only and not an advocated
position).
These sites are Hadar, Ethiopia, and Laetoli, Tanzania,
whose hominid yielding deposits are dated between 3.65 and 4.2 million
years (Johanson et al., 1978; Leakey et al., 1976).
Interpreting the features of the fossil material for A.afarensis,
Johanson and White (1979:325-327) suggest that dental, cranial, and
postcranial characteristics show considerable differences from previously known Plio-Pleistocene hominids.
Such features include:
1) large canines that project beyond the tooth row, 2) a diastema
that interrupts the tooth row between the lateral incisors and
canines, 3) a C/P3 cutting complex, 4) sectorial P3 's, 5) P 3 's with
two and sometimes three distinct roots, and 6) alveolar prognathism.
Furthermore, fossil remains from Hadar and Laetoli are interpreted by
Johanson (1980) to represent a new form of early hominid which is
characterized by size variation, most likely due to sexual dimorphism.
To test the null hypothesis that A.afarensis is not significantly
different from all other Plio-Pleistocene hominids, the following
points will be examined:
1) biostratigraphical and geochronological
evidence, 2) current concepts on A.afarensis' taxonomic status, 3)
anatomical comparisons between A.afarensis and other known australopithecines, and 4) biometric analyses of dental measurements for
3
~.afarensis
hominids.
and a representative sample of Pliocene and Pleistocene
The validity of Weinert's classification of the Garusi I
specimen as Meganthropus africanus will also be discussed (Johanson,
1980).
Therefore, it is the purpose of this paper to test the null
hypothesis that Australopithecus afarensis is not significantly
different from any other Plio-Pleistocene hominid.
hypothesis is that
~.afarensis
The alternate
is significantly different from all
other known Plio-Pleistocene hominids.
The paramount issue is
whether the morphological differences between A.afarensis and other
Plio-Pleistocene hominids are sufficient to justify a separate
taxonomic classification for A.afarensis.
Characteristics of the cranial, dental, and postcranial
morphology can be used to ascertain the taxonomic status of fossil
material.
Teeth, either isolated or associated with other fossil
material, along with mandibles and maxillae, represent the majority
of fossil hominid remains from Pliocene and Pleistocene deposits.
Dental morphology has proved to be invaluable when making taxonomic
distinction between australopithecine species (Robindon and Steudel,
1973).
To analyze dental variation, statistical (biometric) procedures
were performed on measurements from a representative sample of
Pliocene and Pleistocene hominids.
Results from these statistical
analyses were used to test the null hypothesis.
CHAPTER II
LITERATURE REVIEW
The collection of fossil remains of the proposed hominid
Australopithecus afarensis comes from two known Pliocene sites in
Eastern Africa.
These sites are Hadar, Ethiopia (11N, 40 30E) and
Laetoli, Tanzania (3 128, 35 11E) which have been dated between 3.65
and 4.2 million years old (Aronson et al., 1977; Johanson et al.,
1982;
Leakey~
al., 1976; Walter and Aronson, 1982).
The similar-
ities between fossil remains at Laetoli and Hadar suggest that these
remains may represent a single taxon according to Johanson (1980).
Although fossil remains for A.ararensis come from two East African
sites, the majority of hominid material is from Hadar, Ethiopia.
Laetoli Hominid-4 (LH 4) was selected by Johanson (1980) as the
holotype (a single specimen designated as "the type" for a new
species or subspecies in the original description) for both locations
because:
1) its morphology is characteristic of the species and 2)
it has been previously described and illustrated (Johanson, 1980;
White, 1977).
A.
Biostratigraphical and Geochronological Evidence
The Afar sedimentary basis, which is approximately 150 km long
and 60 km wide, is located in a depression at the northern end of the
East African rift valley and is dated to Plio-Pleistocene age (Taieb
et al., 1976:289).
A considerable amount of this basin is capped by
4
5
Pleistocene sand and gravel, with the underlying Pliocene strata
being termed the Central Afar Group.
The Central Afar Group can be
further subdivided into a number of sequences including Amado, Gewane,
Gueraru, Hadar, Haouna, Leadu, and the Meschelle.
It is the Hadar
formation including the Kada Hadar (KH Member), Denen Dora (DD Memher), Sidi Hakoma (SH Member), and the Basal Members (see Figure 1),
totaling about 140 meters of the deposits which has produced the
known hominid material of the Afar region (Taieb et al., 1976).
The majority of fossils collected at Hadar have been surface finds;
however, small-scale excavations have uncovered in situ materials
(Johanson and Taieb, 1978).
Hominid remains have generally been
located within two members:
1) the Sidi Hakoma Member, about 40
meters above the basalt flow, and 2) the Denen Dora Member, approximately 40 meters below the basalt flow (Johanson and Taieb, 1978).
Information gathered from these two stratigraphic layers was analyzed
so that an accurate date could be provided.
Initial isotopic dating (K-Ar decay, utilizing "an extraction
system with an 38Ar spike pipette and a MS-10 mass spectrometer")
performed on the SHT tuff, located about 15 meters below the marker
bed, proved to be inconclusive when three out of the five tests produced dates which were inconsistent (this was later attributed to use
of "weathered" tuff in the analyses) with a range of values between
3.1-5.3 Myr ± 0.03 Myr (Taieb et al., 1976:292).
Faunal material such as fossil remains of pigs and elephants
played an important role in establishing an accurate date for the
Hadar formation.
Cooke's (1978) sequence of several pig lineages,
which span nearly four million years of evolution, provided evidence
6
Figure 1
Geological column of the Hadar Forma.tion
rv. . .
~-'--
BKT 3
'>I vvvv_v>~
BKT 2
.; V;tv .( v "".J
BKT 1
vVVVV
·.~·.;·"lt•'~··/:t~
2.88 f0.08 m.y. (K/Ar)
2.70 ~.20 m.y. (fission
track)
KH MEMBER
'I';;,,, •;,••'•: ~::
,.
""'
·.·~ •11:~1·'
cc
KHT
DD MEMBER
""""~~
DD-3
J!:~~·:~o;:.;,•:;
DD-2
.!•• ~.~-~
TT 2-3
TT 1
~v vv vv'lv.J
Y VVI/ Vl/v'J
~
Basalt
SH MEMBER
Gastropods
T.
v t.:;> ;...<.;_v
·7·'1"r-v,...
--v-~
SH-3
SH-2
BASAL MEMBER
SHT 2
SHT 1
.~~~.·tJ,:,~!:
••
"
t' .. • ' ~
......- • ""' • "i
'-
.,,•.;.(.·t~
"" V'i o,Jv'l/
vi/'V'\1 -l'lV
:§@@,
162
*188
*241, 333
*366, 58
*161
*207
*211, 322
3.65 +0.15 m.y. (K/Ar)
*266 *311
*228
*277,
*137,
*128,
*198,
400, 411
166
129, 145
199, 200, 249
~-~·-l.-P c
-
----,
* Fossil remains of the Hadar Formation
From: Johanson, Taieb, and Coppens (1982:390)
7
that the original 3.0 Myr basalt date was too young.
Additional K-Ar
tests on pure basalt samples collected from the Sidi Hakoma Member
during the 1976-1977 field session produced dates of 3.75 million
years± 0.10 Myr
(Aronson~
al., 1977; Walter and Aronson, 1982).
This new date now shows that the Hadar and Laetoli fossil material,
which are nearly identical in morphology, are also nearly identical
in age (Johanson and White, 1979).
Finally, in addition to K-Ar tests, geomagnetic analyses were
performed on the basalt flow to determine its polarity.
Paleomagnetic
analysis is accomplished by studying the magnetic crystals in rocks
and charting the position of their polarity (normal
= North
Pole
positive and South Pole negative; the reverse is considered abnormal).
Tests conducted by Schmitt and Aronson (1977) indicate that the
basalt layer probably was formed during the Gilbert reversal period,
some 3.4 to 4.2 million years ago.
B.
Osteological Remains
The first significant fragmentary fossil evidence for Australo-
pithecus afarensis, according to Johanson and White (1979), was discovered at Garusi, Tanzania, in 1939 by Kohl-Larsen.
The remains
consist of a maxillary fragment with both upper premolars and a well
preserved alveolus (socket) for a canine tooth (Kohl-Larsen, 1943).
The first Ethiopian fossil evidence was discovered at Hadar in
1973.
These remains consisted of four associated leg bones (right
and left proximal femora and a right proximal tibia and distal femur;
labeled as A1 128, 129) which were located in a mudstone deposit, the
Sidi Hakoma Member (Johanson and Taieb, 1976).
8
The 1974 Hadar field work produced considerable hominid and
mammalian discoveries, including a partial skeleton of a female hominid found in the KHT stratum member and labeled AL 288-I (Johanson
and Taieb, 1978).
This fossil hominid specimen was given the name
"Lucy" and is the most complete Pliocene fossil hominid specimen
(with approximately 40% of the skeleton recovered) known to date
(Johanson and Edey, 1981).
Fossil material for the species A.afarensis characteristically
has "strong dimorphism in body size" and a high degree of robusticity
in respect to muscle and tendon insertions when compared to the known
fossil material for the genus Australopithecus (Johanson et at.,
1978:7).
Analyses of the pelvis, femur, tibia, and patella have
produced evidence that A.afarensis was well adapted to bipedal locomotion (Johanson et al., 1976; Lovejoy, 1974).
However, Stern and
Susman (1982) suggest that the postcranial material from Hadar
indicates locomotor abilities which may have included a significant
amount of arboreal activity.
From this postcranial material, it
appears that Australopithecus afarensis had well developed powerful
peroneal muscles.
Both the peroneus longus and brevis are instru-
mental in extending and everting the foot (Stern and Susman, 1982;
Lovejoy, 1974).
The powerful peroneal muscles, in conjunction with:
1) curvature of the pedal and manual phalanges, 2) orientation of the
scapular glenoid, and 3) a high humerofemora index, support Stern and
Susman's proposal that A.afarensis was capable of arboreal activity.
Furthermore, they suggest that
~.afarensis
possessed a method of
transferring weight from the hip to the front of the foot which was
different from that of modern H.sapiens.
They cite the following
9
evidence to support this contention:
1) the articular surface of the
acetabulum lacks a pubic contribution, 2) several Laetoli footprints
lack an impression for the ball of the hallux, and 3) the variable
length of the lateral toe relative to the length of the hallux.
Fur-
ther evidence for bipedal locomotion was found in footprints left in
volcanic ash at Laetoli, nearly four million years ago.
Leakey and
her research team (1979) strongly suggest that these footprints were
left by a bipedal hominid walking through wet volcanic ash.
The
pelvis of A.afarensis resembles corresponding fossil material for
Sts 14 found at the South African site of Sterkfontein (Johanson and
Taieb, 1976:296).
Finally, associated paleontological evidence indicates that a
lake was present at Hadar some three to four million years ago (Gray,
1979).
Environmental conditions of the lake and the river(s) that
supplied it were important to the australopithecines.
The lake mar-
gins probably supplied food and certainly supplied water but at the
same time these regions were most likely dangerous for early hominids.
Predators such as lions and leopards probably stalked A.afarensis at
the lake's edge but danger extended beyond the simple predator to the
elements themselves, in the form of flash floods.
Certain hominid
remains located at Hadar may represent either a family unit (fossil
site AL 333) or at least a cohesive unit of adults and children.
Although the AL 333 site had fossil remains for both sexes and
represents age groups from infant to adult, the exact number of
individuals represented at this site is uncertain (Johanson, 1976;
Johanson and Edey, 1981).
10
C.
Morphological Characteristics
One method for assessing the validity of the species A.afarensis
is to compare dental characteristics between A.afarensis with those
of later australopithecines and specimens of early Homo (see Table 1;
from Greenfield, 1980:356-357).
This table clearly illustrates that
A.afarensis does indeed exhibit primitive dental characteristics when
compared to later australopithecines and specimens of early Homo.
Finally, a more detailed analyses of dental characteristics displayed
by A.afarensis, later australopithecines, and early members of the
genus Homo (the Plio-Pleistocene hominid sample) can be found in
Chapter 3.
Morphological characteristics which Johanson and co-workers
consider distinctive for A.afarensis are discussed next.
D.
Jaw and Dental Characteristics
Mandibles of the Hadar-Laetoli specimens are variable in size
and are moderately thick dimensionally.
rounded, evenly curved symphysis.
These specimens have a
In the Hadar specimens the sym-
physis is characterized by having two internal transverse tori which
extend across the medial face of the symphysis (Johanson and White,
1979).
A slight variation exists between Hadar and Laetoli hominids,
relative to the length of the mandibular transverse tori (Johanson
~
al., 1978).
At the Hadar site, the two transverse tori are:
1)
nearly identical in length, 2) rounded in configuration, and 3) less
shelf-like in appearance than the Laetoli fossil remains.
Laetoli
hominid remains are identified by a single lower transverse torus
which is shelf-like in appearance and extends further to the rear of
Table 1
Comparison between A.afarensis and
later Australopithecus and early Homo
A.afarensis
later Australopithecus and
early Homo
Incisors
a.
Relative size
X = 26 (N=l)
X = 18 OR 12-21 (N=5)
X = 60° (N=1)
X = 72° OR 69-77° (N=4)
C/P3 Complex
Maxilla:
Maxilla:
a.
Relative size
X = 67 OR 61-77 (N=5)
X = 48 OR 33-73 (N=14)
(C 1 area)
M 1 area
Mandible:
Mandible:
(11 area)
b.
Angle of r1 projection
combined sexes
combined sexes
X = 53 OR 45-68 (N=3)
X=
combined sexes
combined sexes
41 OR 24.63 (N=22)
b.
Canine projection
Both sexes, slight projection,
reduction of crown tip to cheek
tooth occlusal plane delayed
Both sexes, crown tip reduced
to cheek tooth occlusal plane
rapidly compared to A.afarensis
c.
Canine interlock and
wear
Early interlock with P3 and other
canine, eventual loss of interlock
with reduction of canine's height,
shear, and blunting
Rare interlock, little or no
shear, tip blunted
1-'
1-'
Table 1 (continued)
A.afarensis
later Australopithecus and
early Homo
d.
Diastemata (crown)
Variable in size between r2
and cl
Rarely seen - except in some
early Homo
e.
Canine dimorphism
Primarily metric two sizes
Primarily metric two sizes
f.
P3 morphology
Sectorial with major and minor cusps,
elongate and less oval, early shear
but followed rapidly by blunting
Multi-cusped, round blunting
only
g.
P3 orientation
45-60° orientation with tooth row
Not angled in most specimens
P3/P4 heteromorphy
Intermediate-extreme
Slight-none
p3 morphology
Triangular or rectangular, buccal
face broader than lingual, some
mesial edge concavity
Rectangular
Tooth Rows
Primarily straight some curve
medially, V-shaped or elongate
parabola, general shape long
and narrow
Most curved
parabola or
anteriorly,
and broader
Zygomatic insertion
Primarily Ml and MlfM2
Primarily p4fMl, Ml and MlfM2
DM1 morphology
Molarized premolar some honing
wear, raised trigonid
Molariform
Source:
medially, elongated
parabola some square
general shape shorter
than A.afarensis
Greenfield (1980:356-357)
......
N
13
the symphysis than do the Hadar specimens (Johanson and White, 1979;
Johanson et al., 1978).
It has a subrectangular shape and a diastema
interrupts the tooth row between the lateral incisors and canines, in
AL 200-Ia and b (Johanson and White, 1979; Johanson et al., 1978).
The central incisors of A.afarensis are characterized by a large
mesio-distal length while the lateral incisors of A.afarensis are
reduced in size (Johanson et al., 197 8).
Australopithecus afarensis is characterized by variation in
canine size and form which can be attributed to sexual dimorphism,
according to Johanson and White (1979).
The canines for both "sexes"
project beyond the occlusal level of the adjacent teeth and the
canine roots are long and massive, extending well into both upper and
lower jaws.
Wolpoff (1979) suggests that the wear facet which exists
on the distal-lingual face of the upper canine and the associated
exposed dentin of the P3 were caused by a C/P3 dental cutting complex.
White (1981) disagrees with Wolpoff's interpretation since supporting
evidence is confined to the occlusal wear facets on the right P3 of
LH-14.
Instead, White suggests that rotation of the P3's crown caused
a malocclusion with the upper canine and p4, and this resulted in the
unique wear facets described by Wolpoff.
The postcanine teeth of A.afarensis are generally large, and are
broader buccal-lingually than mesial-distally (Johanson and White,
1979).
Premolar teeth normally are comprised of a dominant mesiodistally elongated buccal cusp.
The usual configuration of the
occlusal outline is that of an elongated oval.
The P3 orientation
is "mesio-buccal to disto-lingual at an angle of between 45 to 60
14
degrees to the mesio-distal axis of the tooth row" (see Table 1)
which is not typical of most specimens of later australopithecines or
Homo (Johanson and White, 1979:322).
The lower third premolar (P3)
often has two separate roots, while the upper third premolar (p3)
sometimes has three distinct roots (Johanson and White, 1979).
The
P3 is a sectorial tooth and the P3 is usually a little larger than
the fourth upper premolar (p4) (Johanson and Edey, 1981).
The fourth
premolar does not exhibit "mesio-distal elongation of the buccal
crown" area (Johanson and White, 1979:322).
Lower molars are characteristically squared in outline and "the
cusps are arranged in a simple Y-5 pattern" (Johanson and White,
1979:322).
This is observed in the M1 and M2 teeth and the usual
molar size sequence is M3-M2-M1 (Johanson and White, 1979; Johanson
etal., 1978).
E.
Cranial Characteristics
The adult specimens of A.afarensis exhibit:
1) strong alveolar
prognathism, 2) procumbent incisors, 3) widely flaring zygomatic
arches, 4) shallow palate, and 5) a compound temporal-nuchal crest
which is characterized by strong muscle marking (see Table 1)
(Johanson et al., 1978).
In addition, the mastoid process is large
and the external auditory meatus is tubular in shape (similar to
pongids) from a basal perspective (Johanson and White, 1979).
Cranial
estimates for Australopithecus afarensis are between 380 and 450 cubic
centimeters (Kimbel and White, 1980).
These estimates are within the
known range of cranial capacity for chimpanzees (320-475 cc) as well
15
as gracile (428-500 cc) and robust (500-530 cc) australopithecines
(Holloway, 1978:387).
F.
Postcranial Morphology
The Hadar-Laetoli specimens exhibit both "strong sexual
dimorphism in body size" and a high degree of skeletal robusticity
with "regards to muscle and tendon insertions" (Johanson et al.,
1978:7).
The Hadar hand bones are different from those of modern humans
in several respects (although the South African site of Sterkfontein
has produced fossils with similar characteristics):
1) the capitate
is "waisted," 2) the third metacrapal lacks a styloid process, and
3) the "phalanges are curved longitudinally" (Johanson and White,
1979:324).
The pelvis of Australopithecus afarensis (AL 288-I) has an
elongated shape (as compared to those of the pongids) when viewed
from the transverse plane with an anterior-posterior orientation.
Furthermore, Lovejoy (1980) suggests that broadening of the pelvic
basis, as reflected by the breadth of the pelvic inlets, in
A.afarensis was necessary to support the lower viscera during
upright stance.
This allows for efficient bipedalism, but not the
birth of large-headed infants (Lovejoy, 1980).
Observations made by Johanson and co-workers on the A.afarensis
os coxae indicate the presence of the following:
1) broadened ilium,
posterior extension of the iliac crest, and the position and orientation of the ischial tuberosity with respect to the acetabulum,
which closely resemble those features associated with hominids,
I·
16
2) strongly developed anterior spines (inferior and superior) which
have straight anterior margins, 3) shallow acetabulum compared to
that of Homo sapiens and the fossil specimen Sts 14 (A.africanus),
and 4) presence of a distinct greater sciatic notch (Johanson and
White, 1979; Johanson et al., 1978).
Furthermore, both the ilium
and ischium are short in length, relative to their respective widths
(Lovejoy, 197 4).
The morphology of the femur (AL 128, 129, and 288-I) resembles
that for modern humans (Johanson et al., 1976).
include:
These characteristics
1) large bicondylar angle, 2) deep groove on the patella
with a high lateral ridge, and 3) an anterioposteriorly elongated
lateral condyle which also is characterized by a flattened articular
surface (Johanson and Taieb, 1978).
The knee joint of A.afarensis
has the following hominid characteristics:
1) an oval shape of the
patella and 2) both knees meet at the midline of the body.
These
morphological characteristics indicate that A.afarensis was adapted
to bipedal walking (Lovejoy, 1974, 1980).
Leakey (1979) has examined the foot bones and footprints left in
wet volcanic tuff at Laetoli and concluded that A.afarensis had a
foot similar to that of modern man.
However, Leakey and her research
team failed to specify exactly which tests were performed.
The
A.afarensis foot had a longitudinal arch similar to that of Homo
sapiens, curved foot phalanges, and a hallux (great toe) which showed
no indication of divergence from the other toes (Johanson and White,
1979; Leakey and Hay, 1979).
17
G.
Biological Species Concept
From new phyletic material, taxonomic status must be determined
according to the principles of Systematic Zoology or, more specifically, to the strict interpretations of the International Code of
Zoological Nomenclature.
Furthermore, the fundamental taxon incor-
porated within the Linnaean hierarchy of Systematic Zoology is the
biological species.
A biological species as defined by paleontologists is an objective, nonarbitrary group of populations, which are reproductively
isolated from other such groups (Mayr, 1969; Simons, 1967).
Further-
more, species are populations composed of animals, not "types," which
exhibit different degrees of variability.
A definition of a species
should stress its distinctness rather than its differences (BuettnerJanusch, 1973).
Moreover, the genotype (the genetic constitution of
a taxon) of the population is the fundamental element in speciation,
and mutually exclusive geographical ranges, producing reproductive
isolation, are the prerequisite for this process to occur (BuettnerJanusch, 1973).
Finally, this definition of a biological species
allows for potential evolutionary change to occur without endangering
the integrity of the species.
H.
The International Code of Zoological Nomenclature
and the Taxonomic Status of Hadar-Laetoli Fossils
Johanson and White (1979) have concluded that A.afarensis, the
oldest and most primitive hominid (apart from Ramapithecus) that
can be substantiated by the fossil record be considered the basal
hominid.
In their taxonomic scheme, A.africanus is considered at an
18
intermediate stage of development between A.afarensis and A.robustus.
Moreover, they do not consider A.africanus to be ancestral to Homo.
Objections to Johanson and White's taxonomic scheme have been
voiced by several paleoanthropologists including Brace, Day, Mary and
Richard Leakey, Olson, Walker and Wolpoff.
The Leakeys, along with
Day, Olson and Walker, disagree with Johanson and White's interpretations of the International Code of Zoological Nomenclature as well as
their classification of the Hadar and Laetoli fossil material as
Australopithecus afarensis (Day et al., 1980; Leakey and Walker,
1980).
Day et al. (1980) suggest that Johanson and White violated
certain articles of the International Code of Zoological Nomenclature,
particularly Numbers 53, 74a, and 74e, when they proposed the new
species, Australopithecus afarensis.
Leakey and Day state that
Johanson and White have incorrectly designated one Laetoli hominid
(LH 4) as a holotype, which violates Article 74a, instead of using
the correct term of lectotype (Day et al., 1980).
Day and co-workers
further state that Article 74e is violated by including the Garusi I
"Meganthropus africanus" specimen in the type-series of A.afarensis.
Listing "Meganthropus africanus" as an outmoded systematic name had
the effect of making A.afarensis a replacement name for Weinert's
M.africanus, which is thought to be in violation of Article 53 (Day
et al. , 1980).
According to strict interpretation of the International Code of
Zoological Nomenclature, Weinert did not satisfy Article 13a(i)
because he failed to include a diagnostic statement by which
"Meganthropus africanus" can be differentiated from all other known
taxa (Johanson, 1980; Mayr, 1969).
After prolonged studies of the
19
Garusi I remains, Remane (1951) proposed the following list of its
diagnostic characteristics:
1) three rooted p3, 2) enamel extension
on the buccal face of the p3, and 3) large and projecting canines.
Remane firmly supported Weinert's classification of the Garusi I
specimen and stated that its premolar construction resembled that of
the pongids more than that of the known hominids (Remane, 1954).
Other paleoanthropologists, including Robinson (1953), Tobias
(1965), and Pilbeam (1972), doubt the close affinity between the
Garusi I specimen "Meganthropus africanus" and the Meganthropus II
mandible from Java "Meganthropus paleojavanicus".
Robinson (1953)
stated that M.africanus should be considered an an australopithecine
which is more closely related to the South African specimens than to
·~.paleojavanicus".
Tobias (1965) and Pilbeam (1972) think that the
Garusi I specimen represents a gracile australopithecine.
Therefore, since Weinert failed to substantiate his taxon M.
africanus, it must be considered an invalid binomen (Johanson, 1980).
As a result, two implications are indicated:
1) A.afarensis cannot
be considered a junior homonyn of A.africanus and 2) Johanson did
not violate Article 53 of the International Code of Zoological
Nomenclature.
Finally, Johanson and White (1979) followed the International
Code of Zoological Nomenclature when:
1) proposing the new species
A.afarensis and 2) satisfying Articles 13a(i) and 72 and Recommendations 73B and 73C; therefore, no violation of Article 74a or 74e
occurred.
Richard Leakey's comments have varied from stating that A.
afarensis was not ancestral to Homo to claiming that A.afarensis
20
has Homo characteristics and should be considered a member of that
genus (Leakey and Lewis, 1977; Leakey and Walker, 1980).
Wolpoff (1981) and Brace (1979) contend that A.afarensis resembles !·africanus too closely to be considered a separate species.
They suggest that morphological differences due to dramatic sexual
dimorphism can account for the variation seen in the fossil material
for A.afarensis and should not be considered taxonomically significant from !·africanus (Brace, 1979; Wolpoff, 1980).
Kennedy (1979) challenges the validity of A.afarensis on the
basis of its morphological distinctiveness, and cites inconsistencies
in Johanson's list of primitive features for A.afarensis as support.
Characteristics such as large, projecting canines, the "waisted"
appearance of the capitate, and a lack of a styloid process on the
third metacarpel, can be seen in gracile australopithecine fossil
remains from the South African site of Sterkfontein.
Finally, she
states that the cusps of the anterior premolars and orientation of
the tooth row in A.afarensis are similar to the dental morphology
seen in the Miocene hominid Ramapithecus.
Summary
Johanson and White have stated that fossil specimens recovered
from Laetoli and Hadar exhibit primitive characteristics in dental,
cranial, and postcranial material when compared to the known fossil
remains for the genus Australopithecus (Johanson and White, 1979;
Johanson et al., 1978).
Hadar~Laetoli
Primitive dental characteristics of the
fossils include the following:
1) large projecting
canines, 2) canine/premolar dental cutting complex, and 3) diastema
21
between the canines and the lateral incisors.
Hadar-Laetoli fossil
remains also provide evidence of bipedalism as indicated by analyses
conducted on postcranial material at Hadar and on footprints preserved
at Laetoli.
Furthermore, Johanson and White have suggested that the
fossil material from Laetoli and Hadar represent a new species of
Australopithecus: A.afarensis (Johanson and White, 1979).
Support for Johanson and White's classification of the Hadar and
Laetoli material as Australopithecus afarensis can be substantiated
by the following:
Articles 13a(i) and 72 and Recommendations 73B and
73C of The International Code of Zoological Nomenclature.
Australo-
pithecus afarensis appears therefore, to represent the oldest and most
primitive hominid that can be substantiated by the fossil record.
Validity of the proposed species Australopithecus afarensis has
been challenged by paleoanthropologists including Brace, Day, the
Leakeys, Kennedy, Olson, Walker, and Wolpoff.
The Leakeys, along
with Day, Olson and Walker suggest that Johanson and White incorrectly
assigned Laetoli hominid (LH 4) as the holotype and violated Articles
53, 74a and 74e of The International Code of Zoological Nomenclature,
when the proposed the new species Australopithecus afarensis (Day et
al., 1980; Leakey and Walker, 1980).
Brace (1979) and Wolpoff (1980)
suggest that once sexual dimorphism is considered, there is little
significant difference between A.afarensis and A.africanus.
Finally,
Kennedy (1979) suggests that primitive features (such as large, projecting canines, and the "waisted" appearance of the capitate) associated with A.afarensis can also be found in fossil remains of A.
africanus from Sterkfontein.
CHAPTER III
MATERIAL AND METHODS
The purpose for analyzing the Fossil Hominid sample was to
ascertain if the proposed species A.afarensis is significantly different from other species of the genus Australopithecus.
The fossil
specimens and the statistical methods used in this study are described
in this chapter.
The validity (testing of the null hypothesis) of the
proposed species A.afarensis was partially evaluated by statistical
analysis of dental measurements of a representative sample of Pliocene
and Pleistocene hominids (Fossil Hominid sample).
Mandibular and max-
illary dental measurements of these Plio-Pleistocene hominids were
evaluated by univariate and multivariate statistical methods to compare the variability exhibited by !•afarensis with that of the PlioPleistocene hominid sample.
Material
A.
Fossil Hominid Sample
Table 2 lists the geologic origins of the specimens in the Fossil
Hominid sample.
Each fossil specimen is identified by its museum
accession number and accompanied by the following:
1) its strati-
graphic position and 2) an estimate of its geologic age.
Three spec-
imens, one from each of the three sites at Hadar, Ethiopia, were
included in the analysis.
member.
The sites are located in the Sidi Hakoma
Five specimens are from four sites in the Ileret and Koobi
22
23
Table 2
Fossil Hominid Specimens Included in the
Analysis and Their Geologic Origin
Specimen
Local Stratigraphy
Age (my)
Source
East African Sites
Afar
AL 199-1
AL 200-1a
AL 266-1
3.6
3.6
3.6
3
3
3
Ileret, below middle tuff
Ileret, below Chari tuff
Lower member Koobi Fora Formation,
below the KBS tuff
Lower member Koobi Fora Formation,
below the KBS tuff
Upper member Koobi Fora Formation
1.6-1.8
1.4-1.6
1.9-2.3
5
5
5
1.9-2.3
5
1.57
5
Laetolil
Laetolil
Laetolil
tuff b
3.6
3.6
3.6-3.7
4
4
1.7-2.1
1.75
1
1
1.5
2
Hadar Formation, Sidi Hakoma member
Hadar Formation, Sidi Hakoma member
Hadar Formation, Sidi Hakoma member
Lake Turkana
ER 729
ER 992
ER 1590
ER 1802
ER 1813
Laetoli
Garusi I
LH 3
LH 4
Beds
Beds
Beds between Aeolian
and c
4
Olduvai Gorge
OR 5
OR 7
Surface FLK, Bed 1
FLK NN; middle Bed 2
Lake Natron
Nat ron
Peninj lacustrine facies
South African Sites
Kromdraai
TM 1512
TM 1517
TM
1600
Kromdraai B (Late Swartkrans
Faunal Span)
Kromdraai B (Late Swartkrans
Faunal Span)
Kromdraai B (Late Swartkrans
Faunal Span)
1.5-2.0
7,8
1.5-2.0
7,8
1.5-2.0
7,8
24
Table 2 (continued)
Specimen
Local Stratigraphy
Age (my)
Source
Makapansgat
MLD 2
MLD 18
MLD 40
Gray Breccia (Phase 1 Breccia)
Gray Breccia (Phase 1 Breccia)
Gray Breccia (Phase 1 Breccia)
3.0
3.0
3.0
6,7
6,7
6,7
Limestone
Limestone
Limestone
Limestone
2.5
2.5
2.5
2.5
7,8
7,8
7,8
7,8
2.0-2.6
2.0-2.6
2.0-2.6
2.0-2.6
2.0-2.6
2.0-2.6
6,7
6,7
6,7
6,7
6,7
6,7
Sterkfontein
STS
STS
STS
STS
7
17
52
55
Breccia
Breccia
Breccia
Breccia
Swartkrans
SK
SK
SK
SK
SK
SK
13
23
27
46
48
55
Pink
Pink
Pink
Pink
Pink
Pink
Breccia
Breccia
Breccia
Breccia
Breccia
Breccia
List of Sources:
1. Hay (1976)
2. Isaac and Curtis (1974)
3. Johanson and Taieb (1976)
4. Leakey et al. (197 6)
5. Leakey (1978)
6. Partridge (197 3)
7. To bias (1976)
8. Vrba (1975)
25
Fora formations, east of Lake Turkana, Kenya.
Temporal limits for
these sites are 1.4 to 2.3 million years BP (Leakey, 1978).
Three
specimens are from sites located in the Laetoli Beds, Tanzania, which
are dated between 3.6-3.75 million years BP (Leakey et al., 1976).
Two specimens come from Bed I Olduvai Gorge, Tanzania.
Dating for
the base of Bed I is from 1.7-2.1 million years BP (Hay, 1976).
The Lake Natron (Peninj) specimen has been dated at approximately 1.5 million years BP (Isaac and Curtis, 1974).
The South African site of Kromdraai is represented by three
specimens.
Tobias (1976) and Vrba (1975) have stated that the hominid
bearing breccia of Kromdraai is 1.5-2.0 million years old.
Three hom-
inid fossil specimens come from Makapansgat, the majority of which are
associated with the Phase I Breccia (gray breccia) which is dated at
approximately 3.0 million years BP (Partridge, 1973; Tobias, 1976).
Four hominid specimens come from Sterkfontein breccia which is dated
at approximately 2.5 million years old (Tobias, 1976; Vrba, 1975).
Finally, six hominid specimens come from the "pink breccia" of
Swartkrans, which is dated by Partridge (1973) and Tobias (1976) as
being between 2.0-2.6 million years BP.
B.
Comparative Samples
The sample of Pliocene-Pleistocene fossil hominid specimens has
the composition described as follows:
Australopithecines.
Data on twenty-seven Australopithecus
specimens (!.africanus, A.robustus, and A.boisei; see Table 3 for
taxonomic assignments) were selected from Johanson and Taieb (1976),
Leakey (1978), White (1977), and Wolpoff (1971).
Only specimens with
26
Table 3
Taxonomic Assignments of the
Fossil Hominid Specimens
Specimen
Classification
Source
East African Sites
Afar
AL 199-I
Australopithecus afarensis
1
AL 200-Ia
Australopithecus afarensis
1
AL 266-I
Australopithecus afarensis
1'
ER 729
Australopithecus robust us
2
ER 992
Homo habilis
2
ER 1590
Homo habilis
2
ER 1802
Australopithecus robustus
2
ER 1813
Australopithecus africanus
2
Garusi I
Australopithecus afarensis
3
LH 3
Australopithecus afarensis
3
LH 4
Australopithecus afarensis
3
OH 5
Australopithecus boise!
4
OH 7
Homo habilis
4
AustraloEithecus boisei
4
Lake Turkana
Laetoli
Olduvai Gorge
Lake Natron
Natron
27
Table 3 (continued)
Specimen
Classification
Source
Kromdraii
TM
1512
Australopithecus robustus
4
TM
1517
Australopithecus robustus
4
TM
1600
Australopithecus robust us
4
Makapansgat
MLD
2
Australopithecus africanus
4
MLD
18
Australopithecus africanus
4
MLD
40
Australopithecus africanus
4
STS 7
Australopithecus africanus
4
STS 17
Australopithecus africanus
4
STS 52
Australopithecus africanus
4
STS 55
Australopithecus africanus
4
SK 13
Australopithecus robustus
4
SK 23
Australopithecus robustus
4
SK 46
Australopithecus robustus
4
SK 48
Australopithecus robustus
4
SK 55
Australopithecus robustus
4
Sterkfontein
Swartkrans
List of sources:
1.
2.
·3.
4.
Johanson and Taieb (1976)
Leakey (1978)
White (1977)
Wolpoff (1971)
28
data on the mandibular and maxillary canine, first premolar, and
first molar teeth were selected as suggested by Johanson (Johanson
and Edey, 1981:276).
The Fossil Hominid sample represents several
geographic regions, although not all are equally represented.
Homo.
Data on three Homo habilis specimens were also taken from
Leakey (1978) and Wolpoff (1971).
These specimens have been classi-
fied as belonging to the taxon Homo habilis (OH 7 is considered the
type specimen) following the arguments set forth by Leakey et al.
(1964).
C.
Measurement Data
Data for each specimen were gained from measurements of mesio-
distal and bucco-lingual crown diameters of the upper (C, p3 and M1)
and lower
(~,
P3 and M1) dentitions.
Table 4 presents data for the
Fossil Hominid sample with a key to the sources of data.
Data was obtained from the aforementioned primary sources, as
funding was unavailable for personal examination of the original
fossil specimens.
D.
Methods
The mandibular and maxillary dental measurement data were anal-
yzed by using univariate and multivariate statistical methods.
Uni-
variate statistical analyses were performed to describe variability
within the Fossil Hominid sample.
Multivariate statistical analysis
of the Fossil Hominid sample dealt with among-group variability.
Finally, these statistical analyses were performed to determine the
29
Table 4
Fossil Hominid Sample Data
Maxillary Dentition
c
Specimen
Dimension (mm)
p3
(B)
(L)
M1
(L)
(L)
(B)
AL 199-1 (1)
8.70
9.30
7.30
11.20
10.10
12.00
AL 200-1a (1)
9.40
10.95
8.95
12.10
11.80
13.15
ER 1590 (2)
11.35
12.35
10.15
13.45
13.40
13.90
ER 1813 (2)
8.10
8.40
8.00
11.10
12.20
12.50
LH 3 (3)
11.60
12.50
8.90
13.40
12.90
14.60
OH 5 (4)
8.75
9.80
10.90
17.00
15.20
17.70
Natron (4)
7.35
8.20
16.25
16.00
TM 1512 (4)
8.80
9.40
(B)
Source
8.90
11.90
12.00
13.60
TM 1517 (4)
10.10
13.70
13.70
14.60
STS 17 (4)
8.70
12.90
11.45
13.40
8.65
12.80
12.25
14.05
STS 55 (4)
9.10
13.90
SK 13 (4)
9.75
13.15
13.40
14.90
9.50
13.40
14.00
13.20
8.30
13.20
11.90
15.20
STS 52 (4)
SK 27 (4)
9.85
10.60
9.80
10.40
SK 46 (4)
SK 48 (4)
8.20
8.80
9.20
13.70
13.10
14.00
SK 55 (4)
8.25
8.75
9.50
13.30
14.50
14.40
List of sources: 1) Johanson and Taieb (197 6); 2) Leakey (1978);
3) White (1977); 4) Wolpoff (1971).
30
Table 5
Fossil Hominid Sample Data
Mandibular Dentition
c
(L)
Specimen
(B)
Dimension (mm)
p3
(B)
(L)
M1
(L)
(B)
Source
AL 266-1 (1)
9.15
10.10
12.10
11.95
ER 729 (2)
8.50
10.00
12.00
13.00
15.50
15.50
ER 992 (2)
9.15
8.70
9.35
11.15
11.95
10.80
ER 1802 (2)
10.40
12.10
14.65
13.20
Garusi I (4)
10.10
11.70
14.80
13.60
12.60
10.60
13.40
13.30
10.30
10.00
11.85
12.60
LH 3 (3)
11.70
10.40
LH 4 (3)
OR 7 (4)
9.05
9.05
9.60
10.20
14.30
12.30
Natron (4)
7.35
8.20
9.55
13.50
16.25
15.40
TM 1517 (4)
9.95
11.50
14.40
13.00
TM 1600 (4)
9.80
12.20
13.50
13.20
10.75
13.50
14.80
13.85
MLD 2 (4)
MLD 18 (4)
9.00
10.50
10.00
12.20
11.60
13.00
MLD 40 (4)
8.30
9.50
10.00
11.00
12.80
12.30
STS 7 (4)
9.20
11.00
8.50
12.00
12.00
12.70
STS 52 (4)
9.10
10.00
9.00
11.70
13.20
12.90
SK 23 (4)
7.95
7.90
9.50
11.45
14.75
14.65
9.60
11.00
14.35
13.70
SK 55 (4)
List of sources: 1) Johanson and Taieb (1976); 2) Leakey (1978);
3) White (1977); 4) Wolpoff (1971).
'
~
31
phenetic relationships that exist between the Hadar-Laetoli specimens
and members of the Fossil Hominid sample.
E.
Univariate Analysis
In the univariate analysis, histograms were utilized to describe
within-group variability of the fossil hominids.
The histograms were constructed as follows:
1) the complete
Fossil Hominid sample (see Table 3) was used, 2) dental measurements
(both mandibular and maxillary) were utilized per fossil hominid, and
3) measurements were taken from the following teeth:
first premolar, and first molar.
the canine,
Histogram distributions of dental
measurements should indicate the presence or absence of bimodality.
Bimodality may be due to sexual dimorphism, species, or generic differences between A.afarensis and members of the Fossil Hominid sample.
F.
Multivariate Analysis
Principal component and canonical variate analyses were used to
describe the patterns of variation in the measurements and specimens
included in the Fossil Hominid sample.
Principal component analysis of the Fossil Hominid sample was
based on a variance-covariance matrix.
These statistical tests were
performed using BMDP4M (Dixon and Brown, 1979).
Principal component
analysis seeks to explain the total variance (common variance plus
unique variance) for each variable using the smallest number of components as possible.
In this analysis of dental measurements, prin-
cipal component (variance-covariance) analysis was used to provide
1) new uncorrelated variable sets and 2) to identify patterns of
32
relationships among the specimens within the Fossil Hominid sample
(Oxnard, 1973).
Canonical variate analysis was performed using BMDP7M (Dixon and
Brown, 1979).
Variables used within this analysis "to compute linear
classification functions are selected in a stepwise manner" (Dixon
and Brown, 1979:711).
Also, canonical variate analysis identifies
variables which maximize between-group variance relative to withingroup variance.
Finally, in respect to this study, the most important
aspect of the analysis produced by BMDP7M is the Mahalanobis' D2
statistic, the measure of generalized distance which is tested using
the F-statistic (Dixon and Brown, 1979).
G.
Fossil Hominid Sample
The Fossil Hominid Sample is actually comprised of sub-samples
of specimens:
those represented by the maxillary dentition and those
represented by the mandibular dentition.
Analyses were conducted on
either maxillary or mandibular dentitions using only specimens that
had data for the canine, first premolar, and first molar.
Table 6 summarizes the following information:
1) the number of
complete specimens (those containing dental measurements for the
canine, first premolar, and first molar), 2) the total number of
specimens used per sample, and 3) the frequency of missing dental
data.
33
Table 6
Fossil Hominid Sample Data
Number of Total
Specimens
Number of Complete
Specimens
Maxillary
18
10
Mandibular
17
11
Sample
Population
Frequency of Missing Teeth
Sample
Population
c
p3
M1
Maxillary
6 (2 9. 41%)
1 (5.55%)
1 (5.55%)
Mandibular
8 (44.44%)
0
0
CHAPTER IV
RESULTS
The results obtained from univariate and multivariate methods
described in Chapter 3 will be discussed in this chapter.
Univariate Analysis
A.
Histograms:
Fossil Hominid Sample Variation
Within-group variability exhibited by the Fossil Hominid sample
was demonstrated by the use of histograms.
into these categories:
Histograms are divided
1) jaw type (either maxillary or mandibular)
and 2) type of dental measurements analyzed (mesio-distal or buccalingual measurements).
Twelve histograms (see Figures 2-7) were con-
structed following the criteria outlined in Chapter 3.
Each increment
on the abscissa represents 0.5 standard deviation unit, while the
ordinate represents the number of specimens in the sample.
All histograms exhibit some degree of deviation from normality.
Bimodal distributions can be seen in the following histograms:
1)
the bucca-lingual distribution for the maxillary canine (Figure 2),
2) the mesio-distal distribution for the M1 (Figure 4) and 3) the
mesio-distal distribution for the M1 (Figure 7).
The following
histograms best illustrate normal distributions:
1) mesio-distal
distribution for the maxillary canine (Figure 2) and 2) bucca-lingual
distribution for the P3 (Figure 6).
34
35
Figure 2
Histogram
folaxillary Dentition
Canine
Mesio-Distal
4
3
Ul
c
.....~
2
u
"'c..
....
tf)
~
1
"'
~"'
Peninj
SK 55
SK 48
0!15
ER 1813
AL 199-
I
-
'I'M 1512
-. 5
- 1 .o
STS 52
SK 27
IAL 200-I
ER 1590
Ul3
0
1.0
:>
2.0
1.5
Standard Deviation Units
Bucca-Lingual
.,
E
"'"
.,"
o.
3
..<
l~
....0
2
"''·
'I'M 1512
.D
E
£
1
-
Peninj
ER 1813
SK 55
SK 48
STS 52
0!1 5
ER 1590
SK 27
AL 2Cl0-l
Ul)
AL 199-
I; -1.5
-1.0
5
0
.5
1.0
-•Standard
Dev:<.ation units
1.5
2.0
36
Figure 3
Histogram
Maxillary Dentition
p3
Mesio-Distal
5
~
....E"
,
8.
:
...,
2
I"" 15~
0
~55
.Q
~
1
AL 199-I
Ja 1813
5I: 55
~17
S'lS52 pl:3
SI:4S
SX46 ~2~1:. SI 27
sz:
-1.0
13
'111 1517
IR 1590
OH5
1.0
2.0
Buc_c o-Lingual
·j
7
6
5
4
".,c
3
'1'1(
....
"8.
...
Ul
1517
Sl: 55
B
u
51:48
SX46
2
..
0
SI 27
0
.Q
5I: 13
3
:z:
1
ER 181:3
TK 1512
IAL 199-I i4L
-;;-1.5
-1.0
S'l'S
52 Lll3
200Ia S'l'S 17
-·
Ell. 1813
0
S'l'S
.
OH5
55
1.0
Standard DeviatiDn Unite
1.$
2•0
2.5
J,U
2.5
37
Figure 4
Histogram
Maxillary Dentition
Ml
Mesio-Distal
4
:;
.,~
~
tJ
~
...
2
..
0
'DI 1512
"'
.r>
!i
sz:
'DI 1511
S'l'S 52
1
SK46
AL 199-I
~.o
SK 48
S( 13
Ul.3
At. 200...11 Ef\_1813
m
I S'l'S 11
S(
1590
S(
55
21
Cll5
1.0
-1.0
PcWlj
"2.0
Bucc6-Lingual
4
.,
"
~
"~
:;
tJ
...
VJ
..,
'
2
0
'DI 1512
.J!,
S'1'S 52_ 'DI 1511
SI..r.6
SI4S
St. 55
AL 199-! ER 1813 AL 200...:t ER 1590 LP..3
SK 1.3
S'l'S 17
E
"
sz:
l
SI 27.
-II
-.2.0
-·5
0
·5
C!l5
Psninj
1.0
St.an<iard Deviation Unit.a
2.0
I
:;.o
38
Figure 5
Histogram
Mandibular Dentition
Canine
Mesio-Distal
:1
.,
.,r::
3
$,
"~
If)
...
2
.,...
S'1'S 52
~
Cll7
0
S'1'S
.t:J
1
KLD 18
Sl23
Peninj
7
:m 7.l9
11LD 40
:m 992
Ul3
2..0
-.5
Bucca-Lingual
...
.
0
II
.t:J
J
1
SK 23
..:a.o
:rn
Per.inj
992
I
-·5
OH7
S'l'S52
KLD 18
KLD 40
ER 729
Ul3
.
0
Standard Deviation Unit.e
S'l57
1.0
2.0
39
Figure 6
Histogram
Mandibular Dentition
p3
Mesio-Distal
.
-
".,c:
~
.."'...8.
'1'M 1600 HLD 4D
0
.,
iii 1517 m.D 18
Guuai-,
S1 55
St 2.)
~
..
S'1'S 52
Ell 992- Pemnj
srs '7
AL 26£,..;
1
-1.5
-1.0
Cl!?
-.
BR 11!02
IIIJl 2
Ul4
0
BR '729 IB3
1.0
·5
115
.2.b
2.5
Bucco-Lingual ·
4
.
c:
3
c;
E
...
.,t.
...c 2
0
...
.!
~
liE l
S'rS52
.
Sl 55
01!7
LRJ..
-2.0
'IM 1517 S'1'S 7
MLD lS
Al 199-! I.E)
'
·l.5
-1.0
-.5
S!; 2.)
Garus:i-'I
~
1m 992
ER 1802
MLD 2
0
1600
'
Standard Deviation llr.its
hn1nj
ER "129 HLD 4D
l.O
1.5
2.0
).0
40
Figure 7
Histogram
Mandibular Dentition
Ml
Mesio-Distal
4
.,
f
:;
~
..,
&
..."'
.,..
2
.&>
~
IC
7!! 1517
STS 7
IIUl 18
0
512.3
TM 1~00
L1!4
1
~ER992
AI.
II
2~
St 55
Cll7
S'l'S52
l'.LD AD I.!!3
-1.0
-1.5
JW)
-.5
2
Garu.siER 1802 1CR"I'29
.
0
"1.0
Ptminj
1.5
2.0
Bucca-Lingual
s
:-
.,
..,
!
.
~
....
l
.... 2
'1M 1600
n! 1517
..
1!
0
i
OH7
KLD 18
1
ER 992
-2.5
-2.0
AL 266-I U!4
-1.5
-1.0
STS52
Sl 55
STS7
Garusi-
!!l.D 2
IJ!3
Peninj
MLD 40
-.,
St.anciard Deviation Unite
SK 23
1.0
ER '729
1.5
2.0
41
These histogram distributions also illustrate the relative
position of the Hadar-Laetoli specimens with respect to other members
of the Fossil Hominid sample.
In the majority of these distributions,
Australopithecus afarensis specimens are associated with the gracile
hominids more often than they are with the robust forms.
Finally,
the apparent variability exhibited by the Fossil Hominid sample may
be explained by the presence of:
1) sexual dimorphism, 2) species,
or generic differences.
Multivariate Analysis
B.
Fossil Hominid Sample:
Among-group Relationships
Tables 7 and 8 present the following information obtained from
the principal component analysis for the maxillary and mandibular
dentition:
1) eigenvalues, 2) the percent of variance explained by
each principal component, and 3) cumulative percent of variance.
Tables 7 and 8 show that the first component accounts for nearly 62.5
and 54 percent of variance, respectively, for these analyses.
Fur-
thermore, all variables in Table 7 but not in Table 8 exhibit high
positive loading for the first component, which is an indication that
most of the variance is probably size-related.
Further analysis of the Fossil Hominid sample was achieved
through the use of bivariate plots of the principal component scores
to identify patterns of relationships among the specimens within the
Fossil Hominid sample.
The abscissa (horizontal axis) of the bivari-
ate plots (see Tables 9 and 10 for data used to produce Figures 8 and
9) represents Principal Component 1, while the ordinate (vertical
axis) represents Principal Component 2.
Figures 8 and 9 illustrate
42
Table 7
Principal Component Analysis
Maxillary Dentition
Variables
1
2
Principal Component
3
4
5
6
1
Canine Length
0.38
1.16
0.13
0.10
0.23
-0.053
2
Canine Breadth
0.43
1.22
-0.13
-0.16
-0.20
0.028
3
p3 Length
0.94
0.034
0.20
0.35
-0.16
0.021
4
p3 Breadth
1.49
-0.21
-0.21
-0.034
0.10
0.23
5 M1 Length
1.20
-0.27
0.53
-0.21
-0.0055
-0.053
6 M1 Breadth
1.33
-0.28
-0.38
0.0027
0.0044
-0.22
Eigenvalue
6.65
3.02
0.54
0.20
0.13
0.11
Percent of
Variance
62.48
28.38
5.06
1.88
1.19
1.01
Cumulative
Percent of
Variance
62.48
90.86
95.92
97.80
98.99
100.00
43
Table 8
Principal Component Analysis
Mandibular Dentition
Variables
1
2
Principal Component
4
3
5
6
1
Canine Length
-0.66
0.87
-0.12
-0.24
0.26
2
Canine Breadth
-0.50
0.52
0.67
-0.23
-0.19
-0.13
3
p3 Length
0.30
1.20
-0.16
0.35
-0.073
-0.035
4
p3 Breadth
0.68
-0.16
0.70
0.18
0.22
-0.14
5 M1 Length
1.49
0.10
-0.43
-0.22
-0.007
-0.21
6 M1 Breadth
1. 38
0.31
0.34
-0.12
-0.027
0.27
Eigenvalue
5.36
2.57
1.28
0.33
0.16
0.15
Percent of
Variance
54.42
26.12
12.95
3.36
1.60
1. 55
Cumulative
Percent of
Variance
54.42
80.55
93.49
96.85
98.45
100.00
0.032
44
Table 9
Principal Component Scores
Maxillary Dentition
Specimen
PC 1
Principal Component
PC 2
PC 4
PC 5
PC 3
PC 6
AL 199-I
-1.58
-0.02
-1.91
-0.51
-0.48
1.12
AL 200-Ia
-0.44
0.70
-0.83
0.94
1.64
0.04
ER-1590
0.65
1.64
0.35
1.36
0.72
0.25
ER 1813
-1.12
-0.83
0.42
-0.13
-0.40
-0.93
LH 3
0.53
1.80
-0.10
-1.30
-0.34
-1.00
OH 5
2.32
-1.13
-0.15
0.23
0.18
0.20
SK 27
0.84
0.57
1.52
0.34
-1.30
1.53
SK 48
0.13
-1.01
-0.10
0.46
-0.04
1.40
SK 55
0.41
-1.14
1.63
0.30
0.11
-0.94
STS 52
-0.10
0.15
-0.70
-0.42
-1.72
-0.60
TM 1512
-0.52
-0.29
-0.74
0.93
-0.02
-1.50
45
Figure g
Bivariate Plot of Principal Component Scores
Maxillary Dentition
SK 27
AL 199-I
0 .i-1- - - - - - - - - - - - / - - - - . L . . - f . - . . . . r - - - - - - 1 ' - - - - - - - - - - j
A.robustus
A.boisei
0
OH 5
0
Principal Component I
3
46
Table 10
Principal Component Scores
Mandibular Dentition
PC 1
Principal Component
PC 2
PC 3
PC 4
PC 5
ER 729
1.40
1.13
1.00
0.60
-1.00
-0.60
ER 992
-1.15
0.72
0.20
-1.40
0.57
-0.97
LH 3
-0.46
2.37
-0.77
0.43
2.00
0.32
MLD 18
-0.66
0.90
0.82
0.70
-0.40
1.17
MLD 40
-0.48
-0.33
-0.77
0.10
-1.82
-0.10
Peninj
1.81
-0.77
1.60
-1.13
0.25
-0.70
OH 7
-0.23
-0.24
-1.82
-0.11
-0.35
-1.10
SK 23
0.89
0.67
-0.50
-1.36
-0.17
2.11
STS 7
-0.80
-0.47
0.30
1.60
0.41
0.14
STS 52
-0.32
-0.38
-0.04
0.60
0.54
-0.34
Specimen
PC 6
47
Figure 9
Bivariate Plot of Principal Component Scores
Mandibular Dentition
3
A.afarensis
LH 3
2
H
H
b
MLD 18
1
Q)
~
0
0..
E
0
0
rl
0
A.africanus
fi\ER 729
III
1
A.robustus
I
I
0
ctl
0..
STS
•rl
t)
I
~
H.habilis
•rl
~
p..,
I
-~~ Peninj
1
A.boisei
2
3~-----,,,-------,,--------L-------,,--------rl------~
2
1
0
1
2
3
Principal Component I
48
patterns of relationships produced by principal component analysis.
From these analyses the following interpretations are suggested:
1) in either Figure 8 or 9 the Hadar-Laetoli specimens appear to be
closer to the gracile hominids (A.africanus and Homo habilis) rather
than to the robust hominids (A.robustus and A.boisei) and 2) the
maxillary dentition (see Figure 8) appears to display a larger range
of variability (based on the spread of specimens on each component)
than does the mandibular dentition (see Figure 9).
C.
Canonical Variate Analysis
To test the null hypothesis that the Hadar-Laetoli hominid
fossils (A.afarensis) to not differ significantly from other forms of
australopithecines, canonical variate analysis was performed.
analysis included the following groups (see Table 11):
!·africanus, and A.robustus.
This
A.afarensis,
To maximize sample size, H.habilis and
A.africanus specimens were combined to form a gracile early hominid
group and A.boisei and !·robustus specimens were combined to form a
robust early hominid group.
From the results of the F-tests of the Mahalanobis n2, it would
appear that:
1) Australopithecus afarensis is significantly different
from A.africanus and A.robustus, when their maxillary teeth are compared, but that 2) A.afarensis is not significantly different from
A.africanus and A.robustus when their mandibular teeth are contrasted.
This may be due to the fact that the analysis performed on the mandibular dentition lacks a uniform sample size for the three groups
of hoininids.
49
Table 11
F* Test of Mahalanobis D2
Maxillary Dentition
A.robustus
A.africanus
A.afarensis
A.robustus (n=5)
A.africanus (n=4)
2.24
A.afarensis (n=3)
17.86
8.29
*Critical value of F for 5 and 5 degrees of freedom equals 5.05
(Probability = 0.05)
Mandibular Dentition
A.robustus
A.africanus
A.afarensis
A.robustus (n=3)
A.africanus (n=6)
7.38
A.afarensis (n=1)
3.21
4.77
*Critical value of F for 6 and 2 degrees of freedom equals 19.33
(Probability = 0.05)
50
Figures 10 and 11 are bivariate plots which were produced by the
canonical variate analysis.
These plots suggest the following:
1)
that Australopithecus afarensis is a distinct and separate species
closer to gracile than to robust early hominids and 2) there appears
to be a greater range of variability, based on the spread of specimens
on each component, exhibited by the mandibular dentition (see Figure
11) compared to that for the maxillary dentition (see Figure 10).
The final statistical results produced by the canonical variate
analysis was the jackknifed classification table.
Table 12 presents
the number of cases correctly classified into the groups A.afarensis,
A.africanus, and A.robustus.
Furthermore, the significance of Table
12 is that only a single A.africanus was classified as being a member
of the proposed species A.afarensis.
This specimen represents approx-
imately 16.67% of the sample from Table 11 mandibular dentition.
Summary of Results
The results for the univariate and multivariate statistical
analyses are as follows:
histograms and principal component analyses
suggest that maxillary and mandibular post-canine teeth exhibit considerable variability in mesio-distal and buccal-lingual measurements.
The principal component analysis shows a larger range of variability
for the maxillary dentition than for the mandibular dentition.
reverse is true for the canonical variate analysis.
The
From the results
shown in the bivariate plots, it would appear that the Hadar-Laetoli
specimens are allied closer to (yet separate and distinct from) A.
africanus and Homo habilis specimens (see Figures 8 and 9) than other
members of the Fossil Hominid sample.
The canonical variate analysis
6
·~
I
5
~
I
4
-j
I
!_.afarensis
H
H
Q)
*
2
rl
.g
•rl
1'-1
~
rl
ttl
0
~
1-'•
~'1
!_.robustus
1-'•
~
(1)
SK 48
1
AL 199-I
*
3
0
-1
SK 55
AL 200-Ia
* ____
-----
, , _..
'"d
1-'
3:01-z;!
~ c+ 1-'•
*
1-'·0~
--·-~-·
STS 52.
1-'
1-'
*
•rl
!::
0
tJj
OH 5
3
-2
\
t.:>
-3
'*
ER 1590
::s 1-'•
0
c+!»
1-'• 1-'
c+
I-'•
-4 1
'-. I
'1
(1)
&8
SK 27
*
·,
H)
I» 0
'1~1--'
<:..:::
0
I
/
<I
g 1-'•~
I»
-5
~
I
-6
~
I
-5
-4
-3
(1)
A.africanus
~
I»
~
(I)
1-'•
---.--
r -·----,-- -----.-
-6
c+
-2
1
-1
0
2
Canonical Variable I
(I)
3
4
5
6
Ln
f--0
6
I
5
J
I
4
I
I
3
H
H
Q)
- ---------- --
A.africanus
•r-1
H
ro
:>
...---1
1
'
*
STS 7
*
ER 992 "
H.h. *"'-- ----·---·
ro -1
--
s::
0
§ -2
-~-
--
'I
------
tJj
1-'•
)
~
'i
1-'•
~
'
* ERl729
\STS 5 2
(!)
"tt
\
I--'
:S::Oiozj
*M LD 18
*
t.)
•
* SK 23
(
·r-1
--
Nat ron
A.b.
*
2
0
(
-~·
MLD ~.0
-
...---1
.g
P;_.robustus
-
~
OH 7
H.h.
/
c+
1-'·
0..0~
1-'• H) 'i
g'
0 (!)
1---'llll-'
lll::SI-'
'i
§
t::ll-'•
0
(!)
(")
8-~
-3
1-'•
c+<:
-4
~
I
-5 -l
-6 j
A_.afarensis
I
I
I
I
I
I-'• Ill
0 'i
::s
1-'•
~
(!)
~
Ill
J<
(I)
1-'•
(I)
I
-4
-3
-2
-1
0
1
2
3
4
5
6
Canonical Variable I
IJ1
N
53
Table 12
Jackknifed Classification
Maxillary Dentition
Group
Percent
Correct
Number of Cases Classified into Group
A.robustus
A.africanus
A.afarensis
A.robustus
80.00
4
1
0
A.africanus
75.00
2
3
0
A.afarensis
100.00
0
0
3
85.00
5
4
3
Total
Mandibular Dentition
A.robustus
66.66
2
1
0
A.africanus
83.32
0
5
1
A. af arens is
100.00
0
0
1
83.32
2
6
2
Total
54
suggests that A.afarensis does indeed differ significantly from A.
africanus and A.robustus, for the maxillary but not the mandibular
dentition.
Finally, from data obtained from the jackknifed classi-
fication table produced by canonical variate analysis, it would appear
that the Hadar-Laetoli fossil specimens would be best classified as
being members of the proposed species, Australopithecus afarensis.
CHAPTER V
DISCUSSION
Results of the 1) review of the pertinent literature, 2)
statistical analyses, and 3) implications presented by these results
will be discussed in this chapter.
The purpose of this thesis was to test the null hypothesis that
Australopithecus afarensis is not significantly different from any
other Plio-Pleistocene hominids.
As stated in Chapter 2 (Literature
Review) strong arguments have been presented by Johanson (1980),
Johanson and White (1979), and Johanson et al. (1978) that disagree
with this null hypothesis.
following:
1)
Included within these arguments are the
the fact that the Laetoli and Hadar specimens exhibit
primitive characteristics in dental, cranial and postcranial material, 2) Articles 13s(i) and 72, and Recommendations 72A, 73B and
73C of the International Code of Zoological Nomenclature support
Johanson and White's taxonomic classification of this material, and
3) geographical isolation of the proposed species Australopithecus
afarensis.
Morphological Characteristics
Morphological characteristics associated with the Laetoli and
Hadar specimens described in detail in Chapter 2 (Literature Review)
do exhibit certain primitive features which are diagnostic of the
species Australopithecus afarensis, such as:
55
1) a C/P3 dental
56
cutting mechanism, 2) sectorial P3, 3) presence of a diastema between
the canines and lateral incisors, 4) strong alveolar prognathism, and
5) a high degree of skeletal robusticity in "regards to muscle and
tendon insertions" (Johanson and White, 1979:324).
Certain primitive
features which are diagnostic of the proposed species A.afarensis can
also be associated with fossil remains for the hominid A.africanus
from the South African site of Sterkfontein, as suggested by Kennedy
(1979).
It should be noted, however, that no Pliocene or Pleistocene
fossil hominid remains (according to the information available to
this author) exhibit the total spectrum of primitive morphological
characteristics that are associated with the proposed species
Australopithecus afarensis.
International Code of Zoological Nomenclature
The aforementioned Articles and Recommendations of the International Code of Zoological Nomenclature provide further evidence
for the rejection of the null hypothesis.
Foremost, the taxonomic
validity of the proposed species Australopithecus afarensis can be
substantiated by the following Articles and Recommendations of the
International Code of Zoological Nomenlature:
and 72 and 2) Recommendations 73B and 73C.
1) Articles 13a(i)
By satisfying these
Articles and Recommendations, Johanson (1980) has solidified his
claim to a valid taxonomic name within the constructs of systematic
zoology (Mayr, 1969).
Furthermore, Recommendation 72A of the Inter-
national Code of Zoological Nomenclature assures future researchers
of accessibility to the holotype (LH 4) of the species Australopithecus afarensis.
This is paramount, for the holotype or "type"
57
specimen is the standard of reference for determining the applicability of any taxonomic name.
taxon, and does not change.
The holotype is the focal point of a
Finally, once the holotype of any taxon
conforms with the Articles and Recomendations of the International
Code of Zoological Nomenclature, it is not subject to change except
under the specific plenary powers of Article 79 (Mayr, 1969).
Geographic Isolation
The final argument that I shall discuss from Chapter 2 is the
topic of geographic isolation.
Buettner-Janusch (1973) has stated
that both reproductive and geographic isolation are fundamental
requirements for the allopatric speciation process to occur.
The
process of hominid speciation could have occurred either by 1) anagenesis or phyletic evolution (evolution of one species from another
of the same lineage) or 2) cladogenesis (the splitting of one lineage
into two lineages) (Wolpoff, 1980).
Brace (1972) and Wolpoff (1971,
1973) support the phyletic evolution process.
They suggest that the
differences between the gracile and robust forms of australopithecines
is simply the result of sexual dimorphism.
However, Wolpoff (1980)
has modified his interpretation of hominid taxonomy and now maintains
that two species of the genus Australopithecus, A.africanus and A.
robustus are represented in the fossil record.
Other researchers
such as Louis Leakey (1966), Richard Leakey (1972) and Robinson (1963)
support the cladogensis (two lineages) process of hominid speciation
and consider this variability to represent a phyletic scheme involving
two or more contemporary genera.
58
Robinson's dietary hypothesis, first proposed in 1953, has contributed much to multilinear concepts of hominid evolution.
Robinson
argues that morphological differences within the australopithecine
groups necessitates recognizing two genera, Australopithecus (gracile
hominids and Paranthropus (robust hominids).
Furthermore, Robinson
maintains that these dietary differences exhibited by Australopithecus
(a carnivore) and Paranthropus (a vegetarian) are a reflection of
adaptation to different habitats.
Researchers, such as Louis Leakey (1966) and his son Richard
(1972), who support the multiple lineage theory, have taken an extreme view by claiming that three contemporary hominid lineages
(A.africanus, A.boisei and H.habilis) may be represented in the
Pleistocene deposits of East Africa.
The method of speciation is a crucial issue in hominid evolution
and it would directly affect the nature of the basal hominid adaptive
pattern.
Speciation could either have been:
1) multilinear, which
would allow radiation and subsequent divergence or, 2) unilinear
evolution of a taxon (Wolpoff, 1980).
Statistical Results
From the statistical results discussed in Chapter 4 (Results),
the findings from the principal component and canonical variate
analyses support the rejection of the null hypothesis.
Bivariate plots of principal component scores (Chapter 4,
Results, Figures 8 and 9) illustrate the patterns of relationships
exhibited by the Fossil Hominid sample specimens.
Analysis of the
maxillary dentition (Figure 8) suggests that A.afarensis is distinct
59
from A.africanus and A.robustus and A.boisei.
Furthermore, it would
appear from Figure 8 that A.afarensis displays maxillary dental characteristics which are similar and phyletically closer to those of the
gracile forms,
~.africanus
A.robustus and A.boisei.
and H.habilis, than to the robust forms,
From the analysis performed on the mandib-
ular dentition (Figure 9) it would appear that the single A.afarensis
specimen displays no close dental affinities with other members of
the Fossil Hominid sample.
Finally, the maxillary dentition (see
Figure 8) appears to display a larger range of variability (based on
the spread of specimens on each component) than does the mandibular
dentition (see Figure 9).
The F-test results produced by canonical variate analysis offer
the following interpretations.
First, A.afarensis is significantly
different from either A.africanus or A.robustus for the maxillary
dentition.
Second, there are no significant differences among A.
afarensis, A.africanus, and A.robustus for the mandibular dentition.
Third, bivariate plots obtained from the canonical variate analysis
of maxillary and mandibular dentition (Figures 10 and 11) suggest
that 1) Australopithecus afarensis is a distinct and separate species
and 2) there appears to be a greater range of variability, based on
the spread of specimens on each component, exhibited by the mandibular dentition (see Figure 11) compared to that for the maxillary
dentition (see Figure 10).
Finally, the jackknifed classification
table (Table 12) produced by the canonical variate analysis presents
the number of cases correctly classified into the groups A.afarensis,
A.africanus, and A.robustus.
The significance of Table 12 is that
only a single A.africanus was classified as being a member of the
60
proposed species A.afarensis.
This specimen represents approximately
16.67% of the sample from Table 12 mandibular dentition.
From these statistical results, it would appear that:
1) prin-
cipal component analysis shows a larger range of variability for the
maxillary dentition than for the mandibular dentition, but 2) the
reverse is true for the canonical variate analysis, and 3) it would
appear from the bivariate plots that the Hadar-Laetoli specimens are
phenetically closer to (yet separate and distinct from) A.africanus
and Homo habilis specimens (see Figures 8 and 9) than other members
of the Fossil Hominid sample.
Furthermore, analyses performed on
mandibular dentitions suggest the following as possible explanation
for the apparent lack of significant differences seen between certain pairs of samples of the Fossil Hominid sample.
CHAPTER VI
CONCLUSION
This thesis has been an attempt to test the hypothesis that
Australopithecus afarensis is not significantly different from any
other Plio-Pleistocene hominid.
Fossil remains for this hominid date
to the Pliocene in Eastern Africa.
The similarities between fossil
remains at Hadar and Laetoli suggest that these remains represent a
single taxon (Johanson, 1980).
The proposed fossil hominid, A.afarensis, has an array of
primitive features.
These include the following:
1) presence of a
diastema between the lateral incisors and canines, 2) large projecting canines, 3) two or three distinct roots in the p3•s, and 4) a
parallel dental arcade (LH 4 exhibits posterior divergence) (Johanson
and White, 1979).
Postcranial skeletal remains for A.afarensis
strongly suggest that this hominid was capable of habitual bipedalism and analysis of pelvic and knee bones supports this argument
(Johanson et at., 1976; Lovejoy et al., 1973).
Further evidence for
bipedal locomotion can be found in the analyses foot bones and footprints.
Mary Leakey and co-workers have proved conclusively that not
only did A.afarensis walk erect, but also had a well developed foot
which is similar in construction to that of Homo sapiens (Leakey,
1979; Leakey and Hay, 1979).
Opinions vary on how to classify the fossil material found at
Hadar and Laetoli.
Johanson and White (1979) consider the material
61
62
to represent a new form of australopithecine.
Leakey and Hay (1976)
suggest that material from Laetoli and the Garusi fragment are similar
to specimens assigned to the genus Homo in East Africa.
Wolpoff
(1980) argues that A.afarensis resembles A.africanus too closely to
be considered a separate species.
Results from canonical variate
analysis suggest that !·afarensis does differ significantly from
other forms of Plio-Pleistocene hominids when maxillary dentitions
were analyzed.
Several morphological features that Johanson and White (1979)
thought were characteristics of A.afarensis can be seen in postcranial remains from South Africa.
The capitate of A.afarensis,
which has been described as "waisted," and lack of a styloid process
on the third metacarpal is similar to some fossil remains from Sterkfontein.
Also, the innominate bone AL 288-I is very similar in size
and morphology to fossil remains from Sterkfontein (Sts 14) (Kennedy,
1979).
The fossil remains of A.afarensis do show characteristics that
are not represented in A.africanus such as:
1) upper central incisors
that are very broad, 2) lateral incisors that are relatively small in
A.afarensis, 3) diastema between the lateral incisors and the canines,
and 4) a canine/premolar dental cutting complex.
The morphological
similarities between the Hadar and Laetoli fossils suggest that for
one million years A.afarensis did not undergo any major evolutionary
changes.
A further characteristic of the proposed species !·afarensis
is the fact that these remains come from a geographic area which has
not produced fossil materials for other known Plio-Pleistocene hominids.
Therefore, based on:
1) the results of the statistical
63
analyses of dental measurements, 2) geographic isolation, 3)
morphological characteristics, and 4) review of the pertinent
literature, it is suggested that Australopithecus afarensis be
considered a valid taxon.
LITERATURE CITED
Aronson, J.L., T.J. Schmitt, R.C. Walter, M. Taieb, D.C. Johanson,
J.J. Tiercelin, C.W. Naeser and A.E. Nairn
1977
New geochronologic and paleomagnetic data for the hominidbearing Hadar Formation of Ethiopia.
Nature, 276:323-327.
Sexual dimorphism in human evolution.
Yearbook Physical
Brace, C.L.
1972
Anthropology, 16:31-49.
1979
Biological parameters and Pleistocene hominid life ways,
in I.S. Bernstein and E.O. Smith (eds.); Primate ecology
and human origins.
Garland Press, New York.
Buettner-Janusch, J.
1973
Physical anthropology:
~perspective.
New York, John
Wiley and Sons, Inc.
Cooke, H.B.S.
1978
Pliocene-Pleistocene suidae from Hadar, Ethiopia.
Kirtlandia, 29:15-64.
Cronin, J.E., N.T. Boaz, C.B. Stringer andY. Rak
1981
Tempo and mode in hominid evolution.
Nature, 292.
Day, M.H., M.D. Leakey and R. Olson
1980
On the status of Australopithecus afarensis.
Science,
207:1102-1103.
Dixon, W.J. and M.B. Brown
1979
BMDP biomedical computer programs.
Los Angeles, Univer-
sity of California Press, pages 656-739.
64
65
Greenfield, L.O.
1980
A late divergence hypothesis.
Amer. J. Phys. Anthrop.,
52:351-365.
Gray, T.
1979
Environmental and chronological implication from the Hadar
Formation fauna.
Amer. J. Phys. Anthrop., 50:444-445
(Abstract).
Hay, R.L.
1976
Geology of the Olduvai Gorge.
Berkeley, University of
California Press, Pages 25-55 and 175-186.
Holloway, R.L.
1978
Problems of brain endocast interpretation and African
hominid evolution.
In Jolly, C. (ed), Early hominids of
Africa, London, Duckworth, Pages 379-399.
Howell, F.C.
1969
Remains of Hominidae from Pliocene-Pleistocene formations
in the lower Omo Basin, Ethiopia.
Nature, 223:1234.
Isaac, G.L. and G.H. Curtis
1974
Age of early Acheulean industries from the Peninj Group,
Tanzania.
Nature, 249:624-627.
Johanson, D.C.
1976
Ethiopia yields first "family" of early man.
National
Geographic, 150:791-811.
1980
Early African hominid phylogensis: a re-evaluation.
Konigsson, L.K. (ed); Current
argument~ early~'
York, Pergamon Press, Pages 31-69.
Nobel Syposium, Sweden.
In
New
Given at the 1978
66
Johanson, D.C. and M. Edey
1981
Lucy--the beginnings of humankind.
New York, Simon and
Schuster.
Johanson, D.C. and M. Taieb
1976
Plio-Pleistocene hominid discoveries in Hadar, Ethiopia.
Nature, 260:293-297.
1978
Plio-Pleistocene hominid discoveries in Hadar, Central
Afar, Ethiopia.
In Jolly, C.J. (ed); Early hominids of
Africa, London, Duckworth, Pages 29-44.
Johanson, D.C. and T.D. White
1979
A systematic assessment of early African hominids.
Science, 203:321-330.
Johanson, D.C., T.D. White andY. Coppens
1978
A new species of the genus Australopithecus (primates:
hominidae) from the Pliocene of Eastern Africia.
Kirtlandia, 28:1-14.
Johanson, D.C., C.O. Lovejoy, A.H. Burstein and K.G. Heiple
1976
Functional implications of the Afar knee joint.
Amer. J.
Phys. Anthrop., 44:188 (Abstract).
Johanson, D.C., M. Taieb andY. Coppens
1982
Pliocene hominids from the Hadar Formation, Ethiopia
(1973-1977): stratigraphic, chronologie, and paleoenvironmental contexts, with notes on hominid morphology and
systematics.
Amer. J. Phy. Anthrop., 57:373-402.
Kennedy, G.E.
1979
Difficulties in the definition of new hominid species.
Nature, 278:400-401.
67
Kimbel, W.H. and T.D. White
1980
A reconstruction of the adult cranium of Australopithecus
afarensis.
Amer. J. Phys. Anthrop. 52:246 (Abstract).
Kohl-Larsen, L.
1943
Auf den Spuren des Vormenschen, Forschungen, Fahrten und
Erlenbnisse in Deutsch-Ostafrika, Stuttgart, Germany,
Strecker and Schroder Verlag.
Leakey, L.
1966
Homo habilis, Homo erectus, and the australopithecines.
Nature, 209:1279-1281.
Leakey, L., P. Tobias and J. Napier
1964
A new species of the genus Homo from Olduvai Gorge,
Nature, 202:5-7.
Leakey, M.D.
1979
Footprints in the ashes of time.
National Geographic,
155:446-457.
Leakey, M.D. and R.L. Hay
1979
Pliocene footprints in the Laetolil Beds at Laetolil,
Northern Tanzania.
Nature, 278:317-323.
Leakey, M.D., R.L. Hay, G.H. Curtis, R.E. Drake, M.K. Jackes and
T.D. White
1976
Fossil hominids from the Laetolil Beds.
Nature, 262:
460-466.
Leakey, R.
1972
Further evidence of lower Pleistocene hominids, East
Rudolf, North Kenya.
Nature, 237:264.
68
1978
Koobi Fora Research Project: Vol.
!L
the fossil hominids
and an introduction to their context 1968-1974.
Richard E.
Leakey and Meave G. Leakey (eds); Oxford, Clarendon Press,
Pages 86-169 and 174-178,
Leakey, R.E. and R. Lewis
1977
Origins.
New York, Dutton.
Leakey, R.E. and A. Walker
1980
On the status of Australopithecus afarensis.
Science,
207:1103.
Lovejoy, C. 0.
1974
The gait of australopithecines.
Yearbook of Phys.
Anthrop., 17:147-161.
1980
Hominid origins:
the role of bipedalism.
Amer. J. Phys.
Anthrop., 52:250.
Lovejoy, C.O., K.G. Heiple and A.H. Burstein
1973
The gain of Australopithecus.
Amer. J. Phys. Anthrop.,
38:757-779.
Mayr, E.
1969
Principles of systematic zoology.
New York, McGraw-Hill.
Oxnard, C.
1973
Form and pattern in human evolution.
Chicago, University
of Chicago Press, Pages 37-121.
Partridge, T.C.
1973
Geomorphological dating of cave openings at Makapansgat,
Sterkfontein, Swartkrans, and Taung.
Nature, 246:75-79.
Philbeam, D.
1972
The ascent
of~·
New York, Macmillan Co.
69
Remane, A.
1951
Die Zahne des Meganthropus africanus.
Zeit Morph. U.
Anthrop., 42:311-329.
1954
Structure and relationship of Meganthropus africanus.
Amer. J. Phys. Anthrop., 12:123-126.
Robinson, J.T.
1953
Meganthropus, australopithecines and hominids.
Amer. J.
Phys. Anthrop., 11:1-38.
1963
Adaptive radiation in the australopithecinces and the
origin of man.
F.C. Howell and F. Bourliere (eds);
African ecology and human evolution, Pages 385-416.
Robinson, J.T. and K. Steudel
1973
Multivariate discriminant analysis of dental data bearing
on early hominid affinities.
J. Human Evol., 2:509-527.
Simons, E.L.
1967
The significance of primate paleontology for anthropological studies.
Amer. J. Phys. Anthrop., 27:307-332.
Stern, J.T. Jr., and R.L. Susman
1982
The locomotor behavior of Australopithecus afarensis.
Amer. J. Phys. Anthrop., 57:232 (Abstract).
Taieb, M., D.C. Johanson, Y. Coppens and J.L. Aronson
1976
Geological and paleontological background of Hadar hominid
site, Afar, Ethiopia.
Nature, 260:289-293.
Tobias, P.
1965
Early man in East Africa.
1976
African hominids:
Science, 149:22-33.
dating and phylogeny.
and E.R. McCown (eds); In human origins:
In G.L. Isaac
Louis Leakey and
70
the East African Evidence.
Menlo Park, CA, W.A. Benjamin,
Inc., Pages 377-422.
Vrba, E.
1975
Some evidence of chronology and paleoecology of Sterkfontein, Swartkrans and Kromdraai from the Bovidae.
Nature,
254:301-304.
Walker, A. and R. Leakey
1978
The hominids of East Turkana.
Scientific American, 239:
54-66.
Walter, R.C. and J.L. Aronson
1982
Revisions of K/Ar ages for the Hadar hominid site, Ethiopia.
Nature, 296:122-127.
White, T.D.
1977
New fossil hominids for Laetolil, Tanzania.
Amer. J.
Phys. ANthrop., 46:197-230.
1981
Primitive hominid canine from Tanzania.
Science, 213:
348-349.
Wolpoff, M.H.
1971
Metric trends in hominid evolution,
Case Western Studies
in Anthrop., No. 2; Case Western Univ. Press.
1973
The evidence for two australopithecine lineages in South
Africa.
1979
Yearbook Phys. Anthrop., 17:113-139.
Anterior dental cutting in the Laetolil hominids and the
evolution of the bicuspid P3.
Amer. J. Phys. Anthrop.,
51:233-234.
1980
Paleoanthropology.
New York, Alfred A. Knopf, Inc.