Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa

Abstract

From Australopithecus to Homo
Our genus Homo is thought to have evolved a little more than 2 million years ago from the earlier hominid Australopithecus . But there are few fossils that provide detailed information on this transition. Berger et al. (p. 195 ; see the cover) now describe two partial skeletons, including most of the skull, pelvis, and ankle, of a new species of Australopithecus that are informative. The skeletons were found in a cave in South Africa encased in sediments dated by Dirks et al. (p. 205 ) to about 1.8 to 1.9 million years ago. The fossils share many derived features with the earliest Homo species, including in its pelvis and smaller teeth, and imply that the transition to Homo was in stages.

Full text

Australopithecus sediba: A New
Species of Homo-Like Australopith
from South Africa
Lee R. Berger,
1,2
*Darryl J. de Ruiter,
3,1
Steven E. Churchill,
4,1
Peter Schmid,
5,1
Kristian J. Carlson,
1,6
Paul H. G. M. Dirks,
2,7
Job M. Kibii
1
Despite a rich African Plio-Pleistocene hominin fossil record, the ancestry of Homo and its relation
to earlier australopithecines remain unresolved. Here we report on two partial skeletons with an
age of 1.95 to 1.78 million years. The fossils were encased in cave deposits at the Malapa site in
South Africa. The skeletons were found close together and are directly associated with craniodental
remains. Together they represent a new species of Australopithecus that is probably descended
from Australopithecus africanus. Combined craniodental and postcranial evidence demonstrates
that this new species shares more derived features with early Homo than any other australopith
species and thus might help reveal the ancestor of that genus.
The origin of the genus Homo is widely
debated, with several candidate ancestors
being proposed in the genus Australopith-
ecus (1–3)orperhapsKenyanthropus (4). The
earliest occurrence of fossils attributed to Homo
(H. aff. H. habilis) at 2.33 million years ago (Ma)
in Ethiopia (5) makes it temporally antecedent to
all other known species of the genus Homo.
Within early Homo, the hypodigms and phylo-
genetic relationships between H. habilis and
another early species, H. rudolfensis, remain
unresolved (6–8), and the placement of these
species within Homo has been challenged (9).
H. habilis is generally thought to be the ancestor
of H. erectus (10–13), although this might be
questioned on the basis of the considerable
temporal overlap that existed between them
(14). The identity of the direct ancestor of the
genus Homo, and thus its link to earlier Australo-
pithecus, remains controversial. Here we describe
two recently discovered, directly associated, par-
tially articulated Australopithecus skeletons from
the Malapa site in South Africa, which allow us
to investigate several competing hypotheses re-
garding the ancestry of Homo. These skeletons
cannot be accommodated within any existing
fossil taxon; thus, we establish a new species,
Australopithecus sediba,onthebasisofacom-
bination of primitive and derived characters of the
cranium and postcranium.
The following is a description of Au. sediba:
Order Primates Linnaeus 1758; suborder Anthro-
poidea Mivart 1864; superfamily Hominoidea
Gray 1825; family Hominidae Gray 1825; genus
Australopithecus DART 1925; species Australo-
pithecus sediba sp. nov.
Etymology.Thewordsediba means “foun-
tain”or “wellspring”in the seSotho language.
Holotype and paratype. Malapa Hominin
1 (MH1) is a juvenile individual represented by
a partial cranium, fragmented mandible, and par-
tial postcranial skeleton that we designate as
the species holotype [Figs. 1 and 2, supporting
online material (SOM) text S1, figs. S1 and S2,
and table S1]. The first hominin specimen re-
covered from Malapa was the right clavicle of
MH1 (UW88-1), discovered by Matthew Berger
on 15 August 2008. MH2 is an adult individual
represented by isolated maxillary teeth, a partial
mandible, and partial postcranial skeleton that we
designate as the species paratype. Although MH1
is a juvenile, the second molars are already
erupted and in occlusion. Using either a human
or an ape model, this indicates that MH1 had
probably attained at least 95% of adult brain size
(15). Although additional growth would have
occurred in the skull and skeleton of this
individual, we judge that it would not have
appreciably altered the morphology on which
this diagnosis is based.
Locality.ThetwoAu. sediba type skeletons
were recovered from the Malapa site (meaning
“homestead”in seSotho), situated roughly 15 km
NNE of the well-known sites of Sterkfontein,
Swartkrans, and Kromdraai in Gauteng Province,
South Africa. Detailed information regarding
geology and dating of the site is in (16).
RESEARCH ARTICLES
1
Institute for Human Evolution, University of the Witwatersrand,
Private Bag 3, Wits 2050, South Africa.
2
School of Geosciences,
University of the Witwatersrand, Private Bag 3, Wits 2050, South
Africa.
3
Department of Anthropology, Texas A&M University,
College Station, TX 77843, USA.
4
Department of Evolutionary
Anthropology, Box 90383, Duke University, Durham, NC 27708,
USA.
5
Anthropological Institute and Museum, University of
Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
6
Department of Anthropology, Indiana University, Bloomington,
IN 47405, USA.
7
School of Earth and Environmental Sciences,
James Cook University, Townsville, Queensland 4811, Australia.
*To whom correspondence should be addressed. E-mail:
profleeberger@yahoo.com
Fig. 1. Craniodental elements of Au. sediba. UW88-50 (MH1) juvenile cranium in (A) superior, (B)
frontal, and (C) left lateral views. (D) UW88-8 (MH1) juvenile mandible in right lateral view, (E)
UW88-54 (MH2) adult mandible in right lateral view, (F) UW88-8 mandible in occlusal view, (G)
UW 88-54 mandible in occlusal view, and (H) UW 88-50 right maxilla in occlusal view (scale bars
are in centimeters).
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Diagnosis.Au. sediba can be distinguished
from other species of Australopithecus by a
combination of characters presented in Table 1;
comparative cranial measures are presented in
Table 2. A number of derived characters separate
Au. sediba from the older chronospecies Au.
anamensis and Au. afarensis.Au. sediba exhibits
neither the extreme megadontia, extensive cra-
nial cresting, nor facial prognathism of Au. garhi.
The suite of derived features characterizing
Au.aethiopicus,Au. boisei,andAu. robustus,
in particular the pronounced cranial muscle mark-
ings, derived facial morphology, mandibular
corpus robusticity, and postcanine megadontia,
are absent in Au.sediba. The closest morpholog-
ical comparison for Au. sediba is Au. africanus,
as these taxa share numerous similarities in the
cranial vault, facial skeleton, mandible, and
teeth (Table 1). Nevertheless, Au. sediba can be
readily differentiated from Au. africanus on
both craniodental and postcranial evidence.
Among the more notable differences, we ob-
serve that although the cranium is small, the
vault is relatively transversely expanded with
vertically oriented parietal walls and widely
spaced temporal lines; the face lacks the pro-
nounced, flaring zygomatics of Au. africanus;
the arrangement of the supraorbital torus, naso-
alveolar region, infraorbital region, and zy-
gomatics result in a derived facial mask; the
mandibular symphysis is vertically oriented with
a slight bony chin and a weak post-incisive pla-
num; and the teeth are differentiated by the
weakly defined buccal grooves of the maxillary
premolars, the weakly developed median lingual
ridge of the mandibular canine, and the small
absolute size of the postcanine dentition. These
exact differences also align Au. sediba with the
genus Homo (see SOM text S2 for hypodigms used
in this study). However, we consider Au. sediba
to be more appropriately positioned within
Australopithecus, based on the following cranio-
dental features: small cranial capacity, pronounced
glabelar region, patent premaxillary suture,
moderate canine jugum with canine fossa, small
anterior nasal spine, steeply inclined zygomati-
coalveolar crest, high masseter origin, moderate
development of the mesial marginal ridge of the
maxillary central incisor, and relatively closely
spaced premolar and molar cusps.
Postcranially, Au. sediba is similar to other
australopiths in its small body size, its relatively
long upper limbs with large joint surfaces, and
the retention of apparently primitive charac-
teristics in the upper and lower limbs (table S2).
Au. sediba differs from other australopiths, but
shares with Homo a number of derived features
of the os coxa, including increased buttressing of
the ilium and expansion of its posterior portion,
relative reduction in the distance between the
sacroiliac and hip joints, and reduction of dis-
tance from the acetabulum to the ischial tuberos-
ity. These synapomorphies with Homo anticipate
the reorganization of the pelvis and lower limb in
H. erectus and possibly the emergence of more
energetically efficient walking and running in
that taxon (17). As with the associated cranial
remains, the postcranium of Au. sediba is defined
not by the presence of autapomorphic features
but by a unique combination of primitive and
derived traits.
Cranium. The cranium is fragmented and
slightly distorted. The minimum cranial capacity
of MH1 is estimated at 420 cm
3
(SOM text S4).
The vault is ovoid, with transversely expanded,
vertically oriented parietal walls. The widely
spaced temporal lines do not approach the
midline. Postorbital constriction is slight. The
weakly arched supraorbital torus is moderately
developed and laterally extended, with sharply
angled lateral corners and a weakly defined
supratoral sulcus. A robust glabelar region is
evident, with only a faint depression of the
supraorbital torus at the midline. The frontal
process of the zygomatic faces primarily laterally
and is expanded medially but not laterally. The
zygomatic prominence does not show antero-
lateral expansion. The zygomatics are weakly
flared laterally, resulting in an uninterrupted
frontal profile of the facial mask that is squared
superiorly and tapered inferiorly. The zygomat-
icoalveolar crests are long, straight, and steep-
ly inclined, resulting in a high masseter origin.
The root of the zygomatic begins at the anterior
margin of M
1
. The nasal bones are widened
superiorly, become narrowest about one-third
of the way down, and flare to their widest extent
at their inferior margin. The nasal bones are
elevated as a prominent ridge at the internasal
suture, with an increasingly anterior projection
inferiorly. The bone surface of the maxilla re-
treats gently away from the nasal aperture lat-
erally, resulting in an everted margin of the
superolateral portion of the aperture relative to
the infraorbital region. The inferolateral portion
of the nasal aperture becomes bluntly rounded.
The infraorbital region is slightly convex (18)
and is oriented at an approximately right angle
to the alveolar plane. There is a trace of a pre-
maxillary suture near the superolateral margin
of the nasal aperture. Prominent canine juga
delineate moderately developed canine fossae.
Anterior pillars are absent. The inferior margin
of the nasal aperture is marked by a stepped
nasal sill and a small but distinct anterior nasal
spine. The subnasal region is straight in the cor-
onal plane and only weakly projecting relative
Fig. 2. Associated skeletal elements of MH1 (left)andMH2(right), in approximate anatomical position,
superimposed over an illustration of an idealized Au.africanus skeleton (with some adjustment for
differences in body proportions). The proximal right tibia of MH1 has been reconstructed from a natural
cast of the proximal metaphysis.
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Table 1. List of characters used to diagnose Au. sediba. These characters are commonly used
in hominin phylogenetic studies (11, 38–40) or have been recorded as diagnostic for various
hominin taxa in the past (3,10,36). Recognizing the potential pitfalls of performing a
cladistic analysis on possibly interdependent characters of uncertain valence, we produced a
cladogram from the data in this table as a test of the phylogenetic position of Au. sediba (fig.
S3). Our most parsimonious cladogram places Au. sediba at the stem of the Homo clade.
Numbers in parentheses in the first column refer to measures presented in Table 2;
descriptions of these character states are provided in SOM text S3. Abbreviations are as
follows: A-M, anteromedial; costa supr., costa supraorbitalis; intermed., intermediate; lat.,
lateral; med., medial; mesognath., mesognathic; mod., moderately; MMR, mesial marginal
ridge; orthogn., orthognathic; procumb., procumbent; proj., projecting; TMJ, temperoman-
dibular joint.
Characters Au.
afarensis
Au.
garhi
Au.
africanus
Au.
sediba
H.
habilis
H.
rudolfensis
H.
erectus
Au.
aethiopicus
Au.
boisei
Au.
robustus
Vault
Cranial capacity (1) Small Small Small Small Intermed. Large Large Small Small Small
A-M incursion of
temporal lines on frontal
bone (9)
Strong Moderate Moderate Weak Weak Weak Weak Strong Strong Strong
Position of temporal lines
on parietal bones
Crest Crest Variable Wide Variable Wide Wide Crest Crest Crest
Compound temporal
nuchal crest (males)
Extensive ? Absent Absent Variable Absent Absent Extensive Variable Absent
Postorbital constriction
(5)
Marked Moderate Moderate Slight Moderate Moderate Slight Marked Marked Marked
Pneumatization of
temporal squama
Extensive ? Extensive Reduced Reduced Reduced Reduced Extensive Variable Reduced
Facial hafting Low Low Low Low Low Low Low High High High
Frontal trigon Present Present Absent Absent Absent Absent Absent Present Present Present
Supraglenoid gutter width Narrow ? Narrow Narrow Narrow Narrow Narrow Wide Wide Wide
Horizontal distance
between TMJ and
M2/M3 (6)
Long ? Long Short Short Long Short Long Long Long
Parietal transverse
expansion/tuber
Absent Absent Absent Present Present Present Present Absent Absent Absent
Facial skeleton
Supraorbital expression Costa supr. Costa supr. Intermed. Torus Torus Intermed. Torus Costa supr. Costa supr. Costa supr.
Supraorbital contour Less arched Less arched Variable Arched Arched Arched Arched Less arched Variable Arched
Glabellar region forms as
prominent block
No No Variable Yes No Variable No No Yes Yes
Lat. half of infraorbital
margin blunt
and protruding
No ? No No No No No Yes No Yes
Zygomatic arch relative to
inferior orbital margin
Above ? Level Level Level ? Level Above Above Above
Convexity/concavity of
infraorbital region
? ? Convex Convex Concave Concave Convex Concave Concave Concave
Nasal bone projection
above frontomaxillary
suture
Expanded ? Variable No No No No Tapered Expanded Expanded
Inferior width of
projecting nasal bone (25)
Wide ? Variable Wide Variable Narrow Wide Not proj. Not proj. Not proj.
Infraorbital foramen
height (32)
High ? Variable High High ? High Low Low Low
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Characters Au.
afarensis
Au.
garhi
Au.
africanus
Au.
sediba
H.
habilis
H.
rudolfensis
H.
erectus
Au.
aethiopicus
Au.
boisei
Au.
robustus
Canine juga
prominence/anterior
pillars
Prominent Prominent Variable Prominent Variable Weak Weak Weak Weak Pillars
Patency of premaxillary
suture
Obliterated ? Occasional Trace Obliterated Obliterated Obliterated Obliterated Obliterated Occasional
Inferolateral nasal
aperture margin
Sharp Sharp Variable Blunt Variable Sharp Blunt Blunt Variable Blunt
Eversion of superior nasal
aperture margin
? ? None Slight Slight Slight Slight Slight Variable None
Nasoalveolar triangular
frame/gutter
Triangular ? Triangular Triangular Triangular Triangular Triangular Gutter Gutter Gutter
Nasal cavity entrance Stepped Stepped Stepped Stepped Variable Stepped Stepped Smooth Smooth Smooth
Nasoalveolar clivus
contour in coronal plane
Convex Convex Straight Straight Straight Straight Straight Concave Concave Concave
Subnasal projection (38) Marked Marked Variable Weak Variable Weak Weak Marked Moderate Moderate
Canine fossa Present Present Present Present Present Absent Absent Absent Absent Absent
Maxillary fossula Absent Absent Absent Absent Absent Absent Absent Absent Absent Present
Incisor procumbency Procumb. Procumb. Variable Vertical Variable Vertical Vertical Vertical Vertical Vertical
Anterior nasal spine rel. to
nasal aperture
Absent ? Anterior Anterior Anterior ? Enlarged Posterior Posterior Posterior
Expansion of frontal
process of zygomatic bone
Med. and lat. ? Med. and lat. Medial Medial Medial Medial Med. and lat. Med. and lat. Med. and lat.
Angular indentation of
lateral orbital margin
? ? Indented Curved Curved Curved Curved ? Curved Curved
Zygomatic prominence
development
Prominent ? Prominent Slight Slight ? Slight Prominent Prominent Prominent
Lateral flaring of
zygomatic arches
Marked ? Marked Slight Slight Slight Slight Marked Marked Marked
Outline of superior
facial mask
Tapered ? Tapered Squared Squared Squared Squared Tapered Tapered Tapered
Zygomaticoalveolar
crest/malar notch
Straight ? Straight Straight Notch Notch Notch Straight Straight Straight
Infraorbital plate angle
relative to alveolar plane
Obtuse ? Obtuse Right Right Right Right Obtuse Obtuse Obtuse
Zygomaticomaxillary
steps and fossae present
No ? No No No No No No No Yes
Height of masseter
origin (35)
Low Low High High Low Low Low High High High
Malar thickness (31) Thin ? Thin Thin Thin ? Thin Thick Thick Thick
Projection of zygomatics
relative to nasal bones
Posterior Posterior Variable Posterior Posterior Level Posterior Anterior Anterior Anterior
Facial prognathism (7)
(sellion-prosthion angle)
Prognathic Prognathic Variable Mesognath. Mesognath. Mesognath. Orthogn. Prognathic Mesognath. Mesognath.
Masseteric position
relative to sellion
Anterior ? Posterior Posterior Posterior ? Posterior Anterior Anterior Anterior
Lateral anterior
facial contour
Bipartite Bipartite Variable Straight Variable Straight Straight Straight Straight Straight
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Characters Au.
afarensis
Au.
garhi
Au.
africanus
Au.
sediba
H.
habilis
H.
rudolfensis
H.
erectus
Au.
aethiopicus
Au.
boisei
Au.
robustus
Palate
Protrustion of incisors
beyond bi-canine line
Yes Yes Yes Yes Yes No Yes No No No
Anterior palatal depth Shallow Shallow Deep Deep Variable Deep Variable Shallow Deep Shallow
Dental arcade shape Rectangle Rectangle Variable Parabolic Parabolic Parabolic Parabolic Rectangle Parabolic Parabolic
Maxillary I2/C diastema Present Present Absent Absent Variable Absent Absent Absent Absent Absent
Mandible
Orientation of mandibular
symphysis
Receding ? Receding Vertical Vertical Vertical Vertical Vertical Vertical Vertical
Bony chin
(mentum osseum)
Absent ? Slight Slight Slight Slight Slight Slight Slight Slight
Direction of mental
foramen opening
Variable ? Variable Lateral Lateral Lateral Lateral Lateral Lateral Lateral
Post-incisive planum Prominent ? Prominent Weak Prominent Weak Weak Prominent Prominent Prominent
Torus marginalis and
marginal tubercles
Prominent ? Moderate Moderate Moderate Prominent Prominent ? Prominent Prominent
Mandibular corpus
cross-sectional area
at M
1
(50)
Small ? Small Small Small Variable Small Large Large Large
Teeth
Incisor-to-postcanine ratio
(maxillary) (60)
Large Moderate Moderate Moderate Moderate Moderate Large ? Small Small
Canine-to-postcanine ratio
(maxillary/mandibular) (61, 62)
Large Large Large Large Large Large Large ? Small Small
Postcanine crown area
(maxillary/mandibular) (57, 59)
Moderate Large Large Moderate Moderate Large Small Large Large Large
Maxillary I
1
: MMR
development, lingual face
Moderate ? Moderate Moderate Weak Weak Weak ? Moderate Moderate
Maxillary C: development
of lingual ridges
Marked Marked Marked Weak Weak Marked Marked ? Marked Weak
Maxillary premolar
molarization
None Minor Minor None Minor Minor None Marked Marked Marked
Maxillary premolars:
buccal grooves
Marked Marked Marked Weak Weak Marked Weak ? Weak Weak
Median lingual ridge of
mandibular canine
Prom. ? Prom. Weak Weak Weak Weak ? Weak Weak
Mandibular P
3
root number 2 ? 2 2 1 2 1 ? 2 2
Protoconid/metaconid
more mesial cusp (molars)
Equal ? Equal Protoconid Protoconid Protoconid Protoconid ? Equal Equal
Peak of enamel forms
between roots of molars
No ? Yes Yes No No No ? No Yes
Relative enamel thickness Thick Thick Thick Thick Thick Thick Thick Hyper Hyper Hyper
Positions of apices of
lingual (LC) and buccal
(BC) cusps of premolars
and molars relative to
occlusal margin
LC at
margin, BC
slightly
lingual
LC at
margin, BC
slightly
lingual
LC slightly
buccal, BC
moderately
lingual
LC slightly
buccal, BC
moderately
lingual
LC at
margin, BC
slightly
lingual
LC at
margin, BC
slightly
lingual
LC at
margin, BC
slightly
lingual
LC mod.
buccal, BC
strongly
lingual
LC mod.
buccal, BC
strongly
lingual
LC mod.
buccal, BC
strongly
lingual
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Table 2. Craniodental measurements for early hominins in Africa. Au. sediba is represented by
MH1. Unless otherwise defined, measurements are based on (6). Some measures were
unavailable for specimens of Au. afarensis and Au. garhi, in which case the character states in
Table 1 were estimated. Several character states in Table 1 are recorded as variable, although
only species average values are presented here. Measurements are in millimeters unless
otherwise indicated. Descriptions of character states presented in Table 1 that are based on
measurements from this table are provided in SOM text S3. Abbreviations are as follows: br,
bregma; ek, ectoconchion; ekm, ectomolare; fmt, frontomolare temporale; ft, frontotemporale;
g, glabella; mf, maxillofrontale; n, nasion; ns, nasospinale; or, orbitale; po, porion; pr,
prosthion; rhi, rhinion; zm, zygomaxillare; zy, zygion; zyo, zygoorbitale.
Item Measurement
description in (6)Measurement Au.
afarensis
Au.
africanus
Au.
sediba
H.
habilis
H.
rudolfensis
H.
erectus
Au.
aethiopicus
Au.
boisei
Au.
robustus
1 Cranial capacity (cm
3
) 415 442 420 631 751 900 419 515 530
2 9 Maximum parietal breadth 90 99 100 103 114 126 94 99 100
3 11 Bi-porionic breadth (po-po) 126 99 104 104 127 121 125 116 —
4 Postorbital constriction (narrowest point behind the orbits) 77 69 73 76 85 89 65 64 73
5 Postorbital constriction index (4/14 × 100) 66 71 85 70 72 80 65 61 68
6 Horizontal distance between TMJ and M
2
/M
3
83 61 45 51 58 57 94 82 81
7 Facial prognathism (sellion-prosthion angle) 63 61 65 65 68 72 41 66 69
8 75 Infratemporal fossa depth –31 21 27 –37 51 50 36
9 8 Minimum frontal breadth (ft-ft) 40 54 70 66 72 76 33 36 35
10 17 Glabella to bregma (g-br) 101 80 75 83 86 103 –87 –
11 Frontal chord (n-br) –84 74 80 93 99 –84 –
12 62 Supraorbital torus vertical thickness –888 101210129
13 43 Superior facial height (n-pr) 87 78 68 68 90 76 99 100 80
14 49 Superior facial breadth (fmt-fmt) 117 97 86 100 117 107 100 108 107
15 50 Bi-orbital breadth (ek-ek) 89 84 78 89 100 99 101 93 82
16 52 Bizygomatic breadth (zy-zy) 157 126 102 117 –135 153 165 143
17 Zygomatic breadth index (14/16 × 100) 75 74 84 85 –84 –65 74
18 53 Bimaxillary breadth (zm-zm) –103 84 97 113 105 126 119 106
19 55 Interorbital breadth (mf-mf) 18 19 20 27 24 25 23 24 24
20 56 Orbital breadth (mf-ek) 38 36 31 33 39 39 36 37 33
21 57 Orbital height (perpendicular to 20) 34 32 31 31 33 36 41 33 30
22 71 Nasal bridge length (n-rhi) –27 26 18 20 18 35 30 28
23 73 Nasal bridge breadth superior –5 8 8 8 13 12 14 11
24 Nasal bridge breadth at anterior lacrimal crests –11 5 10 –24 19 11 –
25 74 Nasal bridge breadth inferior –11 13 11 10 18 11 7 8
26 Nasal bridge height (nasion subtense at anterior lacrimal crests) –498 –945–
27 69 Nasal height (n-ns) 58 50 49 45 57 52 72 64 54
28 70 Nasal aperture height (rhi-ns) 29 26 22 28 39 30 38 35 24
29 68 Maximum nasal aperture width 23 23 26 25 27 32 30 31 25
30 Orbitoalveolar height (or-alveolar plane) 55 53 44 47 59 51 53 69 57
31 60 Malar thickness 14 13 13 8 –12 20 18 18
32 Infraorbital foramen height (to inferior orbital margin) –12 15 15 14 16 30 25 26
33 Prosthion to zygomaxillare (pr-zm) –67 57 55 69 67 80 82 71
34 Prosthion to zygoorbitale (pr-zyo) –60 50 57 75 70 73 81 69
35 Masseter origin height index (33/34 × 100) –112 104 96 92 96 110 101 103
36 47 Subnasale to prosthion (horizontal projection) 28 23 13 19 17 16 23 27 26
37 48 Subnasal to prosthion (vertical projection) 15 21 17 18 30 21 12 25 22
38 Subnasale projection index (36/37 × 100) 187 108 76 106 57 79 192 108 122
39 94 Incisor alveolar length –13 16 15 14 16 15 15 13
40 96 Premolar alveolar length –15 18 16 16 13 21 22 17
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to the facial plane. The face is mesognathic.
The palate is consistently deep along its entire
extent, with a parabolic dental arcade.
Mandible. Descriptions apply to the more
complete juvenile (MH1) mandible unless other-
wise stated. The nearly vertical mandibular sym-
physis presents a weak lateral tubercle, resulting
in a slight mental trigone, and a weak man-
dibular incurvation results in a slight mentum
osseum. The post-incisive planum is weakly
developed and almost vertical. Both mandibular
corpora are relatively gracile, with a low height
along the alveolar margin. The extramolar sulcus
is relatively narrow in both mandibles. In MH1,
a moderate lateral prominence displays its
greatest protrusion at the mesial extent of M
2
,
with a marked decrease in robusticity to P
4
;in
MH2 the moderate lateral prominence shows
its greatest protrusion at M
3
, with a marked
decrease in robusticity to M
2
. The alveolar prom-
inence is moderately deep with a notable medial
projection posteriorly. The anterior and posterior
subalveolar fossae are continuous. The ramus
of MH1 is tall and narrow, with nearly parallel,
vertically oriented anterior and posterior bor-
ders; the ramus of MH2 is relatively broader,
with nonparallel anterior and posterior borders
(fig. S2). The mandibular notch is relatively deep
and narrow in MH1 and more open in MH2.
The coronoid extends farther superiorly than
the condyle. The condyle is mediolaterally broad
and anteroposteriorly narrow. The endocondyloid
buttress is absent in MH1, whereas in MH2 a
weak endocondyloid buttress approaches the
condyle without reaching it.
Dental size and proportions. The dentition
of the juvenile (MH1) is relatively small, whereas
preserved molars of the adult (MH2) are even
smaller (Fig. 3 and fig. S4). For MH1, the
maxillary central incisor is distinguishable only
from the reduced incisors of Au. robustus.The
maxillary canine is narrower than all canines of
Au. africanus except TM 1512, whereas the
mandibular canine falls well below the range of
Au. africanus. Premolars and molars are at the
lower end of the Au. africanus range and within
that of H. habilis–H. rudolfensis and H. erectus.
Molar dimensions of the adult individual (MH2)
are smaller than those of Au. africanus,are
at or below the range of those of H.habilis–
H. rudolfensis, and are within the range of those
of H.erectus.Au. sediba mirrors the Au.africanus
pattern of maxillary molars that increase slightly
in size posteriorly, though it differs in that the
molars tend to be considerably larger in the latter
taxon. Conversely, the Au. sediba pattern varies
slightly from that seen in specimens KNM-ER
1813, OH 13, and OH 65 and H. erectus,where-
in the molars increase from M
1
to M
2
but then
decrease to M
3
.Inbroadterms,theteethof
Au. sediba are similar in size to teeth of speci-
mens assigned to Homo but share the closely
spaced cusp apices seen in Australopithecus.
Postcranium. Preserved postcranial remains
of Au. sediba (table S1) denote small-bodied
Item Measurement
description in (6)Measurement Au.
afarensis
Au.
africanus
Au.
sediba
H.
habilis
H.
rudolfensis
H.
erectus
Au.
aethiopicus
Au.
boisei
Au.
robustus
41 98 Intercanine distance 26 30 30 30 33 31 –29 27
42 88 Palate breadth (ekm-ekm) 68 64 63 70 80 66 83 82 67
43 141 Mandibular symphysis height 39 38 32 27 36 34 –47 42
44 142 Mandibular symphysis depth 60 20 19 19 24 19 –28 25
45 147 Mandibular corpus height at P
4
34 33 28 30 38 30 –42 38
46 148 Mandibular corpus depth at P
4
19 21 18 20 22 19 –28 24
47 149 Cross-sectional area at P
4
(calculated as an ellipse) 511 558 382 427 653 458 –910 709
48 150 Mandibular corpus height at M
1
33 32 28 29 36 30 35 41 37
49 151 Mandibular corpus depth at M
1
19 21 18 20 23 20 26 28 26
50 152 Cross-sectional area at M
1
(calculated as an ellipse) 488 532 396 421 667 469 715 913 759
51 154 Mandibular corpus height at M
2
31 31 25 31 36 30 –41 35
52 155 Mandibular corpus depth at M
2
22 25 22 23 26 21 –31 28
53 156 Cross-sectional area at M
2
(calculated as an ellipse) 536 612 436 537 745 504 –980 770
54 162 Height of mental foramen relative to alveolar margin 20 19 13 13 17 13 –20 20
55 Maxillary incisor crown area (I
1
+I
2
) 143 135 109 132 137 136 –117 109
56 Maxillary canine crown area 107 104 79 95 118 96 –76 79
57 Maxillary postcanine crown area 713 868 731 755 829 617 –1012 941
58 Mandibular canine crown area 87 95 68 83 –79 –72 61
59 Mandibular molar crown area 550 651 536 565 668 466 –781 678
60 Maxillary incisor to postcanine ratio 20.0 15.6 14.9 17.4 16.6 22.1 –11.5 11.6
61 Maxillary canine to postcanine ratio 15.0 11.9 10.8 12.6 14.2 15.5 –7.5 8.4
62 Mandibular canine to molar ratio 15.8 14.6 12.7 14.6 –16.7 –9.2 9.0
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hominins that retain an australopith pattern of
long upper limbs, a high brachial index, and
relatively large upper limb joint surfaces
(table S2). In addition to these aspects of limb
and joint proportions, numerous other features
in the upper limb are shared with sibling species
of Australopithecus (to the exclusion of later
Homo), including a scapula with a cranially
oriented glenoid fossa and a strongly developed
axillary border; a prominent conoid tubercle on
the clavicle, with a pronounced angular margin;
low proximal-to-distal humeral articular propor-
tions; a distal humerus with a marked crest for
the brachioradialis muscle, a large and deep
olecranon fossa with a septal aperture, and a
marked trochlear/capitular keel (19); an ulna
with a pronounced flexor carpi ulnaris tubercle;
and long, robust, and curved manual phalanges
that preserve strong attachment sites for the
flexor digitorum superficialis muscle.
Numerous features of the hip, knee, and ankle
indicate that Au. sediba was a habitual biped. In
terms of size and morphology, the proximal and
distal articular ends of the femur and tibia fall
within the range of variation of specimens
attributed to Au. africanus. However, several
derived features in the pelvis link the Malapa
specimens with later Homo. In the os coxa (Fig.
4), Au. sediba shares with Homo a pronounced
acetabulocristal buttress; a more posterior posi-
tion of the cristal tubercle; a superoinferiorly
extended posterior iliac blade, with an expanded
retroauricular area; a sigmoid-shaped anterior in-
ferior iliac spine; a reduced lever arm for weight
transfer between the auricular surface and the
acetabulum; an enlarged and rugose iliofemoral
ligament attachment area; a tall and thin pubic
symphyseal face; and a relatively short ischium
with a deep and narrow tuberoacetabular sulcus.
These features are present in taxonomically un-
assigned postcranial remains from Koobi Fora
(KNM-ER 3228) and Olduvai Gorge (OH 28),
which have been argued to represent early Homo
(20), as well as in early Homo erectus (21). An os
coxa from Swartkrans (SK 3155) has been con-
sideredbysometoalsorepresentearlyHomo
(22) but can be seen to possess the australopith
pattern in most of these features. In addition,
Au. sediba shares with later Homo the human-
like pattern of low humeral-to-femoral diaph-
yseal strength ratios, in contrast to the ape-like
pattern seen in the H. habilis specimen OH 62
(table S2).
Although aspects of the pelvis are derived, the
foot skeleton is more primitive overall, sharing
with other australopiths a flat talar trochlea
articular surface with medial and lateral margins
with equal radii of curvature, and a short, stout,
and medially twisted talar neck with a high
horizontal angle and a low neck torsion angle
Fig. 3. Dental size of a selection of Au. sediba teeth compared to other early
hominin taxa; see fig. S4 for additional teeth. Dental measurements were
taken as described by Wood (6). Owing to small sample sizes, H. habilis and
H. rudolfensis were combined. (A) Upper central incisor mesiodistal (MD)
length. (B) Upper canine MD length. (C) Lower canine MD length. (D) Square
root of calculated [MD × BL (BL, buccolingual)] upper third premolar area.
(E) Square root of calculated (MD × BL) upper second molar area. (F)
Square root of calculated (MD × BL) lower second molar area. Measures
were taken on original specimens by D.J.D. for Au. africanus,Au. robustus,
and Au. sediba. Measurements for Au. afarensis,H. habilis,H. rudolfensis,
and H. erectus are from (6). P
4
is not fully erupted on the right side of MH1,
therefore measures of the maxillary postcanine dentition are presented for
the left side only. Dental metrics for Au. sediba are as follows (MD, BL, in
millimeters): Maxillary: MH1: RI1 10.1, 6.9; LI2 7.7 (damaged), 5.1; RC
9.0, 8.8; LP3 9.0, 11.2; LP4 9.2, 12.1; LM1 12.9, 12.0; LM2 12.9, 13.7;
LM3 13.3, 14.1; MH2: RM3 11.3, 12.9. Mandibular: MH1: LC 8.0, 8.5; RM1
12.5, 11.6; RM2 14.4, 12.9; RM3 14.9, 13.8; MH2: RM1 11.8, 11.1; RM2
14.1, 12.2; RM3 14.2, 12.7; LM3 14.1, 12.5.
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(table S2 and fig. S5). The calcaneus is markedly
primitive in its overall morphology: the bone is
strongly angled along the proximodistal axis,
with the point of maximum inflexion occurring at
an enlarged peroneal trochlea; the lateral plantar
tubercle is lacking; the calcaneal axis is set about
45° to the transverse plane; and the calcaneocu-
boid facet is vertically set and lacks an expanded
posterior projection for the beak of the cuboid
(23).
Discussion. The age and overall morpholo-
gy of Au. sediba imply that it is most likely
descended from Au. africanus, and appears more
derived toward Homo than do Au. afarensis,Au.
garhi,andAu.africanus. Elsewhere in South
Africa, the Sterkfontein cranium Stw 53, dated to
2.0 to 1.5 Ma, is generally considered to represent
either H. habilis (10,24,25) or perhaps an
undiagnosed form of early Homo (26). It played
an important role in the assignment of OH 62 to
H. habilis (27). However, the derived cranioden-
tal morphology of Au. sediba casts doubt on the
attribution of Stw 53 to early Homo [see also
(28)]: Stw 53 appears to be more primitive than
MH1 in retaining closely spaced temporal lines;
marked postorbital constriction; a weakly devel-
oped supraorbital torus; narrow, nonprojecting
nasal bones; anterior pillars; marked nasoalveolar
prognathism; medial and lateral expansion of the
frontal process of the zygomatic bone; and
laterally flared zygomatics. If Stw 53 instead
represents Au. africanus, the assignment of OH
62 to H. habilis becomes tenuous. Attribution of
the partial skeleton KNM-ER 3735 to H.habilis
was tentatively based, in part, on a favorable
comparison with OH 62 and on the hypothesis
that there were no other contemporaneous non-
robust australopith species to which it could be
assigned in East Africa (29). As a result, the
interpretation of KNM-ER 3735 as H.habilis
also becomes uncertain.
The phylogenetic significance of the co-
occurrence of derived postcranial features in
Au. sediba,H. erectus, and a sample of isolated
fossils generally referred to Homo sp. indet.
(table S2) is not clear: The latter might repre-
sent early H. erectus, it might sample the post-
cranium of H. rudolfensis (which would then
imply an evolutionary pathway from Au. sediba to
H. rudolfensis to H. erectus), or it might represent
the postcranium of H. habilis [which would sug-
gestthatOH62andKNM-ER3735(twospeci-
mens with ostensibly more primitive postcranial
skeletons) do not belong in this taxon]. If the lat-
ter possibility holds, it could suggest a phyloge-
netic sequence from Au. sediba to H. habilis to
H. erectus. Conversely, although the overall post-
cranial morphology of Au. sediba is similar to that
of other australopiths, a number of derived features
of the os coxa align the Malapa hominins with
later Homo (H. erectus) to the exclusion of other
australopiths. Additionally, Au. sediba shares a
small number of cranial traits with H. erectus that
are not exhibited in the H.habilis–H. rudolfensis
hypodigm, including slight postorbital constriction
and convexity of the infraorbital region (18).
Following on this, MH1 compares favorably with
SK 847 (H.erectus) in the development of the
supraorbital torus, nasal bones, infraorbital region,
frontal process of the zygomatic, and subnasal
projection. However, MH1 differs from SK 847 in
its relatively smaller size, the robust glabelar re-
gion, the weakly developed supratoral sulcus, the
steeply inclined zygomaticoalveolar crests with a
high masseter origin, and the moderate canine
juga, all features aligning MH1 with Australopith-
ecus. It is thus not possible to establish the precise
phylogenetic position of Au.sediba in relation to
the various species assigned to early Homo.We
can conclude that combined craniodental and post-
cranial evidence demonstrates that this new spe-
cies shares more derived features with early Homo
than does any other known australopith species
(Table 1 and table S2) and thus represents a candi-
date ancestor for the genus, or a sister group to a
close ancestor that persisted for some time after the
first appearance of Homo.
The discovery of a <1.95-million-year-old
(16) australopith that is potentially ancestral to
Homo is seemingly at odds with the recovery of
older fossils attributed to the latter genus (5)orof
approximately contemporaneous fossils attribut-
able to H. erectus (6,30). However, it is unlikely
that Malapa represents either the earliest or the
latest temporal appearance of Au.sediba,nor
does it encompass the geographical expanse that
the species once occupied. We hypothesize that
Au. sediba was derived via cladogenesis from
Au. africanus (≈3.0 to 2.4 Ma), a taxon whose
first and last appearance dates are also uncertain
(31). The possibility that Au.sediba split from
Au.africanus before the earliest appearance of
Homo cannot be discounted.
Although the skull and skeleton of Au. sediba
do evince derived features shared with early
Homo, the overall body plan is that of a hominin
at an australopith adaptive grade. This supports
the argument, based on endocranial volume and
craniodental morphology, that this species is
most parsimoniously attributed to the genus
Australopithecus. The Malapa specimens dem-
Fig. 4. Representative ossa coxae, in lateral view, from left to right, of Au.
afarensis (AL 288-1), Au. africanus (Sts 14), Au. sediba (MH1), and H. erectus
(KNM-WT 15000). The specimens are oriented so that the iliac blades all lie in the
plane of the photograph (which thus leads to differences between specimens in
the orientation of the acetabula and ischial tuberosities). MH1 possesses derived,
Homo-like morphology compared to other australopithecines, including a relative
reduction in the weight transfer distance from the sacroiliac (yellow) to hip (circle)
joints; expansion of the retroauricular surface of the ilium (blue arrows)
(determined by striking a line from the center of the sphere representing the
femoral head to the most distant point on the posterior ilium; the superior arrow
marks the terminus of this line, and the inferior arrow marks the intersection of
this line with the most anterior point on the auricular face); narrowing of the
tuberoacetabular sulcus (delimited by yellow arrows); and pronouncement of the
acetabulocristal (green arrows) and acetabulosacral buttresses.
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onstrate that the evolutionary transition from a
small-bodied and perhaps more arboreal-adapted
hominin (such as Au. africanus)toalarger-
bodied, possibly full-striding terrestrial biped
(such as H. erectus) occurred in a mosaic fashion.
Changes in functionally important aspects of
pelvic morphology, including a reduction of the
sacroacetabular weight-bearing load arm and
enhanced acetabulosacral buttressing (reflect-
ing enhancement of the hip extensor mecha-
nism), enlargement of the iliofemoral ligament
attachment (reflecting a shift in position of the
line of transfer of weight to behind the center of
rotation of the hip joint), enlargement of the
acetabulocristal buttress (denoting enhancement
of an alternating pelvic tilt mechanism), and re-
duction of the distance from the acetabulum to
the ischial tuberosity (reflecting a reduction in the
moment arm of the hamstring muscles) (20,32)
occurred within the context of an otherwise aus-
tralopith body plan, and seemingly before an
increase in hominin encephalization [in contrast
to the argument in (33)]. Relative humeral and
femoral diaphyseal strength measures (table S2)
also suggest that habitual locomotor patterns in
Au. sediba involved a more modern human-like
mechanical load-sharing than that seen in the
H. habilis specimen OH 62 (34,35). Mosaic evo-
lutionary changes are mirrored in craniodental
morphology, because the increasingly wide spacing
of the temporal lines and reduction in post-
orbital constriction that characterize Homo first
appeared in an australopith and before significant
cranial expansion. Moreover, dental reduction,
particularly in the postcanine dentition, preceded
the cuspal rearrangement (wide spacing of post-
canine tooth cusps) that marks early Homo.
The pattern of dental eruption and epiphyseal
fusion exhibited by MH1 indicates that its age at
death was 12 to 13 years by human standards,
whereas in MH2 the advanced degree of occlusal
attrition and epiphyseal closure indicates that it
had reached full adulthood (SOM text S1). Al-
though juvenile, MH1 exhibits pronounced devel-
opment of the supraorbital region and canine juga,
eversion of the gonial angle of the mandible, and
large rugose muscle scars in the skeleton, all in-
dicating that this was a male individual. And, al-
though fully adult, the mandible and skeleton of
MH2 are smaller than in MH1, which, combined
withthelessrugosemusclescarsandtheshapeof
the pubic body of the os coxa, suggests that MH2
was a female. In terms of dental dimensions, MH1
has mandibular molar occlusal surface areas that
are 10.7% (M
1
) and 8.1% (M
2
) larger than those
of MH2. Dimorphism in the postcranial skeleton
likewise is not great, though the juvenile status of
MH1 tends to confound efforts to assess adult
body size. The diameter of the proximal epiphysis
for the femoral head of MH1 (29.8 mm) is ap-
proximately 9.1% smaller than the superoinferior
diameter of MH2's femoral head (32.7 mm). It is
likely that MH1 would have experienced some
appositional increase in joint size before matu-
rity, thus this disparity would probably have de-
creased somewhat. The distal humeral epiphysis
of MH1 is fully fused and its articular breadth
(35.3 mm) is only marginally larger than that of
MH2 (35.2 mm). Thus, although the dentition
and postcranial skeleton are at odds in the de-
gree of apparent size differences, the overall
level of dimorphism, if these sex attributions are
correct, appears slight in the Malapa hominins
and was probably similar to that evinced by mod-
ern humans.
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41. We thank the South African Heritage Resources Agency
for the permits to work at the Malapa site; the Nash
family for granting access to the Malapa site and
continued support of research on their reserve; the South
African Department of Science and Technology, the South
African National Research Foundation, the Institute for
Human Evolution, the Palaeontological Scientific Trust,
the Andrew W. Mellon Foundation, the AfricaArray
Program, the U.S. Diplomatic Mission to South Africa,
and Sir Richard Branson for funding; the University of the
Witwatersrand’s Schools of Geosciences and Anatomical
Sciences and the Bernard Price Institute for
Palaeontology for support and facilities; the Gauteng
Government, Gauteng Department of Agriculture,
Conservation and Environment and the Cradle of
Humankind Management Authority; E. Mbua, P. Kiura,
V. Iminjili, and the National Museums of Kenya for access
to comparative specimens; Optech and Optron; Duke
University; the Ray A. Rothrock Fellowship of Texas
A&M University; and the University of Zurich 2009 Field
School. Numerous individuals have been involved in the
ongoing preparation and excavation of these fossils,
including C. Dube, B. Eloff, C. Kemp, M. Kgasi,
M. Languza, J. Malaza, G. Mokoma, P. Mukanela,
T. Nemvhundi, M. Ngcamphalala, S. Jirah, S. Tshabalala,
and C. Yates. Other individuals who have given
significant support to this project include B. de Klerk,
C. Steininger, B. Kuhn, L. Pollarolo, B. Zipfel, J. Kretzen,
D. Conforti, J. McCaffery, C. Dlamini, H. Visser,
R. McCrae-Samuel, B. Nkosi, B. Louw, L. Backwell,
F. Thackeray, and M. Peltier. T. Stidham helped construct
the cladogram in fig. S3. J. Smilg facilitated computed
tomography scanning of the specimens. R. Clarke and
F. Kirera provided valuable discussions on these and
other hominin fossils in Africa.
Supporting Online Material
www.sciencemag.org/cgi/content/full/328/5975/195/DC1
SOM Text 1 to 4
Figs. S1 to S5
Tables S1 and S2
References
19 November 2009; accepted 26 February 2010
10.1126/science.1184944
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