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New hominid fossils from Woranso-Mille (Central Afar Ethiopia) and taxonomy of early Australopithecus.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 141:406–417 (2010)
New Hominid Fossils From Woranso-Mille (Central Afar,
Ethiopia) and Taxonomy of Early Australopithecus
Yohannes Haile-Selassie,1* Beverly Z. Saylor,2 Alan Deino,3 Mulugeta Alene,4 and Bruce M. Latimer5
1
The Cleveland Museum of Natural History, Cleveland, OH 44106
Department of Earth Sciences, Case Western Reserve University, Cleveland, OH 44106
3
Berkeley Geochronology Center, Berkeley, CA 94709
4
Department of Earth Sciences, Addis Ababa University, Addis Ababa, Ethiopia
5
Department of Anthropology, Case Western Reserve University, Cleveland, OH 44106
2
KEY WORDS
Australopithecus; Pliocene; taxonomy; Woranso-Mille; Ethiopia
ABSTRACT
The phylogenetic relationship between
Australopithecus anamensis and Australopithecus afarensis has been hypothesized as ancestor-descendant.
However, the weakest part of this hypothesis has been
the absence of fossil samples between 3.6 and 3.9 million
years ago. Here we describe new fossil specimens from
the Woranso-Mille site in Ethiopia that are directly relevant to this issue. They derive from sediments chronometrically dated to 3.57–3.8 million years ago. The new
fossil specimens are largely isolated teeth, partial mandibles, and maxillae, and some postcranial fragments.
However, they shed some light on the relationships
between Au. anamensis and Au. afarensis. The dental
morphology shows closer affinity with Au. anamensis
from Allia Bay/Kanapoi (Kenya) and Asa Issie (Ethiopia)
than with Au. afarensis from Hadar (Ethiopia). However,
they are intermediate in dental and mandibular mor-
It was only 30 years ago that Australopithecus afarensis was recognized as the ‘‘oldest indisputable evidence of
the family Hominidae’’ at 3.6 million years ago (Myr)
(Johanson et al., 1978). It remained as such until the discovery of Ardipithecus ramidus [1994, Ethiopia, 4.4 Myr
(White et al., 1994, 1995)], and Australopithecus anamensis [1995, Kenya, 3.9–4.2 Myr (Leakey et al., 1995, 1998;
Ward et al., 1999, 2001)]. More recent fieldwork in Ethiopia, Kenya, and Chad has resulted in the discovery of
even older hominid species (Ardipithecus kadabba, Ethiopia, 5.2–5.8 Myr (Haile-Selassie, 2001; 2004); Orrorin
tugenensis, Kenya, 5.7–6.0 Myr (Senut et al., 2001; Pickford et al., 2002); Sahelanthropus tchadensis, Chad, 6–7
Myr (Brunet et al., 2002, 2005), and Ar. ramidus (Semaw
et al., 2005). The phylogenetic relationships among these
earlier hominids remain a point of contention (HaileSelassie et al., 2004).
New hominid fossil discoveries from the Pliocene of
eastern Africa have begun to shed light on the origin of
the genus Australopithecus (White et al., 2006) and the
phylogenetic relationship between the two earliest species of the genus (Leakey et al., 1995, 1998; Ward et al.,
1999, 2001; Kimbel et al., 2006; White et al., 2006). Au.
anamensis (3.9–4.2 Myr) and Au. afarensis (3.0–3.6 Myr)
are time successive species and generally considered to
sample a single evolving lineage (Kimbel et al., 2006)
with the former rapidly evolving anagenetically from its
putative ancestor Ardipithecus ramidus (White et al.,
2006). Although the relationship between Ar. ramidus
and Au. anamensis remains to be more rigorously tested,
C 2009
V
WILEY-LISS, INC.
phology between Au. anamensis and the older Au. afarensis material from Laetoli. The new fossils lend strong
support to the hypothesized ancestor-descendant relationship between these two early Australopithecus species. The Woranso-Mille hominids cannot be unequivocally assigned to either taxon due to their dental morphological intermediacy. This could be an indication that
the Kanapoi, Allia Bay, and Asa Issie Au. anamensis is
the primitive form of Au. afarensis at Hadar with the
Laetoli and Woranso-Mille populations sampling a
mosaic of morphological features from both ends. It is
particularly difficult to draw a line between Au. anamensis and Au. afarensis in light of the new discoveries from
Woranso-Mille. The morphology provides no evidence
that Au. afarensis and Au. anamensis represent distinct
taxa. Am J Phys Anthropol 141:406–417, 2010. V 2009
C
Wiley-Liss, Inc.
the hypothesized ancestor-descendant relationship
between Au. anamensis and Au. afarensis (Leakey et al.,
1995, 1998; Ward et al., 1999, 2001; Wolpoff, 1999;
White, 2002; Kimbel et al., 2006) has been explored by
various methods including cladistic analysis (Kimbel
et al., 2006). These analyses have thus far failed to
falsify the proposed ancestor-descendant relationship.
However, a weak point in this assessment has been the
paucity of hominid fossils in the interval of 3.6–3.9 Myr
ago (Kimbel et al., 2006).
We describe here new hominid fossils from the Woranso-Mille study area, Afar rift, Ethiopia (see Fig. 1),
that are directly relevant to this question. These hominids derive from sediments chronometrically bracketed
between 3.6 and 3.8 Myr (Haile-Selassie et al., 2007;
Deino et al., in review). This new study area (see HaileGrant sponsor: The National Science Foundation; Grant numbers:
BCS-0234320, BCS-0542037, BCS-0321893; Grant sponsors: The
Leakey Foundation; The Wenner-Gren Foundation; The National
Geographic Society.
*Correspondence to: Yohannes Haile-Selassie, 1 Wade Oval Drive,
Cleveland, OH 44106. E-mail: yhailese@cmnh.org
Received 27 April 2009; accepted 9 July 2009
DOI 10.1002/ajpa.21159
Published online 16 November 2009 in Wiley InterScience
(www.interscience.wiley.com).
407
NEW PLIOCENE HOMINIDS FROM WORANSO-MILLE, ETHIOPIA
Fig. 1. Satellite imageries showing the location of Am-Ado (AMA), Aralee Issie (ARI), Mesgid Dora (MSD), and Makah Mera
(MKM) vertebrate fossil collection areas in the Woranso-Mille study area.
TABLE 1. List of dentognathic hominid specimens from four collection areas in the Woranso-Mille study area
Specimen
AMA-VP-2/30
AMA-VP-2/64
ARI-VP-1/7
ARI-VP-1/28
ARI-VP-1/90
ARI-VP-1/173
ARI-VP-1/190
ARI-VP-1/215
ARI-VP-1/337
ARI-VP-1/352
ARI-VP-1/385
ARI-VP-1/420
ARI-VP-1/462
ARI-VP-1/484
ARI-VP-3/34
ARI-VP-3/35
ARI-VP-3/36
ARI-VP-3/80
ARI-VP-3/176
ARI-VP-3/248
ARI-VP-3/249
ARI-VP-3/250
MKM-VP-1/69
MSD-VP-1/53
MSD-VP-3/24
MSD-VP-5/16
Discovery date
Element preserved
Discoverer
2/5/08
2/5/08
1/20/04
1/28/04
2/1/05
2/3/05
2/8/05
2/12/05
2/2/07
2/2/07
2/2/07
2/1/08
2/2/08
2/13/08
2/17/06
2/17/06
2/17/06
2/19/06
2/4/07
2/13/08
2/13/08
2/13/08
2/14/05
2/28/06
2/18/05
2/7/06
R. LP4; R. LC frag.
R. LC fragment
I. fragment
R. LP4 fragment
R. UM3
UM frag.
R. Ldc
L. UM2 or 3
L. LM2 or 3 fragment
R. LM3
M frag.
R. LM2 fragment
L. LM1
R. UM1
L. Udm1
R. LM2 fragment
L. UP4
Associated upper and lower teeth
R. LM2 w/ MAN fragment
R. UP4
L. LP4
L. LM1 or 2
L. UP4 fragment
L. MAX (M1-2)
L. LM3
L. MAN (M1-2)
Ali Mohammed Ebrahim
Group
Kampiro Kayranto
Kampiro Kayranto
Mohammed Hussein
Barao Mohammed
Kampiro Kayranto
Habib Wogris
Kampiro Kayranto
Alemayehu Asfaw
Group
Ahmed Elema
Ahmed Elema
Ahmed Elema
Kadir Helem
Yohannes Haile-Selassie
Yohannes Haile-Selassie
Ali Idris
Mohammed Hussein
Wegenu Amerga
Habib Hussein
Mohammed Haydera
Kampiro Kayranto
Alemayehu Asfaw
Alemayehu Asfaw
Alemayehu Asfaw
Selassie et al., 2007) is located in the central Afar
region, about 360 km northeast of the capital, Addis
Ababa. Its full potential was discovered in 2003, and
four radiometrically dated collection areas in its northeastern part has thus far yielded more than 1,500 vertebrate fossils including 26 hominid specimens (as listed in
Table 1), which are described here.
GEOLOGICAL CONTEXT AND DATING
The Woranso-Mille paleontological research project
study area lies within the western part of the central
Afar depression (Haile-Selassie et al., 2007). Chronostratigraphic studies have focused on early Pliocene strata
exposed over a distance of 5 km along the Mille River,
near the confluence with the Waki River between the
towns of Mille and Chifra (Fig. 1; Haile-Selassie et al.,
2007; Deino et al., in review). Extending from Am-Ado
(AMA) in the northwest to Makah Mera (MKM) in the
southeast, these strata overlie basalt flows and are
largely encircled by fault-bounded elevated plateaus of
basalt. The subhorizontal lithostratigraphic sequence
consists of basalt flow units overlain by primary and
reworked tuffs, intercalated with occasionally pedogeniAmerican Journal of Physical Anthropology
408
Y. HAILE-SELASSIE ET AL.
Kilaytoli Tuff (KT; WM-KSD-1 and WM-KSD-3) capping
the fossiliferous horizons yielded a weighted mean age of
3.570 6 0.014 Myr. The basalt (WM-W-1) at the bottom
of the sequence yielded an age of 3.82 6 0.18 Myr. Some
of the fossils derive from channel deposits above or contained within the Aralee Issie tuff (AT), which is radiometrically dated to 3.72 6 0.03 Myr (see Fig. 2). The
hominids from ARI-VP-3 locality are stratigraphically
below the AT and those from MSD-VP-5 are above an
unnamed air-fall pumice lapillistone (WM-W-2) radiometrically dated to 3.76 6 0.02 Myr.
Paleontological context and paleoenvironment
Fig. 2. Measured lithostratigraphic sequences at Am-Ado
(AMA), Aralee Issie (ARI), Mesgid Dora (MSD), and Makah
Mera (MKM), showing fossiliferous horizons, dated tuffs, and
marker horizons used for correlation across the four fossil collection areas.
cally modified, fossiliferous medium-grained clastic units
in the middle, capped unconformably by a dominantly
conglomeratic layer.
A composite section greater than 30-m thick is constructed from exposures of the Pliocene strata at WakiMille Confluence (WMC), Mesgid Dora (MSD), and Makah
Mera (MKM) (see Fig. 2). The base of the composite section is exposed at the Waki-Mille Confluence (WMC),
where basalt flows are overlain by 9 m of conglomerate,
tuffaceous sandstone, and siltstone. This predominantly
sedimentary section is overlain by 10-m thick succession
of volcaniclastic-rich deposits containing multiple tuffs
with interbedded tuffaceous sandstone and siltstone.
Four distinctive tuffs in this succession are also recognized at Mesgid Dora (MSD), providing a strong basis
for correlating sections (see Fig. 2). In stratigraphic
order, from bottom to top, the sequence of distinctive
tuffs consists of a 3-m thick, pumice lapillistone tuff,
known as the Mille tuff (‘‘MLT’’), a 30-cm thick bimodal
composition basalt-rhyolite tuff (‘‘BRT’’), a 25-cm thick
fine grained tuff known as the Waki tuff (‘‘WT’’), and a
1-m thick pumice lapillistone tuff, which is quite similar
in appearance to the MLT and named the Mesgid Dora
tuff (‘‘MDT’’). At MKM, the MDT is overlain by 5 m of
pebbly to silty sandstone and siltstone, above which lies
a 1-m thick, white, fine grained, planar laminated tuff,
called the Kilaytoli tuff (‘‘KT’’). The KT is overlain by
siltstone and sandstone followed unconformably by a
thick conglomerate sequence. A complete stratigraphic
section of about 30-m thick from the basal basalt to the
KT is exposed at Aralee Issie (ARI; Fig. 2).
Absolute age calibration of this stratigraphic succession, utilizing 40Ar/39Ar dating of volcanic units, and
paleomagnetic determinations on volcanic units and sedimentary strata was conducted. The details are presented in Deino et al. (in review). Two samples of the
American Journal of Physical Anthropology
The associated vertebrate fossils represent diverse
taxa of terrestrial and aquatic animals. The faunal
assemblage is significant in that it records changes in
the African faunal community from the end of the early
Pliocene to the beginning of the middle Pliocene, with
the appearance of a number of new species from more
primitive taxa. More than 1,500 specimens have been
collected from the Am-Ado, Aralee Issie, Mesgid Dora,
and Makah Mera collection areas representing at least
42 large mammalian genera in 18 families (Table 2 Fig.
3). The number of individual specimens in each large
mammal family is given in insert table in Figure 3.
Aquatic animals such as fish and crocodiles are also
present in addition to birds and turtles. Hominid
remains are relatively abundant with 26 dentognathic
specimens identified through the end of the 2008 field
season and constitute 1.7% of the total number of collected specimens. More than 46% of the specimens
belong to Cercopithecidae with the earliest Theropithecus oswaldi aff. darti being the most abundant. One
small cercopithecine and at least two colobine species
are also present. The genus Galago has also been identified from one dental specimen. Among the carnivores,
large felids such as Homotherium, Dinofelis cf. petteri,
and Panthera cf. leo are very common. The hyaenids are
represented by three species (Chasmaporthetes cf. nitidula, Crocuta cf. deitrichi, and Hyaena sp.). Enhydriodon sp. and Lutra sp. represent the mustelids. Other
recovered carnivores include viverrids, canids, and herpestids. At least 10 bovid species have been recovered
thus far with bovines and aepycerotines being the most
abundant (50% of the bovid specimens). Hippotragines,
reduncines, and antilopines are less abundant. Among the
suids, Nyanzachoerus kanamensis, Nyanzachoerus jaegeri,
Kolpochoerus sp., and an early Notochoerus euilus are represented. Other large mammals include Hippopotamidae,
two species of elephantids, one equid species, three giraffid
species, and one large aardvark species.
Most of the mammalian species from the WoransoMille study area, and dated to 3.6–3.8 Myr, appear to be
the ancestral forms of numerous mammalian species at
Hadar (see Reed, 2008). However, there are also a number of new species that are not present in either the earlier Kanapoi and Allia Bay deposits or the penecontemporaneous Laetoli deposits. There seems to be a clear difference in the faunal composition between WoransoMille and Laetoli. For example, alcelaphines and neotragines are the most dominant bovids at Laetoli (Su, 2005)
and the suid Nyanzachoerus and the cercopithecid
Theropithecus are absent at this site (Harris, 1987). At
Woranso-Mille, bovines and aepycerotines are the dominant bovids, alcelaphines are very rare, Nyanzachoerus
jaegeri and Nyanzachoerus kanamensis are abundant,
NEW PLIOCENE HOMINIDS FROM WORANSO-MILLE, ETHIOPIA
409
(Continued) Preliminary faunal
TABLE 2. Preliminary faunal list for Aralee Issie (ARI), Mesgid
(MSD),
Am-Ado
(AMA),
and(MSD),
MakahAm-Ado
Mera (AMA),
list forDora
Aralee
Issie (ARI),
Mesgid
Dora
(MKM) collection areas and Makah Mera (MKM) collection areas
MAMMALIA
Primates
Cercopithecidae (741)
Cercopithecinae
Theropithecus oswaldi aff. darti
Colobinae
cf. Cercopithecoides sp.
Hominidae (30)
Australopithecus sp.
Galagidae (1)
Galago sp.
Carnivora
Felidae (30)
Felinae
Dinofelis cf. petteri
Pantherinae
Panthera cf. leo
Machairodontinae
Homotherium sp.
Hyaenidae (49)
Hyaeninae
Chasmaporthetes cf. nitidula
Crocuta cf. dietrichi
Hyaena sp.
Mustelidae (11)
Lutrinae
Enhydriodon sp.
Lutra sp.
Viverridae (5)
Canidae (7)
Herpestidae (1)
Artiodactyla
Bovidae (332)
Bovinae
Tragelaphini (51)
Tragelaphus cf. scriptus
Tragelaphus sp. nov.
Bovini (19)
Simatherium sp.
Ugandax coryndonae
Alcelaphinae
Aepycerotini
Aepyceros sp. nov. (93)
Alcelaphini (50)
‘‘Damalops’’ sp. (3)
Antilopinae
Antilopini
Gazella sp. (9)
Neotragini
Neotragus sp. (2)
Hippotraginae
Hippotragini (8)
cf. Hippotragus sp.
Reduncinae
Reduncini (6)
Cephalophinae
Cephalophus? sp. (3)
Suidae
Tetraconodontinae
Nyanzachoerus kanamensis
Nyanzachoerus jaegeri
Notochoerus euilus
Suinae
Kolopochoerus sp. nov.
Giraffidae
Giraffinae
Giraffa cf. stillei (3)
Giraffa sp. (9)
Sivatheriinae
Sivatherium sp. (4)
Hippopotamidae (15)
Perissodactyla
Equidae (92)
Eurygnathohippus sp.
Rhinocerotidae (8)
Diceros sp.
Ceratotherium sp.
Proboscidea
Gomphotheriidae
Anancinae (2)
Anancus sp.
Elephantidae (13)
Elephas recki brumpti
Loxodonta cf. audorora
cf. Mammuthus sp.
Tubulidentata
Orycteropodidae (5)
Orycteropus sp.
Rodentia
Muridae (4)
Gerbillinae
Tatera sp.
Hystricidae (8)
Hystrix sp.
Thryonomyidae (1)
Thryonomys sp.
Insectivora
Soricidae (1)
Lagomorpha
Leporidae (1)
Uranotheria
Procaviidae (1)
Procavia sp.
AVES
OSTEICHTHYES
Cyprinidae
Barbus sp.
REPTILIA
Crocodilia
Chelonia
Numbers in parentheses are individual specimen counts for each taxon.
and Theropithecus is the most dominant cercopithecid.
These differences could be due largely to differences in
habitat and depositional environment of the two sites
with Laetoli sampling more open habitat. In fact, the
Woranso-Mille faunal assemblage shares more genera
with Kanapoi (Harris and Leakey, 2003). However,
detailed comparison is necessary between the faunal
assemblages from Woranso-Mille, Laetoli, and Kanapoi/
Allia Bay to understand the causes for these differences
and the overall early-middle Pliocene paleobiogeography
of eastern Africa.
The fossiliferous deposits described here are mostly
fluviatile. Preliminary paleoecological interpretations
indicate that the site had a mosaic of habitats, primarily
a riverine gallery forest laterally extending to closed and
open woodland and grassland. This is largely based on
the presence of multiple species of cercopithecids followed by the dominance of animals with closed/open
woodland habitat preferences such as the aepycerotines
and tragelaphines, as well as the presence of taxa such
as alcelaphine bovids that are adapted to more open
grasslands (Kingdon, 1982).
American Journal of Physical Anthropology
410
Y. HAILE-SELASSIE ET AL.
Fig. 3. Pie chart showing the percentage of mammalian taxa collected from Am-Ado (AMA), Aralee Issie (ARI), Mesgid Dora
(MSD), and Makah Mera (MKM). The table on the right shows the number of specimens of individual taxon collected from the four collection areas. Numbers in parentheses indicate number of localities in each collection area. NISP 5 number of individual specimens.
MATERIALS AND METHODS
The Woranso-Mille hominids (Figs. 4 and 5) dated to
between 3.6 and 3.8 Myr are mostly isolated dental
remains, associated upper and lower teeth, maxillary
and mandibular fragments, and few postcranial fragments. The list of hominid specimens described here is
given in Table 1. The new Woranso-Mille hominids were
metrically and morphologically compared with Au. afarensis, Au. anamensis, and Ar. ramidus specimens. The
comparative sample of Au. afarensis used in this analysis includes all published specimens from Hadar, Laetoli,
and the Middle Awash. The Au. anamensis sample
includes all published specimens from Kanapoi, Allia
Bay, and Asa Issie. The Ardipithecus ramidus sample
includes specimens published in White et al. (1994).
Dentognathic measurements of the Woranso-Mille hominids were taken on the originals, which are housed in
the Paleoanthropology Laboratory of the National Museum of Ethiopia. The descriptive methods follow White
et al. (2000) and dental measurements were taken following White (1977) and White and Johanson (1982). Enamel
thickness measurements were taken on naturally fractured
teeth using a digital caliper under a microscope.
Comparative description
MSD-VP-5/16 is a left hemimandible with C/1-P/4
roots and M/1-2 crowns preserved intact (see Fig. 4). It
is similar in corpus size to Au. afarensis specimen A.L.
128-23 (White and Johanson, 1982). Its alveolar margin
in the M/1-2 region is sharp and straight. However, its
molars are larger relative to the corpus size than in A.L.
128-23. The latter specimen represents one of the smallest individuals in the Hadar sample of Au. afarensis particularly in the size of its molars (White and Johanson,
1982; Kimbel et al., 2004). As in Au anamensis (Leakey
et al., 1995) and some Au. afarensis specimens such as
the subabult A.L. 145-35 (White and Johanson, 1982),
the mandible’s greatest anterior breadth occurs at the
canine because of its more lateral positioning relative to
American Journal of Physical Anthropology
the P3. This is the plesiomorphic condition in which the
canine is aligned with the postcanine axis (Ward et al.,
2001; Kimbel et al., 2004). Corpus height measured on
the lateral side decreases substantially from C/1 (31.3
mm) to M/2 (24.7 mm). MSD-VP-5/16 has two mental foramina situated inferior and mesial to P/3. The largest
is positioned at midcorpus and opens anterosuperiorly.
In Au. anamensis and most Au. afarensis mandibles, a
single mental foramen is usually situated below P/3-P/4
and is positioned at, or slightly below midcorpus level
(White and Johanson, 1982; Ward et al., 2001; Kimbel et
al., 2004). MSD-VP-5/16 is similar to Au. afarensis in its
less retreating symphysis but resembles Au. anamensis
in having a shallow fossa superior and posterior to the
mental foramen, and in having a well-developed lingual
subalveolar fossa.
A right maxillary fragment, MSD-VP-1/53, preserves
M1/-M2/, both of which are wider mesially than distally
(see Fig. 4). The root of the zygoma lies above the M1/
(see Fig. 4). The cusps of both molars exhibit exposed
dentine. The poor preservation of this specimen precludes further detailed description particularly of the
maxillary sinus region.
ARI-VP-1/190 and ARI-VP-3/34 are left dc1 and left
dm1, respectively. Dental measurements are given in
Table 3. The dm1 is worn and lacks roots, most likely as
a result of resorption. The canine is a complete crown
and the root is preserved intact. ARI-VP-3/34’s occlusal
morphology is more primitive than known Au. afarensis
dm1s, particularly in the presence of a strong uninterrupted crista obliqua running from the protocone to the
metacone that is observable even though the tooth is
heavily worn. The dm1 of LH 21 is only moderately
worn but its occlusal outline is similar to ARI-VP-3/34
and both specimens have a protuberant mesiobuccal corner (White, 1980). However, the crista obliqua of LH 21
appears to be thinner (White, 1980) and more shallow
than that of ARI-VP-3/34. The mesiodistal to buccolingual ratio is similar in both. The heavy wear of ARI-VP3/34, which is worn down close to the cervicoenamel
junction, is commonly seen in Pan, where this kind of
NEW PLIOCENE HOMINIDS FROM WORANSO-MILLE, ETHIOPIA
411
Fig. 4. Hominid mandible and maxilla from Woranso-Mille: A. occlusal, lateral, and medial views of MSD-VP-5/16, a left mandible with M/1-M/2; B. occlusal, lateral, and medial views of MSD-VP-5/53, left maxillary fragment with M1/-M2/. Arrow indicates
the origin of the zygomatic process of the maxilla.
wear pattern is possibly due to the delayed eruption of
the permanent premolars (Smith, 1994). This tooth is
unknown for Au. anamensis (Ward et al., 2001). However, the Au. anamensis dm1 is considered to be morphologically intermediate between earlier Ar. ramidus and
more recent Au. afarensis (Ward et al., 2001).
The unworn dc1 crown (ARI-VP-1/190) is asymmetrical
when viewed buccally with the apex mesial to the crown
center. It is metrically and morphologically similar to
Au. afarensis specimens such as A.L. 333-35 and A.L.
333-77 (White and Johanson, 1982) but has a longer and
more robust root relative to the crown. Although both
dc1’s of KNM-KP 34725 (Ward et al., 2001) are occlusally
and distally worn, as preserved they appear to be similar
to their counterparts in Au. afarensis.
The associated dentition of ARI-VP-3/80 (see Fig. 5) is
likely a female based on the size of the teeth. It includes
a P/3 with the smallest relative buccolingual dimension
compared to its counterparts in Au. anamensis and Au.
afarensis specimens reported to date (see Fig. 6). The
associated upper and lower molars fall within the metric
and morphological range of both Au. anamensis and Au.
afarensis (see Table 3 for dental measurements). However, the mesiodistal-buccolingual ratio of its P/3 (126)
exceeds the currently documented range for Australopithecus afarensis (100.3 6 12.4 for Laetoli (n 5 5); 88.6 6
9.2 (n 5 21) for Hadar) and Au. anamensis (93.4 6 13.5;
n 5 6). It is on the higher end of the range of Pan troglodytes (119.6 6 8.8; n 5 19). All comparative ratios were
taken from Kimbel et al. (2006). However, it is difficult
to determine the taxonomic significance of this measure
since it is only a single specimen. It is morphologically
intermediate between Au. anamensis from Kanapoi and
Au. afarensis from Laetoli. The larger anterior fovea is
comparable to those observed in Kanapoi specimens such
as KNM-KP 27286 (Ward et al., 2001), whereas metaconid size is intermediate between Kanapoi and Laetoli
conditions. Moreover, as in Au. afarensis P/3s, the mesial
marginal ridge (MMR) is well-developed and high above
the cervicoenamel junction. Some Australopithecus afarensis specimens have relatively large anterior fovea (e.g.,
LH 3) combined with a well developed metaconid (White,
1980). When viewed buccally, the P/3 cusp apex in ARIVP-3/80 is positioned mesially and the long distal crest
of its protoconid descends steeply to form the buccal occlusal rim of the posterior fovea. In this respect it is
more similar to ARA-VP-6/1 (Ar. ramidus; White et al.,
1994, 1995). Australopithecus afarensis specimens such
as A.L. 207-13 have a P/3 with a more mesially positioned protoconid apex, but the metaconid is also well
developed and tall (Johanson et al., 1982). In Au. anamensis P/3s, the protoconid cusp apex is positioned more
centrally than mesially. However, the metaconid is consistently small and low, if not absent entirely. Certain
characters of the P/3 appear to be phylogenetically important. For example, two characters that are considered
useful indicators of directional trend in the evolution of
the P/3 are the mesiodistal/buccolingual ratio (Lockwood
American Journal of Physical Anthropology
412
Y. HAILE-SELASSIE ET AL.
Fig. 5. Associated and isolated hominid teeth from the Woranso-Mille. A. ARI-VP-3/80, occlusal views of RP/3, RP/4, RM/1, RM/
2, LM/2 (top row); LP3/, LM2/, RP4/ (bottom row). B. ARI-VP-3/249, LP/4; occlusal, buccal, mesial, lingual, and distal views. C.
AMA-VP-2/30, RP/4; occlusal, buccal, mesial, lingual, and distal views. D. ARI-VP-3/250, LM/1 or 2; occlusal, lingual, and mesial
views. E. ARI-VP-1/90, RM3/; occlusal, mesial, and distal views. F. ARI-VP-1/190, Rd/c; buccal, distal, and mesial views. G. ARI-VP1/215 LM2/ or 3; occlusal, mesial, and distal views. H. ARI-VP-3/176, RM/2; occlusal, buccal, and lingual views. I. ARI-VP-1/462,
LM/1; occlusal, mesial, and distal views.
et al., 2000; Kimbel et al., 2006) and metaconid size and
height (Suwa, 1990). An absent or small metaconid of
low relief relative to the height of the main cusp is plesiomorphic (Suwa, 1990; Haile-Selassie et al., 2009).
Although the single P/3 from Woranso-Mille (or the single P/3 from Allia Bay) does not permit broader conclusions, the ARI-VP-3/80 P/3 does appear to be intermediate between the more primitive P/3s of Ar. ramidus and
Au. anamensis and the more derived morphs of Au. afarensis; in particular it is intermediate between Au. anamensis specimens such as KNM-KP 27986 and earlier
Au. afarensis specimens from Laetoli such as LH 3.
The three unworn P/4s from the Woranso-Mille exhibit
relatively small anterior foveae positioned much higher
on the crown than the larger posterior foveae. This character state is also seen in Au. anamensis. In Au. afarensis P/4s, the anterior fovea appears to be relatively
larger, possibly as a result of a distal shift of the main
cusps. However, this is a substantially variable trait.
Even so, there might be taxonomically significant information because of a derived trend toward more symmeAmerican Journal of Physical Anthropology
try by positioning the main cusps more distally. In chimpanzees (n 5 20) and gorillas (n 5 20), anterior fovea of
the P/4 is positioned high on the crown relative to the
posterior fovea, the main cusps are positioned more
mesially, and the mesial marginal ridge (MMR) is thin.
In this case, a relatively and absolutely smaller anterior
fovea associated with more mesially positioned main
cusps and thin MMR would be plesiomorphic. This is
also the condition seen in the earliest known hominids
such as Ar. kadabba (Haile-Selassie et al., 2009). However, more unworn Au. anamensis and Au. afarensis
P/4s are necessary to test this hypothesis.
The premolars and molars have generally thick
enamel. Measurements at naturally broken surfaces of
numerous molars and premolars yield nonstandard
enamel thickness ranging from 1.3 to 1.8 mm for premolars and 1.5 to 2.1 mm for molars (see Fig. 7). These
measurements were taken at different naturally fractured (both longitudinally and transversely) cusps of
upper and lower molars. The thicknesses were taken at
the occlusal tip of the dentinoenamel junction. These
413
NEW PLIOCENE HOMINIDS FROM WORANSO-MILLE, ETHIOPIA
TABLE 3. Dental metrics for Woranso-Mille hominids
P3/
Specimen
MD
ARI-VP-1/90
ARI-VP-1/215
ARI-VP-1/484
ARI-VP-3/36
ARI-VP-3/80
ARI-VP-3/176
ARI-VP-3/248
MKM-VP-1/69
MSD-VP-1/53
P4/
BL
MD
MD
M3/
BL
14.2
15.5
11.4
13.1
12.4
15.7
MD
BL
15.0
16.3
13.2
(13.9)a
11.6
11.1
9.1
8.8
13.1
11.4
P/4
BL
13.9
M/1
MD
BL
9.8
(9.5)
11.4
MD
M/2
BL
MD
M/3
BL
MD
BL
14.3
11.9
14.3
11.8
13.7
(12.8)
9.5
7.5
9.8
9.7
10.1
(12.6)
6.3
14.2
(16.4)
12.0
12.6
16.2
14.2
12.2
10.2
12.1
11.9
dm1
dc
ARI-VP-1/190
ARI-VP-3/34
M2/
BL
8.5
8.0
MD
AMA-VP-2/30
ARI-VP-1/28
ARI-VP-1/337
ARI-VP-1/352
ARI-VP-3/35
ARI-VP-3/80
ARI-VP-3/80
ARI-VP-3/176
ARI-VP-3/249
MSD-VP-3/24
MSD-VP-5/16
MD
11.1
P/3
Specimen
M1/
BL
6.6
8.7
10.4
MD, Mesiodistal; BL, buccolingual.
a
Measurements in parentheses are preserved dimensions without correction for interproximal wear.
measurements, albeit not standard, fall within the range
of early Au. afarensis specimens such as MAK-VP-1/12
(White et al., 2000), Au. anamensis (Ward et al., 2001),
and Au. africanus (Schwartz et al., 1998).
Postcanine dental dimensions of the Woranso-Mille
hominids overlap with both Au. anamensis and Au. afarensis, indicating that dental size does not discriminate
these two species (see Fig. 6). Morphologically, however,
the Woranso-Mille dental specimens share a number of
dental characters with Au. anamensis (Ward et al., 2001)
and Au. afarensis from Laetoli (White, 1977, 1980,
1985). For example, the molars show substantial lingual
(uppers) and buccal (lowers) flare, and the mesial half of
the upper first molar crown is much wider than the distal half. In the younger Au. afarensis material from
Hadar, the mesial and distal buccolingual dimensions
are subequal (Johanson et al., 1982), or sometimes wider
distally (A.L. 200-1, for example). As in Au. anamensis
from both Allia Bay and Kanapoi (Leakey et al., 1995),
the size and morphology of the M1 and M2 from Woranso-Mille do not differ significantly.
Variation in early Australopithecus
The earliest representatives of Australopithecus are
assigned to Au. anamensis based on the fossil record
from Kanapoi/Allia Bay (Kenya) and Asa Issie (Middle
Awash, Ethiopia). These are dated to between 3.9 and
4.2 Myr. Its putative descendant, Au. afarensis, is wide
spread (Ethiopia, Kenya, Tanzania, and possibly Chad)
and is dated to between 3.6 and 2.9 Myr. Metric and
morphological evaluations of the combined early Australopithecus sample show that the Hadar material of Au.
afarensis is more derived than the earlier Au. afarensis
material from Laetoli (White, 1985; Suwa, 1990; Leakey
et al., 1995; Lockwood et al., 2000; Ward et al., 2001).
However, the observed metric and morphological differences did not warrant separation of the two samples at
the species level, because they lie within the ranges
observed in living taxa (White, 1977; Kimbel and White,
1988; Lockwood et al., 1996).
Lockwood et al. (2000) argued that the discovery of
additional Au. afarensis specimens from Hadar increased
the mandibular corpus size variation as far as exceeding
that seen in extant African apes. On the other hand,
even with the post-1990 Hadar Au. afarensis sample
included, the dental size variation of Au. afarensis
remained the same as the range of variation observed
from the 1970s Hadar Au. afarensis collection (Kimbel et
al., 2004). What is more important besides the documented size variations is that the older Laetoli sample of
Au. afarensis shares some dentognathic characters with
the more primitive Au. anamensis from Kanapoi and
Allia Bay (Leakey et al., 1995). Despite the amount of
size variation seen in the combined Hadar-Laetoli Au.
afarensis sample, the current consensus is that the Laetoli hominids represent a morphologically and temporally intermediate population between Au. anamensis
and Au. afarensis from Hadar (Kimbel et al., 2004,
2006). The large amount of intraspecific variation
between the Hadar and Laetoli Au. afarensis is likely to
be due to the temporal difference between the two distinct site samples.
American Journal of Physical Anthropology
414
Y. HAILE-SELASSIE ET AL.
Fig. 6. Boxplots showing buccolingual and mesiodistal dimensions of permanent dentition of Au. anamensis, Au. afarensis, and
the new hominids from Woranso-Mille. Dental metrics for Au. anamensis from Kanapoi and Allia Bay (Kenya) were taken from
Ward et al. (2001). Measurements for Au. anamensis from Asa Issie and Aramis (Middle Awash, Ethiopia) were taken on the original specimens by G. Suwa and T. White. Dental metrics for Au. afarensis were taken from Johanson and White (1982; Hadar),
Kimbel et al. (2004; Hadar), White (1977, 1979; Laetoli), and White et al. (2000; Maka). Measurements of the Woranso-Mille
hominids were taken from the original specimens. Numbers above each boxplot indicate sample size. All measurements are in mm.
Taxonomic status of the Woranso-Mille hominids
To assess the taxonomic status of the Woranso-Mille
hominids, it is necessary to identify the main characters
that distinguish Au. anamensis from Au. afarensis.
Based on dental, maxillary, and mandibular morphology,
the Woranso-Mille hominids share a number of characters with Au. anamensis from Kanapoi/Allia Bay (Ward
et al., 2001) and Au. afarensis from Laetoli (White, 1977,
1980). As in Au. anamensis, the Woranso-Mille hominids
display a strong buccal flare on their lower molars, a lingual flare on their upper molars, and a more primitive
P/3 with less developed metaconid and large anterior
fovea. On the other hand, the significantly longer mesiodistal dimension of the P/3 is a feature known to be present in Au. afarensis P/3s from Laetoli (White, 1977,
1980). The mandible from Woranso-Mille combines a
derived Au. afarensis-like, less retreating mandibular
symphysis, with an Au. anamensis-like corpus that
American Journal of Physical Anthropology
includes a lingual subalveolar groove and a canine that
is aligned with the postcanine axis. The Woranso-Mille
hominids lack some of the derived features of the Au.
afarensis dentition (e.g., well-developed metaconid on
the P/3, more vertical crown faces on the molars) and
instead retain the more primitive Au. anamensis condition (Leakey et al., 1995, 1998; Ward et al., 1999, 2001).
Assignment of the Woranso-Mille material to Au. afarensis appears to be reasonable given the shared derived
dental and mandibular characters. Moreover, despite being
slightly more plesiomorphic and older, the new evidence
from Woranso-Mille is not significantly different from the
Laetoli hypodigm of Au. afarensis. On the other hand, the
Woranso-Mille hominids share more individual dental
characters with Au. anamensis than with Au. afarensis.
However, the currently available hominid material
from the Woranso-Mille does not warrant unequivocal
assignment to Au. anamensis. The few claimed autapomorphic features of Au. anamensis mandibles are not
NEW PLIOCENE HOMINIDS FROM WORANSO-MILLE, ETHIOPIA
415
Fig. 7. Naturally fractured teeth showing enamel thickness: A. ARI-VP-1/337; B. ARI-VP-3/250; C. ARI-VP-3/80.
documented in the Woranso-Mille hominids. In this comparative context the major taxonomic problem would be
where to draw the line between Au. anamensis and Au.
afarensis.
The null hypothesis is that Au. anamensis is ancestral
to Au. afarensis and the Woranso-Mille hominids represent a temporally intermediate population between the
Allia Bay and Laetoli hominids. The Laetoli hominids
were broadly dated to between 3.59 and 3.77 Myr
(Leakey et al., 1976; White, 1980) but generally believed
to be about 3.5–3.6 Myr based on the stratigraphic provenience of the hominid specimens (Leakey, 1987). However, recent 40Ar/39Ar dating of the sequence indicates
that the Australopithecus afarensis specimens from the
Upper Laetolil Beds (ranging between Tuffs 1 and 2 to
above Tuff 8) are constrained to 3.85–3.63 Myr (Deino,
in review). Most of the diagnostic Au. afarensis specimens, including the holotype LH 4, are surface discoveries from above, or less than 2-m below, Tuff 7 (see
Table 5.1 in Leakey, 1987), which has an interpolated
age of 3.66 Myr (Deino, in review). The Woranso-Mille
hominids from localities ARI-VP-3 and MSD-VP-5 are
more tightly dated to between 3.72 and 3.76 Myr (Deino
et al., in review), and appear to be more primitive in
some dental characters than the Laetoli hominids higher
in the section. This is what would be expected in a single
evolving lineage, particularly with the temporal placement of the Woranso-Mille hominids. It is difficult, at
least on the basis of the present evidence from the Woranso-Mille, to unequivocally assign hominid fossils from
the time interval between 3.6 and 3.9 Myr to either Au.
afarensis or Au. anamensis.
American Journal of Physical Anthropology
416
Y. HAILE-SELASSIE ET AL.
DISCUSSION
Early hominid systematics is currently one of the most
debated issues in paleoanthropology. The relationships
among the earliest hominids, Sahelanthropus tchadensis,
Orrorin tugenensis, and Ar. kadabba are currently unresolved. Some researchers have suggested that they represent different genera and species; others suggest they
could all belong to a single genus (Haile-Selassie et al.,
2004, 2009). The 4.4 Myr Ar. ramidus from the Middle
Awash (White et al., 1994, 1995; WoldeGabriel et al.,
1994), could very well be the anagenetic predecessor of Au.
anamensis and Au. afarensis although other possibilities
cannot be ruled out (White et al., 2006). However, new evidence from the Middle Awash shows that although the Asa
Issie Au. anamensis material shows temporal and morphological intermediacy between Ar. ramidus and Au. afarensis, it also suggests a ‘‘rapid replacement of Ardipithecus
by Australopithecus . . ., involving either replacement or
accelerated phyletic evolution’’ (White et al., 2006, p 883).
The hypothesis of ancestor–descendant relationship
between Au. anamensis and Au. afarensis has been
assessed through morphological and cladistic analysis of
dental and cranial characters of four temporally successive samples representing the two species (Kimbel et al.,
2006). Results of this analysis revealed temporal and
morphological concordance in support of the hypothesis
that the two species sample a single evolving lineage
(Kimbel et al., 2006). However, the analysis suffered
from an absence of fossil data from the time period
between 3.6 and 3.9 Myr (Kimbel et al., 2006). The Woranso-Mille hominids partially fill the fossil record from
the time in question.
The Woranso-Mille hominids are significant for
understanding the evolutionary history of early Australopithecus, particularly due to critical placement
within a previously poorly known time period, 3.5 and
3.8 Myr. They are of paramount importance in testing
hypotheses about the ancestor–descendant relationship
between Au. anamensis and Au. afarensis. The Woranso-Mille hominids shed some light on whether Au.
anamensis and Au. afarensis are two distinct species,
or parts of a single evolving lineage undergoing morphological change through time. Dentally they are
more similar to Au. anamensis from Allia Bay than to
Au. afarensis from Laetoli. However, they also share
some derived characters with Au. afarensis from Hadar
and Laetoli. Based on the currently available evidence,
the Woranso-Mille hominids are temporally and morphologically intermediate between the more primitive
Au. anamensis from Allia Bay and the slightly derived
Au. afarensis sample from Laetoli (Ward et al., 2001;
Kimbel et al., 2006). They appear to potentially represent a transitional population within an anagenetically
evolving Au. anamensis-Au. afarensis chronospecies
(White et al., 2006; Kimbel et al., 2006) providing further support to the well-established hypothesis of
ancestor–descendant relationship between the two species. To test this and other alternative hypotheses rigorously, and elucidate the evolutionary history of early
Australopithecus, more complete fossil specimens are
needed from the critical time period between 3.6 and
3.8 Myr. However, what appears to be evident with
the discovery of new fossils spanning the 4- to 3.5-Myr
interval is that morphological differences between Au.
anamensis and Au. afarensis do not warrant a species
level distinction.
American Journal of Physical Anthropology
In conclusion, at least based on the currently available
but limited evidence from the Woranso-Mille, (for example, premolar crown morphology), Au. afarensis and Au.
anamensis do not appear to represent distinct taxa.
Unless further fossil discoveries falsify this observation,
the Au. anamensis-Au.afarensis lineage, which is further
confirmed by the Woranso-Mille hominids, appears to be
one of the best examples of anagenetic evolution in the
hominid fossil record.
ACKNOWLEDGMENTS
The authors thank the Authority for Research and
Conservation of Cultural Heritage and the National Museum of Ethiopia of the Ministry of Culture and Tourism
for field and laboratory permissions and facilities. They
also thank the Afar Regional Government, its local
administrative units, and the Afar people of Mille District, for facilitating and directly participating in their
research endeavors. They thank the Cleveland Museum
of Natural History, Case Western Reserve University,
and Berkeley Geochronology Center for access to comparative collections and laboratory use. They thank A.
Ademassu, H. Ahmed, W. Amerga, J. Angelini, A. Asfaw,
B. Asfaw, E. Assefa, E. Benson, C. Mesfin, A. Elema,
M.A. Haydera, L.J. Hlusko, A. Kassu, K. Kayranto, C.O.
Lovejoy, M. Mekonen, S. Melillo, R. Schulze, A. Shiferaw,
D. Su, G. Suwa, M. Umer, C. Ward, T. White, H. Wogris,
and many others for fieldwork, laboratory work, discussion, and access to casts of comparative material. M.
Asnake, S. Frost, D. Geraads, and L. Werdelin assisted
in faunal identifications. They thank D. Su and S.
Melillo for assistance with figures and E. Russell for
photography. They also thank B. Asfaw, Y. Beyene, T.
White, and G. WoldeGabriel of the Middle Awash project
for advice and logistical support. Finally, the comments
of two anonymous reviewers significantly improved the
clarity of this manuscript.
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central, taxonomy, woranso, mill, ethiopia, afar, australopithecus, new, early, fossil, hominis
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