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Revisiting the Developmental Stage and Age-at-Death of the Mrs. Ples Э Sts 5 and Sts 14 Specimens from Sterkfontein South AfricaDo They Belong to the Same Individual

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THE ANATOMICAL RECORD 291:1707–1722 (2008)
Revisiting the Developmental Stage and
Age-at-Death of the ‘‘Mrs. Ples’’ (Sts 5)
and Sts 14 Specimens from Sterkfontein
(South Africa): Do They Belong to the
Same Individual?
ALEJANDRO BONMATÍ,1,2* JUAN-LUIS ARSUAGA,1,2 AND CARLOS LORENZO1,3
1
Centro de Investigación (UCM-ISCIII) de Evolución y Comportamiento Humanos,
c/Sinesio Delgado 4, 28029 Madrid, Spain
2
Dpto. de Paleontologı́a, Facultad de Ciencias Geológicas, Universidad Complutense
de Madrid, Ciudad Universitaria, 28040 Madrid, Spain
3
Institut Català de Paleoecologia Humana i Evolució Social, Área de Prehistoria,
Facultat de Lletres, Universitat Rovira i Virgili, Pl Imperial Tarraco 1, 43005 Tarragona, Spain
ABSTRACT
During the 1947 fieldwork season, Member 4 (2-3 My) of the South
African Sterkfontein site yielded two important Australopithecus africanus fossils: a cranium popularly nicknamed ‘‘Mrs. Ples" (Sts 5), and a partial skeleton (Sts 14). Previous reports have proposed that Sts 5 was a
nonfully grown adolescent individual (Thackeray et al., S Afr J Sci
2002a;98:21–22), and that Sts 14 was a sub-adult specimen (according to
various signs of immaturity in the skeleton) (Berge and Gommery, C R
Acad Sci Paris, Sciences de la terre et des planètes 1999;329:227–232;
Häusler and Berger, J Hum Evol, 2001;40:411–417; Thackeray et al., S
Afr J Sci, 2002b;98:211–212). It was subsequently proposed that these fossils actually belonged to the same individual (Thackeray et al., S Afr J
Sci, 2002b;98:211–212), a proposition supported by their spatial positions
within the site. The present work attempts to revise these different assertions. The results obtained: (i) show that the Sts 5 fossil represents a
fully grown adult cranium; (ii) provide new evidence of immaturity in the
Sts 14 skeletal elements (sustaining the proposed young adult age of this
specimen), and (iii) suggest that although the revised ages-at-death for
these fossils are partially compatible, there is no evidence to support the
idea that they represent a single individual. Finally, the encephalization
quotient associated with a hypothetical union of Sts 5 and Sts 14 (calculated using data from both specimens) lies between the upper and lower
limits of the currently estimated range for this species and H. habilis,
respectively. Anat Rec, 291:1707–1722, 2008. Ó 2008 Wiley-Liss, Inc.
Key words: Sts 5; Sts 14; Australopithecus africanus; development; age-at-death; Sterkfontein
*Correspondence to: Alejandro Bonmatı́ Lasso, Centro UCMISCIII de Evolución y Comportamiento Humanos, c/ Sinesio
Delgado 4, Pabellón 14, 28029 Madrid, Spain. Fax: 134918222855. E-mail: abonmati@isciii.es.
Grant sponsor: Spanish Ministry of Education and Science;
Grant number: CGL2006-13532-C03-02 and 01; Grant sponsor:
Duques de Soria Foundation/Atapuerca Foundation.
Ó 2008 WILEY-LISS, INC.
Received 26 December 2008; Accepted 14 July 2008
DOI 10.1002/ar.20795
Published online 24 October 2008 in Wiley InterScience (www.
interscience.wiley.com).
1708
BONMATÍ ET AL.
Fig. 1. (a) Location of the Sterkfontein site (modified from Partridge et al., 1999) where the (b) Sts 5
cranium and (c) Sts 14 partial skeleton were discovered. Scale bar 5 2 cm.
INTRODUCTION
The Sterkfontein site lies in northeastern South
Africa, 10 km NNW of Krugersdorp in the Gauteng province (Fig. 1a). Located within a complex endokarstic system formed by the dissolution of Precambrian dolomite
limestone along bedding planes and vertical joints via
the action of weakly acidic groundwater (Kuman and
Clarke, 2000, p. 829), the cavities at the site became
filled with calcareous bone-bearing breccia. As a consequence of its land-use history and the repeated collapsefill sequences involved in its genesis, great efforts were
required to ascertain the spatial and temporal sequences
of the site (see Brain, 1957, 1958; Robinson, 1962; Robinson and Manson, 1962; Howell, 1967; Tobias and
Hughes, 1969; Wilkinson, 1973, 1983; Partridge, 1978;
Stiles and Partridge, 1979; Tobias, 1979; Clarke, 1985,
1994; Partridge and Watt, 1991; Kuman and Clarke,
2000). Six lithostratigraphic members were originally
identified (Partridge, 1978; Partridge and Watt, 1991),
numbered 1 to 6 (oldest to youngest). Post Member 6,
the Stw 53 Infill and the Oldowan Infill were described
at a later date (Kuman and Clarke, 2000).
Since 1936 about 500 hominid fossil specimens have
been recovered from this site (Partridge et al., 2003), the
bulk coming from Member 4 (MNI 5 87 individuals;
Pickering et al., 2004). Among the most famous of these
fossils are the cranium Sts 5 (commonly known as ‘‘Mrs.
Ples’’; Fig. 1b) and the partial skeleton Sts 14 (Fig. 1c).
Both specimens were discovered during the 1947 fieldwork season within the same lithostratigraphic unit
(Member 4C). After having originally been attributed to
different species, by the early 1950s the entire Sterkfontein collection (Member 4) was commonly assigned to
Australopithecus africanus (Schwartz and Tattersall,
2005).
Member 4 broadly corresponds to the Type Site but its
geological age has been widely debated. According to
Clark (2002), the stratigraphic position and the archaeological and palaeontological content of Member 4 indicate it to encompass the age interval of 2–3 My. Partridge (2005) proposed an age for the Sts 5 cranium of
between 2.14 and 2.15 My.
According to the original description of Sts 5 by Broom
et al. (1950), the degree of closure of the cranial sutures
STS 5 AND STS 14: AGE-AT-DEATH REVISITED
is in agreement with an individual who was ‘‘no longer
young’’ (Broom et al., 1950, p. 14). However, Thackeray
et al. (2002a) later identified immature traits in the dentition. In particular (thanks to the use of high-quality
CT scan techniques) they indicated that the apical ends
of the roots of the right third molar (RM3) were not fully
closed. Similarly, Sts 14 was also originally considered to
represent an adult (Robinson, 1972), but again, subsequent studies revealed signs of immaturity in the iliac
crest, the ischial tuberosity, the pubic spine, the anterior
superior iliac spine (ASIS), the synchondrosis between
the first and the second sacral vertebrae, and the epiphyseal plate of the sacro-iliac joint (Berge and Gommery, 1999; Häusler and Berger, 2001; Thackeray et al.,
2002b). All these latter studies consider Sts 14 to be a
subadult individual. In particular, Berge and Gommery
(1999) established its owner’s age-at-death to be little
more than 12 years from the ossification stage of the
sacrum. On the basis of their very similar developmental
stages and matching sex attributions, Thackeray et al.
(2002b) and Gommery and Thackeray (2006) proposed
that Sts 5 and Sts 14 might belong to the same individual, a gravitational slump explaining their relative spatial positions within the site.
The aim of this study was to reassess the developmental stage and the biological and chronological ages-atdeath of the Sterkfontein Sts 5 and Sts 14 fossils, using
developmental information for chimpanzees and extant
humans. The results were then used to test whether
these specimens are developmentally compatible, and
therefore might represent a single individual. Finally,
the consistency of the encephalization quotient (EQ) of
this hypothetical individual with that currently estimated for A. africanus was investigated. To date, no
other Australopithecus skeletons recovered have been
well enough preserved to make an accurate assessment
of this key aspect of the biology of extinct hominins.
Development of Australopithecus africanus
Numerous studies have addressed the maturation pattern and growth rate of the extinct species A. africanus,
focusing mainly on the calcification and incremental histological patterns of the dentition and the sequence of
tooth emergence and facial growth, but also on the development of the postcranial skeleton. Although some
authors (Mann, 1975, 1988; Mann et al., 1987, 1990;
Lampl et al., 1993) have supported the idea that the developmental pattern for South African Australopithecus
is essentially human-like, it is currently widely accepted
that the pattern and timing of postnatal maturation in
this species is essentially ape-like (Bromage, 1985, 1986,
1987; Bromage and Dean, 1985; Beynon, 1986; Smith,
1986, 1987, 2004; Conroy and Vannier, 1987, 1988, 1991;
Beynon and Wood, 1987; Dean, 1987a,b, 1988, 2000;
Beynon and Dean, 1988; Berge, 1998; Dean et al., 2001;
Anemone, 2002).
Relative Maturation of the Cranial and
Postcranial Systems
Sts 5 is edentulous; only indirect information on the
length of the roots can be gleaned from the depths of the
alveoli (see later). Therefore, to test the consistency
between Sts 5 cranial and Sts 14 postcranial develop-
1709
ment, skeletal traits were examined. In particular, by
taking into account the preservation of these specimens
and making use of information in the literature, the
slightly earlier closure of the spheno-occipital synchondrosis (SOS) relative to the ossification of the epiphysis of
the iliac crest was confirmed (Stewart, 1934; Zilhman,
2007). However, the time span between these maturational events is quite small and reversals of this
sequence are not uncommon in modern human populations (Stewart, 1934). Therefore, it was considered that
both events take place at roughly the same time, and
that small advances or delays of one relative to the other
are within the normal range of variation. These advances/delays occur because certain sets of bones are more
sensitive to factors affecting skeletal development (see
Tanner, 1962), causing some degree of variability in the
ossification sequence.
MATERIALS AND METHODS
The Sts 5 specimen is a near complete cranium with
some parts of the cranial vault and the dentition missing
(Fig. 1b). Sts 14, on the other hand, is a partial skeleton
composed of six lumbar (Sts 14a, Sts 14b, Sts 14c, Sts
14d, Sts 14e, Sts 14f, caudo-cranially oriented) and nine
thoracic (Sts 14g, Sts 14h, Sts 14i, Sts 14k, Sts 14l, Sts
14m, Sts 14n, Sts 14o, Sts 14p, caudo-cranially oriented)
vertebrae (in different states of preservation), several rib
fragments (MNE 5 9, Pickering et al., 2004), both innominate bones (Sts 14r, Sts 14s; quite complete in their
preservation), a partial sacrum (Sts 14q), and the proximal half of the left femur (Sts 14t) (Robinson, 1972)
(Fig. 1c).
Data were collected from the Sts 5 and Sts 14 original
fossils housed in the Transvaal Museum in Pretoria.
Morphological descriptions, photographs of these specimens, and a high-resolution computer tomography (CT)
(0.2-mm slice thickness, 120 kV, 299 mA, 512 3 512 matrix, 0.152 mm pixel size) scan of Sts 5 (conducted at the
Little Company of Mary Hospital, Pretoria) were made.
A commercial tomography scan of Sts 5 (Weber et al.,
1997a) was also used as a data source.
The comparative sample was composed of a set of CT
scans from nine specimens of Pan troglodytes from
Equatorial Guinea but of unknown age-at-death (all
held at the Estación Biológica de Doñana [EBD], Spain)
(0.5 mm slice thickness, 170–160 kV, 4.0–3.75 mA, 1024
3 1024 matrix, 0.217–0.253–0.289 mm pixel sizes)
(Table 1). The original specimen of the partial adult cranium Sts 71 (A. africanus) from Sterkfontein, held at
the Transvaal Museum in Pretoria, was also examined.
A commercial CT scan of this specimen (Weber et al.,
1997b) was also used as an information source. The comparative sample was completed with information from
the literature on the pattern and schedule of development of the traits studied in chimpanzees and modern
humans. The reason for including extant humans was
the incomplete data regarding the maturation of certain
features in the chimpanzee essays. Tables 2 and 3 show
most of the information used, pertaining to chimpanzees
and humans. The patterns and timing of closure of the
cranial sutures were obtained from Krogman (1930),
Schultz (1940) and Ashley-Montagu (1935, 1937 in Chopra, 1957) for chimpanzees, and from Todd and Lyon
(1924, 1925a,b,c), Krogman (1939), Wood Jones (1946 in
1710
BONMATÍ ET AL.
TABLE 1. Developmental stages of the cranial features of the chimpanzee sample (EBD)
Sample
6877
17140
17957
6842f
15772
6845g
15774
709
708
Dental
emergencea
Tooth
calcificationb
Spheno-occipital
synchondrosisc
Petro-exoccipital
synchondrosisd
Sphenoidal
sinuse
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
–
3
3
3
3
3
3
2
2
3
3
2
3
2
2
3
3
1
3
3
3
2
4
3
EBD, Estación Biológica de Doñana.
Stage 1—M2 erupted and fully functional; M3 close to eruption or recently erupted. Stage 2—M3 erupted but not functional. Stage 3—M3 fully functional.
b
Stage 1—Incomplete M3 root length (funnel-shaped openings). Stage 2—Complete M3 root length (parallel walls); open apical ends. Stage 3—Complete M3 apical closure.
c
Stage 1—No evidence of ossification. Stage 2—Partial ossification. Stage 3—Complete ossification.
d
Stage 1—No evidence of ossification. Stage 2—Partial ossification and/or evidence of osseous bridging on one side. Stage
3—Complete ossification on one side. Stage 4—Complete ossification on both sides.
e
Based on the posterior extension of the sinus in the sagittal plane. Stage 1—Sella turcica. Stage 2—Dorsum sellae. Stage
3—First half of the clivus. Stage 4—Second half of the clivus.
f
Most of the basisphenoid and occipital bone are missing.
g
Part of the occipital bone is missing. The jugular synchodronsis score was assessed with reference only to the left side.
a
Chopra, 1957), Abbie (1950 in Chopra, 1957), Singer
(1953 in Chopra, 1957), Acsádi and Nemeskéri (1970),
Meindl and Lovejoy (1985), Mann et al. (1991), Gruspier
and Mullen (1991) and Key et al. (1994) for humans.
Taking into account the degree of preservation of Sts
5 and Sts 14, the features studied are those of developmental significance. These features were scored in the
chimpanzee comparative sample (for stage definitions
see footnote in Table 1) and for the Sts 5 and Sts 14 fossils. Using the chimpanzee data, a modal pattern was
established for the development of the petro-exoccipital
synchondrosis and the pneumatization of the sphenoidal
sinus relative to the dentition (tooth calcification and
dental emergence) and the SOS. However, the chronological age-of-death of the chimpanzees studied was
unknown; thus, only the relative development of these
features was recorded.
The gathered data allowed the developmental status
of both fossil specimens to be established, followed by
the biological age-at-death of the individual(s) represented. This procedure was also used to attempt an
approximation of the chronological age-at-death. To
show that Sts 5 and Sts 14 belong to a single individual
requires that the corresponding ages-at-death be compatible and that the relative development between the
iliac crest epiphysis of Sts 14 and the SOS of Sts 5 be
consistent within the framework of the chimpanzee and
human patterns (as mentioned earlier).
RESULTS
Chimpanzee Sample
Table 1 reveals a common pattern of relative development between the cranial traits of the chimpanzee sample. Once the dentition is erupted and completely calcified, the SOS appears fused (or about to fuse) (Fig. 2a).
With respect to the sphenoidal sinus, the pneumatization of the greater wings and the area beyond the dor-
sum sellae occurs with the complete fusion of the SOS
and the fully developed dentition (Fig. 2). These statements are in agreement with the pattern described by
some authors for chimpanzees and humans (see references in Tables 2 and 3). Finally, the petro-exoccipital synchondroses show partial or complete ossification on one
side at the time of completion of the dentition and SOS
closure.
Sts 5
Dentition. External inspection of the Sts 5 maxilla
reveals no evidence of dentition (Tables 2 and 3). The
commercial axial CT images (Weber et al., 1997a) show
some rounded and homogeneous structures with a
brighter signal than the surrounding areas in what
appears to be the position of the dental roots within the
maxilla (Fig. 3a). In contrast, the CT scan images of the
teeth of Sts 71 (Weber et al., 1997b) show one lingual
and two oral roots in the maxillary molar series to have
rounded and structured morphologies, that is, a bright
external layer (cementum), a darker internal area (dentine), and a central white area (root canal) resembling
the cementum in shade (Fig. 3b). In comparison with
the tomography of the roots of Sts 71, the apparent tooth
cavities of Sts 5 have an irregular outline and are poorly
structured internally (Fig. 3). The formations seen in
Sts 5 are therefore probably casts of the alveolar sockets,
formed as a result of mineralization and/or sedimentary
filling after the complete loss of the dentition. Sts 5 was
therefore concluded to be edentulous (contrasting with
Thackeray et al., 2002a)..
Alveoli are perfect natural casts of the root of each
tooth, and their size and shape change as the roots
grow. In the sagittal tomogram of Sts 5, the suggested
natural casts of all the alveoli cut through most of the
alveolar bone of the maxilla (Fig. 4a). Further, when
compared to Sts 71, these alveoli show similar develop-
Stage 2e
Sphenoidal sinus
Unfused
Partially fused
Sacrum: sacro-iliac
joint epiphysis
Ridge and furrow
structure
attenuation. Welllimited borders
Completely fused
Sacrum: S1-S2 annular
epiphysis
Sacrum: S1-S2 costal
elements
Pubic symphysis
Ribs: articular region
epiphyses
Iliac crest epiphysis
Ranging from the
beginning of union to
almost complete
union
Almost completely
fused
Partially fused
Stage 3d
Petro-exoccipital synch.
Vertebrae: annular
rings
Stage 3c
Spheno-occipital synch.
(SOS)
Developmental stage
Stage 2b
Feature
Tooth calcification
Biological age
Chronological age
–
–
–
14.5 years (Zilhman, 2007).
10.1 6 0.84 years (Anemone,
2002).
Young adult or older. These elements fuse
before the sacral vertebral bodies (Schutlz,
1940).
No precise age can be obtained. It may
remain unfused in fully grown individuals
(Schutlz, 1940).
–
Between 13 and 35 years, since the
sacrum fuses between these ages
(Kerley, 1966).
Young adult, with slight dental attrition
From 11 to 17 years (Schutlz, 1940;
(Schultz, 1940; Schultz, 1942 in Curgy,
Schultz, 1942 in Curgy, 1965;
1965; Zilhman, 2007).
Kerley, 1966; Zilhman, 2007).
No correlation with Pan was seen due to progressive symphyseal ankylosis (Schultz,
1940; Schultz, 1942 in Curgy, 1965; Kerley, 1966).
Early adulthood or later. Root completion
occurs shortly after M3 eruption (Anemone
et al., 1991, 1996; Anemone and Watts,
1992; Kuykendall 1996, 2002; Anemone,
2002).
From the attainment of adulthood, that is,
just before the eruption of all teeth
(Krogman, 1930), to young adult, that is,
early after the eruption of all teeth and
around the time of first reproduction
(Schultz, 1940; Zilhman, 2007) (Table 1),
or older.
Adult, showing completion of the permanent
dentition and closed SOS (Table 1).
Adult, with the completion of the permanent
dentition and closed SOS (Table 1).
No precise age can be obtained. Union
occurs in adults, that is, after the
completion of the permanent dentition
(Schultz, 1940).
–
All data are for pooled sex samples. In the blank cells no current data are available. The value after the (6) symbol refers to the standard deviation.
(b–e) Feature stages defined in Table 1 (see footnote).
Sts 14
skeleton
Sts 5
cranium
TABLE 2. Chimpanzee biological and chronological ages-at-death for the developmental stage of the features studied in Sts 5 and Sts 14
STS 5 AND STS 14: AGE-AT-DEATH REVISITED
1711
Sts 14
skeleton
Sts 5
cranium
Partially fused
Ridge and furrow
structure
attenuation. Welllimited borders
Iliac crest
epiphysis
Pubic
symphysis
Ribs: articular
region
epiphyses
Ranging from the
beginning of union to
the achievement of
almost complete
union
Almost completely
fused
Stage 2e
Sphenoidal
sinus
Vertebrae:
annular
epiphyses
Stage 3d
Stage 3c
b
Stage 2
Developmental stage
Petroexoccipital
synch.
Tooth
calcification
Sphenooccipital
synch. (SOS)
Feature
Young to fully adult (Todd, 1920,
1921a,b,c; Meindl et al., 1985).
From the adolescent period to the
onset of full adulthood (see
adjoining chronological ages).
Just older than the latter stages of
adolescence, according to first rib
ossification (Kunos et al., 1999).
No precise age can be obtained; no
data on unilateral fusion are
available. Bilateral fusion ranges
from late adolescence-young
adulthood through to fully adult
individuals (Maat and Mastwijk,
1995; Hershkovitz et al., 1997).
Juvenile or older. Most probably
fully adult due to nondetectable
SOS (Scuderi et al., 1993; Spaeth
and Krugelstein, 1996; Weiglein,
1999; Yonetsu et al., 2000;
Barghouth et al., 2002).
From late adolescence to young
adulthood (Albert and Maples,
1995).
Adolescence to early adulthood or
older (Scheuer and Black, 2000).
From the end of the adolescent
growth period, that is, before, but
more commonly after, M3
eruption (Stewart, 1934; Melsen,
1969, in Scheuer and Black,
2000), or later.
Biological age
From above 17 to around 25 years according to first rib
ossification: fusion occurs from 14 to 17–19 years. The
rounded edges and lenticular profile of the facet might be
expected until 21 years. The dense surface with smooth
irregularities suggests 20–25 years (Kunos et al., 1999).
Remaining ribs: poorly documented, the onset of fusion to
the tubercle suggests an age 18 years (Fawcett, 1911;
Stevenson, 1924, in Scheuer and Black, 2000).
From 15 to 26 years (Galstaun, 1937, Lurie et al., 1943,
Mckern and Stewart, 1957, Jit and Singh, 1971, Birkner,
1978, Webb and Suchey, 1985, in Scheuer and Black,
2000; Veschi and Facchini, 2002; Coqueugniot and
Weaver, 2007), but most probably in the 19–22 years
range (80% of the population would be expected to show
this from data in Veschi and Facchini, 2002).
Around mid-late 20s: moderate to slight billowing and
active rampart formation suggests 24–37 years.
Appearance of distinct lower extremity suggests 25 to
about 30 years. Reduced billowing together with full
lower extremity definition suggests an age older than 29
(Meindl et al., 1985) to 25–30 years (Phase IV/V; Todd
1920, 1921a,b,c)
From 17 (youngest age of early Stage 2; Albert and Maples,
1995) to 27 years (oldest age of late Stage 2; Albert and
Maples, 1995).
From 15 years (Scuderi et al., 1993; Spaeth and
Krugelstein, 1996) to the end of the third decade of life
(this occurs in 93% of the population by this time;
Yonetsu et al., 2000)
From 13 to 25 years, as determined by direct inspection or
from CT scans studies (Hrdlička, 1920, in Chopra 1957;
Madeline and Elster, 1995; Sahni et al., 1998; Veschi and
Facchini, 2002; Coqueugniot and Weaver, 2007). Probably
at the end of the second decade or in the first half of the
third decade, when high percentages of the population
_ can,
would normally show full closure (Krogman and Is
1986; Sahni et al., 1998; Veschi and Facchini, 2002).
No precise age can be obtained; no data on unilateral fusion
are available. Bilateral fusion occurs from mostly above
20 years of age (this occurs in 90%–93% of the population
by this time; Hershkovitz et al., 1997), or 22–36 years
according to Maat and Mastwijk (1995).
17.5 years (Smith, 1991).
Chronological age
TABLE 3. Modern human biological and chronological ages-at-death for the developmental stage of the features studied in Sts 5 and Sts 14
1712
BONMATÍ ET AL.
SOS. The basisphenoidal region shows no sclerotic
remnants of this synchondrosis in either the CT scans or
on the external surface of the fossil, indicating that its
full closure was far from being recent (in agreement
with Broom et al., 1950) (Fig. 5a).
Sphenoidal air sinus.
The sphenoidal aeration
extends to the border between the dorsum sellae and the
clivus, the sphenoidal wings and the anterior pterygoid
processes. It is partially filled with what are probably
calcite crystals, since the brain case is lined with this
material (Broom et al., 1950). The pattern of pneumatization of this sinus in humans and chimpanzees and the
absence of traces of the SOS in Sts 5, suggest that the
sinus of Sts 5 had reached this synchondrosis and
exceeded it dorsally (Fig. 5a,b).
All data for pooled sex samples. The value after the (6) symbol refers to the standard deviation.
(b–e) Feature stages defined in Table 1 footnote.
Juvenile to full adulthood (see
adjoining chronological ages).
Partially fused
Unfused
1713
ment relative to the maxillary sinus (Fig. 4b). Although
the alveoli of Sts 5 could have been broken, allowing the
loss of the teeth, their deep ends are not likely to have
been affected. This would imply that the roots of the
third molars were completely developed.
Likely under 27 years (Mckern and Stewart, 1957, in
Scheuer and Black, 2000; Coqueugniot and Weaver,
2007).
From 16 to 30 years (Johnston, 1961; Szilvássy 1988 in
Berge and Gommery, 1999; Berge and Gommery, 1999;
Rogers and Cleaves, 1935, Bollow et al., 1997, in Scheuer
and Black, 2000).
19 years (first occurrence of complete fusion; Coqueugniot
and Weaver, 2007).
Late adolescence to full adulthood
or later (see adjoining
chronological ages).
Juvenile to young adult (see
adjoining chronological ages).
Completely fused
Sacrum: S1-S2
costal
elements
Sacrum: S1-S2
annular
epiphysis
Sacrum: sacroiliac joint
epiphysis
Chronological age
Biological age
Developmental stage
Feature
TABLE 3. Modern human biological and chronological ages-at-death for the developmental stage of the features
studied in Sts 5 and Sts 14 (continued)
STS 5 AND STS 14: AGE-AT-DEATH REVISITED
Petro-exoccipital synchondrosis.
This stage
was only assessed on the left side, where the occipital
and temporal bones are continuous, signifying at least
unilateral complete fusion (Fig. 5c).
Cranial sutures. The dynamite blast that uncovered Sts 5 left portions of bone adhered to the calcified
matrix of the breccia, making it difficult to observe most
of the sutures (Broom et al., 1950; Thackeray, 1997; Prat
and Thackeray, 2001). Most of the facial and palatal
group of sutures are unidentifiable to the naked eye.
However, the right side of the fronto-zygomatic—the left
side is affected by a fracture that prevents observation
of the suture—and the naso-premaxillary sutures are
closed although still recognizable on the ectocranial surface (in agreement with Broom et al., 1950). In the cranial vault, only a small ectocranial portion of the sagittal
suture within the bregma-lambda region is visible; it is
closed (in agreement with Broom et al. 1950; Thackeray,
1997; Prat and Thackeray, 2001). The parieto-squamosal, the spheno-temporal, and the spheno-frontal
sutures (belonging to the circum-meatal group of
sutures) are fused but remain noticeable ectocranially
on both sides (in agreement with Broom et al., 1950).
Finally, in basal view, most of the occipito-mastoid
suture is somewhat perceptible endocranially on the
right side, and identifiable but closed ectocranially on
both sides (in agreement with Broom et al., 1950),
whereas in the splanchnocranium, the anterior and posterior median palatines and the spheno-palatine sutures
are closed but still recognizable.
Developmental stage and age-at-death of Sts 5.
The lack of signs of recent closure of the SOS and the
high degree of obliteration of the cranial sutures, especially those of the vault, are indicative that Sts 5 represents a fully grown cranium. Irrespective of whether the
chimpanzee or human pattern is used as a model for Sts
5 (Tables 2 and 3), the state of these features signify
that this cranium was part of an adult individual with a
fully developed dentition. Moreover, the aerated portions
1714
BONMATÍ ET AL.
Fig. 2. Basicranium of Pan troglodytes (EBD 17957). (a) Sagittal and (b) transversal CT-scans. BO,
basiocciput; BS, basisphenoid; CL, clivus; DS, dorsum sellae; FM, foramen magnum; MF, middle fossa;
OP, olivary process; PET, petrous bone; SO, supraocciput; SOS, spheno-occipital synchondrosis; SS,
sphenoidal sinus; ST, sella turcica. Scale bar 5 2 cm.
of the sphenoidal sinus, the fusion status of the petroexoccipital synchondrosis, and the probable completion
of the M3 roots, are all consistent with this statement.
Thus, the Pan and modern human schedules of maturation support ages-at-death of 14.5 years or older, and
older than around 20 years, respectively (Tables 2 and 3).
Sts 14
Vertebrae.
The annular rings of the spine of Sts 14
show a variety of stages of ossification (Fig. 6a) (Tables
2 and 3). Following the scoring system of Albert and
Maples (1995), these epiphyses appear to range from the
early (beginning of union; Sts 14b, Sts 14h) to late (progressing union; Sts 14d, Sts 14e, Sts 14f, Sts 14g, Sts
14i, Sts 14k, Sts 14l, Sts 14m, Sts 14n, Sts 14o, Sts 14q)
phases of Stage 1, through to the early (almost complete
union; Sts 14a, Sts 14c) phase of Stage 2.
Ribs. Those ribs with a preserved tubercle region
(none of which were identified as a first rib) show the
articular epiphyseal plate with nearly complete fusion,
though the suture is still identifiable (Fig. 6b). In addition, the profile of the tubercle is no longer elliptical but
distinctively lenticular, and its boundaries are mostly
rounded and slightly raised above the shaft. The surface
texture of the tubercle is dense with smooth depressions
and ridges.
Pelvis. The iliac crest is mostly fused on the left
side (Sts 14r), showing only traces of the suture, while
the right coxal (Sts 14s) bone shows partial loss of
the anterior portion of the epiphysis, probably due to
incomplete ossification (in agreement with Berge and
Gommery, 1999; Häusler and Berger, 2001) (Fig. 7a).
The sacrum shows incomplete fusion of the S1-S2 annular epiphysis. Further, even though the epiphyseal
plate of the left sacro-iliac joint is fragmentary, the
suture with the sacral alae remains discernible (in
agreement with Berge and Gommery, 1999) (Fig. 7b).
The pubic symphysis of Sts 14 appears to have a characteristic ridge and furrow structure on its ventral
STS 5 AND STS 14: AGE-AT-DEATH REVISITED
1715
Fig. 3. Maxilla. Transversal tomograms of (a) Sts 5 (Weber et al.,
1997a) and (b) Sts 71 (Weber et al., 1997b). Circles surrounding teeth
(Sts 71) or alveoli (Sts 5): RPM3, right third premolar; RPM4, right
fourth premolar; RM1, right first molar; RM2, right second molar; RM3,
right third molar; LM1, left first molar; LM2, left second molar; LM3, left
third molar. Scale bar 5 5 cm.
margin, albeit mostly attenuated along the dorsal border. Additionally, its dorsal, superior and inferior margins are well limited by a continuous rim, whereas its
anterior wall shows the beginning of the formation of
the ventral rampart (Fig. 7c).
likely fully grown in terms of height (as shown by the
ossified acetabulum, and the probably-fused long bone
epiphyses) and close to—thought not completely—grown
in terms of body breadth (as shown by the incomplete
iliac crest and sacrum epiphyses) (in agreement with
Berge and Gommery, 1999). Therefore, this fossil assemblage represents part of a young adult probably between
14.5 years to 17 years according to chimpanzee standards, or somewhere in its early mid-20s according to the
modern human schedule of maturation (Tables 2 and 3).
Femur. This lacks most of the greater trochanter
and the most basal part of the lesser trochanter; they
cannot, therefore be used for age diagnosis.
Developmental stage and age-at-death of Sts
14. The several signs of immaturity in the ossification
of the epiphyses of Sts 14 show that this skeleton had
not completed its development. With respect to both the
Pan and Homo sapiens patterns (Tables 2 and 3) these
epiphyses are among the last to complete ossification.
The individual to whom this skeleton belonged was
DISCUSSION
One and the Same Individual?
According to the present results, the biological and
chronological ages-at-death of both specimens are
partially compatible. However, Sts 5 shows no sign of
1716
BONMATÍ ET AL.
Fig. 4. Maxilla. Sagittal tomograms of (a) Sts 5 (Weber et al., 1997a) and (b) Sts 71 (Weber et al.,
1997b). (1) maxillary sinus, (2) alveolar bone, (3) fillings of the alveolar sockets, (4) roots of the maxillary
dentition. Scale bar 5 5 cm.
having recently reached adulthood. Since the SOS of Sts
5 is no longer detectable, its closure does not appear to
have occurred recently before death. Even when considering the intrapopulation variation of chimpanzees and
modern humans, such a degree of the SOS closure in Sts
5 does not seem to be consistent with the still fusing
iliac crest in Sts 14.
Although cranial vault closure may occur over an
extended period of time in extant human populations,
severe obliteration of this vault is common in fully adult
individuals (Acsádi and Nemeskéri, 1970, Meindl and
Lovejoy, 1985; Key et al., 1994). Therefore, against the
human standard, the high degree of vault obliteration
shown by Sts 5 does not suggest a young adult age.
In conclusion, no evidence supporting the idea that
the studied fossils belong to a single individual was
found; in fact, some data clearly suggest they belong to
different individuals.
The EQ
Using previous estimates for the body mass for Sts 14
(27.6 kg by McHenry, 1976 and 34.8 kg by Jungers,
1988) and an endocranial volume for Sts 5 of 485 cm3
(Falk et al., 2000), the method of Ruff et al. (1997) was
used to calculate the brain mass and EQ for a hypothetical association between Sts 5 and Sts 14. This resulted
in an EQ value of 2.9–3.4, depending on the body mass
estimate used. This interval lies between the uppermost
estimates for A. africanus (2.4–3.0 as derived from data
in McHenry and Coffing, 2000) and the lowermost limits
for Homo habilis (3.4–3.8 as derived from data in
STS 5 AND STS 14: AGE-AT-DEATH REVISITED
Fig. 5. Basicranium of Sts 5. (a) Sagittal, (b) transversal (Weber
et al., 1997a) and (c) coronal tomograms of Sts 5. L EXO, left exoccipital portion of the occipital bone; L PETEXO, left petro-exoccipital
1717
synchondrosis (note its complete fusion); PF, post-depositional fracture (note its continuation with the dorsal border of the sphenoidal
sinus). See Fig. 2 for other abbreviations. Scale bar 5 2 cm.
1718
BONMATÍ ET AL.
Fig. 6. Sts 14 trunk. (a) Stages of ossification of the ring epiphyses (arrows) in the Sts 14 spine: beginning of union (Sts 14b), progression of union (Sts 14m), and almost complete union (Sts 14a). (b) Articular
region of one rib with the epiphyseal plate showing traces (arrows) of the suture. Scale bar 5 2 cm.
McHenry and Coffing, 2000). The result for the Sts 5-Sts
14 fossil assemblage is therefore only partially compatible with our current knowledge of the encephalization of
A. africanus. If these fossils do represent a single specimen, the range for the relative brain capacity of this
species would be necessarily increased.
CONCLUSIONS
A thorough re-evaluation of the developmental stage
and age-at-death of the landmark Sts 5 and Sts 14 A.
africanus fossils has been attempted in this work.
Contrary to the conclusions of a previous assessment
(Thackeray et al., 2002a), Sts 5 was found not to belong
to an adolescent specimen but to a fully grown adult
whose estimated chronological age-at-death was 14.5
years or above, or more than around 20 years, according
to the chimpanzee and modern human schedules of development respectively. This conclusion rests upon the
following evidence: the mostly obliterated cranial vault
sutures, the complete closure of the spheno-occipital and
petro-exocccipital synchondroses (as observed on the left
side), the pneumatization of the sphenoidal sinus to the
dorsum sellae, and the adult size of the alveolar sockets
in the maxilla.
Sts 14 shows signs of immaturity in the pelvis, ribs,
and vertebrae. On the basis of data for chimpanzees and
modern humans, the ossification stage of the studied
features in Sts 14 suggests this partial skeleton
belonged to a young adult that died between 14.5 to
around 17 years of age according to chimpanzee standards, or within the first half of its third decade of life
STS 5 AND STS 14: AGE-AT-DEATH REVISITED
1719
Fig. 7. Sts 14 pelvis. (a) Iliac crest. (b) Sacrum. (c) Pubic symphysis. Circles highlighting the stage of
the traits above inspection. Scale bar 5 2 cm.
according to extant human standards. Previous studies
on the pattern of development in A. africanus suggest
that the chronological ages of both Sts 5 and Sts 14 are
best determined using the chimpanzee developmental
pattern.
These results also show the age-at-death of these two
specimens to be partially consistent which one another.
However, no evidence was found to support the idea that
Sts 5 had just attained full growth, nor, therefore, that
Sts 5 is the cranium of the young adult Sts 14 partial
skeleton. Further, the stage of development of some of
the Sts 5 features suggest it unlikely that this be the
skull of a young adult.
Finally, the lower value of the EQ range resulting
from a hypothetical association between Sts 5 and Sts
14 lie at the top end of that currently supposed for A.
africanus. Should future research confirm such an association, the relative brain capacity of this species would
necessarily increase, shortening the distance separating
Homo and Australopithecus.
1720
BONMATÍ ET AL.
ACKNOWLEDGMENTS
The authors thank the staff of the Transvaal Museum
(Pretoria, South Africa), especially Francis Thackeray,
for allowing us to study the original fossils Sts 14, Sts 5,
and Sts 71. They are also indebted to the Estación Biológica de Doñana, Spain, for granting access to its chimpanzee collection, and to the University of Burgos,
Spain, where some of the CT scans were performed.
Their thanks also go to A. Gracia, I. Martı́nez, F. Gracia,
and A. Alcazar de Velasco for their helpful commentaries
and guidance, to E. Poza, R. Quam and E. Santos for
their help, and to the staff at the Centro UCM-ISCIII de
Evolución y Comportamiento Humano.
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