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High occurrence of a basicranial feature in Homo erectusAnatomical description of the preglenoid tubercle.

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THE ANATOMICAL RECORD (PART B: NEW ANAT.) 274B:148 –156, 2003
FEATURE ARTICLE
High Occurrence of a Basicranial Feature in
Homo erectus: Anatomical Description of the
Preglenoid Tubercle
VALERY ZEITOUN*
The degree of differentiation between Western and Eastern Early Middle Pleistocene hominids (Homo erectus) is still
under debate. On the one hand, the two populations are believed by some to belong to two separate taxonomic
categories possessing their own exclusive features. On the other hand, they are considered by others to belong to a
single but ubiquitous global population with regional specificities that are mainly due to variations in the frequency
of certain features. In this context, an additional trait, the preglenoid tubercle (tuberculum anterius fossae
mandibularis), may well shed light on the matter. The tubercle is often present on the anterior part of the fossa
mandibularis at the anterior extent of the joint capsule and articular tubercle (tuber articulare) of fossils usually
assigned to Homo erectus. This study describes the anatomy of the preglenoid tubercle, to indicate its occurrence
and to try to improve its use in taxonomy and phylogeny, although its origin and functional significance have not yet
been clarified. Anat Rec (Part B: New Anat) 274B:148 –156, 2003. © 2003 Wiley-Liss, Inc.
KEY WORDS: Homo erectus; temporomandibular joint; preglenoid tubercle; fossil; bone
INTRODUCTION
There is an ongoing debate in paleoanthropology concerning whether the
Early and Middle Pleistocene Homo
erectus should include specimens
from across Eurasia and Africa or
should be limited to specimens from
eastern Eurasian (Rightmire, 1984;
Dr. Zeitoun has a master degree in geology. He obtained his PhD in Physical
Anthropology in 1996. As a paleoanthropologist his research interest is the reappraisal of the definition of the species
Homo erectus using cladistics. Since
1992, he has been working in Indonesia
in collaboration with T. Jacob and since
1999, he collaborated on a three-dimensional imaging program with J.J. Hublin.
An Assistant Professor for 2 years in the
Chaire de Préhistoire et Paléoanthropologie in College de France, and since
2001, he is a Researcher in CNRS at the
UPR 2147 in Paris. He is the director of
the Thai–French Paleosurvey, looking
for Pleistocene human remains in the
caves of Northern Thailand.
*Correspondence to: Valery Zeitoun, 44
rue de l’Amiral Mouchez, 75014 Paris,
France. Fax: ⴙ33-143-1356-30; E-mail:
zeitoun@ivry.cnrs.fr
DOI 10.1002/ar.b.10028
Published online in Wiley InterScience
(www.interscience.wiley.com).
© 2003 Wiley-Liss, Inc.
Hublin, 1986; Turner and Chamberlain, 1989; Brauer and Mbua, 1992;
Kennedy, 1991). If the latter approach
is taken, the western Old World members of Early and Middle Pleistocene
hominids would be assigned to
“Homo ergaster ” (Andrews, 1984;
Groves, 1989; Wood, 1992; Stringer,
1996). The “two-species” interpretation maintains that the eastern Eurasian members of this taxonomic
group (see Box 1 ) exhibit a suite of
derived characters relating to ancestral African members of the genus
Homo. The traditional one-species interpretation argues principally that
any differences between the remains
attributed to eastern and western populations are due to a combination of
normal, within-species variations.
These variations in turn are due to a
combination of temporal spread and
isolation by distance.
Many of the traits used to separate
Early and Middle Pleistocene hominid
eastern and western populations appear to differ between regions more in
terms of frequency and degree of expression than in terms of presence or
absence. Independently of the strictly
taxonomic issues, the degree of differentiation between western (principally African) and eastern (principally
Southeast Asia) Old World sequences
of Early and Middle Pleistocene archaic Homo raises questions regarding the degree and pattern of hominid
differentiation after the first major
geographical dispersal of hominids in
the Early Pleistocene. Additional paleontological data that might have a
bearing on these issues are therefore
of interest. In this context, an additional morphological feature, the
preglenoid tubercle (tuberculum anterius fossae mandibularis) is described
and discussed with respect to its distribution through hominid evolution.
SPECIMENS EXAMINED
Initially, presence/absence of a tubercle was recorded on the anterior part
of the temporomandibular joint
within the original fossil human specimens from the Ngawi, Ngandong,
Sangiran, and Sambungmachan sites
in Indonesia (Figures 1– 4). For the
basis of further comparisons, observations on the tubercle of Australopithecines and several Homo speci-
FEATURE ARTICLE
THE ANATOMICAL RECORD (PART B: NEW ANAT.) 149
Box 1: Glossary of Terms
Taxon (singular, Taxa plural): A group of organisms that are recognized as
a formal unit at each level of the classification (Simpson, 1961). A group of
organisms that is given a name (Wiley et al., 1991).
Paraphyletic groups: groups for which one or more descendants of an
ancestor are excluded from the group (Wiley et al., 1991).
Hyperostotic traits: traits for which there appears an excess of bone
growth (Hauser and De Stephano, 1989).
Apomorphic character: it is the descendant character by opposition to the
ancestral character a feature is apomorphic (Wiley et al., 1991).
Autapomorphic: a feature is autapomorphic if it is apomorphic and if it is
not shared by other taxa than a single taxon (Darlu and Tassy, 1993).
mens from across the Old World
(Europe, Asia, and Africa) were made
on original specimens and high-quality casts of them. Designations of fossil Homo specimens in this study are
given (Table 1) for the convenience of
common referral and do not reflect
my own taxonomic assignments. Presence/absence of this tubercle was also
recorded on the skull of male and female Pan, Gorilla, and Pongo (Collection of Museum National d’Histoire
Naturelle, Paris and National Museum of Natural History, Leiden; Table 2) and in 1,500 adult modern human individuals sampled globally
(collection of Musée de l’Homme,
Paris; Table 3).
ANATOMICAL DESCRIPTION OF
THE PREGLENOID TUBERCLE
In norma basilaris (Figure 5), a tubercle can be seen on the anterior part of
the fossa mandibularis, at the anterior
limit of the glenoidal fossa of the temporomandibular joint, at the anterior
extent of the joint capsule on the tuber
articulare. The tubercle has a rounded
conic shape with a diameter of approximately 1.1 mm at the bottom
with a height of approximately 0.3
mm. It is proposed here that this tubercle be called the tuberculum anterius fossae mandibularis or preglenoid
tubercle. According to what is shown
in anatomical literature, it should be
the insertion point of the short tendinous bunches that is linked to the superior head of the musculus pterygoideus lateralis before the anterior edge
of the discus articularis. Unfortunately, these short tendinous bunches
are not described by all authors who
make the description or study of this
anatomical area (Paturet, 1951; Rouvière, 1954; Burch, 1970; Griffin et al.,
1975; Schmolke, 1994; Abe et al.,
1997). Nevertheless these bunches are
illustrated and called anterior temporomeniscal fibres of the musculus
pterygoideus lateralis (Figure 6) by
Nicolas et al. (1926).
OCCURRENCE OF THE
PREGLENOID TUBERCLE
The preglenoid tubercle is present in
the main Homo erectus fossils from
Indonesia. It is present in all fossils of
the Ngandong series whenever the anatomical area is preserved. It may be
observed in the Sangiran 2, 10, 17,
Ngawi 1, and Sambungmachan 1
specimens (the anatomical area is absent in Sambungmachan 3). The size
of the tubercle is constant for all the
Asian specimens. It is noticeable that
the preglenoid tubercle is not present
on the temporal bone of Sangiran 26.
In Africa, among specimens assigned to or closely affiliated with
Homo erectus, the preglenoid tubercle
is only present in KNMER 3883. This
is one of the earliest African Homo
erectus specimens (Rightmire, 1990;
Wood, 1991). The tubercle here is
more pronounced than on any Indonesian specimen (approximately five
times larger in volume). Indeed, at the
bottom, the diameter is a little bit less
than two times the diameter of Indonesian specimens when measured on
enlarged picture. The casts of the juvenile specimen KNM-WT 15000
seem to show a little knob at the position of the preglenoid tubercle, but,
as a result of taphonomical disturbance, the preservation of the temporal bone is not good enough to con-
firm this (Prat, in a personal
communication, has the opportunity
to check the original specimen and
assesses that the feature is absent).
The preglenoid tubercle is absent in
Great Apes and very rare in modern
humans. However, the reservation has
to be made that there is no possible
confusion between the large size of
the tuberculum anterius fossae mandibularis in Homo erectus and what
has been observed in 2.7°/°° of modern humans (Table 3), where the volume is evaluated to be approximately
20% of what may be seen in Homo
erectus. Rather than a tubercle, it is an
extremely slight vestigial knob at the
insertion point of the anterior temporomeniscal fibres up to the superior
head of the m. pterygoideus lateralis
(Figure 6).
Unfortunately, the
anatomy of the
temporomandibular joint
capsule and its possible
relationships to other
structures near the joint
are not fully understood.
HYPOTHESES SURROUNDING THE
TUBERCLE
If the simplest anatomical hypothesis
is that the tuberculum anterius fossae
mandibularis is the bony insertion
point of the anterior temporomeniscal
fibers up to the superior head of the
musculus pterygoideus lateralis, the
next questions to ask are what is the
function of these fibers and how do
they work.
Unfortunately, the anatomy of the
temporomandibular joint capsule and
its possible relationships to other
structures near the joint are not fully
understood (Schmolke, 1994). Opinions vary in the literature as to the role
of the ligaments associated with the
temporomandibular joint. In a bibliographic survey of temporomandibular
joint function, Sato et al. (1995) noted
that the functional role of the temporomandibular joint ligaments is
150 THE ANATOMICAL RECORD (PART B: NEW ANAT.)
Figure 1. Right temporal bone of Ngandong 12 in norma basilaris. The anterior part of the
skull is to the right.
poorly known and that additional investigation is needed. The same applies to the exact role of the lateral
pterygoid muscle, especially in controlling horizontal jaw movements
(Murray et al., 2001). Although it is
well known that (1) the joint capsule
has primarily an anterior relationship
with the lateral pterygoid muscle and
(2) the latter muscle has two heads
that exhibit functionally reciprocal activation, the exact insertion point and
function of the superior head of the
lateral pterygoid muscle remains controversial (Piette, 1993; Murray et al.,
2001).
The existence and the functional
role of inconsistent associated structures such as the anterior temporomeniscal fibres are difficult to assess.
However, according to Griffin et al.
(1975), the ligament of the lateral
pterygoid muscle appears to be the
restraining ligament for the joint. Its
fibres both draw the articular disc
from the anterior side and balance it
by supporting it from the posterior
side. The ligament fibres attached to
the articular disc draw the disc from
the posterior side in its course of mandibular closing, thus enabling the articular disc to move smoothly (Abe et
al., 1997). At the same time, the shaping of the articular cavities and the
texture of the joint capsule allow
movements of the articular disc, predominantly in the anteromedial direction (Schmolke, 1994). This latter author specifies that, on the entire medial
side of the joint, the articular disc and
its capsular attachments are in close
contact with the fascia of the musculus
pterygoideus lateralis whereby a small
portion of the superior head of this
muscle inserts directly into the anteromedial part of the discus articularis. It is
not said that there is any insertion on
the tuberculum articulare that could
confirm the nature of the preglenoid tubercle and there is no mention of differences concerning the occurrence or the
strength of the anterior temporomeniscal fibres of the musculus pterygoideus
lateralis as illustrated in Nicolas et al.
(1926). The same is true of the compilation of epigenetic variants of the human skull published by Hauser and De
Stefano (1989), where nothing is said
on this subject.
Because both the superior and the
inferior heads of the musculus pterygoideus lateralis are agreed upon to
influence the position of the articular
disc during temporomandibular joint
movements (Schmolke, 1994), the
proximity of the location of the anterior temporomeniscal fibres should
give some clue on its role. It is also
reported that, apart from viscoelastic
deformation, the other important disc
stabilisation mechanism seems to be
related to attachments of the disc (Piette, 1993). Moreover, particular
structural properties of disc attachment are due to the morphology of the
human temporomandibular joint ligament that is ligamentous without
distinct structure and the sheath-like
FEATURE ARTICLE
structure and other components of
the lateral ligaments store energy and
protect the capsule from stress and
tension during movements of the jaw
(Sato et al., 1996) and could transfer
power until the fibres insertion. Thus,
according to Sato et al. (1996) and
Schmolke (1994), the preglenoid tubercle may be an invariant superior
attachment of the anterior temporomeniscal fibres on the anterior part of
the discus articularis that can play a
role in the anteromedial mechanism
of that area of the temporomandibular joint. As a general and common
property, it can be proposed that the
strength of the preglenoid tubercle is
at least indirectly linked to the activity
of the short tendinous fibres of musculus pterygoideus lateralis.
Three hypotheses may be considered to explain the occurrence of the
preglenoid tubercle: (1) hyperostotic
as a genetic inheritability linked to the
global robustness of Homo erectus as
formerly proposed by Hublin (1989);
(2) hyperostotic as a biomechanical
function due to a specific geometry of
the temporomandibular joint among
Homo erectus; (3) hyperostotic as a
pathological excrescence.
Genetic Inheritability and
Global Robustness
If the preglenoid tubercle is a developed insertion point among others,
some hyperostotic changes should be
observed in the neighbouring cranial
area. This is the case in the Ngandong
series, where the base of the skull dis-
Figure 2. Left temporal bone of Sambungmachan 1 in norma basilaris. The anterior
part of the skull is to the right.
FEATURE ARTICLE
THE ANATOMICAL RECORD (PART B: NEW ANAT.) 151
Figure 3. Left temporal bone of Ngawi 1 in norma basilaris. The anterior part of the skull is
down to the right.
or lesser obliquity of the posterior
slope of the tuberculum articulare; the
proportional length or breadth of the
anterior wall of the fossa mandibularis; the length of a subtemporal
plane.
This list of features is linked with
biomechanical properties of the temporomandibular articulation. Thus, it
seems that, in biomechanical terms,
there is no morphological particularity in Homo erectus that might be
linked to the occurrence of the preglenoid tubercle due to specific biomechanical properties. If there is no
structural pattern that suggests the
presence of the tubercle, the distinction between presence and absence of
preglenoid tubercle should be at another level, as a geographic specificity,
may be in terms of inheritability on
soft tissues. That point could support
the interpretation of Brauer and
Mbua (1992) regarding Homo erectus
vs. Homo ergaster as two different
populations, but it is very difficult to
prove. It can also be due to a particular activity that may intimately be tied
to diets. The answer to that hypothesis
should be found in the environment
as far as it can allow us to distinguish
Indonesian, Chinese, and most of the
African specimens.
Biomechanical Function
A review of different parameters relevant to the anatomy of the temporomandibular articulation found by
Picq (1983) and Zeitoun (1996)
among all the specimens described
Table 1 does not show any correlation
to the presence of a preglenoid tubercle. To sum up these parameters,
there is no relationship between the
occurrence of the tuberculum anterius
fossae mandibularis and the following:
the greater or lesser contribution of
the tympanal plate to the posterior
wall of the fossae mandibularis; the
existence of a big or small postglenoidal process; the occurrence of a postglenoidal process transversally extended or laterally offset; the greater
The tuberculum anterius fossae mandibularis could serve as a strong anterior brake for the temporomandibular
joint (Picq, personal communication).
It is noteworthy, that a lengthening
contraction of the musculus pterigoideus lateralis has the effect of slowly
letting out a rope controlling the condyle as it travels back into the fossa
(Wilkinson, 1988). Because the flatness of the anterior portion of the
temporomandibular joint fails to provide a bony buttress against movements, a stronger muscular insertion
has to be present for compensation. In
this view, the flatness of the temporomandibular joint could be seen as a
lack of anatomical protection for the
anterior part of the tympanal plate
and would need to be compensated by
strong fibres.
Figure 4. Left temporal bone of Sangiran 2 in norma basilaris. The anterior part of the skull
is to the right.
plays hyperostotic clues such as a
well-developed precondylar tubercle,
a pharyngeal tubercle, a peribasic
basal excrescence or postcondyloid
tuberosities (Figure 5 and also
Durband, 2002). After Hublin (1989),
all Homo erectus id est, including African and Chinese have a global robusticity of their skeleton nevertheless
almost only the Indonesian specimens
possess this particularity. In other respects, it should be stressed that almost all fossil and living human and
Great Ape taxa with hyperostotic features do not exhibit any tuberculum
anterius fossae mandibularis.
Pathologic Excrescence
Elyaqtine (in an oral communication)
informs me that a weak preglenoid
tubercle, in association with a patho-
152 THE ANATOMICAL RECORD (PART B: NEW ANAT.)
FEATURE ARTICLE
TABLE 1. Occurrence of the preglenoid tubercle among fossils
Australopithecines
Kenya
Kenya
Kenya
Ethiopia
Ethiopia
South Africa
South Africa
South Africa
South Africa
South Africa
Homo sp.
Ethiopia
Kenya
Homo habilis
Kenya
Homo rudolfensis
Kenya
Homo erectus
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
Indonesia
China
China
Occurrence
Homo ergaster
°KNMER 406
°KNMER 407 a
°KNMER 732
*AL 33345
°OH 5
°Sts 5
°Sts 71
°Stw 505
°SK 47
°SK 48
N
N
N
N
N
N
N
N
N
N
°OH 24
°KNMER 1805
N
N
°KNMER 1813
N
°KNMER 1470
N
°Ngandong 1
°Ngandong 6
°Ngandong 7
°Ngandong 10
°Ngandong 12
°Ngawi 1
°Sambungmachan 1
°Sangiran 2
°Sangiran 4
°Sangiran 10
°Sangiran 17
°Sangiran 26
*Sinathropus III
*Sinathropus XI
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Kenya
Kenya
Kenya
Homo sapiens
Archaic
Tanzania
Tanzania
Kenya
Ethiopia
Zambia
Morocco
India
China
Modern
France
Near East
Near East
Neandertal
Near East
Greece
Italy
Italy
Croatia
Germany
Belgium
Belgium
France
France
France
Uzbekistan
Occurrence
°KNMER 15000
*KNMER 3883
*KNMER 3733
N
Y
N
*LH 18
*Ndutu 1
*ES 11693
*Omo Kibish 2
°Kabwe 1
°Sale
*Narmada
*Dali
N
N
N
N
N
N
N
N
°Malaurie
*Skhul V
*Qafzeh 9
N
N
N
*Amud
*Petralona
*Monte Circeo 1
*Saccopastore 2
*Krapina 3
*Steinheim
*Spy 1
*Spy 2
*La Ferrassie 1
*La Quina H5
*La Chapelle aux Saints
*Teshik Tash
N
N
N
N
N
N
N
N
N
N
N
N
Y, preglenoid tubercle present; N, preglenoid tubercle absent; *, checked on cast; °, checked on original.
logic stretching of the tuberculum articulare, is present on the tardenoisian
Homo sapiens sapiens from Malaurie
that is published by Couture et al.
(1990). In this study, this stretching is
interpreted, by Crubezy, as a recurrent luxation of the mandible. This
clinical argument tends to confirm the
hyperostotic property, because the
luxation triggers high strain on the
musculus pterygoideus lateralis and
also indirectly on the anterior temporomeniscal fibres. Nevertheless, it
is difficult to support the hypothesis
that all the Indonesian specimens
could have the same pathology. It
should also be stressed that almost all
fossil and living human and Great Ape
taxa with hyperostotic features do not
exhibit any tuberculum anterius fossae
mandibularis.
At that step of the survey, no conclusive argument has been able to explain
the evolutionary process of the preglenoid tubercle. The hyperostotic hypothesis as a clue to a particular use of the
temporomandibular joint of Homo
erectus specimens seems to be the best,
although there is no evidence for a link
with any particular bone morphology
as seen in the second hypothesis.
It is nevertheless clear that, insofar as
the anatomical area is well preserved,
no common occurrence of preglenoid
tubercle exists between Homo erectus
and other hominids. The problem remains as to how to define a way of understanding the significance of a feature
seen on a poor fossil specimen sample
TABLE 2. Occurrence of the preglenoid tubercle among great apes
Gorilla gorilla*
Pan troglodytes*
Pongo pygmeus*°
Gorilla
Chimpanzee
n ⫽ 26
(13 females, 13 males)
Occurrence
Orangutan
n ⫽ 23
(12 females, 11 males)
Occurrence
0
0
*Galerie d’Anatomie, Museum National d’Histoire Naturelle, Paris.
°National Museum of Natural History, Leiden.
n ⫽ 52
(32 females, 20 males)
Occurrence
Total
101
0
0
FEATURE ARTICLE
THE ANATOMICAL RECORD (PART B: NEW ANAT.) 153
TABLE 3. Occurrence of the preglenoid tubercle among modern humans, Homo sapiens sapiens
Modern humans
Individuals
Asia (Japan, Indochina, Indonesia, China, Turkey)*
Africa (Morocco, Algeria, West Africa, Central Africa)*
Europe (France, Russia, Romania, Italy, Germany)*
America natives (Argentina, Chili, Peru)*
Australia natives (Aborigines)*
Total
n
n
n
n
n
n
⫽
⫽
⫽
⫽
⫽
⫽
627
472
323
60
18
1500
Occurrence
1 (Japan), 1 (Turkey)
1 (West Africa)
1 (Russia)
0
0
4
*Musee de l’Homme, Museum National d’Histoire Naturelle, Paris.
through a comparison with a numerous
living population where the feature is
absent. Even if the problem of causation arises when differences occur between populations in the frequency of
discrete traits, can the differences be
attributed to biological distance, or
have events played a significance? A
more in-depth study is needed to understand the significance of the feature, although some works have already focused on the phylogenetic interest of
discrete traits (Anthony, 1946; Falk,
1986; Barriel, 1991, 1994; Barriel and
Tassy, 1991; Braga, 1995; Msuya and
Harrisson, 1996). To support the use of
any feature to build phylogeny, one
should be reminded that problems of
inheritability are relevant because discrete traits are based on phenotypic expression, and the question is to determine just how far appearances reflect
their genetic base. However, this point
objectively concerns all features in paleoanthropology.
POTENTIAL SIGNIFICANCE
When dealing with fossils, one can
only make analyses from the original
Figure 5. Base of the skull of Ngandong 6.
database at the level of individual
specimens. One of the main goals of
paleoanthropology is to identify relationships between these specimens,
whatever they represent (populations,
species, or supraspecific taxa). Because phylogeny is supposed to reflect
the history of biological events that
lead to the appearance of taxa (populations, species, or supraspecific taxa),
taxa are suggested by phylogeny (although the hierarchy between “clusters” needs justification, and sometimes arbitrary, and a posteriori, rules
are used to divide specimens into
154 THE ANATOMICAL RECORD (PART B: NEW ANAT.)
FEATURE ARTICLE
Figure 6. Lateral view of the anterior temporomeniscal fibres and superior head of the musculus pterygoideus superior, as illustrated in
Nicolas et al. (1926), modified.
groups). Unfortunately, in many articles in paleoanthropology, an a priori
grouping of the fossils is considered
before any phylogenetic analysis is
carried out. This kind of work can
only propose a pattern of relationships between taxa that are arbitrarily
defined a priori on the basis of subjective criteria, such as their common
occurrence in the same locality or
chronological proximity. This practice is deeply rooted in the belief that
species differ from higher taxa. But
we know that species are in no way
different from higher taxa; at best
they are higher taxa in the process
formation (Løvtrup, 1987), although
they can clearly be paraphyletic, as
pointed out by Nelson (1989), however similar their component individuals may seem.
Referring a fossil individual to a
particular species before any analysis
of its character distribution therefore
generates a serious flaw in the taxonomic conclusions of a study. A priori
groupings generate additional reversions and convergences. If, by chance,
this is not the case, the implication is
that one already knows which state is
derived and which is primitive. Thus,
strictly speaking, in the Hennigian
sense, the approach suggests that one
already knows the phylogeny that one
is trying to reconstruct, which does
not make sense. The point that has to
be made is nevertheless the taxonomical level on which discussion should
take place if it is possible to do so.
Should the occurrence of the preglenoid tubercle be considered in terms
of variation, as in Brauer and Mbua
(1992), which suggests that the limit
of the species is known? Or, as in
As a general and
common property, it
can be proposed that
the strength of the
preglenoid tubercle is at
least indirectly linked
to the activity of
the short tendinous
fibres of musculus
pterygoideus lateralis.
Trinkaus (1990), should we address
only the distribution of the feature,
because “the delineation of the units
of analysis becomes largely arbitrary,
determined by relatively abundant
temporal geographic gaps in the fossil
record and by an a priori morphological decision as to where the breaks
should occur”? A correlative alterna-
tive would be just to consider the feature and take it into account before
carrying out a phylogenetic analysis.
If we take it that the existence of autapomorphic features for Homo erectus is unproven (Stringer, 1984; Hublin, 1986; Kennedy, 1991; Brauer and
Mbua, 1992), each feature has to be
taken into account, with no reason to
exclude it a priori. Thus, the existence
of a preglenoidal tubercle, which is
common to Indonesian Homo erectus
and to the KNMER 3883 specimen,
which was considered as one of the
first African Homo erectus (Rightmire,
1990, Wood, 1991) most commonly
accepted as Homo ergaster (Groves,
1989; Wood, 1994; Strait et al., 1997),
suggests regional differences in the
frequency of traits within Homo erectus sensu lato but no clear-cut east–
west differences. At that step of the
survey on the significance of the
preglenoid tubercle, its absence in
Pongo, Gorilla, Pan, and Australopithecine supposes that this could be a
derived state in these Homo erectus
sensu lato. On the one hand, with no
clear autapomorphic feature for
Homo erectus species, it is not possible to assert that Homo erectus is a
monophyletic species (Hublin, 1986),
and at least one apomorphy needs to
be found to define Homo erectus.
Thus, it may be that the preglenoid
tubercle appeared in Homo ergaster
FEATURE ARTICLE
and disappeared in Homo sapiens, or
at least in the most recent Homo erectus. If African Homo erectus is taxonomically different from Asian Homo
erectus as claimed by Andrews (1984),
Stringer (1984), Wood (1984), and
Hublin (1986), the disappearance of
the preglenoid tubercle could have become a new feature (by reversion) in
archaic Homo sapiens and Neandertal. On the other hand, many features
can be useful in distinguishing eastern
and western Homo erectus by region
(Brauer and Mbua, 1992), and the
preglenoid tubercle is one of these. In
these terms, the trait expresses both
Homo erectus and Homo ergaster as
regional populations of Homo erectus
sensu lato. Because of the lack of
knowledge on its origin, the preglenoid tubercle should more certainly
be considered as a clue to differences
between populations, perhaps resulting from particular masticatory practises or dietary habits linked to the
regional environment. But, as previously reported by Trinkaus (1990) and
also Brauer and Mbua (1992, p. 82),
who consider the specimens from
Ngandong as archaic Homo sapiens
(see also Dubois, 1940; Campbell,
1963; Jelinek, 1981; Tobias, 1985;
Stringer, 1987; Bonde, 1989), the
question of taxonomic level (is Homo
erectus one single species, or shall we
have to consider several geographically different species) remains unanswered.
The same question arises for all the
Chinese specimens, including the Sinanthropus, where the preglenoid tubercle is absent (as far as can be assessed from the remaining material—
only casts made of plaster still
existing). If it was certainly the case,
the absence of the preglenoid tubercle
could be a clue to split Chinese Homo
erectus population from Indonesian
Homo erectus population and to assign them to an other species. From
this point of view, the problem is similar between Continental and Insular
Asia and between Africa and Asia.
CONCLUSION
Undoubtedly further research has to
be done to determine where the
preglenoid tubercle is present and
also to better understand its functional significance in terms of its anat-
THE ANATOMICAL RECORD (PART B: NEW ANAT.) 155
omy. This last point is still unclear
according to the available anatomical
literature on the temporomandibular
joint. At that step of the art, and going
in quest of new features to shed light
on phylogeny of human fossil, the occurrence of the preglenoid tubercle
can be used to raise questions regarding the degree and pattern of Homo
erectus. Is the tubercle more likely to
be a feature that allows distinctions to
be made among Homo erectus populations? Or is it a preliminary clue
leading to questions as to the actual
grouping of specimens at species
level? At that step, it seems possible to
say that this feature is probably linked
to the diet or paramasticatory activity
of at least one full population (Indonesian Homo erectus even if it is
present on one African fossil).
The interpretation and the use of
Further research has to
be done to determine
where the preglenoid
tubercle is present and
also to better
understand its functional
significance in terms of
its anatomy.
the features is one of the big questions
to which answers differ among the
various anthropological schools, and
which cannot be definitively answered
here. Nevertheless, regardless of the
theoretical approaches that lead people to accept one definition or another
for a species and the taxonomic level
at which the feature is used as a conclusion, I can propose my own scenario. Following the Hennigian principle, any feature can be used to make
phylogeny.
In this context, the preglenoid tubercle could be a feature that happened
among some old African Homo erectus
sensu lato (KNMER 3883), called Homo
ergaster by authors (Andrews, 1984;
Groves, 1989; Wood, 1992; Stringer,
1996) and that I considered as the type
of another species (Zeitoun, 2000). The
preglenoid tubercle still existed among
Indonesian Homo erectus (Sangiran series) and also Archaic Homo sapiens or
Homo soloensis (Ngandong-NgawiSambungmachan series). This interpretation suggests to consider the lack of
the preglenoid tubercle among Sinanthropus as their belonging to another
taxon. Thus, Sinanthropus were different from Indonesian taxa. More than
merely shedding light onto what can be
the differences between African Homo
erectus sensu lato (Homo ergaster) and
Asian Homo erectus sensu lato, the occurrence of the preglenoid tubercle triggers more definitive splitting of the
taxon Homo erectus that, at least, appears to be paraphyletic.
The history of the occurrence of the
preglenoid tubercle may prove to be a
key to understanding the links among
Homo erectus sensu lato. Adopting
other phylogenetic scholars’ points of
view, the story can be different; but to
conclude, the presence of a strong
preglenoidal tubercle appears to be
discriminating for some populations
usually assigned to Homo erectus.
ACKNOWLEDGMENTS
I thank Professor T. Jacob, J. De Vos,
J. Franzen, A. Langaney, M. Tranier,
Dr. H. Widianto, and Mister Himawan
for access to original material. I also
thank J. Braga, M. Elyaqtine, P. Picq,
S. Prat, P. Tassy, and A.M. Tillier for
their contributions and suggestions;
P. Janvier, E. Trinkaus, J. Dufour, M.
Paalman, I. Tattersall, and three
anonymous reviewers for their comments on the text. This work was supported by the Foundation Fyssen and
the fellowship M. Bleustein-Blanchet.
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