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Are Homo sapiens nonsupranuchal fossa and neanderthal suprainiac fossa convergent traits.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 144:552–563 (2011)
Are Homo sapiens Nonsupranuchal
Fossa and Neanderthal Suprainiac Fossa
Convergent Traits?
Wioletta Nowaczewska*
Department of Anthropology, University of Wroclaw, ul. Kuźnicza 35, 50-138 Wroclaw, Poland
KEY WORDS
concavity above the inion; functional meaning; development
ABSTRACT
The autapomorphic status of the Neanderthal suprainiac fossa was recently confirmed. This
was a result of a detailed analysis of the internal bone
composition in the area of the suprainiac depression on
Neanderthal and Homo sapiens specimens. However,
while anatomical differences between Neanderthal
suprainiac fossa and the depression in the inion region
of the occipital bone of fossil and recent Homo sapiens
have been discussed in detail, the etiology of these structures has not been resolved. In this article, the hypothesis that the Homo sapiens non-supranuchal fossa and
the Neanderthal suprainiac fossa both formed to maintain the optimal shape of the occipital plane (to minimize
strain on the posterior cranial vault) is tested. First, the
variation in the expression of the fossa above inion in
the crania of recent Homo sapiens from European, African, and Australian samples was examined, and the
degree of structural similarity between these depressions
and the Neanderthal suprainiac fossa was assessed.
Next, the relationship between the shape of the occipital
squama in the midsagittal plane and two particular features (the degree of the occipital torus development and
the occurrence of a depression in the inion region that is
not the supranuchal fossa) were analyzed. Based on the
results, it is suggested that the Homo sapiens non-supranuchal fossa and Neanderthal suprainiac fossa are convergent traits. Am J Phys Anthropol 144:552–563,
2011. V 2010 Wiley-Liss, Inc.
The small elliptical concavity above the inion that
occurs in some hominins was first described as the
suprainiac fossa by Klaatsch (1902) and GorjanovićKramberger (1902). This feature was first proposed to be
unique to Neanderthals by Hublin (1978a,b) and Santa
Luca (1978). The common Neanderthal form of this
structure has been used as the prototype for the suprainiac fossa definition. The suprainiac fossa concavity is
usually defined as a distinctly separated and transversely oval depression with a rough and porous floor. It
is expressed above the middle region of the modest occipital torus. In the occipital bones of adult Neanderthals,
this structure is one of the external traits of the inion
region. This set of features includes the absence of an
external occipital protuberance and a weak occipital
torus developed in the central region of the occipital
bone, which is bilaterally arched, namely, it shows two
points of lateral projection (Arsuaga et al., 1997; Trinkaus, 2004; Caspari, 2005). The size and shape of this
depression vary, but this variability always occurs in
conjunction with the transverse occipital torus (or broad
area of thickened bone) in Neanderthals (Caspari, 2005,
2006; Balzeau and Rougier, 2010). For this reason, many
researchers believed that the shape of this depression in
the inion region of the occipital bone and the associated
superstructures are interrelated (e.g., Trinkaus, 2004;
Caspari, 2005; Harvati et al., 2007; Soficaru et al., 2007).
According to some researchers, a similar depression
above the inion is visible in several other fossil hominins
and anatomically modern humans; thus, they did not
regard this trait as unique to Neanderthals (Kramer et
al., 2001; Haile-Selassie et al., 2004; Trinkaus, 2004,
2007; Caspari, 2005; Smith et al., 2005; Wolpoff et al.,
2006; Soficaru et al., 2007). Other authors considered
the suprainiac fossa to be a Neanderthal autapomorphic
feature (Stringer et al., 1984). However, there were no
published data until 2010 concerning the internal composition of the occipital bone in the suprainiac fossa
region in Neanderthals (Balzeau and Rougier, 2010).
Therefore, previous comparisons between Neanderthal
and other hominin suprainiac depressions only considered the external cranial surface of this area (i.e., the resemblance to Neanderthal suprainiac fossae in shape,
size, and gross structure).
Additionally, there is an ongoing, substantial dispute
surrounding the identification of this Neanderthal feature in hominin crania due to the lack of a precise definition of this trait (Lieberman, 1995; Caspari, 2005;
Ahern, 2007; for the Cioclovina 1 specimen, see Soficaru
et al., 2006, 2007; Trinkaus, 2007 contra Harvati et al.,
2007; for the Mladeč 6 specimen, see Caspari, 2005;
Frayer et al., 2006; Wolpoff et al., 2006 contra Bräuer
and Broeg, 1998).
The type of the depression above inion that predominates in Upper Paleolithic modern Europeans (e.g., in
C 2010
V
WILEY-LISS, INC.
C
Additional Supporting Information may be found in the online
version of this article.
*Correspondence to: Wioletta Nowaczewska, Department of
Anthropology, University of Wroclaw, ul. Kuźnicza 35, 50-138 Wroclaw, Poland. E-mail: nowacz@antropo.uni.wroc.pl or wnowacz@wp.pl
Received 14 March 2010; accepted 6 October 2010
DOI 10.1002/ajpa.21437
Published online 23 December 2010 in Wiley Online Library
(wileyonlinelibrary.com).
IS NONSUPRANUCHAL FOSSA A CONVERGENT TRAIT?
1
Předmostı́ 3 and Mladeč 5; personal observation ) and in
recent humans, described by Sládek (2000) as the supranuchal fossa, is commonly regarded as being correlated with a
more robust external occipital protuberance and thus as
non-homologous to the Neanderthal suprainiac fossa
(Sládek, 2000; Trinkaus, 2004, 2006, 2007; Caspari, 2005;
Frayer et al., 2006; Wolpoff et al., 2006). Other types of concavities above the inion that are similar to the Neanderthal
suprainiac fossa (described in this study as non-supranuchal fossae) were observed by Caspari (2005) in recent and
in fossil Homo sapiens (Hs) individuals. Recently, Balzeau
and Rougier (2010) provided a detailed description of the
depression above inion for Neanderthals and for anatomically modern humans (both fossil and recent specimens),
indicating that the Neanderthal fossa is different in its
underlying internal bone composition from the analogical
depression observed in some Hs. Balzeau and Rougier
(2010) showed that the Neanderthal depression above inion
is related to a thinning of the diploic layer (without a variation in the external table thickness). In contrast, the fossae
observed in Hs (supranuchal fossa and non-supranuchal
fossa) are characterized by a thinning of the external table
in this area of the occipital bone.
Assuming that the types of non-supranuchal fossae
observed in some Hs are not homologous to Neanderthal
suprainiac fossa, including the depression that shows the
greatest morphological similarity in terms of external
expression to Neanderthal suprainiac fossae (Balzeau and
Rougier, 2010), it is important to determine whether
these structures in Hs and Neanderthals could have
developed in a similar fashion. If the Hs and Neanderthal
structures share the same function and form (resulting
from similar factors that influence the occipital bone), it
would mean that these structures are convergent features. Thus, the main aim of this study was to determine
if the non-supranuchal fossae observed in some recent Hs
and the Neanderthal suprainiac fossae can be regarded
as convergent features.
Little is known about the pattern of development or the
functional meaning of the Neanderthal suprainiac fossa.
Therefore, it is difficult to determine whether the development of the Neanderthal suprainiac fossa was caused by
the same factors as that of the non-supranuchal fossae in
some Hs (Lieberman, 1995; Caspari, 2005; Ahern, 2007).
The ontogeny of the hominins discussed above cannot be
directly examined; it can only be proposed through developmental models. According to Trinkaus (2004), the Neanderthal suprainiac fossa is a ‘‘neutral trait’’ that is understood
as a nonadaptive feature of unknown etiology. Other
authors have proposed functional explanations for its development, i.e., this trait may provide an additional area for
the attachment of the nuchal muscles (Lieberman, 1995) or
that it could stem from the specific growth of the occipital
bone above and below the occipital torus as a result of different positions of ossification centers (Heim, 1982; Srivastava,
1992). Caspari (2005) proposed two developmental models
common for the suprainiac and non-supranuchal fossae.
The first model describes these features mainly as the
retention of the juvenile condition, which results from the
process through which the shape of the cranial vault is
achieved. This hypothesis stems from the fact that the
suprainiac fossa is discernible in Neanderthal children less
1
The collections of European Upper Paleolithic Hs skulls belong
to: the Moravian Museum—Brno, Archaeological Institute of the
Czech Academy of Sciences—Brno (Dolnı́ Věstonice) and Musée de
l’Homme—Paris.
553
than 2 years of age (Tillier, 1992; Akazawa et al., 1995;
Dodo et al., 2002; Ishida and Kondo, 2002).
In the second model, the suprainiac and non-supranuchal fossae are regarded as areas of resorption that resist
the stress generated mainly by the nuchal muscles in the
midsagittal profile of the posterior cranial vault. The incidence of these depressions causes a flattening of the back
of the cranium by creating a more vertical contour in the
occipital plane, which minimizes strain on the posterior
region of the vault. In this model, the formation of the different fossae is related to mechanical stress that causes
remodeling of the external surface of the occipital bone,
which was described by Caspari (2005) as an adaptive
response to strain. Caspari (2005) suggested that the deposition of the bone occurring at the midline of the occipital
squama in the angulated external contour of the occipital
bone should be in the form of the occipital torus (e.g., the
robust occipital torus in Homo erectus) as a result of
increased stress. It was assumed that the formation of the
Neanderthal suprainiac fossa is associated with the development of superstructures and with the maintenance of
an optimal occipital bone shape.
In the present study, the second hypothesis (second
model) concerning the suprainiac fossa and non-supranuchal fossa development, described by Caspari (2005), was
tested. First, the variation in the expression of the depression above the inion was analyzed in crania of recent Hs
samples (from Europe, Africa, and Australia) using four
classifications of this trait (including the supranuchal
fossa and three types of non-supranuchal fossae). Next,
the relationship between the shape of the occipital bone in
the midsagittal profile (quantified using four variables)
and the degree of development of the supreme and superior nuchal lines was assessed by applying a modification
of Lahr’s (1996) scale of the development of these superstructures. It was predicted that establishment of a relationship could support the hypothesis that the shape of
the external occipital contour in the midsagittal plane,
and hence the occurrence of the fossa in the inion region,
could have the adaptive meaning that was described by
Caspari (2005). If the second model proposed by Caspari
(2005) is valid, a more angulated external occipital contour should correspond to a more massive nuchal line
region. If the Neanderthal suprainiac fossa and nonsupranuchal fossa have a functional meaning, understood
as a reduction in the strain from the nuchal muscles, the
probability of the occurrence of the non-supranuchal fossa
should be highest in examined crania with the most convex posterior external contour of the occipital bone.
MATERIALS AND METHODS
Samples
The crania of recent adult Hs from Europe (n 5 44),
Africa (n 5 33), and Australia (n 5 36) were examined.
The skulls in the best state of preservation, with special
focus on the external surface of the occipital bone, were
chosen from the available skeletal material. Only the
crania (and mandibles when available) were used to estimate age and sex. Most of the European and Australian
specimens lack postcrania, as do all of the African specimens (Milicerowa, 1955; Górny, 1957; Magnuszewicz and
Rajchel, 1980). Two criteria were used to make a distinction between adult and adolescent specimens: the closure
of the basisphenoid synchondrosis and the presence of
the entirely developed third upper molars (Workshop of
American Journal of Physical Anthropology
554
W. NOWACZEWSKA
European Anthropologists, 1980). The assessment of sex
was based on several qualitative features, ones recommended by the Workshop of European Anthropologists
(1980). The relationships between the chosen variables
describing the shape of the occipital squama and the
degree of development of the supreme and superior
nuchal lines (including the occipital torus) analyzed in
this study are relevant to the skulls of both males and
females, especially since Caspari (2005) did not regard
the feature as sex-specific. Attempts were nonetheless
made to include equal numbers of males and females in
each sample; however, such inclusion was impossible due
to the limited amount of accessible cranial material.
The European crania derive from a late 13th to early
14th century cemetery in Czeladź Wielka (Poland) (Magnuszewicz and Rajchel, 1980); it includes 34 males and
10 females. The African sample is from Uganda and was
collected in the 1930s by E. Loth; it includes 26 males
and 7 females (Górny, 1957). The early 20th century
Australian crania are in the Klaatsch collection, but
they originally belonged to W.E. Roth. This sample
includes 25 males and 11 females, with documented sex
(Milicerowa, 1955).
Data analyses
To assess the variation in the expression of the depression above the inion, four forms of this trait were distinguished. The first type, the supranuchal fossa, is defined
as the structure associated with the external occipital
protuberance and/or well-developed superior nuchal lines
(Sládek, 2000; Caspari, 2005). This type of fossa does not
resemble the Neanderthal suprainiac fossa. The fossa is
triangular instead of elliptical in this case (its apex
points inferiorly), gradually grades into the upper occipital squama, and has an inferior boundary created by the
external occipital protuberance, which was identified in
this study as an area of relief that appears in the median contact of the lineae nuchae supremae (Hublin,
1978a; Lahr, 1996; Sládek, 2000). If the supreme nuchal
lines are missing, this fossa is marked inferiorly by the
medial parts of superior nuchal lines. There is no transverse occipital torus (Fig. 1a).
The following two variants of the depression above the
inion have been described as similar to those of Neanderthals (Caspari, 2005). Both variants are characterized
by the occurrence of a transversely elliptical or round
fossa in the area of thicker bone on the occipital plane
and the lack of an external occipital protuberance. In the
second form, the occipital torus is not visible and the elliptical depression occurs in the area of thickened bone
(Fig. 1b). The third variant of the depression above the
inion is characterized by an occurrence of the occipital
torus that is not identical to those of Neanderthals
(Fig. 1c). This variant is visible in the Mladeč 6 Upper
Paleolithic Hs cranium. In this specimen, the occipital
torus was taller than the analogous structure in the
Neanderthals and was not bilaterally arched (Caspari,
2005; personal observation of the Mladeč 6 cast). The
fourth variant of the depression exhibits the greatest resemblance to the typical Neanderthal suprainiac fossa
(Fig. 1d). It has a transversely elliptical fossa above the
medial portion of the occipital torus, which is bilaterally
arched, poorly expressed laterally, and rather weakly
developed. The upper margin of this structure is usually
obscure (Hublin, 1978a; Santa Luca, 1978; Arsuaga
et al., 1997).
American Journal of Physical Anthropology
Fig. 1. The four types of expression of the fossae above
the inion proposed by the author: the supranuchal fossa—the
first type (a), non-supranuchal fossae—the second type (b),
the third type (c), and the fourth type (d). Abbreviations in
Figure 1: F 5 fossa, EOCP 5 external occipital protuberance,
OCR 5 occipital crest; SRNL 5 supreme nuchal line; SPNL 5
superior nuchal line; TL 5 tuberculum linearum; OT 5 occipital
torus.
IS NONSUPRANUCHAL FOSSA A CONVERGENT TRAIT?
555
TABLE 1. The system of grades of the nuchal line (supreme and superior, including the occipital torus) development, modified by
the author
Grade description
Grade number (OT)
OT 1
OT 2
OT 3
OT 4
OT 5
OT 6
OT 7
OT 8
OT 9
Visible superstructures (can be visible)
Superior nuchal lines
External occipital protuberance (superior nuchal
lines)
Supreme and superior nuchal lines, convexity
between these lines—only in the central part of
the occipital squama; bilaterally arched supreme
nuchal lines; (tuberculum linearum); see Figure
4b,c
Supreme and superior nuchal lines (the external
occipital protuberance and the tuberculum
linearum)
Supreme and superior nuchal lines; the external
occipital protuberance joined medially with
superior nuchal lines (tuberculum linearum)
Supreme and superior nuchal lines and convexity
between them; the external occipital
protuberance superimposed on a torus and
joined medially with the inferior margin of the
torus; (tuberculum linearum; supratoral sulcus)
Occipital torus; the external occipital protuberance
along the superior toral margin (supratoral
sulcus, tuberculum linearum)
Supreme nuchal lines forming bilateral arches
(supratoral sulcus, tuberculum linearum;
bilaterally arched whole torus); see Figures 5c–f
and 6a,b
Occipital torus; supratoral sulcus; (tuberculum
linearum); see Figure 5a,b
Non-visible superstructures
Supreme nuchal lines
Lateral parts of the supreme nuchal
lines
External occipital protuberance
Joint between supreme and superior
nuchal lines in midline—between
external occipital protuberance and
the tuberculum linearum
Convexity between suprema and
superior nuchal lines
–
Joint between superior and inferior
toral margins
External occipital protuberance
External occipital protuberance
OT 3 and the OT 8 were added by the author to Lahr’s original scale (Lahr, 1996). The external occipital protuberance and tuberculum linearum were located following Hublin (1978a): the first of these structures is at the point of connection of the supreme nuchal
lines, and the second is at the point of connection of the superior nuchal lines. The supratoral sulcus was defined as the concave superior margin of the torus (Lahr, 1996). In this study, the occipital torus was identified even if the supratoral sulcus was not discernible.
To assess the degree of development in the supreme
and superior nuchal lines and the occipital torus (OTD)2
in all examined crania, the author used a modified scoring system of grades described by Lahr (1996). Originally, Lahr (1996) defined seven grades of the expression
of these features and termed them as categories of the
occipital torus development. This scale was modified by
adding two new categories (3 and 8) that were found in
several examined crania (see Table 1). The classification
to an individual grade was based on analysis of the
robusticity, the extent of the supreme and superior
nuchal lines, and the occurrence of torus formation.
These features were scored twice on each cranium, with
a 1-week break between the scoring sessions. The observations were different between the first and second
scoring sessions for only two of the 113 crania (1.77%),
indicating that the scoring is reliably repeatable.
Four variables (three angles and one ratio) were used
to assess the shape of the occipital squama in the midsagittal profile. Supporting Information Table S1 presents
a description of these variables and the measurements
used for their calculation. These exocranial measurements were taken three times on each skull with an accuracy of 0.5 mm using spreading caliper and coordinate
calipers (with straight arms). The mean measurement
error was 0.42%.
2
The abbreviation ‘‘OTD’’ replaces the phrase, ‘‘the degree of development of the supreme and superior nuchal lines and the occipital torus.’’
The first variable was the occipital curvature angle
l-i-o [M33(4)], trigonometrically derived from the k-opisthion (OCC 5 M31), the k-inion [OPC 5 M31 (1)], and
the inion-opisthion [M31 (2)] chords (cf., Howells, 1973;
Bräuer, 1988; Figs. 2 and Supporting Information S1); a
lower value corresponds to a more angled squama (see
Fig. 2) (Bräuer, 1988). The occipital curvature angle
describes the position of the occipital plane relative to
the nuchal plane. However, this angle does not precisely
reflect the shape of the external contour of the occipital
squama in the midsagittal profile, especially if the occipital plane is convex (e.g., two occipital bones with a large
difference in the degree of occipital plane convexity can
have the same value for this angle). Nevertheless, it was
predicted that the occipital curvature angle should be
related to the OTD in that a more angulated occipital
squama implies a higher probability of the occurrence of
the occipital torus (a higher OTD). It is expected that
the occipital curvature angle should be negatively correlated with the OTD.
The occipital plane angle (OPA) was the second variable used; a lower value of this angle reflects a more convex occipital plane (see Fig. 2). This angle describes the
degree of the occipital plane convexity at the midline
and was calculated based on trigonometric functions
from the k-inion chord (OPC), the k-inion subtense
(OPS), and the k-subtense fraction (OPF) (see Supporting Information Fig. S2; also Nowaczewska and Kuźmiński, 2009). It was predicted that a relationship would
exist between the convexity of the occipital plane and
American Journal of Physical Anthropology
556
W. NOWACZEWSKA
Fig. 2. The angles and measurements used to describe the
shape of the occipital squama in the midsagittal plane depicted
on the contour of a recent African Hs cranium. Abbreviations in
Figure 2: l 5 lambda, i 5 inion, o 5 opisthion; x 5 the point at
which the greatest convexity of the occipital plane was localized.
OPA 5 occipital plane angle. To calculate this angle, three
measurements were used: OPC 5 k-inion chord, OPS 5 k-inion
subtense, and OPF 5 k-subtense fraction. EOA 5 external occipital curvature angle. This angle is a sum of two angles: l-i-o
and l-i-x. Occipital curvature angle 5 l-i-o. Three measurements
were used to calculate this angle: OPC, OCC 5 occipital sagittal
chord, and M31(2) 5 inion-opisthion chord (see the Supporting
Information Table S1 for definitions of all angles and measurements and Supporting Information Figures S1–S3 for methods
of computing these angles).
the OTD in the examined crania, and that the OPA
should be correlated with the OTD. In other words, a
greater convexity of this plane (lower value of OPA)
would correspond to a weaker OTD. This prediction was
made in accordance with the second model of suprainiac
and non-supranuchal fossa development (Caspari, 2005),
which stresses the relationship between the shape of the
external contour of the occipital bone and development
of the superstructures in the inion region.
The external occipital curvature angle (EOA) was the
third variable; a higher value of this angle reflected a
more convex external contour of the occipital squama
(see Fig. 2). The EOA was the best variable for testing
the hypothesis of suprainiac and non-supranuchal fossa
development proposed by Caspari (2005), because this
variable describes the degree of convexity of the external
contour of the posterior occipital squama. The angle is
the sum of the occipital curvature angle (l-i-o) (Bräuer,
1988) and the l-i-x angle. In the l-i-x angle, the ‘‘x’’ indicates a point on the external table of the occipital plane
in the midsagittal profile of greatest convexity. OPC,
OPS, and OPF were used to calculate the l-i-x angle:
(see Fig. 2 and Supporting Information Fig. S3). Assuming that the external contour of the occipital plane is important for the development of an occipital torus, it was
predicted that the EOA should be negatively correlated
American Journal of Physical Anthropology
with the OTD [i.e., that a greater convexity of the occipital squama (higher value of EOA) would reflect a weaker
OTD] and that the relationship between these variables
should be stronger than the other relationships examined in this study.
Following Caspari (2005), we predict that the incidence
of non-supranuchal fossae will be lower in the case of an
angled external contour of the occipital bone or a vertical
external profile of the occipital plane. The highest probability of the occurrence of this fossa is expected for
the greatest convexity of the occipital plane and/or the
convex external contour of the occipital squama. This
prediction is in accordance with the observations of
the shape of the external contour of the Neanderthal
occipital bone (e.g., the occurrence of the occipital bun)
(Trinkaus and LeMay, 1982; Lieberman et al., 2000;
Gunz and Harvati, 2007).
The ratio of the inion-opisthion chord [M31(2)] to the
k-inion chord [M31(1)] was the fourth variable used in
this study (Fig. 2, Supporting Information Table S1),
(Bräuer, 1988). This index describes the relative length
of the nuchal plane; a higher value of this variable
reflects a relatively longer nuchal plane. It was predicted
that the index should be correlated with the OTD, such
that relatively longer nuchal planes should correspond
with higher OTDs (Lahr and Wright, 1996).
These four variables should assess the shape of the
occipital bone (including the shape of the occipital plane)
in the midsagittal profile more accurately than other
variables that have been described in the literature (e.g.,
the ratio of k-inion chord [M31(1)] to k-inion arc
[M28(1)], the occipital angle (OCA), or the angle
described by the orientation of the occipital plane relative to the Frankfurt horizontal plane [33 (1)]), (Howells,
1973; Bräuer, 1988).
The relationship between the occurrence of the two
categories of the depression above the inion, i.e., the
supranuchal fossa and non-supranuchal fossa (including
the second, third and fourth type of the fossa), and the
sexes of the individuals studied were additionally examined. Because male crania are usually more robust than
female crania, we can expect that the appearance of the
supranuchal fossa should be more frequent in male crania. Suprainiac fossae occur in Neanderthal males and
females, so its appearance should not be correlated with
sex. If the development of the non-supranuchal fossa is
mostly connected with the midsagittal shape of the occipital bone (Caspari, 2005), we can expect that the
appearance of this category of fossa should not be correlated with sex.
Statistical analyses
All analyses were carried out using Statistica version
7.1 (StatSoft, 2005) and Microsoft Office Pro 2003.
Spearman rank correlation was used to assess relationships between the occipital shape variables and the
OTD for the pooled modern human sample. KruskalWallis tests were used to compare the African sample
with the European and Australian samples. Additionally, a post hoc test for the Kruskal-Wallis test was
applied as needed. The level of significance of P 5 0.05
was used in these analyses. To check the pooled sample
of crania (n 5 113) for a relationship between the
occurrence of two main categories of fossa (the supranuchal fossa and the non-supranuchal fossa) and
the sexes of the examined individuals, the V-square
IS NONSUPRANUCHAL FOSSA A CONVERGENT TRAIT?
557
and chi-square tests for a two-way table were used
(the level of significance of P 5 0.01 was used in these
analyses).
RESULTS
All types of the fossa can be found in the pooled sample. However, only the first type of this depression was
observed (43.2%; Fig. 3a) in the European crania. In the
African sample, the first type of this trait was identified
in four crania (12.1%; Fig. 3b). The second type occurred
in six crania (18.2%; Fig. 4a,b). None of the African
specimens had the third or fourth form of the depression. In the Australian sample, all categories of this feature were observed, occurring in 22.2, 5.6, 8.3, and 2.8%
for categories one to four respectively (Figs. 3c, 4c, 5 and
6). In summary, the incidence of the supranuchal fossa
was highest in the pooled sample of the specimens (n 5
31/113) and was observed in each group of crania. The
forms of depression similar to the Neanderthal suprainiac fossae were identified in the African and Australian
samples. The type of structure most similar to those of
the Neanderthals was observed in the Australian sample
(see Fig. 6).
The summary of the statistics for the four shape variables are in Table 2. Analyses of the relationship between
the shape of the external contour of the occipital squama
and the OTD indicate that there was no statistically significant relationship between the occipital curvature
angle and the OTD (Table 3). This result is not as predicted. However, the occipital curvature does not reflect
the curvature of the external contour of the occipital
squama (except when the occipital plane is not convex,
although this was not the case in most of the crania that
were examined in this study; see Table 2). It is possible
that a sample of crania with more occipital curvature
angle variation than was observed in this study would
be more appropriate to determine whether there is a
relationship between this variable and the OTD. In the
cranial sample used here, the relationship between the
shape of the external contour of the occipital bone (based
on the data concerning the occipital curvature angle)
and the robusticity of the iniac superstructures (Caspari,
2005) cannot be addressed.
The results also indicate a weak but significant correlation between OPA and the OTD (rs 5 0.2959, P 5
0.001); a moderate, negative and significant correlation
between EOA and the OTD (rs 5 20.3330, P 5 0.000);
and a weak, significant correlation between the ratio of
the inion-opisthion chord to the k-inion chord and the
OTD (rs 5 0.2763, P 5 0.003). These results are in accordance with the predictions. It is worth noting that, as
predicted, the relationship between EOA and the OTD
was strongest. The first result from the last of the three
analyses presented above supports the view that the
degree of occipital plane convexity can influence the development of the occipital torus; the second result supports the hypothesis of the importance of the shape of
the external contour of the occipital squama (particularly
the posterior aspect) to the OTD, and the third is in line
with the suggestion that the relative length of the
nuchal plane can influence the OTD.
The results of the Kruskal-Wallis (and post hoc) comparison between the three samples of crania examined
revealed a significant difference between the OTD of
Australian and African samples and between the Australian and European samples. There was no difference in
Fig. 3. Examples of the supranuchal fossae visible in recent
adult Hs crania from Europe: 242 (a), Africa: 307 (b), and Australia: R34 (c). The fossa visible in Figure 3a is the best example
of the structure presented in Figure 1a (photographs were taken
by the author—courtesy of the Department of Anthropology,
University of Wroclaw and the Institute of Anthropology Polish
Academy of Science, Wroclaw). The black lines visible on the
surface of these occipital bones were not made by the author.
this trait between the African and European samples.
The Australian crania exhibited the highest mean value
of OTD (Tables 2 and 4).
American Journal of Physical Anthropology
558
W. NOWACZEWSKA
Fig. 4. Examples of the second type of fossa above the
inion expression in recent adult Hs crania from Africa: 411
(a) and 382 (b), and from Australia: R74 (c). OT 1 is visible
in the first specimen (a) and OT 3 is visible in the last two
specimens (b and c). The fossa visible in Figure 4a is the best
example of the structure presented in Figure 1b (photographs
were taken by the author: courtesy of the Department of Anthropology, University of Wroclaw and the Institute of Anthropology Polish Academy of Science, Wroclaw). The black lines
visible on the surface of these occipital bones were not made
by the author.
American Journal of Physical Anthropology
When each variable was used to assess the shape of
the occipital bone, the African sample was significantly
different from the European and Australian samples.
There were no significant differences in these features
between the European and Australian crania. The African crania showed a higher mean l-i-o angle, a lower
mean OPA, a higher mean EOA, and a lower mean ratio
of the inion-opisthion chord to the k-inion chord when
compared to the European and Australian samples (see
Table 4). As predicted, the probability of the depression
above the inion being dissimilar to the supranuchal fossa
in modern human crania should be highest among specimens that exhibit a convex occipital plane and/or convex
external contour of the occipital squama in the midsagittal plane. In other words, the lower values of OPA and/
or the higher values of EOA indicate a higher probability
of the types of depressions described as non-supranuchal
fossae in modern human crania. Taking this expectation
into consideration, the African cranial sample exhibited
the lowest mean OPA and the highest mean EOA among
the samples (Tables 2 and 4). Moreover, the highest percentage of crania that exhibited the second type of fossa
(without the occipital torus) was observed in the African
sample. The majority of the occipital bones in the African crania were not robust, and the occipital torus was
only visible in two specimens (see Fig. 7). This finding
can be attributed to the absence of crania in the samples
exhibiting the third and fourth types of fossae (the categories of this trait with the occipital torus). These data
are in accordance with the prediction concerning the
probability of occurrence of the non-supranuchal fossae
in modern human crania.
Three crania with the third type of fossa and one specimen with the fourth type of this feature were found in
the Australian sample. If these structures in Australian
crania have a functional meaning and thus indicate a
relationship with the shape of the external contour of
the occipital squama (as suggested by Caspari, 2005),
the mean OPA in the case of these four crania with fossae should be lower than the mean of the same variable
for Australian crania without any fossae (and with the
same OTD value observed in the case of the four crania
with the third and fourth types of depression: OT8 and
OT9). An assumption can also be made that the mean
EOA for the four crania with fossae should be higher
than the mean of the same angle for the Australian crania without any fossae (for the same group of crania
that was used in the case of the OPA comparison). In
the Australian sample, there were four crania with no
fossae in the inion region and with OTD grade numbers
8 and 9. These were compared to four Australian crania
with the third and fourth types of fossae and OTD numbers 8 and 9. For the first group, the mean OPA was
148.78 and the mean EOA was 139.48. In the second
group, the mean OPA was 142.78 and the mean EOA
was 145.38.
The differences in the means of the OPA and
EOA between these groups were in accordance with
the prediction, but a Mann-Whitney U test does not
confirm this prediction (there were no significant differences between these groups in reference to these
angles: for OPA, U 5 4, P 5 0.248; for EOA, U 5 6, P
5 0.564).
The pooled sample included 28 female crania and 85
male crania. The supranuchal fossa was identified in 31
of 113 specimens: 4 female crania (3 from Europe and
1 from Australia) and 27 male crania (16 from Europe, 4
IS NONSUPRANUCHAL FOSSA A CONVERGENT TRAIT?
559
Fig. 5. Examples of the third type of fossa above the inion expression in recent adult Hs crania from Australia (R81—a, b;
R80—c, d; R49—e, f). OT 8 is visible in the following specimens: R80 (c, d) and R49 (e, f). OT 9 is visible in specimen R81 (a, b).
The fossa visible in Figure 5a is the best example of the structure presented in Figure 1c (photographs were taken by the author:
courtesy of the Department of Anthropology, University of Wroclaw). The black lines visible on the surface of these occipital bones
were not made by the author.
from Africa and 7 from Australia). The non-supranuchal
fossa was observed in 12 of 113 specimens: 6 female crania (1 from Africa, 5 from Australia) and in 6 male crania (5 from Africa, 1 from Australia). The predominantly
male distribution of supranuchal fossae is in accordance
with Caspari’s (2005) and Sládek’s (2000) assertion, i.e.,
that the occurrence of this category of fossa is correlated
with the robusticity of the nuchal lines (the presence of
the external occipital protuberance). However the statistical analysis indicates that there is no significant relationship between the sexes of the individuals studied
and the presence of the two categories of fossae mentioned above (supranuchal fossa: V-square test, 3.20, P 5
0.074; non-supranuchal fossa: chi-square test with Yates
correction, 3.19, P 5 0.074). The lack of relationship
between the presence of the non-supranuchal fossae in
the individuals studied and their sex is in accordance
with the prediction, but the unexpected result that the
supranuchal fossa is unrelated to sex can be explained
by the fact that the numbers of male and female crania
examined in this study were not equal. This factor could
influence the results.
American Journal of Physical Anthropology
560
W. NOWACZEWSKA
Fig. 6. Example of the fourth type of the fossa above the inion expression in recent adult Hs cranium from Australia (OT 8 is
visible in this specimen—R4). The fossa visible in Figure 6a is an example of the structure presented in Figure 1d (photographs
were taken by the author: courtesy of the Department of Anthropology, University of Wroclaw). The black lines visible on the surface of these occipital bones were not made by the author.
TABLE 2. The descriptive statistics of all variables used in this study and measurements applied to calculate these variables
Samples
Variables
Europe
Africa
Australia
All samples
n 44 (M 34/F 10)
n 33 (M 26/F 7)
n 36 (M 25/F 11)
n 113 (M 85/F 28)
Mean
SD
Range
Mean
SD
Range
Mean
SD
Range
Mean
SD
Range
OT
3.57 1.78
1–6
2.51 1.87
1–8
5.44 2.10
1–9
3.86 2.23
1–9
M33(4) 5 (l-i-o) 119.3
5.3 101.8–127.4 123.2
5.7 112.9–133.5 119.7
4.9 108.8–131.5 120.6
5.5 101.8–133.5
OPA 5 (l-x-i)
143.4
5.7 133.3–157.1 138.4
6.6 128.7–156.9 145.6
6.0 135.9–158.9 142.6
6.7 128.7–158.9
EOA 5 (o-i-x)
138.2
6.8 121.2–150.4 145.6
6.2 131.2–157.3 137.3
7.8 124.7–157.7 140.1
7.8 121.2–157.7
M31(2)/
69.99 11.81 38.81–94.34
64.77 10.74 52.17–106.12 74.58 13.19 49.27–109.09 69.93 12.47 38.81–109.09
OPC 5 i-o/l-i
Measurements
OPC (M31(1))
65.89 5.35 53.00–76.00
65.64 7.14 48.00–80.00
61.21 6.24 48.00–78.00
64.32 6.50 48.00–80.00
OPS
10.92 2.35 5.50–15.50
12.42 2.84 5.00–19.00
9.23 2.07 5.00–13.00
10.82 2.71 5.00–19.00
OPF
34.14 3.79 28.00–45.00
35.51 4.46 24.00–43.00
30.97 5.93 22.00–46.00
33.53 5.06 22.00–46.00
OCC (M31)
96.66 4.06 88.00–107.00 95.18 5.48 80.00–106.00 92.21 5.24 83.00–103.00 94.81 5.20 80.00–107.00
M31(2)
45.60 5.27 29.50–55.00
41.91 3.42 36.00–52.00
45.04 5.24 34.00–60.00
44.34 5.01 29.50–60.00
See Supporting Information Table S1 for variable (and measurement) details and abbreviations. OT—the supreme and superior
nuchal line development scale (from Grades 1–9); SD, standard deviation. All quantitative variables in millimeters or degrees.
TABLE 3. Spearman rank correlation coefficients concerning
the relationship between the scale of nuchal line development
(OT) and variables used in this study
Variables correlated with OT
Pooled sample, n (113)
M33(4) 5 (l-i-o)
OPA 5 (l-x-i)
EOA 5 (o-i-x)
M31(2)/OPC 5 i-o/l-i
20.1698
0.2959
20.3330
0.2763
Significant correlations in bold (P \ 0.05); see Supporting Information Table S1 for variable abbreviations.
DISCUSSION AND CONCLUSIONS
The results support the hypothesis that the shape of
the external contour of the occipital squama in the midsagittal plane is related to the development of the occipital torus and the non-supranuchal fossa. The significant
negative correlation between the EOA and the OTD and
the significant correlation between the OPA and the
OTD suggest the aforementioned relationship. The incidence of the non-supranuchal depression above inion
was observed in the crania, with a great convexity of the
American Journal of Physical Anthropology
occipital plane and of the occipital squama. A similar
regularity can be found in Neanderthals. Neanderthal
crania exhibit convexity of the occipital plane occurring
together with the suprainiac fossa (Trinkaus and LeMay,
1982; Arsuaga et al., 1997). The development of the
weak occipital torus that is characteristic of these hominins was probably also affected by the shape of the occipital squama (as is the case with Hs crania). The results
of this research support Caspari’s (2005) hypothesis on
the second model of Neanderthal suprainiac fossa and
non-supranuchal fossa development, which states that
the depressions above the inion formed to maintain the
optimal shape of the posterior cranial vault and minimize the influence of strain on this part of the neurocranium. These results suggest that Neanderthal suprainiac
fossae and the second, third, and fourth types of depressions in the inion region observed in some recent Hs
have a functional meaning (Caspari, 2005).
This study only examined the relationships between
the shape of the occipital bone and the development of
two features: the occipital torus and the non-supranuchal fossa. Lahr (1996) and Lahr and Wright, (1996)
indicated that the metric features of the cranium (e.g.,
measurements of the facial skeleton, traits related to
IS NONSUPRANUCHAL FOSSA A CONVERGENT TRAIT?
561
TABLE 4. Comparisons between the samples of H. sapiens
crania concerning the grades of OT and variables used in
this study
Kruskal-Wallis test and post hoc test
Variables
OT
M33(4) 5 (l-i-o)
OPA 5 (l-x-i)
EOA 5 (o-i-x)
M31(2)/OPC 5 i-o/l-i
H (significant difference—sdf:)
H(2) 5 31.72
P 5 0.000
(sdf: AUS [ AF; AUS [ EU)
H(2) 5 10.17
P 5 0.006
(sdf: AF [ AUS; AF [ EU)
H(2) 5 22.78
P 5 0.000
(sdf: AUS [ AF; EU [ AF)
H(2) 5 25.83
P 5 0.000
(sdf: AF [ AUS; AF [ EU)
H(2) 5 12.54
P 5 0.002
(sdf: AUS [ AF; EU [ AF)
Abbreviations in Table 4: EU, Europe; AF, Africa; AUS,
Australia.
temporal muscle size, and qualitative features such as
pronounced supraorbital ridges) affect the OTD in Hs. In
light of these previous studies, expression of the occipital
torus can be interpreted as a response to specific cranial
dimensions and mechanical forces. An oval depression
above the robust occipital torus was found in Australian
specimen R81. However, the occipital plane of this specimen was very convex. The OPA for specimen R81 was
135.98, which is within the Neanderthal range of variation (119.18–138.68, n 5 6, see Nowaczewska and Kuźmiński, 2009). The development of the robust occipital
torus in this cranium probably resulted from a stronger
impact of other factors than from the shape of the occipital squama, which is suggested by the robusticity of this
cranium (Fig. 5a,b). There is an oval depression above
the bilaterally arched occipital torus (the fourth type) in
the Australian R4 specimen (Fig. 6a,b). The dimensions
of this fossa (transverse breadth 5 31 mm 6 0.5 mm,
vertical height 5 15 mm 6 0.5 mm) are within the Neanderthal range of variation [mean breadth 5 40.0 mm
6 7.4 SD (n 5 10) and mean height 5 17.5 mm 6 3.5
SD (n 5 11); see Trinkaus, 2004)]. The inion region of
the R4 cranium has a morphology that is very similar to
that of the analogous region of the occipital bone in
Neanderthals. This similarity suggests that the depression in the Australian specimen is homologous to the
Neanderthal suprainiac fossa. It is important to note
that in the R4 specimen, as in Neanderthal crania, supernumerary ossicles along the lambdoid suture are
observed (see Fig. 6a,b). The presence of these sutural
ossicles is usually understood to reflect the influence of
mechanical stress on the bone structures during the
early stages of cranial vault development. This type of
epigenetic trait, observed in the R4 specimen, is characteristic for Neanderthal cranial vaults and is considered
to be a marker of the ‘‘ontogenetic stress’’ that is derived
from differences in the rate of brain development and
ossification of the bones (Manzi and Vienna, 1997; Manzi
et al., 2000; Manzi, 2003). Taking into account the correlation between the occurrence of the epigenetic features
and variations in cranial dimensions (Corruccini, 1976;
Cheverud et al., 1979) and that the occipital torus can
develop in response to the specific stresses acting on the
Fig. 7. Grades of development of suprema and superior
nuchal lines (including occipital torus)—OT scale from 1 to 9,
observed in the pooled sample of examined Hs. Abbreviations in
Figure 7: EU, Europe; AF, Africa; AUS, Australia.
occipital bone, the formation of the bilaterally arched
occipital torus might be related to the presence of the supernumerary ossicles along the lambdoid suture in
Neanderthals and in modern Hs.
The incidence of the second type of fossa (without the
occipital torus) observed in this study indicate that the
development of this depression above the inion was not
related to the occurrence of the occipital torus but was
probably connected to the shape of the occipital squama.
A similar relationship is suggested for the third and
fourth types of fossae observed in Hs and for the suprainiac fossae in Neanderthals. This opinion is not in accordance with the common view that the presence of
the Neanderthal suprainiac fossa is associated with the
development of the occipital torus (see Caspari, 2005).
Despite the lack of a significant difference between the
two groups of the crania (in other words, crania with
and without non-supranuchal fossae possessed the same
stage of the OTD development), it is probable that further analyses that examine a greater number of specimens (fossil and recent Hs) will detect the expected
differences.
According to the results of Balzeau and Rougier
(2010), the internal composition of the occipital bone in
the region of Hs non-supranuchal fossae is different
from that observed in Neanderthal suprainiac fossae.
Thus, they cannot be considered to be homologous
structures; however, it is worth noting that Balzeau
and Rougier (2010) examined the internal structure of
the suprainiac area (CT) only in two early anatomically
modern humans. Therefore, further analyses are
needed that include a larger sample of fossil Hs
remains, along with other hominins (e.g., Eyasi 1).
Assuming that the observation described above concerns all representatives of our species and taking into
account the results of this study that show that nonsupranuchal fossae and Neanderthal suprainiac fossae
can have the same functional meaning, these depressions are likely to be convergent features. It has been
noted (e.g., Lieberman, 1995) that non-homologous similarities can occur in regions of the cranium that experience a high level of strain. However, the proximate
mechanisms of bone remodeling as a result of strain
are not entirely understood (Lieberman, 1995). In light
of the results of this study, it is probable that the
depressions discussed above can be considered to result
from a specific occipital bone response in the region
above the inion to nongenetic stimuli (strain). It was
American Journal of Physical Anthropology
562
W. NOWACZEWSKA
recently suggested by Balzeau and Rougier (2010) that
different types of fossae (including supranuchal fossa)
observed in Hs share a common etiology due to similarities in their internal composition (these depressions
correspond to a resorptive region on the external surface of the occipital bone). However, based on the
results of this study, the difference between the external morphology of the supranuchal fossae and nonsupranuchal fossae occurring in some Hs suggests that
these depressions formed as the result of different processes; thus, they do not share a common etiology. This
finding suggests that, in contrast to non-supranuchal
fossa, the external morphology of the supranuchal
depression can be considered to be a specific response
to the high degree of expression of the external cranial
superstructures.
Further research is needed to determine the development of the depressions above the inion and to clarify
the variations in internal and external occipital bone
morphology in this region of the occipital bone of fossil
and recent humans. Nevertheless, the results suggest
that the non-supranuchal fossae of some recent Hs and
Neanderthal suprainiac fossae have the same adaptive
meaning. By accepting this interpretation, we can
assume that the Neanderthal suprainiac fossae and nonsupranuchal fossae are probably convergent traits.
ACKNOWLEDGMENTS
I thank Krzysztof Boryslawski, Barbara Hulanicka, and
Boguslaw Pawlowski for their permission to study the
skeletal collections of recent Homo sapiens. I am grateful
to Marta Dočkalová, Jiřı́ Svoboda, Jean-Louis Heim, and
Philippe Mennecier for permission to study the fossils in
their care. Editor-in-Chief Christopher Ruff, the associate
editor, and two anonymous reviewers provided insightful
comments that helped to improve this article. I also thank
my husband for his unconditional support.
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homo, neanderthal, nonsupranuchal, fossa, suprainiac, traits, sapiens, convergence
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