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Evidence for a dual pattern of cranial venous sinuses on the endocranial cast of taung (Australopithecus africanus).

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Evidence for a Dual Pattern of Cranial Venous Sinuses on the
Endocranial Cast of Taung (Australopithecus africanus)
Department of AnatomylPalaeo-anthropologyResearch Unit, Uniuersity of
Witwatersrand Medical School. Parktown. Johannesburg 2193. South
Africa (P.V.T.);Department of Anthropology, SUNY AlbGny, Aibany, NY
12222 (D.F.)
Occipital-marginal sinus, Brain vasculature,
Australopithecine, Polymorphism
According to published accounts, an enlarged occipital-marginal sinus system is absent in Australopithecus africanus, although it occurs
in high frequencies in A. robustus, A. Boisei, and Hadar hominids commonly
designatedd. afarensis.In this report, we describe, for the first time, an enlarged
occipital-marginalsinus system on the endocranial cast of the Taung specimen,
which is part of the holotype of A. africanus. In addition, well-developed right
transverse and sigmoid sinuses are represented on the Taung endocast. The
various components of the dual venous sinus system on the Taung endocast are
measured, and the system is compared to those of other fossil hominids. The
compresence of a lateral sinus system and enlarged occipital and marginal
sinuses occurs in two Hadar specimens, 2 specimens of A. robustus crassidem,
1 A. boisei specimen, and several early H . sapiens crania. Hence, the presence
of strong transverse sinus impressions in a fragmentary specimen may not be
interpreted as an indication that an enlarged occipital-marginal sinus system
was not present in the original specimen. Conversely, lack of transverse sinus
grooves in a fragmentary specimen does provide indirect evidence than an enlarged occipital-marginalsystem would probably have been present in the whole
specimen, as in 2 specimens of A. boisei. Including Taung, enlarged occipital
and marginal sinuses occur in 1 out of 5 , or 20%,of A . africanus specimens.
This figure compares well with the range of mean frequencies in modern human
cranial series (1.5 to 28%), but is much lower than are the frequencies for A.
boisei, A. robustus, and the Hadar hominids. Although sample sizes for ancient
hominids remain small, it appears that we are dealing with a genetic polymorphism that expresses itself in widely varying frequencies in populations of
different hominids.
An enlarged occipital-marginal venous
sinus sytem occurs in very high frequency
in horninids assigned to the australopithecine species, Australopithecus boisei and A.
robustus (Tobias, 1967,1968;Falk and Conroy, 1983; Kimbel, 1984) and among the
Hadar hominids commonly designated A.
ufarensis (Falk and Conroy, 1983; Kimbel,
1984; Falk, 1986). From the key observation
on the type specimen of A . boisei, OH 5 from
the Olduvai Formation, it was inferred that
“most if not all of the blood from the superior
sagittal and straight sinuses ran into the
occipital and marginal sinuses, thus by-
passing the transverse-sigmoid sinus system” (Tobias, 1967; p. 65).
On the other hand, in all Sterkfontein and
Makapansgat specimens of A. africanus in
which the relevant area is adequately preserved, well-developed grooves for the transverse and sigmoid sinuses implied that, in
this species, most, if not all, of the blood from
the sagittal and straight sinuses followed the
drainage path most commonly encountered
in modern Homo sapiens, namely, the transReceived August 11, 1987; accepted January 25,1988.
3 10
Fig. 2. Detailed illustration of the Taung endocast as
Fig. 1. Photograph of the occipital region of a copy of the
natural endocranid cast from the Taung specimen (AILS- photographed in Figure 1. For abbreviations, see Figure 1.
trubpithecus ufncunus).Venous sinuses: M, marginal; 0,
occipital; S, sigmoid; T, transverse. Not to scale; see text
for discussion.
verse-sigmoid sinus route to the bulb of the
internal jugular vein (Tobias, 1967, 1968).
From these early studies, it was “provisionally concluded that the drainage pattern of
the dural sinuses of [A. boiseil constitutes a
variation which was commoner in the robust
australopithecines than it is in modern man,
among whom it may occur as a rare individual varation” (Tobias, 1967, p. 70; c.f., 1968,
p. 9).
To describe a variant as more common in
one taxon than in others is not, however, to
regard it as diagnostic of that taxon (Falk
and Kasinga, 1983). Rather, Tobias saw it
in the light of a probably genetic polymorphism, having a high incidence in robust and
hyperrobust australopithecines and a low
incidence in A. africanus and most populations of past and present members of Homo.
Interest in this feature was revived with
the discovery that most or all Hadar crania
showed enlarged occipital and marginal sinus
impressions, and with this came what were
apparently the first attempts to use this trait
as a diagnostic criterion (Howell, 1978; Holloway, 1981). Holloway (19811, in effect,
claimed that the presence of the occipitalmarginal drainage system in two Hadar
specimens made it likely that they were robust australopithecines rather than A. afarensis; while its absence from the Omo cranium
L338Y-6 (which Rak and Howell [19781 had
identified as a juvenile A. boisei) was used
by Holloway (1981) to support his reluctance
to accept that the Omo specimen belonged
to A. boisei.
A detailed examination of the trait by
Kimbel(l984) led him to regard the two main
drainage patterns of the hominids as adaptively equivalent and neutral character states.
On the other hand, Falk and Conroy (1983)
and Falk (1986) endeavored to relate the
presence of an occipital-marginal sinus
drainage system to a functionally important
adaptation for the more efficient delivery of
blood to the vertebral venous plexus in bipedal hominoids.
The renewed interest led us to examine,
once again, the relevant area of the endocast
of Taung, the type specimen of A. africanus. apparent in the cast of the posterior part of
To our surprise, we discovered the unmis- the cerebrum.
takable impression of a n enlarged right marThus the casts of both a lateral sinus sysginal sinus.
tem (transverse plus sigmoid) and an enlarged occipital and right marginal sinus
system coexist on the Taung endocast (the
The natural endocranial cast of the fossil left side is missing). The lateral sinus cast
infant cranium of Taung reproduces most of has the greater caliber. The diameter of the
the outer surface of the right cerebral and transverse sinus cast varies from 4.2 to 5.2
cerebellar hemispheres of the brain. Prom- mm, that of the sigmoid from 5.5 to 6.8 mm,
inent and distinct casts of the right trans- whereas that of the marginal sinus is only
verse and sigmoid sinuses are manifest on 3.6 mm. If the respective rates of blood flow
the posterior portion of the endocast (Figs. through these two sinuses were propor1, 2). In addition, a right marginal sinus is tional, a t least in large measure, to their
reproduced near the jugular end of the sig- relative diameters, it would seem that the
moid sinus impression (Fig. 1). The diame- primary route of blood flow from the superior
ters of these sinuses were measured (by sagittal sinus of Taung would have been
P.V.T.) on the original endocast, and the through the right lateral sinus system. In
venous sinus pattern of the Taung specimen addition, if an anastomosis existed between
is here described in detail for the first time. the confluence and the occipital sinus, a posThe transverse sinus cast is excellently sible secondary route for blood from the supreserved from the confluens sinuum as far perior sagittal sinus would have been through
as the area where it turns downward as the the occipital and marginal sinuses. The blood
sigmoid sinus impression. At the turning from the straight sinus seems to have drained,
point, close to the usual point of entry of the at least in large part, to the occipital-marginal
superior petrosal sinus, the lateral sinus cast sinus system; in addition, some might have
is marred for a short distance by an area of drained to a left transverse sinus (but of this
damage. Thereafter, the beautifully pre- possibility we must remain uncertain, as the
served cast of the sigmoid sinus is apparent, Taung endocast lacks the left posterior part).
until it turns anteriorly toward the jugular The detailed flow patterns could well have
notch of the lateral part of the occipital. Here, fluctuated between the central and lateral
just before the sigmoid sinus cast disappears (transcerebellar) routes, since in living inunder cover of the surviving pars lateralis dividuals this venous system is dynamic and
of the occipital bone, the sigmoid cast is joined blood flow may shift with posture, respirafrom posteromedially by a small, well-defined tion, and possibly other conditions.
right marginal sinus cast. The latter lies in
the sulcus of the cerebellar vallecula, beAt
important considerations
tween the cast of the caudal lobe of the cerebellar hemisphere laterally and that of the emerge from our observations on the Taung
endocast. First, our finding provides a furtuber vermis medially.
From its ending in the terminal sigmoid ther example of a specimen in which an ensinus, the marginal sinus cast may be traced larged occipital-marginal sinus system may
back, posteromedially, toward the conflu- coexist with a well-developed lateral sinus
ence. Superiorly and more medially, it is suc- system, as Tobias (1968, p. 6) pointed out.
ceeded by another sinus cast running Indeed, relatively few early hominid fossils
vertically and sagittally up the posterior cer- show signs of a total replacement of lateral
ebellar notch to the confluence. There is lit- sinus drainage by occipital-marginal sinus
tle doubt that the superior cast represents drainage. The specimen that comes closest to
the occipital sinus. A distinct indentation a complete “take over” by the occipitalseparates this cast from that of the confluens marginal system is OH 5, the holotype of A.
sinuum proper, from which it may be in- bozsei (Tobias, 1967, 1968).
Other fossil hominid specimens that exferred that the straight sinus probably
drained directly into the occipital-marginal hibit both a lateral sinus system and ensinus system. The right transverse sinus larged occipital and marginal sinuses are the
clearly received drainage from the superior Hadar specimens AL 288-1 and Al 333-45
sagittal sinus, the impression of which, con- (Kimbel, 1984); two Swartkrans specimens
trary to an earlier claim (Schepers, 19461, is of A. robustus crassidens, SK 859 (Tobias,
1967) and SK 1585 (Kimbel, 1984); KNMCh 304 of Chesowanja, Kenya (Gowlett et
al., 1981); a Pi-edmosti cranium from Moravia (Matiegka, 1923; Tobias, 1967); and
Skhiil I (Falk, 1986).
An important implication of these data is
that, as Falk (1986) has pointed out, the
presence of strong transverse sinus impressions in a fragmentary specimen does not
necessarily indicate that enlarged occipital
and marginal sinuses could not have been
present as well in the original intact specimen. On the other hand, a study of a large
number of ancient and modern hominids
suggests that the lack of transverse sinus
grooves in a fragmentary specimen does provide indirect evidence that an enlarged occipital-marginal sinus system would probably
have been present (as in OH 5, ER 407, and
Guomde) (Falk, 1986).
The second major point to emerge is that
Taung is the first A. africanus specimen to
manifest enlargement of the occipital and
marginal sinuses. In six other A. africanus
specimens studied by Tobias (19681, Kimbel
(1984),and Falk (19861, five from Sterkfontein
and one from Makapansgat, well-developed
lateral sinus impressions are present. On four
of these six specimens (Sts 5, Sts 19, Sts 26,
and MLD l),enough is preserved below the
level of the internal occipital protuberance
t o enable us to affirm the absence from both
sides of enlarged occipital and marginal sinuses. On one of the other two A. africanus
specimens (Sts 60mM 15111, the area below
the protuberance is not adequately preserved to permit us to determine whether or
not enlarged occipital and marginal sinuses
were present. On the sixthA. africanus specimen (Sts 711, although to the right of the
internal occipital crest an occipital sinus
groove and a right marginal sinus groove are
lacking, the bone to the left of the internal
occipital crest is missing: hence, it cannot be
determined whether an occipital sinus groove
was present to the left of the crest or whether
a left marginal sinus groove was present.
As we have said above, from the findings
in Taung and in several other early hominid
endocasts,the mere presenceof well-developed
lateral sinuses in Sts 60 and Sts 71 does not
exclude the possibility of enlarged occipital
and marginal sinuses having coexisted in
them; we simply do not know (Kimbel, 1984,
p. 253). If we exclude Sts 60 and Sts 71, and
include Taung, we have a frequency of 1out
of 5, or 20%, of enlarged occipitaL'margina1
sinuses in A. africanus. This percentage is
much lower than are the figures pertaining
to A. boisei, A. robustus, and the Hadar hominids (Kimbel, 1984; Falk, 1986), but it is of
the approximate order of magnitude shown
by a variety of modern human cranial populations. Values for a number of modern H .
sapiens series range from 1.5 to 28.0% (data
collated from earlier studies as well as new
data collected by Tobias 119681 and Kimbel
[1984]). The new evidence supports the concept that we may be dealing with a genetic
polymorphism that expresses itself with
widely varying frequencies among populations of ancient and modern hominids.
We are grateful to Mrs. Val Strong for her
valued help. The National Science Foundation is gratefully acknowledged for support
for D.F. (BNS-8796195)and the Foundation
for Research Development for generous subvention to P.V.T.
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venous, cranial, cast, endocranial, patterns, dual, taung, evidence, sinuses, australopithecus, africanus
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