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Apples oranges and the lunate sulcus.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 67:313-315 (1985)
Apples, Oranges, and the Lunate Sulcus
DEAN FALK
Department ofAnatomy and the Caribbean Primate Research Center,
Uniuersity ofPuerto Rico School of Medicine, San Juan, Puerto Rico 00936
KEY WORDS Australopithecines, Brain evolution, Chimpanzees,
Endocasts, Lunate sulcus, Taung
ABSTRACT Holloway (1984) used a method of direct tape-arc measurements on chimpanzee brain casts to reject the hypothesis that the lunate sulcus
is located in an anterior position in the Taung endocast. However, Holloway
neglected to measure the occipital pole-lunate sulcus (OP-LS) arc directly on
the Taung endocast as he did on chimpanzee brain casts (a crucial part of his
methodology); instead, he determined the relative position of Taung’s lunate
sulcus on the basis of a calculation that confounds direct measurements and
measurements from photographs. When arc OP-LS is measured directly on
Taung according to Holloway’s methods, the feature that has been identified
as the medial end of the lunate sulcus is shown to be located within the range
that Holloway determined for chimpanzees. Thus Holloway’s methodology and
data support rather than refute the claim that the lunate sulcus is located in a
pongid-like position in australopithecines.
In the fourth publication of an ongoing exchange regarding australopithecine endocasts, Holloway (1984)refuted my claim of an
anterior, pongid-like position for the lunate
sulcus (L) on the Taung endocast. Holloway
determined arc measurements directly on six
chimpanzee brain casts and calculated the
ratios of the arc distances between the occipital pole and lunate sulcus (OP-LS) and between the occipital and frontal poles (OP-FP).
He also measured an OP-FP arc of 165 mm
directly on a reconstruction of the Taung endocast (the original specimen lacks the frontal pole). However, although Holloway (1984)
stated that “the 0.P.-L.S. arc distance (per
Falk’s 1980 placement) was measured” on
the Taung endocast, Holloway did not measure this arc directly on the Taung endocast.
Instead, he apparently multiplied his direct
165-mmarc OP-FP by my OP-LS/OP-FPratio
of 0.259 that I determined (Falk, 1983) from
his published photograph of the Taung specimen (showing my placement of the lunate
sulcus; Holloway, 1981) to obtain “Falk’s
(1980) L.S. portion on Taung = 43” (Holloway, 1984)! In this calculation (which it
should be noted is Holloway’s, not Falk‘s), a
measurement taken directly from the Taung
endocast has been confounded by multiply-
0 1985 ALAN R. LISS, INC
ing it by a ratio based on slightly different
measurements (see below) taken from photographs. Apples have been multiplied by oranges. A preferable procedure would have
been to measure the arc OP-LS directly on
the Taung endocast, since both of these points
are available on the endocast, and to use this
direct measurement as the numerator in the
ratio OP-LS/OP-FP.
Using the procedures discussed above, Holloway (1984)concludes that the feature I suggest might be the medial end of the lunate
sulcus on the Taung endocast is located too
far rostra1 to be L because it “falls between
two and three standard deviations anterior
to the position expected for a L.S., if it were
following a pongid (chimpanzee)pattern.” In
the present paper, I report the arc OP-LS
measured directly from a copy of the Taung
endocast and divide it by the arc OP-FP that
was determined directly on a reconstruction
of the Taung endocast by Holloway. The resulting ratio is shown to be within the range
of comparable ratios reported for chimpanzees by Holloway, demonstrating once again
that the location of this feature is compatible
Received December 31,1985; accepted March 25,1985.
D. FALK
314
with the interpretation that it could be the
medial end of a pongid-like lunate sulcus.
U T E R I A L S AND METHODS
The OP-FP and OP-LS arc measurements
were taken on three occasions directly from
both hemispheres of a chimpanzee brain in
the author’s collection and on the left hemisphere of a chimpanzee brain cast (which is
a copy of cast 5 in Holloway’s Table 1, 1984)
according to procedures outlined by Holloway (1984). The ratios OP-LS/OP-FP were
calculated from the mean arc measurements
for the three hemispheres. Similarly, arc OPLS was measured on three occasions directly
from my copy of the Taung endocast and its
average value divided by Holloway’s direct
arc OP-FP to obtain a ratio that would be
internally consistent (i.e., based only on direct measurements) and therefore comparable to those listed for chimpanzees by
Holloway (see Table 1).
If, as Holloway claims, the direct ratio OPLS/OP-FP is the same as Falk’s “profile index” (1983),it would not be necessary to avoid
combining measurements taken directly
from endocasts with ratios determined from
photographs. However, the arcs included in
my profile index taken from photographs are
located along the midline of the brain or endocast, whereas arcs taken directly on brains
or casts run along the plane that actually
contains both poles rather than being projected onto the sagittal plane. For example,
the occipital poles are located laterally compared t o the frontal poles in all three chimpanzee hemispheres measured for this study,
TABLE 1. Actual arc measurements on chimpanzee
brain casts, a chimpanzee brain, and the Taung
endocast (millimetersjl
Specimen
Arc
Arc
OP-FP _ OP-LS
~
_
RH DF RH DF
Ratio OP-LSI
OP-FP
_
RH
DF
5
6
132
125
125
130
151 152
124
Chimpanzee brain
Right hem.
Left hem.
Taung
165
endocast
RESULTS
Table 1 combines Holloway’s measurements with my own. Holloway’s and my ratios for chimpanzee brain cast 5 differ by 6%,
although our arc measurements are very
similar (151 vs. 152; 36 vs. 34). The ratios of
OP-LS/OP-FP in the two hemispheres of the
chimpanzee brain differ by 12%,which shows
that the relative position of the lunate sulcus
can vary considerably within one brain. A
photograph of the right hemisphere of this
juvenile chimpanzee brain is provided by
Falk (1983) and it should be noted that the
0.268 ratio determined directly from the
hemisphere according to Holloway’s procedures again demonstrates that the lunate
sulcus in this hemisphere is located rostra1
to the location of the feature that I identify
as the possible medial end of L in the juvenile
Taung endocast. This is true whether measurements are taken from photographs or
directly from brainskasts (Falk, 1983).
Finally, the arc OP-LS for Taung averages
40 mm and the ratio OP-LS/OP-FP,utilizing
Holloway’s denominator, is 0.242, which is
identical to that determined by Holloway
(1984, Table 1) for chimpanzee brain cast 1.
This finding alone unequivocally demonstrates that the medial end of the feature I
identify as a possible L in Taung is within the
pongid range.
DISCUSSION AND A PLEA
Chimpanzee brain cast
1
2
3
4
and the arcs directly measured on these hemispheres therefore course in a rostromedial
direction. Even if the difference between arcs
determined from photographs and those determined directly from casts or brains is as
little as 4% (Falk, 1983), the arc OP-LS in
Holloway’s Table 1 should have been measured directly from the Taung endocast to
reduce potential error, because Holloway’s
arc OP-FP for the Taung endocast itself resulted from a direct measurement, as did all
of the other arc measurements in his table.
142
142
32
26
27
21
36
26
34
38
34
40
0.242
0.208
0.216
0.208
0.238
0.210
0.224
0.268
0.239
0.242
‘RH, entries from Holloway (1984); DF, entries from this study;
LS, lunate sulcus; FP, frontal pole; OP, occipital pole.
This paper is the fifth publication in a recent exchange between Holloway and myself. Prior to these papers, Radinsky (1979)
opened the question of whether the lunate
sulcus is in a pongid-like or human-like position on the Taung endocast, and the discussion between Holloway and myself seems
now to have become focused on this one question. In this brief note, I have again demonstrated that the tiny feature (dimple) that I
have identified as a possible medial end of L
315
LUNATE SULCUS
is in a pongid-like position consistent with
that identification. However, to focus the
wider discussion regarding the organization
of australopithecine cortical sulcal patterns
on this one dimple is literally begging the
question. Whether or not the feature in question actually is L, ample evidence demonstrates that all of the other numerous sulci
reproduced on the Taung and other australopithecine endocasts appear to be pongid-like,
rather than human-like (Falk, 1980, 1983).
In other words, the total sulcal pattern on
the Taung endocast is similar to that seen in
other primates of approximately equivalent
brain size, which is what one would expect
from an allometric point of view (Radinsky,
1970, 1972).
I hope that one year from now I will not be
writing the seventh paper in this series. Obviously, neither Holloway nor I are changing
our opinions about the cortical morphology
of australopithecines (see also Falk, 1984). It
is time that other workers examine the evidence and contribute to this discussion. My
laboratory and endocast collection are available to other researchers (or their students)
who are interested in this problem.
Collins for prodding me to write this response (5)to Holloway’s rejection (4) of my
reply (3) to Holloway’s revisit (2) to my reanalysis (1) of South African australopithecine natural endocasts. I also thank the National Science Foundation for supporting this
work (BNS8318253).
LITERATURE CITED
Falk, D (1980)A reanalysis of the South African australopithecine natural endocasts. Am. J. Phys. Anthropol.
53:525-539.
Falk, D (1983)The Taung endocast A reply to Holloway.
Am. J.Phys. Anthropol. 60r479-489.
Falk, D (1985)Hadar AL 162-28 endocast as evidence
that brain enlargement preceded cortical reorganization in hominid evolution. Nature. 313:4547.
Holloway, RL (1981)Revisiting the South African Taung
australopithecine endocast: The position of the lunate
sulcus as determined by the stereoplotting technique.
Am. J. Phys. Anthropol. 56:43-58.
Holloway, RL (1984)The Taung endocast and the lunate
sulcus: A rejection of the hypothesis of its anterior
position. Am. J. Phys. Anthropol. 64:285-287.
Radinsky, LB (1970)The fossil evidence of prosimian
brain evolution. In C Noback and W Montagna (eds):
The Primate Brain. New York Appleton-CenturyCrofts, pp. 209-224.
Radinsky, LB (1972)Endocasts and studies of primate
brain evolution. In R Tuttle (ed): The Functional and
Evolutionary Biology of Primates. Chicago: Aldine pp.
175-184.
Radinsky, LB (1979)The Fossil Record of Primate Brain
Evolution. 49 t h James Arthur Lecture, 1979. American M u m m of Natural History, New York.
~~
ACKNOWLEDGMENTS
1 thank wally Welker for providing the
copy of the chimpanzee brain cast and Del
~~
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