In order to determine if the Kebara 2 hyoid bone is more human-like or more ape like a series o f statistical analyses was carried out.
The metric dimensions o f the Kebara 2 hyoid bone were compared to those o f the known aged human sample from chapter 2 o f this thesis.
The quahtative morphological features o f the Kebara hyoid were compared to the humans and African apes in chapter 2. This morphology includes the anterior tubercle, the posterior depression and the muscle attachment markings.
The metric dimensions o f the Kebara 2 hyoid bone were included in a discriminant function analysis to determine the grouping o f this hominin bone.
Percentiles o f hyoid bone measurements were generated for humans, chimpanzees and gorillas. The percentiles for humans chimpanzees and gorillas were taken from the full adult sample for each species used in chapter 2. This was the total adult sample not the sub-sample with cranial measurements. The observed hyoid bone measurements for the Kebara 2 Neanderthal were compared to the pattern o f measurements o f the human and chimpanzee hyoid bones using these percentiles.
Multiple regression analysis was used to determine which cranial measurements were the most accurate in predicting hyoid bone size and shape in humans (Table 2.29) and in chimpanzees (Table 2.30). These equations were then used to predict the hyoid bone size and shape using the cranial measurements for the La Chapelle-aux-Saints Neanderthal and an average Neanderthal. The inferred hyoid bones were then compared to the observed size and shape o f the Kebara hyoid bone using human and chimpanzee percentiles.
Predictions o f hyoid bone size and shape were also made for P. boisei, A.
africanus, Homo sp. and Homo erectus. The estimated hyoid measurements for these four species were also compared to the human, chimpanzee, and in one case gorilla,
percentiles. These measurements were also compared to the observed measurements o f the Kebara hyoid to determine the differences and similarities inferred from the estimates.
R
e s u l t sHy o i d b o n e p r e d i c t i o n s
The Kebara 2 hyoid bone is the only published Neanderthal hyoid bone and is taken as representative for the taxon. This bone was used as the standard against which to
measure the predictions o f hyoid bone dimensions generated from the multiple regression analysis.
Th e Ke b a r a h y o i db o n e c o m p a r e d t om o d e r nh u m a n sa n d c h i m p a n z e e s
To test the accuracy o f the regression equations the average human and cranial measurements were used in the regression equations and compared to the average observed hyoid bone measurements for each species. The human equation gave
measurements close to the observed human measurements and the chimpanzee equation using the chimpanzee cranial measurements produced measurements close to the observed chimpanzee hyoid bone measurements. However, these equations are not interchangeable. They give estimates o f hyoid bone dimensions very different from the observed
measurements when human cranial measurements are used in the chimpanzee equation or the chimpanzee cranial measurements in the human equations. The average human hyoid bone and the estimated human hyoid bone using the human equations are closest to the observed Kebara 2 hyoid bone measurements (Table 5.2).
Table 5.2 The Kebara hyoid bone measurements, the observed human and chimpanzee hyoid bone measurements and the estimated measurements using human and chimpanzee equations
Measurements Kebara Human Chimpanzee
Obs Obs Human Pan Obs Pan Human
XML 35.5 38.5 37.5 64.7 50.2 50.3 29.2 TMB 45.0 40.4 38.7 19.5 32.8 30.9 -26.5 MTD 24.6 24.0 23.8 22.0 24.1 24.4 24.1 MMH 13.4 10.0 10.4 n.s. 11.9 n.s. 16.1 APT 5.8 5.1 5.4 32.7 12.5 11.7 -1.7 LGH 25.0 27.8 26.0 24.3 32.3 31.3 27.9 WGH 5.2 6.4 6.3 11.4 3.7 3.6 13.1 DPS 3.8 6.1 6.8 n.s. 10.8 n.s. -1.5
The observed Kebara hyoid bone measurements were plotted on to percentile charts generated respectively from the adult human and adult chimpanzee hyoid bone measurements used in chapter 2. The human percentile chart (Fig. 5.3) shows that the Kebara hyoid bone is within the range o f variation for all measurements. The maximum
medial height (MMH) tails on the 95'^ percentile, while the width o f the greater horns falls on the s'*" percentile. The Kebara hyoid bone follows the same pattern as found in the human percentiles, with for example total maximum breadth being greater than total maximum length. On the chimpanzee percentile chart (Fig. 5.4), many o f the
measurements fall outside the range o f percentiles. Furthermore, the overall pattern is very different to that o f produced by the chimpanzee percentiles.
80 70 60 S e 1--- 2
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0) E o 30I
0 TML TM B MTD MMH A P T LGH H yoid b o n e d i m e n s io n s 5 --- 2 5 — 5 0 - 7 5 ---9 5 • K e b a r a W G H D P SFigure 5.3 The Kebara hyoid bone measurements compared to the human hyoid bone percentiles
80 70 60 E E, I
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50 Î W G H TML TMB MTD MMH A P T LGH D P S H yoid b o n e d i m e n s io n s ■5 --- 2 5 --- 5 0 --- 7 5 9 5 • K e b a r aWhen the human cranial measurements were used with the chimpanzee equations, they produced a pattern that was very different from both the Kebara 2 hyoid and the pattern produced by the chimpanzee percentiles (Fig. 5.5). The total maximum length is far longer than found in the chimpanzee. The anterio-posterior thickness (APT) is greater than that found in either the chimpanzee or gorilla. Many o f the measurements are outside the range o f the chimpanzee percentiles. The two measurements that are within the percentiles are the two measurements that discriminate least between the humans, chimpanzees and gorillas in chapter 2.
Using the chimpanzee cranial measurements and the human equations produced a pattern that would not be found in life (Fig. 5.6), several measurements were negative, including total maximum breadth (TMB), anterio-posterior thickness (APT) and depth o f the posterior depression (DPS). This would mean for example that the greater horns would cross each other, a situation not found in any known mammal. The measurements that fell within the range o f the human percentiles were those that discriminated least between humans and chimpanzees (chapter 2).
80 E E I
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E o 30 10 TM B MTD TML MMH A P T LGH W G H D P S - 2 5 H y o id b o n e d i m e n s io n s ■50 — 7 5 ---9 5 • K e b a r a ■ h u m a s c h im pFigure 5.5 Hyoid measurements predicted using human cranium and chimpanzee equations compared to the observed Kebara measurements and the chimpanzee percentiles
80 6 0 E E 4 0 g I
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I X TM L TM B MTD MMH A P T LG H W G H D P S -20 - 4 0 H yoid b o n e d im e n s io n s 5 --- 2 5 — 5 0 --- 7 5 9 5 # K e b a r a A c h im p a s h u mFigure 5.6 Hyoid bone measurements predicted using chimpanzee cranium and human equations compared to observed Kebara measurements and human percentiles.
No cranium exists for the Kebara 2 Neanderthal. Therefore, the La Chapelle-aux- Saints Neanderthal and an average o f Neanderthal cranial measurements were used to test the hypothesis that the Kebara hyoid bone is human-like. Both the La Chapelle-aux-Saints and the average Neanderthal crania were used in each set o f regression equations. Two sets o f measurements were therefore produced for each cranium. The measurements generated using the Neanderthal cranial measurements and the human equations gave measurements closest to the observed Kebara 2 hyoid measurements (Table 5.5).
Table 5.3 The Kebara hyoid bone measurements, and the estimated measurements for La Chapelle- aux-Saints and an average Neanderthal using human and chimpanzee equations
Measurements Kebara La Chapelle Av. Neanderthal
Observed Human Pan Human Pan
T M L 35.5 36.0 32.3 T M B 45.0 37.4 5 5 ^ 33.6 45.5 M T D 24.6 33.5 2 2 6 32.6 21.3 M M H 13.4 APT 5.8 7.4 23.8 6.7 46.5 LGH 25.0 28.3 2 5 ^ 27.7 28.7 W GH 5.2 4.8 7.5 DPS 3,8 9.2 8.4
The estimated hyoid bone dimensions for both the La Chapelle-aux-Saints and an average Neanderthal follow the same pattern as that for both the observed Kebara hyoid
measurements and the human percentiles (Fig. 5.7). For example, the total maximum breadth is greater than the total maximum length. The anterio-posterior thickness o f the hyoid body (APT), the length o f the greater horns (LGH) and the depth o f the posterior depression (DPS) are within or very close to the human percentiles. It was not possible to predict two o f the measurements, maximum medial height (MMH) and width of the greater horn (WGH) as the cranial measurements were not available in the literature. It would seem that the relationship between the hyoid bone and the cranium is the same in the Neanderthals as that found in modem humans.
The pattern shown by the La Chapelle-aux-Saints Neanderthal and an average Neanderthal is very different to that o f the chimpanzee percentiles (Fig. 5.8). These dimensions show a similar relationship to the chimpanzee percentiles, as the human
estimates using the chimpanzee equations (Fig. 5.5). The predicted measurements for both the Neanderthals and modem humans are very different to the relationship o f the observed Kebara hyoid bone measurements to the chimpanzee percentiles. The use o f the
chimpanzee equation, for example, predicts an extremely thick hyoid body for the
Neanderthals, The size of this measurement is comparable with that predicted for a human hyoid using a human cranium and the chimpanzee equations. The observed anterio
posterior thickness (APT) o f thé Kebara 2 hyoid is very similar in size to that foimd in a modem human hyoid bone. This indicates that a different relationship exists between the chimpanzee cranium and the hyoid bone than that found in either modem humans or the Neanderthals. It would seem that chimpanzee crania could not predict the Neanderthal hyoid bone.
80 7 0 6 0 E E î X MTD A P T LGH W G H O R S TML TM B MMH - 2 5 H yoid b o n e d i m e n s io n s - 5 0 --- 7 5 9 5 O K e b a r a ■ L a C h a p e l le ♦ Av N e a n d e r th a l
Figure 5.7 The observed and predicted hyoid bone measurements for Kebara 2 compared to human percentiles
7 0 6 0
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E o 3 0 Î X MTD LGH W G H D P S TML TM B MMH A P T H y o id b o n e d i m e n s io n s 5 ---2 5 ---5 0 — 7 5 ---9 5 O K e b a r a ■ L a C h a p e l le ♦ Av N e a d e r th a lFigure 5.8 The observed and predicted hyoid bone measurements for Kebara 2 compared to chim panzee percentiles
Th e k e b a r a h y o i d b o n e c o m p a r e d t o h o m i n i n e s t i m a t e d h y o i d b o n e d i m e n s i o n s
The cranial measurements for the four earlier hominin species were used in both the human and chimpanzee regression equations. Tliis produced two sets o f equations for each species (Table 5.4). Comparison with the observed Kebara hyoid measurements show that the one shape measurement, anterio-posterior thickness (APT), that can be predicted from both sets o f equations varied according to whether the human or chimpanzee
equation was used. Total maximum breadth and total maximum length were also very different in the australopithecines depending on which equation was used.
Table 5.4 The Kebara hyoid measurements compared to the earlier fossil hominin hyoid bone estimates
Kebara P. boisei A. africaniis Homo sp. H. erectus
Human Pan Human Pan Human Pan Human Pan
TML 35.5 31.6 67.6 33.3 57.8 31.4 57.8 35.1 74.7 TMB 45.0 -21.0 45.3 -13.5 35.4 42.3 35.8 39.8 44.0 MTD 24.6 28.9 25.6 22.1 21.5 24.6 28.2 29.2 27.4 MMH 13.4 15.1 n.s. 13.0 n.s. 12.9 n.s. 11.2 n.s. APT 5.8 1.8 14.0 0.2 12.4 4.9 4.9 5.2 18.1 LGH 25.0 34.9 29.5 31.7 27.9 25.4 29.5 31.2 26.3 DPS 3.8 2.6. n.s. 0.7 n.s. 6.2 n.s. 6.6 n.s. WGH 5.2 17.3 3.3 12.8 12.7 11.7 11.2 10.6 3.2
The predicted measurements for each o f the four hominin species were compared to both the human and chimpanzee percentiles. The measurements generated using the human equations were plotted on to the human percentiles. The hyoid measurements generated by the chimpanzee equations were plotted on to the chimpanzee percentiles. The observed Kebara 2 measurements were included on each graph to show how this
Neanderthal bone differs from the predicted hyoid bone for each species.
The predicted measurements for P. boisei using the human equations show a different pattern from both the human percentiles and the Kebara 2 hyoid bone (Fig. 5.9). The pattern is similar to that generated by the chimpanzee when the measurements were predicted using the chimpanzee cranium and the human equations. One measurement, total maximum breadth (TMB) is negative as in the chimpanzee estimate. This would not be found in any hyoid bone. Several other measurements are very different from those found in the Kebara Neanderthal or the human percentiles. Anterio-posterior thickness (APT) is very small. Only very small primates such as the tamarin have a hyoid thickness o f this size. In contrast, the vridth o f the greater horn (WGH) is much larger than that observed in either the Kebara Neanderthal or modem humans. The human equations do not seem to be the appropriate ones to use for this species. The chimpanzee equations produced a pattern much closer to that o f the chimpanzee percentiles (5.10). However, several measurements are larger than those found in the chimpanzee. The size o f this hyoid would be closer to that for the gorilla (Fig. 5.11). P. boisei has a predicted total maximum length (TML) greater than predicted total maximum breadth. This is the reverse o f the human pattern (Fig. 5.3).
80 E & 4 0 S
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X TM L TM B M TD MMH A P T LG H W G H D P S -20 -4 0 H y o id b o n e d im e n s io n s 5 --- 2 5 5 0 - 7 5 9 5 O K e b a r a ♦ P b o is ie (H u m )Figure 5.9 The estimated hyoid bone measurements for P. boisei using human equations compared to Kebara 2 and the human percentiles.
8 0 7 0 6 0 E E ÿ s E 0 3 0 1 I 20 TM B MTD W G H TML MMH A P T LGH D P S H y o id b o n e d im e n s io n s 5 --- 2 5 5 0 — 7 5 ---9 5 O K e b a r a ♦ P b o is ie (c h im p )
Figure 5.10 The estimated hyoid bone measurements for P. boisei using chimpanzee equations compared to Kebara 2 and the chimpanzee percentiles.
80 E E i i ''° E
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S §. ^ 20 TM B MTD LGH W G H D P S TML MMH A P T H yoid b o n e d i m e n s io n s 5 --- 2 5 5 0 - - 7 5 9 5 ♦ P b o is ie (c h im p ) O K e b a r aFigure 5.11 The predicted measurements for P. boisei using chim panzee equations compared to Kebara 2 and gorilla percentiles
The predicted hyoid bone measurements for A. africanus generated from the human equations (Fig. 5.12) show a similar pattern to those o f P. boisei and to the predicted measurements based on the average chimpanzee cranial measurements and the human equations (Fig. 5.7). The total maximum length (TML) is again negative and the anterio-posterior thickness (APT) is very small only just above zero.
The predicted measurements for this species using the chimpanzee equations showed a more chimpanzee-like pattern (Fig. 5.13). The predicted total length (TML) and greater horn width (WGH) oTT. africanus were outside the range o f the chimpanzee percentiles, even so, they do follow the same sort o f pattern. Although some aspects o f the predicted A. africanus hyoid bone differ from both human and African apes, it seems likely that A. africanus would have had a hyoid bone closer to an African ape than to a modem human one.
7 0 6 0 E E i 3 0 0)
i -
I X TM B MTD LG H W G H TM L MMH A P T D P S -10 -20 H y o id b o n e d im e n s io n s - 5 ---2 5 5 0 — - 7 5 9 5 O K e b a r a ▲ A a f r ic a n u s ( h u m )Figure 5.12 Estimated hyoid bone measurements based on the human equations for A. africanus compared to the observed Kebara 2 measurements and human percentiles
8 0 7 0 E 5 0 b 3 0 TML TM B MTD MMH A P T LGH W G H D P S H y o id b o n e d im e n s io n s 5 ---2 5 5 0 7 5 9 5 O K e b a r a A A a f r i c a n u s (ch im p )
Figure 5.13 The estimated hyoid bone measurements based on the chimpanzee equations lor /I. africanus compared to observed Kebara 2 measurements and the chimpanzee percentiles.
The position for Homo sp. is more equivocal. Both sets o f equations produce the overall pattern appropriate for either humans or chimpanzees. The human equations (Fig. 5.14) for example produce an estimated total length (TML) that is smaller than maximum breadth (TMB). While the chimpanzee equations produced the reverse pattern (Fig. 5.15) with total maximum length (TML) greater than maximum breadth (TMB). Some
measurements, total maximum length (TML) and greater horn width (WGH), on both the human and chimpanzee graphs and anterio-posterior thickness (APT) on the chimpanzee graph are outside the range o f the percentiles. However, both sets o f equations produced the same result for two measurements, anterio-posterior thickness (APT) and greater horn width (WGH). The anterio-posterior thickness (APT) is predicted as more human-like by both equations. It seems likely that early Homo had reduced the thickness o f the hyoid body but other aspects o f the morphology probably differed from both the human and chimpanzee patterns. 8 0 7 0 E E 5 0 S E 0 3 0 1 ^ 20 W G H TML I M S MTD MMH A P T LGH D P S H yoid b o n e d im e n s io n s 5 ---2 5 5 0 7 5 9 5 • K e b a r a + H o m o s p (h u m )
Figure 5.14 The estimated hyoid bone measurements for Homo sp. using the human equations compared to Kebara 2 hyoid measurements and the human percentiles