Dental Topography in Early Homo

A dental topographic analysis for early Homo specimens was recently published (Ungar, 2004). High resolution replicas of all available undamaged M2s of Homo erectus (KNM-ER 806, KNM-ER 992, KNM-WT 15000, OH 22), H habilis (OH 16), H rudolfensis (KNM-ER 1506, KNM-ER 1802), and early Homo sp. indet. (KNM-ER 3734) were included in this study.

Data for these specimens were pooled into a single sample given the number of individuals of each species and compared with results for Australopithecus afarensis (n = 15 individuals from Hadar, Ethiopia and Laetoli, Tanzania) and the extant African apes Gorilla gorilla gorilla (n = 47) and Pan troglodytes troglodytes (n = 54). Australopithecus afarensis was selected as a reasonable model for a generalized australopith occlusal morphology from which early Homo might have been derived (see Ungar, 2004 for discussion). The western lowland gorilla and central African chimpanzee were chosen as the extant baseline for comparison because of moderate differences in their diets (see M'Kirera and Ungar, 2003; Ungar and M'Kirera, 2003 for references and details), and because their teeth follow the same general "Bauplan" as those of early hominins. More information on these samples can be found in Ungar (2004).

Results for comparisons of occlusal slope are shown in Figs. 11.1 and 11.2 and Table 11.1. A two-way analysis of variance was run on ranked slope data with taxon and wear stage as the factors. There is significant variation in both taxon and wear stage, but no significant interaction between the factors. This means that the species differ in average slope, and that slope varies by wear stage. On the other hand,

Fig. 11.2 Comparisons of mean surface slopes for taxa at given wear stages (Modified from Ungar, 2004).

differences between species remain consistent across wear stages, suggesting that slopes can be compared between species at given stages of dental wear.

Multiple comparisons tests indicate significant differences between most pairs of species examined. Early Homo occlusal slope values are intermediate between those of gorillas and chimpanzees, suggesting an adaptation for foods with fracture properties intermediate between those of gorillas and chimpanzees. Both Pan troglodytes troglodytes and Gorilla gorilla gorilla prefer soft, ripe fruits when available, though the steep slopes of the gorilla molars allow them to efficiently shear tough, less preferred leaves and stems at times of resource scarcity (see Ungar and M'Kirera, 2003 and references therein). This suggests that early Homo molars could have fractured tough foods more efficiently than can chimpanzees but less efficiently than can gorillas.

Fig. 11.1 Digital elevation models of representative specimens of (a) Homo erectus (KNM-WT 15000), (b) Homo rudolfensis (KNM-ER 1506), (c) Gorilla gorilla (CMNH B1781), and (d) Pan troglodytes (CMNH B3437).

Fig. 11.1 Digital elevation models of representative specimens of (a) Homo erectus (KNM-WT 15000), (b) Homo rudolfensis (KNM-ER 1506), (c) Gorilla gorilla (CMNH B1781), and (d) Pan troglodytes (CMNH B3437).

Table 11.1 Results for the dental topography study (Data from Ungar, 2004)

A. Summary statistics for occlusal slope (in degrees). Dashes indicate

no data at that wear stage

Wear

Australopithecus

Gorilla

Homo

Pan

Mean

SD

N

Mean

SD

N

Mean

SD

N

Mean

SD

N

1

37.89

-

1

-

-

-

37.9Z

-

1

-

-

-

Z

3Z.01

B.154

4

37.75

5.03B

7

3B.5

4.B77

Z

3Z.88

5.859

5

3

Z5.4B

3.81

7

3B.Z9

Z.BB5

10

35.83

9.519

3

30.15

5.771

Z8

4

Z5.Z1

Z.45

Z

3Z.13

5.0B9

14

ZB.5Z

3.Z9B

Z

ZB.48

4.B8

18

5

-

-

-

Z7.53

4^9

13

-

-

-

Z5.B9

8.B07

Z

B

3Z.05

-

1

3Z.14

B.445

3

-

-

-

Z9.31

-

1

B. Analyses of rank-transformed slope data

Two factor ANOVA results

Effect

df F

p

Taxon

3.90 8.B07

0.00

Wear class

Z.90 8.409

0.00

Interaction

B.90 0.B83

0.BB

Pairwise mean differences (Bonferroni test results)

Australopithecus Gorilla

Homo

Gorilla

5Z.Z95'

Homo

34.493'' -17.80Z

Pan

19.17Z -33.^3'

-15.321

'p < 0.05, **p

< 0.1.

Of particular interest is the comparison with Australopithecus afarensis molars. The shallow sloped australopith molars were not well-suited to fracturing tough foods, but would have been better at crushing hard, brittle items. Indeed, the average slope difference between A. afarensis and the combined sample of early Homo is on the same order of magnitude as that between the extant chimpanzee and gorilla samples examined. Perhaps then, differences between these hominins relate to adaptations for fallback resource differences, as has been suggested for chimpanzees and gorillas.

Ungar (2004) suggested that both Australopithecus afarensis and early Homo probably preferred nutrient rich foods with less challenging fracture properties, but that early Homo might have relied more on tough fallback foods, whereas their australopith predecessors would have consumed more hard, brittle items at "crunch times." Tougher foods eaten by early Homo might have included pliant plant parts and/or meat (see Lucas and Peters, 2000).

Was this article helpful?

0 0

Post a comment