Early Homo Molars

The foregoing analyses support previous studies that have suggested molar cusp sizes to be of some utility in the assessment of the taxonomic affinities of hominin fossils (Wood et al., 1983; Wood and Engleman, 1988; Suwa, 1988; Suwa et al., 1994, 1996; Bailey, 2004). Accordingly, it is reasonable to employ such data in the assessment of the species attribution of the early Homo specimens from South Africa. However, because of the extremely small comparative fossil samples from East Africa, extreme caution must be exercised in the interpretation of these results.

Data pertaining to the discriminatory power of absolute and relative cusp sizes among East African specimens attributed to H. habilis, H. rudolfensis and H. erectus are presented in Table 6.6. Only in the relative cuspal proportions of the Mj are the three significantly distinct according to the Wilks' Lambda statistic, but in no instance does the H. rudolfensis sample exceed two specimens, and only for the lower molars do the H. habilis and H. erectus samples exceed two specimens.

When the South African Homo fossils are added as a separate sample, the relative cuspal proportions of both the M1 and M2 suggest significant inter-group distinctions, although the sample sizes are still exceedingly small (Table 6.7). Nevertheless, it is interesting to note that South African specimens were predicted to have membership in one of the East African samples only with reference to the M1 and M3. With regard to the M1, three of the five South African specimens (SKW 3114, SKX 267, DNH 70) were categorized as belonging with H. habilis on the basis of both absolute and relative cusp sizes. With regard to the M3, absolute cusp sizes predicted one of two South African specimens (Stw 80) to belong with H. habilis, while the other (SK 15) was predicted to be a member of the H. erectus sample. However, neither the M1 nor M2 of SK 15 suggested any such affinity.

Because the sample sizes involved in these analyses are so small as to preclude meaningful statistical inference, it is instructive to examine the distribution of the fossils according to the discriminant functions, and the dendrograms of the Mahalanobis D2 distances between them.

Among maxillary molars, absolute cusp sizes of the M1, place all five South African specimens within the Homo habilis sample cluster, although three (SK 27, SKW 3114, SE 255) have their closest affinities with one another

Table 6.6 Predicted group membership of East African Homo species groups from absolute and relative cuspal proportions

Species - percent correctly classified

Table 6.6 Predicted group membership of East African Homo species groups from absolute and relative cuspal proportions

Species - percent correctly classified

Taxon

Abs

Rel

Abs

Rel

Abs

Rel

Abs

Rel

Abs

Rel

Abs

Rel

H. habilis

n =

10

6

3

4

3

5

H. rudolfensis

n =

1

1

0

2

2

0

H. erectus

n =

2

2

0

5

7

5

H. habilis

90.0

90.0

83.3

100.0

xxx

xxx

100.0

100.0

66.7

100.0

80.0

20.0

H. rudolfensis

100.0

0.0

100.0

100.0

xxx

xxx

50.0

100.0

100.0

100.0

xxx

xxx

H. erectus

50.0

100.0

50.0

100.0

xxx

xxx

100.0

100.0

100.0

85.7

83.3

50.0

Wilks' Lambda

0.379

0.222

0.140

0.402

xxx

xxx

0.189

0.024

0.125

0.151

0.563

0.947

X2

8.3

12.8

8.8

4.1

xxx

xxx

10.0

22.4

14.6

13.2

4.1

0.4

df

8

8

8

8

xxx

xxx

10

10

10

10

5

5

P <

ns

ns

ns

ns

xxx

xxx

ns

0.01

ns

ns

ns

ns

Functions

xxx

xxx

1-2

Table 6.7 Predicted membership of Homo groups from absolute and relative cuspal proportions

Species - percent correctly classified

Table 6.7 Predicted membership of Homo groups from absolute and relative cuspal proportions

Species - percent correctly classified

Taxon

Abs

Rel

Abs

Rel

Abs

Rel

Abs

Rel

Abs

Rel

Abs

Rel

H. habilis

n =

10

6

3

4

3

5

H. rudolfensis

n =

1

1

0

2

2

0

H. erectus

n =

2

2

0

5

7

5

South Africa

n =

5

2

2

2

1

2

H. habilis

90.0

90.0

100.0

83.3

100.0

100.0

100.0

100.0

66.7

100.0

80.0

20.0

H. rudolfensis

100.0

0.0

100.0

100.0

xxx

xxx

50.0

100.0

100.0

100.0

xxx

xxx

H. erectus

50.0

50.0

50.0

0.0

xxx

xxx

100.0

100.0

100.0

85.7

83.3

50.0

South Africa

40.0

40.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

0.0

100.0

Wilks' Lambda

0.380

0.353

0.124

0.372

0.099

0.112

0.102

0.029

0.086

0.027

0.470

0.438

X2

12.6

13.5

12.5

5.9

3.5

3.3

17.1

26.4

18.4

27.1

6.0

6.6

df

12

12

12

12

3

3

15

15

15

15

10

10

p <

ns

ns

ns

ns

ns

ns

ns

0.05

ns

0.05

ns

ns

Functions

1-3

1-3

(Fig. 6.1). Relative cusp proportions of the M1 place three South African fossils within the H. habilis sample envelope, while two (SE 255, SKW 3114) are comparatively distant outliers that link with one another. With reference to the M2 (Fig. 6.2), the two South African specimens (SK 27, SE 1508) fall within or close to the H. habilis sample envelopes. In both instances the Sterkfontein and Swartkrans fossils are linked, and separately so for absolute cusp size. Unfortunately, no H. erectus or H. rudolfensis M3 is represented in the current sample. Although the only comparison for the two South African fossils (Stw 19, Stw 53) is with H. habilis (Fig. 6.3), both Sterkfontein specimens are linked at a distance from the three Olduvai Gorge fossils in their absolute and relative cus-pal proportions.

Among mandibular molars, the absolute and relative M1 cusp proportions (Fig. 6.4) find the two South African specimens (SK 15, SKX 257) falling outside the envelopes for H. habilis, H. erectus and H. rudolfensis. These Swartkrans Member 2 specimens exhibit no special affinity to any one of the East African specimens/samples. With regard to the M2 (Fig. 6.5), absolute cusp sizes place SK 15 within the H. erectus envelope, but although it is nested with that sample, it is an outlier to all of the specimens that comprise it. On the other hand, relative cusp proportions of the M2 clearly distinguish SK 15 from the H. habilis, H. erectus and H. rudolfensis clusters. Absolute cusp sizes of the M3 (Fig. 6.6) place the two South African specimens (SK 15, Stw 80) within or just outside the H. erectus and H. habilis sample envelopes, and they are nested with specimens of both species. Relative cuspal proportions, on the other hand, place the South African fossils outside the H. habilis and H. erectus sample clusters; neither SK 15 nor Stw 80 has special affinity with either of the East African species samples.

Among the South African specimens, only SK 27 and SK 15 possess more than one molar that is amenable to cusp size analysis. With regard to SK 27, its M1 suggests close affinity with H. habilis, and its M2 suggests a somewhat more distant relationship with this species. In neither instance do cuspal proportions suggest that SK 27 has special affinity to H. erectus. With regard to SK 15, the relative cuspal proportions for all three molars suggest no particular affinity to any species sampled from East Africa; the absolute cuspal sizes of the SK 15 M2 and M3 (but not the Mt) suggest affinities with H. erectus and/or H. habilis.

Fig. 6.1 Canonical discriminant functions and dendrograms from relative and absolute cusp areas of early Homo M's. Triangles = East African H. habilis molars; square = East African H. rudolfensis molar; circles = East African H. erectus molars; stars = South African specimens. Relative area analysis: function 1 (70.4%) is driven by the protocone and hypocone (positive) and paracone (negative); function 2 (22.5%) is driven by the hypocone and paracone (positive), and the metacone and protocone (negative). Absolute area analysis: function 1 (60.3%) is driven by the metacone and hypocone (positive); function 2 (34.2%) is driven by the paracone (positive), and the protocone and hypocone (negative).

«

h. erectus

k \ A

H rudolfensis.

/h. habilis

Q-

H. erectus/ /

/ / à \ H. rudolfensis

/ , A \m- habUla

Air

Ù A

A A

A A

A)

KNM-WT 15000-

KM-ER 1590-OH 39-KIMM-ER 808 -

SKW 3114

SKW 3114 SE 255 OH 16 OH 24 OH 44 KNM-ER 1813 SKX 267 OH 6 OH 41-OH 21-DNH 70-AL 666-1 -OH 13"

KNM-WT 15000-

SKW 3114

KM-ER 1590-OH 39-KIMM-ER 808 -

Fig. 6.2 Canonical discriminant functions and dendrograms from relative and absolute cusp areas of early Homo M2s. Triangles = East African H. habilis molars; square = East African H. rudolfensis molar; circles = East African H. erectus molars; stars = South African specimens. Relative area analysis: function 1 (47.5%) is driven by the paracone (positive), and the hypocone and metacone (negative); function 2 (33.0%) is driven by the hypocone and metacone (positive), and paracone (negative). Absolute area analysis: function 1 (71.9%) is driven by the metacone and hypocone (positive); function 2 (21.9%) is driven by the paracone (positive).

Fig. 6.3 Dendrograms from relative and absolute cusp areas of early Homo M3s. OH specimens are all attributed to H. habilis, Stw specimens are from Sterkfontein.

Fig. 6.4 Canonical discriminant functions and dendrograms from relative and absolute cusp areas of early Homo M1s. Triangles = East African H. habilis molars; squares = East African H. rudolfensis molars; circles = East African H. erectus molars; stars = South African specimens. Relative area analysis: function 1 (88.7%) is driven by the entoconid (positive); function 2 (9.3%) is driven by the proto-conid (positive), and entoconid (negative). Absolute area analysis: function 1 (66.9%) is driven by the entoconid and hypoconulid (positive); function 2 (22.4%) is driven by the protoconid, metaconid, and hypoconulid (positive).

Fig. 6.5 Canonical discriminant functions and dendrograms from relative and absolute cusp areas of early Homo M2s. Triangles = East African H. habilis molars; squares = East African H. rudolfensis molars; circles = East African H. erectus molars; stars = South African specimens. Relative area analysis: function 1 (76.7%) is driven by the metaconid (positive) and the protoconid and hypoconid (negative); function 2 (19.0%) is driven by the protoconid (positive) and hypoconid (negative). Absolute area analysis: function 1 (79.1%) is driven by all five cusps (positive); function 2 (14.5%) is driven by the protoconid and hypoconulid (positive).

Fig. 6.6 Canonical discriminant functions and dendrograms from absolute and relative cusp areas of early Homo M3s. Triangles = East African H. habilis molars; circles = East African H. erectus molars; stars = South African specimens. Relative area analysis: function 1 (86.9%) is driven by the entoconid (positive) and the protoconid and hypo-conid (negative); function 2 (13.1%) is driven by the metaconid (positive) and the entoconid and hypoconulid (negative). Absolute area analysis: function 1 (95.3%) is driven by the hypoconulid and protoconid (positive); function 2 (4.7%) is driven by the protoconid, hypoconid, and metaconid (positive), and entoconid (negative).

Was this article helpful?

0 0

Post a comment