The KNM-WT 17000 premolar

Current

F. E. Grine

events

The KNM-WT

17000 premolar

Journal

( 199 I ) 20,505-5

Departments of Anthropology and Anatomical Sciences, State lJniuersi[v of .‘Vew l‘ork. Stony Brook, XY’II794, I:.S.A.

R. E. Leakey Zhtional h4useuns oj’kbnva, 40658. .Vairohi, hbnva.

M. F. Teaford A. C. Walker

P.O. Box

&

D$artment ofCell Biology and .-lnatoq, Johns Hopkins Uniuersi(v .School ofMedicine, 725 North Wolfe Street, Bnltimore. MD 21205, U.S.A.

The identification

of an isolated,

the KNM-WT original

account

of the specimen

to Dr G. Suwa,

could

has concluded its apparent

that

that the crown

‘robust’

that

At a workshop

& Walker

the present

specimen

ofdispute.

as a RP3 because

(in various In a recent

that

this is germane

17000 cranium. of this crown’s

its identification.

possible

Analyses originally

significantly of KNM-WT

to the taxonomic significance,

of the reported

and the interproximal

as was suggested

have estimates

contact

(Walker

In order

to assess the goodness the root from

fragment

the crown

cranium,

polyvinylsiloxane

larger

combinations)

(Coltene

and, more importantly, He (Suwa,

P4s relative

phylogenetic

interpretation

of the

the evidence

connection,

crown

that the premolar

& Walker,

0047-2484/91/060505

+09 $03.00/0

ofthis

thus,

size. He

to re-examine

crown-root-cranium

to P3s”; dental

for mor-

is a RP3,

1988).

and methods the crown epoxy

and root fragment,

(Araldite

President

Jet

956 with Regular)

and the contact

295 hardener) molds

paper,

as we follow the alphabet

casts

of the original

specimens. These were examined by scanning electron microscopy (SEM). All Paranthropus robustus (the first author recognizes Paranthropus whereas the other prefer Australopithecus; for the purposes

have

Suwa ( 1989)

paper,

17000 postcanine

it is necessary

as a

out that it

as to P3 or P4 is not trivial

facets lead us to conclude

of fit between and

and

et al., 1986; Leakey

Materials between

of this tooth

of

the fuller description

to Dr Gen Suwa for pointing authors

with In the

in 1987 a cast of this tooth

( 1988) still described

with Dr Suwa.

the “identification

australopithecines

has argued

made

in association

is a LP4 on the basis ofits morphology

KNM-WT

were

found a matter

fit with a small bit of root that he was able to afix to the cranium.

will influence

phology,

time,

crown become

that it could be a LP4. When

Leakey

the original

its identification

Because

facets.

that they were “grateful

1989, p. 795) has argued because

contact

who considered

be a left P4.” Since and examined

premolar

has recently

I3

et al., 1986) it was recognized

(Walker

17000 was published,

RP”, but they commented

maxillary

cranium

of its interproximal

of KNM-WT

discussed

worn

17000 fossil hominid

the disposition was shown

of Human Evolution

authors

so we follow the

0 1991 Academic

Press Limited

506

F. E. GRINE ET AL.

first author in the use of taxonomic names) and P. boisei specimens that preserve the P3 and/or p in position in the maxilla were examined for details of premolar crown morphology. This sample includes 14 P. robustus specimens with the P3 and P4 (SK 13/ 14, SK 46, SK 48, SK 49, SK 52, SK 57, SK 65/67, SK 83, SK 826, SK 845, SK 1590, SKW 11, SKW 12, TM 1517), four P. robustus specimens with the P4 (SK 11, SK 12, SK 79, SK 877), four P. boisei specimens with the P3 and P4 (OH 5, KNM-CH 1, KNM-ER 1804, KNM-WT 17400) and one P. boisei specimen with a partial P4 (KNM-ER 732). The disposition of interproximal contact was recorded for these specimens with the sole exception of the KNM-ER 732 P4, which lacks the mesial part of the crown and has an eroded distal contact facet. The buccolingual (BL) diameters ofthe facets or the contacts between adjacent crowns in maxillae were measured on the foregoing specimens except for SK 11, SK 12, SK 46, SK 826, SK 877, SKW 12, KNMCH 1, KNM-ER 732 and KNM-WT 17400 because of damage or the lack of distinct interproximal contact. Observations Fit between the cranium, rootfragment

and crown

The strongest evidence presented by Suwa (1989) in support ofhis identification of the crown as a LP4 is the claim that one of a number ofsmall root fragments collected in association with the cranium serves to bridge the crown to the maxilla. He observed that one side of the small root fragment “exhibits a fresh break which fits perfectly with the lingual root break on the left P4 of the cranium”. Examination of these two surfaces by SEM reveals several minute, reciprocal features (Figure 1) that support his observation. This root fragment indeed forms a perfect fit with the broken lingual part of the LP4 root in the maxilla. He also stated (p. 798) that, “the other break surface of the root fragment is not as fresh but the overall fit with the premolar crown is excellent . . . most importantly, two small segments ofenamel exist on the root fragment. . . one ofthe enamel segments forms a perfect fit with the premolar crown including a vertical stain in the enamel that runs straight through the join.” The only physical contact that can be made between the crown and root fragment, in fact, is by the bits of enamel located at the mesial and distal ends of the root fragment (Figure 2a). The larger piece ofenamel on the root fragment and the enamel rim of the crown at the point of contact are of comparable thickness (267 pm vs. 280 pm respectively). The enamel on either side of the smaller purported contact differs in thickness; that on the root fragment is between 260 pm and 317 pm, while the crown rim is between 345 pm and 387 urn. It is difficult to place much reliance on the “vertical stain” that appears to run through the larger purported enamel contact in view of the numerous small dark stains on the crown that conceivably could be connected with those on the enamel of the root fragment. Examination ofthe internal aspect ofthe purported connection between the root fragment and crown reveals that the pulp cavities of the crown and root are misaligned by about 1.0 mm. Furthermore, the pulp cavity in the root fragment is more than twice the diameter of that in the crown, making it impossible to align and attach these two pieces as has been suggested by Suwa (Figure 2b). Crown morphologll

Suwa ( 1989) listed seven features that he considered to be a “reliable set of indications” as to the side identification of an upper premolar. While he conceded (p. 795) that “some of the above features may be related (e.g., features 1,3 and 6)“, it is evident that this list represents

507

THEKNM-WT17000PREMOLAR

a

Figure 1. Scanning electron micrographs ofreciprocal features on (a) the edge of the root fragment and (b) the lingual root of the LP in the alveolus of the KNM-WT 17000 cranium. Micrographs on right are enlargements ofboxes on left. Scales, 1 mm (left) and 100 pm (right).

simply

the atomization

of the crown-into occlusal

heights

directly molar heights

makes

of the lingual

artificially

example,

extent,

appears

as an apical

ridges

dentine

to a somewhat and

the occlusal

greater

the lingual

wear

piece

portion

the relative

difficult.

The lingual

from

degree

of tilt is

the protocone

that

exposure. of undisputed

of variation of the crown

in a few instances

the features

contour

LP4 is more convex

of the OH5

17000 pre-

including

but its apparent

of enamel

in the

be attributed

to the KNM-WT

7), extremely

mesially,

moiety

the difference 7) cannot

of his features,

(feature

premolars degree

of the lingual

Only

(his feature

occlusal of several

to be skewed

of Paranthropus maxillary

in some specimens

notable

Moreover,

assessment

ridges

by the loss of a triangular

be misinterpreted

Examination

trait.

displacement

components.

ends of the marginal

ends of the marginal

certainly

mesial

morphological

the accurate

heightened

they are subject Thus,

of the lingual

to this morphological crown

side of the crown could

of a single attribute-the its constituent

than

allocation indicated

is not displaced

display

“reversed mesially

suggests

that

by Suwa

(1989).

mesially

to any

asymmetry”.

than distally,

For

whereas

508

Figure 2. Scanning electron micrographs of replicas of the root fragment and KNM-WT 17000 premolar crown viewed from the lingual and buccal aspects. The pieces are joined as indicated by Suwa (19139). (a) shows the lack ofcontact except at the mesial and distal ends ofthe root fragment; the enamel contacts are 14 and 1.7 mm long. (b) shows the buccal aspect of the purported join using the lingual portion of the sectioned crown replica. This reveals the lack of congruity between the two pieces; the lines indicate the lateral margins ofthe pulp cavity on the two pieces. Scale bar, I mm.

the

RP4

is more

premolars

in keeping

tend to display

degree

of variation

almost

all occlusal

Suwa’s

observation.

the morphological

with

attributes

that is present detail

in the available

from the KNM-WT

on these traits in the identification

Paranthropus maxillary

Although enumerated

samples,

by Suwa

and the obliteration

17000 crown

mitigate

against

(1989),

the

by wear of

a strict reliance

of this specimen.

Interproximalfacet disposition and size One

of the contact

triangular

outline

facets (Figure

12.6 mm*; it broadens buccal

and

lingual

on the KNM-WT

lingually

edges

17000 premolar

is poorly

developed,

3a). It is 4.5 mm BL and 3.1 mm occlusocervically, from

of the crown.

a point

that

is almost

Its occlusal-most

exactly

border

midway

is located

with

a

with an area of between about

the

2.0 mm

cervical to the occlusal margin of the crown. The second facet (Figure 3b) has an ovorectangular outline and is somewhat better developed; it is 6.8 mm BL and 4.5 mm occlusocervically, with an area of27-7 mm*. This facet is situated in the middle of the crown surface, and its occlusal-most edge is coincident with the occlusal margin of the crown.

--Figure 3. Scanning electron micrographs of the interproximal contact premolar crown. (a! buccal to right; (b) buccal to left. Scale bar, 1 mm.

Interproximal contact

between

which

to quantify

reasonable

attrition

may

adjacent

crowns.

the BL diameter

P3s and

comparison

P’s in those

4). Only on the very slightly

the mesial

and in this case the difference

Should

larger,

the KNM-WT

is clearly

aberrant

Also, the unusually

faint development

nature

specimens.

These

the P”. In some

them

tends

of the maxillary specimens (e.g., OH5)

(e.g., SK 65/67)

canine

also display

be about nature

(Figure

only the distal-most

between

5 1 o/0 larger

than

of the supposed than

the mesial

are of

the facets the distal.

distal

facet is

(Figure

4) and

reflects

the

to the size of the P4 in Puranthropus

in the orientation

surface

for

facets

is only 9.8”,b.

than on the P4. This presumably

variation

contact

5).

facet is larger

in comparison

the distolingual

of by

than the mesial facet

as a LP*, the relationship

to be greater

entire

(5.6 mm vs. 5.1 mm)

would

wear

or zone method

and distal

where

17000

worn SK 49 tooth is the BL diameter

and diminutive

at this stage of occlusal

between

diminutive

others

be regarded

4) in that the mesial

on all Purunthropus P3s the distal

By contrast, the difference

17000 crown

(Figure

even more striking

of mesial instances

to the P4, the distal facet is as large as, or larger

in 12 of 13 cases (Figure facet

of the facet

this may not be the most accurate

it enables

of Paranthropus

With regard

using

Although

facet development,

samples

inaccessible.

he assessed

facets on the KNM-WT

of the canine

edge of the canine

of the canine contacts

abuts

against

relative

to

the P3, while

in

the premolar.

510

F.

E. GRINE ET AL.

lo93

8-

;i; e0 71t

6-

;

5-

r E 4d 1

32l-

, 1

,

2

3

,

4

BL diameter

,

5

,

,

6

7

distal facet

,

a

*

9

10

(P’)

10

91

P4

KNM-WT f

.

/ 17000

7-

1

2

3

4

BL diameter

5

6

7

distal facet

0

9

10

(M’)

Figure 4. Comparison of the BL diameters ofmesial (y-axis) and distal (x-axis) interproximal contact facets on Paranthropus P’s and ParanthropusPs. Solid circles, P. robustus.Open circles, P. boisei. Solid diamond, KNM-WT 17000. The diagonal line represents a 1: 1 correspondence in facet size.

This may be at least partially

responsible

for the variability

in the relationship

between

mesial and distal facet sizes on Purunthropus P3s. When the KNM-WT

17000 crown is regarded as a RP3, the size relationship

and distal facets is in keeping with other Puranthro~us specimens

17000 the distal facet is some 51 y0 larger than the mesial, a relationship observed

ranges for both P. robustus and P. boisei. The faint triangular

17000 could have resulted from the type of contact duced by the distolingeal distal marginal eminence.

described

of the mesial

(Figure 4). On KNM-WT that falls within the facet on KNM-WT

above, where the facet pro-

surface ofthe canine broadens lingually in correspondence

ridge of the canine, which increases in breadth

with the

closer to the lingual cervical

Interproximal attrition between cheek teeth results in facets that are coincident with the occlusal margins of the crowns, whereas canines produce facets that are commonly situated

511

Figure 5. Scanning electron micrographs showing (a) the size and disposition of the distal interproximal contact facet on a P. robustusLP (SK 65/67) viewed from the distolingual aspect compared to (b) the size and disposition of the “distal” contact facet of the KNM-WT 17000 premolar viewed from the “distolingual” aspect. The crowns have comparable degrees ofocclusal wear. Scale bar, 1 mm.

cervical

to the occlusal

the distal location WT

ofthe

ofthe

P3. This is especially

of the canine

two contact

17000 crown

cervical

margin

prominence

remains

facets relative

is a RP3. The small,

and occlusal

margins

salient.

to the occlusal triangular

is indicative

margin

facet

ofcontact

so when C-P3 attrition In this context,

is slight,

the difference

also suggests

that is located

that the KNM-

midway

with a maxillary

and

in the

canine

between rather

the

than an

M’. Finally,

the smaller,

the midcrown of the crown.

Examination

facet is displaced is displaced centrally positioned

facet on KNM-WT

positioned

side ofthe

facet

(70%)

midway

P4s reveals midline.

side of the midline

and it is buccally

on the majority

triangular

is located

ofParanthropus

to the lingual

to the lingual

facets on the KNM-WT small

triangular

axis, while the larger

17000 is situated between no instance

17000 crown

in which

On the other hand,

side of

and lingual the distal

edges contact

the mesial contact

facet

on some 21 o/0 of Paranthropus P3s (in 42’j/, it is

disposed

in 3796). The distal contact

of Purunthropus P3s. Thus, is extremely

to have been produced

to the lingual

the buccal

the BL placement

facet is centrally of the contact

unusual were it to be a LP4. In order for the would have to have by the M’, the premolar

512

F. E. GRINE ET AL.

been rotated, and/or the molar would have to have been displaced lingually. The roots preserved in the maxilla show no evidence of this. On the other hand, facet disposition is consistent with the crown’s identification as a RPs. ,, Thus, the shapes, relative sizes, cervico-occlusal placement, and BL disposition of the interproximal facets on the KNM-WT 17000 premolar point to its identification as a RP3. Summary and conclusions The isolated premolar crown associated with ,t’he KNM-WT 17000 cranium was identified originally as a RP3 (Walker et al., 1986; Leakey & Walker, 1988). Suwa (1989) has argued that it is a Lp primarily because he believed that it could be joined to the cranium. The reported contact between the crown and root fragment, however, has not withstood close microscopic examination. Because the crown cannot be connected to the cranium by means of the LP4 root, it is unlikely to be that tooth. The KNM-WT 17000 crown shows slight mesial displacement of its lingual moiety in which it resembles the majority of Puranthropus left maxillary premolars. However, the individual morphological components of this configuration display individual (and even antimeric) variation, and because wear has obliterated almost all occlusal detail from the KNM-WT 17000 crown, it is difficult to rely heavily on these features in its identification. At the same time, the shapes, relative sizes, occlusocervical placement, and BL dispositions of the interproximal facets on the KNM-WT 17000 crown point to its being a RP3. The MD and BL diameters of the KNM-WT 17000 premolar crown recorded by Leakey & Walker ( 1988) fall within the observed sample ranges for P. boisei P3s and P4s and P. robustus P4s; while its MD diameter falls within the observed range for P. robustus P3s, the BL diameter exceeds the P. robustus P3 range (Grine, 1988). Suwa (1989) has argued that if the crown is recognized as being a LP4, then the KNM-WT 17000 cranium possessed a relatively large anterior dentition (as judged by its II-C alveolar length). The palate of KNM-WT 17000 is wide anteriorly and although its relative size may be diminished somewhat by recognition of the premolar as a P3, it is unlikely that this bears in any significant manner on taxonomic and/or phylogenetic arguments. Perhaps the most that can be stated with any assurity is that the KNM-WT 17000 cranium possesses a comparatively large P3. We thank the Government of Kenya and the Governors of the National Museums of Kenya for permission to carry out research in Kenya, Meave Leakey and Emma Mbua for their invaluable help at the National Museum in Nairobi, and C. K. Brain for permission to examine the specimens at the Transvaal Museum. We thank Rose Keller and Elizabeth Peterson for their help in preparing casts and taking some of the SEM micrographs, and Lucy Betti for the artwork. We are also grateful to J. G. Fleagle, D. W. Krause, L. B. Martin and three anonymous referees for their comments on this paper. This work was supported in part by NSF grants BNS-8904327, BNS-8803570, and BNS-8918695; the L. S. B. Leakey Foundation; the National Geographic Society; and a John D. and Catherine T. MacArthur Foundation Fellowship to A.C.W. References Grine,

F. E. ( 1988). New cranicdental fossils ofParanlhro&r from the Swartkrans Formation and their significance in “robust” australopithecine evolution. In (F. E. Grim, Ed.), Evolutionary History of the “Robust” Austmlopithccincs,

pp. 223-243.

New York: Aldine de Gruyter.

THE KNM-WT

17000PREMOLAR

513

Leakey, R. E. F. & Walker, A. C. (1988). New Aurtralopithccus bo&i specimens from East and West Lake Turkana. Kenya. Am. J. Phys. Anthrop. 76, l-24. Suwa, G. (1989). The premolar of KNM-WT 17000 and relative anterior to posterior dental size. J. hum. Ed. 18, 795-799. Walker, A. C., Leakey, R. E. F., Harris, J. M. & Brown, F. H. (1986). 2.5SMyr Australopithecus boisei from west of Lake Turkana, Kenya. Nature322,5 17-522.