Cartesian Coordinate Analysis of the Hominoid Second Lower Deciduous Molar ROBERT S. CORRUCCINI Division of Physical Anthropology, Smithsonianlnstitute, Washington, D.C. 20560, USA Following the methodological example provided by BIGGERSTAFF (Am J Phys Anthrop 31:163, 1969), I have conducted a preliminary experimental comparative analysis of the second lower deciduous molar (fourth lower deciduous premolar in paleontological terminology) in hominoids. Ten landmarks define the major features of the crown: the most mesial point on the mesial marginal ridge, the most buccal extent of the mesial fovea, the lowest point on the distal trigonid crest (from the mesio-buccal to the mesio-livigual cusns), the intersection of the protoconid-hypoconid (mesio-buccal and disto-buccal cusps) buccal ridges with the transverse developmental groove, the intersection of the buccal protoconid-hypoconid groove with the cingulum, the intersection of the metaconid-entoconid (mesio-lingual and disto-lingual cusps) lingual ridges with the transverse groove, the talonid basin (central occlusal fovea), the low point on the crest from hypoconid to hypoconulid (distal cusp), the distal talonid crest (hypoconulid-entoconid), and the distal fovea. The X and Y coordinates of these are recorded by projection of the coronal plane onto grid paper using a camera lucida. Samples consist of 25 Homo sapiens (Amerindians), 8 Pan troglodytes, 3 Pan gorilla, 12 Pongo pygmaeus, and plastic casts of 3 Australopithecus robustus. The fossil casts only justify very tentative comparisons but should be of interest. The proper analytical technique for these data (SNEATH J Zool 151:65, 1967; BENFER Am J Phys Anthrop 42:371, 1975) is to center each specimen and equalize its size (accomplished by normalization of coordinates) and rotate it to best fit with a standard specimen (the most typical human); canonical variates Received for publication September 16, 1976. Accepted for publication October 5, 1976.

TABLE CANONICAL VARIATE SCORES FOR HOMINOID SAMPLES

Taxon Homo sapiens Pan troglodytes Pan gorilla Pongo pygmaeus

Australopithecus

Second Variate First Variate Standard Standard Mean Deviation Mean Deviation

-63.14 -70.39 -72.16 -70.59 -63.35

0.62 1.05 0.91 1.25 0.35

-51.63 -49.23 -51.55 -51.40

-43.10

0.98 1.11 1.08 0.91 1.13

analysis is then done directly on the transformed coordinate values. The table lists projections of the samples onto the first two canonical variates, the only ones to attain statistical significance or interpretability. The first variate (subsuming 73.7% of the total inter-sample variance) discriminates hominids from pongids; the second (20.1%) distinguishes the fossils. The morphological pattern underlying the variates is easily interpretable. Hominids show a relatively short mesial fovea, distally shifted trigonid crest, mesially shifted and larger hypoconid, large entoconid indicating an enlarged talonid, broad and very centrally situated talonid basin, and mesiobucally shifted hypoconulid reflecting a broader and squarer tooth. Robust australopithecine casts appear unique in their combination of broader mesial fovea, mesio-buccally shifted protoconidhypoconid ridge reflecting a square tooth and reduced protoconid, mesio-lingually shifted distal talonid crest, and lingually deviated distal fovea. The discrimination and interpretability afforded by the technique insure its utility in comparative dental studies.

J Dent Res June 1977 Vol. 56 No. 6 Downloaded from jdr.sagepub.com at University of Sydney on March 14, 2015 For personal use only. No other uses without permission.

699