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Biomedical subjects

L O Greenfield

Publications and source records attributed to L O Greenfield.

10 recordsLinked to original sources
PubMed1998

Canine tip wear in male and female anthropoids.

One component of the "dual selection hypothesis" (Greenfield [1992a] Year. Phys. Anthropol. 35:153-185) is that the tips of female canines are commonly blunted and more frequently so than those of conspecific males. Data derived from two randomly selected age-graded samples of Macaca fascicularis (n = 70) and Colobus badius (n = 59) show that at least 80% of the females exhibit tip blunting on one or both canines and that frequencies of blunting are far greater than those of conspecific males in both jaws. Sexual dimorphism in mandibular canine morphology and wear and other recently critiqued aspects of the "dual selection hypothesis" (Plavcan and Kelley [1996] Am. J. Phys. Anthropol. 99:379-387.) are also discussed.

Aging↗
PubMed1995

The anterior dentition of adapids and anthropoid origins.

A recent discussion of the anterior teeth of adapids led to the conclusion that similarities to anthropoids are convergent. It is shown here that alternative functional and phylogenetic interpretations can be supported. These alternative interpretations are based on a different perspective on the anterior dentitions of extant and fossil anthropoids, which cannot be characterized by a single pattern of morphology and occlusion. More importantly, when this interspecific variation is placed within a phylogenetic framework it reveals persistent evolutionary trends that can be extrapolated back to infer a modest range of probable conditions in an Eocene anthropoid ancestor. The morphology and occlusion of adapid anterior teeth fall within this extrapolated range. This is compatible with an adapid ancestry for anthropoids.

Alouatta↗
PubMed1992

Polymorphic aspects of male anthropoid honing premolars.

A recent study has indicated that heritage may be an important component in explanations of interspecies variation in male anthropoid maxillary canines. To further test this hypothesis, comparative data for the maxillary canine's occlusal partner, the honing mandibular premolar, are presented. Relative to body mass, measurements of the honing premolar--length of the honing facet, mesiodistal length, and buccolingual breadth and shape (as expressed by the ratio of length to breadth)--show a similar but stronger heritage component than measurements of the maxillary canine. Results indicate that canine variation among male anthropoids has not yet been explained and that quantitative analyses of this issue will necessarily require a methodological approach which incorporates heritage as a factor.

Animals↗
PubMed1992

Incisification of anthropoid deciduous mandibular canines.

Interspecific variation of the deciduous mandibular canine's mesial cristid in 51 anthropoid taxa is assessed. In 84% of the taxa observed, mesial cristids were well developed and provided incisor-like occlusion with di2. In 5 of the remaining 8 taxa, lingual cristids provided incisor-like occlusion with dc1. Comparisons between dc1s and C1s of conspecific adult males and females show that in 85% of the species observed the magnitude of mandibular canine incisor traits follows this order: deciduous > adult female > adult male. This within-species variation is inversely related to the likely adaptive value of the canine as a weapon and to canine crown height. A selection model based on these data is derived and applied to human canine evolution. The relevance of these data to the field vs. clone theory debate about dental development is also discussed.

Age Factors↗
PubMed1991

Polymorphic aspects of male anthropoid canines.

Interspecific variation in the architecture of male anthropoid maxillary canines is documented. Extant taxa are polymorphic, and most can be sorted into two major groupings based on quantitative measures of shape, distal edge sharpness, and interspecific changes in their linear dimensions (projection, mesiodistal length, and buccolingual breadth) relative to each other and to body mass (scaling). One group includes the great apes and ceboids; the other includes cercopithecoids and hylobatids. Statistically significant differences between these groups were found for canine shape, for trajectories of regressions for canine projection on canine length and canine breadth, and for canine projection and canine breadth relative to body mass. The data indicate that explantations of canine variation in male anthropoids must include a mechanical interpretation of form in addition to assessments of habitus, heritage, and body mass.

Animals↗
PubMed1990

Canine "honing" in Australopithecus afarensis.

The maxillary canines of Australopithecus afarensis show a distal wear facet that extends from the apex of the crown to a point near the distal cingulum. Although these facets bear a superficial resemblance to the honing facets found on the projecting portions of the canines of other anthropoids, a more detailed examination provided in this paper shows that they are not homologous or functionally equivalent. The facets are not related to the use of the maxillary canine as a weapon or as an additional masticatory surface. Instead, their presence in A. afarensis represented a blunting or dulling of the posterior edge of C so that its occlusion with P3 would be consistent with cheek tooth occlusion.

Animals↗
PubMed1990

Unicausal theories of human canine evolution: are they sufficient?

Most theories of human canine evolution are unicausal and only purport to explain size and related shape changes in human canines. The present work tests whether one of the morphological changes, dulling of the distal edge of the maxillary canine, can be entirely explained as a byproduct of changes in the overall shape of the canine. The data show that the distal edge of maxillary canines of A. afarensis became far duller than would be predicted from changes in crown shape. The greater than expected dullness of the distal edge can be explained by evolutionary changes in the genetic field for cheek tooth morphology. This suggests that human canine evolution is complex and cannot be accounted for by unicausal theories.

Animals↗
PubMed1979

On the adaptive pattern of "Ramapithecus".

A reconstruction of the adaptive pattern of the Miocene hominoid "Ramapithecus," supported by comparative data and morphological comparisons, is presented. It is based upon the completely known dentition, inferior portion of the face, and on the paleoecology and geographic distribution of "Ramapithecus" bearing deposits. The known adaptive and morphological patterns of the "Ramapithecus" species are almost indistinguishable from those of the contemporary species of Sivapithecus, which has taxonomic priority. The "Ramapithecus" species are therefore referred to Sivapithecus, a dryopithecine genus which apparently radiated throughout Eurasia and Africa during the Middle Miocene.

Adaptation, Physiological↗