Analysis of mammalian masticatory mechanisms: progress and problems.

Introduction Table o f contents: Introduction, Mastication Cautions for analysis. First level analysis, Muscle arrangements, Meaning of the electromyograrn, Recording of movements, Strain and strain gauges, Ener etic costs of reduction, Control of masticatory orbits, References. The mammafs are unique among the vertebrates in the tremendous diversit of their masticatory apparatus. Most taxonomic schemes (cf. SIMPSON, 1945) rely heavib on the arrangement and structure of mammalian teeth and even the classification of fossils is based primarily upon dentitional characteristics (ROMER, 1966; OLSON, 1971 ; BUTLER, 1972; CROMPTON/JENKINS, 1973). This diversification of the adult dentition perhaps reflects in some way the relatively slight growth during the period in which most mammals use this set of teeth for feeding; a recent study suggests that this may be a reflection of the promotion of initial growth in the young by combined placentation and lactation (POND, 1977) and of limiting the absolute size of adults by determinate growth. In any case, mammals are unique in the extent to which their radiation reflects feeding habits, a situation shown by past morphological and theoretical analyses of the mammalian masticatory apparatus (SMITH/SAVAGE, 1959; SCHUMACHER, 1961 ; TURNBULL, 1970). Many studies relating teeth to mastication approach the subject from the aspects of wear patterns and the formation of tooth facets (cf. ANTHONY, 1935; ANTHONY/FRIANT, 1936; MILLS, 1967; GINGERICH, 1972, 1973, 1974, 1976; CROMPTON, 1971, 1972; KAY, 1975; KAY/HIIEMAE, 1974 a; OSBORN/CROMPTON, 1973; RENSBERGER, 1973). This approah is obviously important in the analysis and reconstruction of masticatory patterns in fossils. The last decade has seen an explosive increase both in the number of and the data provided by experimental studies of the masticatory apparatus of several orders of mammals. We now have detailed measurements of the movements, coupled with the muscular activity and sometimes rhe forces generated by mammals from several major groupings (Table 1). Many of these studies have now been carried out on conscious, unanesthetized, freely feeding animals, SO that the observed behavior is presumably close to normal. Similar analytical studies are becoming available on various reptiles, such as Sphenodon (ROSENBERG/GANS, 1977), agamid lizards (THROCKMORTON, 1976) and snakes (CUNDALL/GANS, 1977). Analyses of diverse other lizards are in process.