Meeting Abstract
17.1 Thursday, Jan. 3 Ontogeny of rhythmic chewing and masseter activity in a selenodont artiodactyl WILLIAMS, S.H.*; SIDOTE, J.V.; Ohio University, Athens; Ohio University, Athens willias7@ohio.edu
Morphological maturation of the masticatory system in selenodont artiodactyls is a relatively slow process. In domesticated species, the full complement of postcanine teeth is not present until 3-5 years. However, their stereotypical transverse chewing movements develop as infants begin to test adult foods prior to weaning, suggesting that chewing motor patterns develop early. Here, we investigate the functional maturation of the chewing cycle and masseter activity during rhythmic chewing in juvenile alpacas (Lama pacos) from four months to one year in the context of craniodental development. Superficial and deep masseter electromyograms were recorded each month with indwelling bipolar electrodes while the animals chewed hay. Chewing cycle length, duration of muscle activity, and relative timing of peak activity were characterized for each individual every month. Data were compared to existing data from adult individuals with a full and evenly worn dentition. Chewing cycle length in the juveniles averages approximately 400-450 milliseconds (ms), with no difference observed between the different ages. In adults, chewing cycle length is almost twice as long, averaging 700-750 ms. There is a marked increase in the absolute duration of muscle activity between juveniles and adults. However, when activity duration is expressed as a percentage of chewing cycle length no differences are observed. The balancing-side deep masseter consistently has the shortest duration of activity, and around 6-7 months its peak activity shifts from early in the power stroke to later in the power stroke, similar to that in adult alpacas. This shift may be important for facilitating increased transverse jaw movements associated with eruption and occlusion of the first molar and may also be linked to ossification of the mandibular symphysis. Supported by NSF IOB-0520855.
