Three hypothetical models of tongue movement of the walrus during suction feeding are examined. These models encompass the entire range of simple tongue retraction movements possible by examining 1) movement of the tongue directly to the rear following the curvature of the palate, 2) to the rear and ventrally in a straight line, and 3) ventrally in a straight line. The percent of muscular force available from the hyoglossus, genioglossus, and styloglossus that could be applied toward retraction as predicted by each model is calculated. The resistance that the tongue would provide during retraction is calculated using projected tongue areas and is combined with the above data from the muscles to provide an estimate of the percent of the total available force that is needed to retract the tongue for each model. A separate examination of the direction of tongue-induced wear striations on the palatal and lingual aspects of the teeth is used to help support or reject the three models. The model where the tongue is moved directly to the rear is supported by studies of both muscle force and tooth wear. In the mammalian groups that were compared to the walrus, there is a great deal of interspecific variation in movements of the tongue during suction feeding; no two groups can be considered to have identical stereotyped tongue movements.
The aquatic and terrestrial locomotion of the walrus are described using the frame‐by‐frame analysis of 16 mm cine film and the manipulation of bone‐muscle preparations. The hind limbs of the walrus are the major source of aquatic propulsion; the forelimbs are used for manoeuvring as well as for propulsion.
Suckling is universal among terrestrial mammals, but it is not clear whether mechanisms of suckling are the same in mammals of differing morphology or feeding ecology. An evaluation of the literature on tongue movements during suckling suggests that pigs and dogs may use the tongue differently, with humans being intermediate. Electromyographic (EMG) recordings of the middle and posterior portions of genioglossus of pigs and dogs were compared in order to (1) see whether neuromotor patterns for tongue movement during suckling can be recognized and (2) identify interspecific differences in neuromotor patterns if present. A single pattern of coordination was found in dogs, but results from pigs indicated plasticity, both within and between individuals. The literature on humans indicates that, as in pigs, suckling patterns may vary. In addition to the difference in variability, pigs and dogs differed in EMG burst duration and cycle length. The performance of suckling in pigs, dogs and humans, respectively, resembled the tongue movements used in drinking in each species. The greater plasticity of suckling behavior in pigs (and possibly humans) may be related to an ability to acquire milk under a variety of environmental conditions or to a generally variable feeding process characteristic of omnivorous mammals.
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