|SREL Reprint #1953|
EVOLUTION AND FUNCTION OF LINGUAL SHAPE IN LIZARDS, WITH EMPHASIS ON ELONGATION, EXTENSIBILITY, AND CHEMICAL SAMPLING
WILLIAM E. COOPER, JR.
Abstract-Major squamate taxa exhibit extreme variation in lingual morphology,
presumably due to correlated variation in trophic and chemosensory functions.
Data are presented on evolution of lingual shape documenting several trends: (1)
Resting lingual elongation is greatest in families specialized for lingual
chemosensory sampling. (2) The greatest increase in elongation achievable by
intralingual means including elasticity and foretongue retractility occurs in families
with intermediate degrees of lingual specialization for chemosensory sampling.
Sampling efficiency may be enhanced by the ability to extend the tongue well
beyond the mouth, with resting elongation and intralingual extensibility perhaps
jointly determining distance extended. In families lacking sufficient resting
elongation, augmentation of intralingual extensibility may be a means of
approaching optimal protrusion distances. Decreased extensibility evolved in
tandem with the greatest resting elongation, suggesting that resting elongation may
be more efficient for protrusion and that elasticity declines as optimal resting length
is approached. The optimal shape for chemosensory sampling may be predicted
to be highly elongate, as in teiids, varanids, and colubfids. The tongue should be
broad at the tip for prehension (as in iguanians), fleshy for manipulation and
swallowing, and broad at the base for tamping prey into the esophagus. (3)
Lingual surface area relative to that of a rectangle of dimensions length x base
width varies accordingly. Relative area is high in families that do not tongue-flick
much while foraging because tongues are broad and fleshy throughout their length.
It is low in families that have wedge-shaped tongues and intermediate
specialization for chemosensory sampling. Narrowing of the anterior tongue may
improve chemical sampling. Relative lingual area in chemosensory specialists is
very high, with progressive narrowing toward the base as optimal sampling shape
is approached in taxa lacking lingual function in swallowing, prehension or prey
SREL Reprint #1953
Cooper, W.E., Jr. 1995. Evolution and function of lingual shape in lizards, with emphasis on elongation, extensibility, and chemical sampling. Journal of Chemical Ecology 21:477-504.