Bodyplan
Two _Varanus albigularis_ lounging




Varanid bodyplans all revolve around the same basic structure; that of a long sinous body complete with four robust legs, a long neck, slender snout and a long whiplike tail. Some varanids have less sinous bodies while others may have disproportionately long bodies.

Varanid limbs are proportionate and very robust. Varanids use these limbs for tearing up the soil to make their homes, or for ripping into termite mounds, climbing trees, wrestling prey and for covering great distances overland.

The necks of varanids are very long and birdlike (though varanids tend to keep their necks straighter than birds). Their jaws contain an extra joint on the mandible that allows them to swallow large and bulky food items.

The varanid tongue is very interesting as it is extremely long and deeply forked. It has also lost the rough dorsal surface that is typically found in other saurians. In fact, upon first glance, the varanid tongue looks practically identical to a snake's. This tongue is used in conjunction with the the Jacobson's Organ to give monitors a highly developed sense of smell.

Along with these changes the hyoid apparatus (the free floating bone that anchors the tongue in vertebrates) is stronger and more mobile than in other lizards, having a well defined joint between the ceratohyal and the anterior process. as well as a series of distinct muscles inserted on the anterior hyobranchial region.

Varanid tongues do not aid in the transport of food, instead varanids employ their modified hyobranchial apparatus.

_Varanus albigularis_ tears into an ophidian relative


Once food has been caught with the mouth, it is literally thrown into the gullet by inertial feeding movements (Gans, 1969). During the inertial thrust the head is pulled rapidly backward, imparting a posteriorly directed motion to the prey. The jaws are quickly opened and thrust forward to surround the food particle. Once it enters the gullet, movements of the hyoid apparatus compress the pharyngeal region and move the food posteriorly through the esophagus. During this phase the hyoid first moves forward, so that it is anterior (closer to the top of the throat) to the prey, then dorso-posteriorly (back and down) to force the prey farther along. Repeated lateral neck bending and additional hyoid movements push the food to the stomach (largely after K.Smith, 1986). The lateral neck swinging is also helpful for removing larger chunks of meat from prey animals. It also makes for messy eating.

Varanid tails, unlike iguanian and autarchoglosian tails, do not have the break lines in the caudal vertebrae which allows for tail separation, so varanids cannot separate their tails. This is a good thing for them, since monitors use their tails for defense, balance and fat storage.

This keen bodyplan is just one of the reasons why varanids make excellent predators.


Back
Lacertillians
Home


Gans, C. 1969. Comments on inertial feeding. Copeia 1969:(4)855-57.
Smith, K.K.. 1986. Morphology and function of the tongue and hyoid apparatus in _Varanus_ (Varanidae: Lacertilia). J.Morphol. 187:261-87.