Feeding patterns in turtles

The feeding mechanics of vertebrates depend on physical constraints of the surrounding media, water or air. Nevertheless, four kinematic phases during a feeding cycle are common: Slow Opening, Fast Opening, Fast Closing, and Slow Closing. This pattern is used to detect trends in evolution of several feeding mechanisms within vertebrates. During a long independent evolution, turtles underwent a great radiation, occupying - as the only reptile order - every possible habitat from purely aquatic to purely terrestrial with all intermediate possibilities. It is assumed that turtles started out as terrestrial animals and changed to aquatic habitats several times independently within both infraorders, Pleurodira and Cryptodira. Within the context of this project all available methods have been used: High speed - cinematography coupled with x-ray, cinematography and high speed x-ray video. To study the form, gross morphology as well as histology and ultrastructure of tongue and esophagus have been conducted. The project produced the following results: * A general model for the feeding behaviour was established (LEMELL & al., 2000) to serve as a base for further analyses. * Kinematics of aquatic feeding were analysed and described, two main mechanisms could be distinguished: grasping the prey with the jaws by moving the head towards the prey - "ram feeding" ("jaw prehension"), and "suction feeding" by transporting the prey item into the oral cavity without moving the head, by generating a stream of water by rapid hyoid depression. It could be seen that both mechanisms could be modulated according to seize and consistency of the prey. * Terrestrial feeding was analysed for Testudo hermanni and a "lingual transport" mechanism was found. For the very first time intraoral foodtransport could be documented by x-ray video shots (WOCHESLÄNDER & al., 1999, 2000). *Terrapins as inhabitants of aquatic as well as semiaquatic and terrestrial habitats were examined on three species of the genus Cuora sp. to find transitions between different feeding spezialisations. It turned out that Coura amboinensis is able to feed on land as well as under water, a kind of "universal feeding mechanism" could be described (WOCHESLÄNDER, 2001; WEISGRAM & al., 2001). This findings have some meaning for the knowledge of the phylogeny of turtles, because it could be possible that turtle ancestors were not fully terrestrial but maybe semiaquatic animals. Further studies will be necessary to clear this problem. * Investigations on the morphological components of the feeding apparatus (hyoid-jaw apparatus, tongue, oral glands) showed that aquatic feeders have a rather massive and bony hyoid but a poorly developed tongue with only very few simple oral glands; terrestrial turtles on the other hand show a thin and flexible hyoid but a very musculous tongue with very complex oral glands in great number.