Mechanical theory is used to erect a paradigm predicting the manipulations used by carnivorous aquatic amphibians, reptiles, birds and mammals to catch, subdue, process and swallow their prey. These predictions are confirmed by observational evidence. Most aquatic predatory tetrapods use long, prehensile tooth‐armed jaws as pincer jaws to snap shut onto the prey and catch and kill it, although some use the flexibility of long necks in spear fishing and some odontocetes may stun prey with sonar. Most do not have cutting or nipping dentitions as these cannot be used on prey which is freely floating. They use caniniform dentition to hold and kill prey, or in some cases crushing dentition to break open hard‐shelled prey. They dismember prey by dynamic loading, snatching bites so quickly that the prey tears. They use shake feeding, shaking the prey apart from side to side above the water. If the prey is too large to lift above the water they use twist feeding, twisting pieces off. Small pieces are easily swallowed but larger pieces are held above the water and swallowed by tilting the head back in gravity feeding, or by jerking the head back and forth in incrtial feeding. Some animals use mobile jaws to pull prey back into the mouth in ratchet feeding. Filter feeding evades these problems by feeding on very small prey. The use of paradigms in functional analysis is discussed with special reference to this work. The paradigm method is shown to be the most suitable one. There has been repeated convergent and parallel evolution of adaptations to feed in water.
Fossil marine reptiles have been collected in some abundance from several sites along the Yorkshire coast over the last 225 years. Much of this materia] has remained unstudied and there is confusion over the provenance of most specimens. A detailed study of early collectors' reports has revealed the sources of some specimens, and others have been dated by means of associated ammonites and matrix. A complete list of all specimens known to us is given, and these include 55 crocodiles, 69 ichthyosaurs, 33 plesiosaurs and one pterosaur. Reptiles are rare in the Lower and Middle Lias of Yorkshire. The richest horizons are within the Upper Lias (Lower Toarcian, Whitbian), with 14 specimens from the Jet Rock Formation and 144 from the Alum Shales Formation (predominantly the Main Alum Shales). The best localities have been the Whitby-Saltwick section (137 specimens) and the old alum quarries at Kettleness (5 specimens) and Loftus (4 specimens). The faunas from these sites are unrivalled in the Upper Lias of Britain, and they show significant differences from the Upper Lias faunas of SW Germany (e.g. Holzmaden) and France. I.
The skull and mandible of the type specimen of the large pliosauroid plesiosaur
Rhomaleosaurus zetlandicus
from the Toarcian of England are elongate, and adapted for powerful predatory activity in water. The mandible contains all elements found in primitive reptilian mandibles. The broadly caniniform dentition suggests that
Rhomaleosaurus
fed on a wide range of active prey, and forcibly dismembered larger prey by shaking and twisting them. The cranial musculature is reconstructed for the first time in plesiosaurs. It was adapted for feeding in water. The adductor musculature included a large anterior pterygoideus attached to the suborbital fenestra, a large posterior pterygoideus, and a group of large dorsal muscles including the adductor mandibulae externus. The anterior pterygoideus exerted maximum torque when the jaws were wide open, snapping them shut quickly, and the dorsal muscle mass exerted maximum torque when the jaws were closed on prey to subdue and dismember it. The role of the posterior pterygoideus is uncertain or intermediate. The musculature combines elements of the "kinetic inertial’ system ascribed to aquatic tetrapods by Olson (1961), with his ‘static, pressure’ system ascribed to terrestrial tetrapods. Olson suggested that the large pterygoideus musculature typical of the ‘kinetic inertial’ system functioned to confer kinetic energy on the mandible. However, its function may instead have been to compensate for the inertia and drag of the mandible. The depressor musculature comprised the depressor mandibulae and the longitudinal pharyngeal muscles, and opened the jaw quickly against drag. The cervical musculature cannot be reconstructed in detail. There was a strong nuchal ligament. The forces within the head are analysed by using box and girder beams as analogues. Gross form, shape of constituent bones, and sutural morphology confirm adaptations to resist great bending moments arising from the action of the muscles when biting on prey. When the jaws were closed, the pterygoid flange supported the mandible against the inward component of the adductor muscle force.
Rhomaleosaurus
was a visual predator. The eyes were large. The stapes is present. Underwater olfaction was likely. There is no evidence for an eardrum, but it is not known whether this is the plesiomorphic reptilian state or secondarily derived from a tympanate ancestor. The ears were not acoustically isolated from the braincase, so underwater directional hearing was poor, and sonar was not possible. The structure of the head of
Rhomaleosaurus
is a functional compromise between the needs to maximize structural strength and to maximize swimming and feeding efficiency. Especially important were the ability to sustain large muscle and reaction forces to provide an adequate bite force at the end of a long snout, and the wide gape allowing the swallowing of large pieces of prey. Even larger items were dismembered into smaller pieces by shake and twist feeding. The major unresolved problems are the effects of scaling factors, and the torsional loadings induced when biting asymmetrically, or twisting large prey to pieces.
SynopsisAn apparent series of eight plesiosaurian cervical vertebrae and an isolated tooth are described from the Rhaetian (or possibly Lower Jurassic) erratic block at Linksfield, Elgin, Morayshire. The vertebrae are comparable to Rhaetian and Hettangian material from SW England, especially the Rhaetian species Plesiosaurus costatus O w e n , 1840 and Plesiosaurus rugosus O w e n , 1840. The vertebrae comprise a rare occurrence of associated Rhaetian plesiosaurian skeletal material.
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