With their large heads and streamlined bodies, pliosaurs were probably capable of quick movement and sustained chases at high speed. They were pursuit predators, but not as fast as ichthyosaurs. They would chase large prey until they could grab them in their powerful jaws. Pliosaur teeth were sturdy, cone-shaped, and sharp, capable of cutting through thick flesh and even bones. Their mouths were huge, making any sea creature of the time a possible meal, including the long-necked plesiosaurs, ichthyosaurs, and the largest fishes and mollusks of the time. Pliosaurs were the top predator of the oceans throughout much of the Mesozoic, filling a niche similar to that of the killer whale today.
The stomach contents of one specimen of a subadult Liopleur-odon ("smooth-sided tooth") revealed that it ate fishes and belem-nites—small squidlike creatures with a hard, conelike inner shell. Paleontologist Darren Naish has suggested that young pliosaurs may have subsisted on a diet of smaller prey such as small mollusks and fishes, trading up to large prey when they became adults. Evidence that a pliosaur once ate a dinosaur is slim, but tantalizing. It consists of armor plates from the hide of a dinosaur that were found within proximity of a pliosaur skeleton.
Characteristics of the pliosaur body included:
Long length. Pliosaurs were huge, up to 50 feet (15 m) long. They were the largest members of the Plesiosauria.
Huge skull. The skull was long and strong with a long, tapering snout. The head was shaped like an elongated triangle when viewed from above. The skulls of some pliosaurs were one-quarter their total body length. The largest skulls were more than 10 feet (3 m) long.
Short necks, short tails. The necks of pliosaurs were short when compared to those of plesiosaurs. They had from 17 to 26 neck vertebrae, with a tendency towards shorter necks in the later kinds of pliosaurs. Their tails were short.
Broad, long, streamlined body. Unlike the plesiosaurs— where the neck was long—the body of a pliosaur made up most of its length. Pliosaurs were streamlined, powerful swimmers. Near-ing the end of the Mesozoic Era, their body shape had begun to approach that of the ichthyosaurs. This undoubtedly made them faster swimmers than their long-necked relatives, the plesiosaurs. The spine was rigid, providing strength and leverage for the paddles to swing up and down.
Strong ribs and belly ribs. Like plesiosaurs, pliosaurs had extensive side and belly ribs. This added stiffness to the body and may have allowed a pliosaur to crawl out of the water onto dry land without collapsing under its own weight, although this idea is disputed by some scientists today who think that these creatures were simply too heavy to leave the water.
Teeth and jaws. Pliosaur teeth were stout, sharp, and conical. They lined the sides and front of the upper and lower jaws and were widely spaced. The teeth in the front part of the jaws were longer than those in the rear. Some protruded outwards. Considering the large size of the prey that a pliosaur ate, the teeth were mainly used to grab and crush its victims with the brute force of its muscular jaws.
Long, wing--shaped paddles. The wing-shaped paddles of pliosaurs were highly elongated, as in plesiosaurs. Once difference between plesiosaur and pliosaur paddles was that in a pliosaur, the hind paddles were longer and stronger than the front paddles. This suggests a slightly different form of propulsion that relied more on the "flight" of the rear paddles than the front ones, perhaps because this animal was capable of swimming fast in pursuit of its prey.
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