Family Mosasauridae

The mosasaurs were a successful, though short-lived, offshoot from the monitor lizard group. They were fully adapted to a marine life, living in inshore waters during the Late Cretaceous period. Some of them were giants.

name: Platecarpus time: Late Cretaceous locality: Europe (Belgium) and North America (Alabama, Colorado, Kansas and Mississippi) size: 14 ft/4.3 m long Many specimens of this marine lizard have been found in the chalk deposits of Kansas, laid down in the warm, shallow seas that covered much of North America during Late Cretaceous times.

Platecarpus swam in these waters some 75 million years ago. Its tail was as long as its body, and judging from the vertebrae, it was flattened from side to platecarpus plotosaurus

megalania name: Megalania time: Pleistocene locality: Australia (Queensland) size: up to 26 ft/8 m long

This monitor lizard was much larger and maybe weighed 4 times as much as its living relative, the Komodo dragon, Varanus komodensis, of Indonesia. Although the Komodo dragon is the giant of modern lizards — with some individuals growing up to 10 ft/3 m long, and weighing some 360 lb/163 kg — it is small in comparison to some of its extinct relatives.

Megalania hunted on the plains of Australia less than 2 million years ago, ambushing the large marsupials, such as kangaroos, that grazed there (see pp. 202-205). It would have torn away great chunks of flesh with its powerful jaws and long, sharp teeth, serrated along their edges.

plotosaurus megalania platecarpus hyperodapedon pachyrhachis pachyrhachis


hyperodapedon kuehneosaurus side, and probably had a broad, vertical fin running along its length, above and below. Snakelike undulations of the long, sinuous body, combined with the finned tail, would have propelled Plate-carpus forward, while the short legs and broad, webbed feet steered.

This marine lizard would have eaten fish and soft-bodied cephalopods, snapping them up in its long, pointed jaws, equipped with many sharp, conical teeth. But it could also have tackled the most abundant cephalopods around at the time — the ammonites, whose soft bodies were enclosed within a hard, coiled shell. Evidence for this comes from a number of fossilized shells of these creatures, scored by a similar pattern of V-shaped tooth marks as that of the mosasaurs. The shells seem to have been bitten about a dozen times from different angles, in attempts to crack them open and get at the flesh inside.

name: Plotosaurus time: Late Cretaceous locality: North America (Kansas) size: 33 ft/10 m long

Found in the same North American chalk deposits as Platecarpus (above), Plotosaurus was a giant among mosasaurs. About 50 vertebrae made up its body and neck, with at least the same number again making up the long tail. The rear part of its tail was expanded into a vertical fin, which must have helped to move the great body of this marine lizard through the water.

Its limbs were developed into short flippers, with the front pair longer than the hind pair due to a greater number of bones in each toe. (This hyperphalangid condition was also developed in many other marine reptiles.) Impressions preserved in the chalk near the bones of the limbs suggest that Plotosaurus was covered in a scaly skin, like that of a modern snake.

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  • Marvin
    How heavy were plotosaurus?
    7 years ago

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