Although the head was generally more lightly built with a long, narrow snout, extinct marine crocodiles resembled today's crocodiles in many ways. Here are some of the anatomical features that marine crocodiles share:
Long, narrow skull. The skulls of marine crocodiles were lightweight and had a long, narrow snout. When viewed from above, they had an extremely elongated triangular shape.
Eyes on the sides. The eyes of marine crocodiles were on the sides of the skull rather than the top as in most living crocodiles. This gave them a wider field of vision while underwater.
Jaws and teeth. The long jaws had closely spaced, pointed, cone-shaped teeth. These were for grabbing fish.
Tail and feet adapted for swimming. Marine crocodiles propelled themselves by waving their tails back and forth. This was aided by thrusts from the hind legs. The front legs were probably of little use during swimming and were probably held at the side. The crocodiles that were most highly adapted for ocean life were the metriorhyn-chids. They had replaced their webbed reptilian feet with paddles. The rear paddles were larger than the front paddles. In other marine crocodiles, the feet were webbed but had not evolved into paddles. The front limbs were often reduced in size so that they could be tucked back while the animal was swimming.
Loss of armor. Some marine crocodiles showed a reduction in body armor, especially on the back. Protective armor on the back was a holdover from their land-dwelling days and was unnecessary in the water. Losing armor would have also lightened the body and made it more streamlined for swimming. In the metriorhynchids, the body armor was nonexistent, replaced by a smooth skin. The other clades of marine crocodiles were much less advanced in this way. The dyrosaurids had only light armor on the back.
Streamlining of body and tail. The body of marine crocodiles was long and somewhat narrow when compared with that of their land-living relatives. The head and snout came to a narrow point. The tail was long and flattened vertically to offer less water resistance and to serve as a more effective paddle. In the metriorhynchids, the end of the tail had a vertical fin to provide additional thrust, a sign that these animals could probably dive deeply. One metriorhynchid, Metriorhynchus ("moderate snout"), even had small armor plates in front of the eyes to protect them and improve the smooth contour of the head for swimming.
Extinct marine crocodiles fell into four main groups, or clades. Of these, the members of the Metriorhynchidae were clearly best designed for ocean life. Metriorhynchids such as Metriorhynchus and Geosaurus ("Earth lizard") were probably capable of sustained outings in the ocean and deep diving. Other forms of marine crocodiles show indications that they were evolving ocean-going body features similar to those of the metriorhynchids. The clade that was least adapted for ocean life was the Pholidosauridae, a group dominated by freshwater crocodiles. At least one member of this clade, named Terminonaris ("end nose"), has been found in ocean deposits, however. Its thick tail and heavy back armor
gave it an appearance that is much more like those of today's inland and freshwater crocodiles than those of typical marine crocodiles.
Marine crocodiles were probably similar to mosasaurs in their hunting and eating habits. They were probably not capable of long, sustained periods of high-speed swimming. This suggests that they were ambush predators, waiting for prey to come near and then thrusting out with their powerful bodies to snatch them. Unlike mosasaurs, marine crocodiles had 1 ightly built, narrow jaws. This would have made them ill-equipped for doing battle with large creatures. Their teeth were short and pointed and best suited for grabbing fleshy prey such as fishes and squids.
It is assumed that marine crocodiles primarily ate fish. Some interesting stomach contents, however, have been discovered for one species of Metriorhynchus. A set of fossil remains from England show that the animal had eaten small, hard-s helled ammonites, squidlike belemnites, parts of a large fish, and even a pterosaur.
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