After the ice age number of crocodiles, last representatives of prospering in far past Archosauria subclass, had sharply reduced and they have died out practically at all area. But in warm and damp climate of Neocene when many finny rivers and lakes have appeared, the place of large fish-eating predators did not remain empty: it was occupied with representatives of large monitor lizards. Once in Cretaceous period monitor lizards have already achieved short-term success, having evolved to predatory mososaurs – true horror of seas. In Neocene the opportunity to make the second attempt has appeared at them, and they again have taken advantage of it, becoming ancestors of separate family of water monitors, including predators similar to crocodiles of last geological epoch. They are settled in rainy tropic areas of Old World: in Africa, at East-African subcontinent, south of Arabia, Hindustan, in South-Eastern Asia and Indonesia. In Nile which in Neocene had changed the channel and flows across former Sahara desert as in prehistoric times, representatives of water monitors are not found: there they are replaced by other predatory river reptile, huge crocoturtle (Archotrionyx vorax), the representative of soft-shelled turtles.
At the coast of Tanganyika passage separating the East-African subcontinent from Africa, the crocodile monitor lizard, one of widespread species of this family, lives. It is the huge water reptile (its length is up to 5 - 6 meters), externally similar to crocodile with longer neck and without characteristic skin osseous plates. The skull of crocodile monitor lizard is more than half meter long. It is rather wide and flat. Eyes of reptile are shifted in top part of head and stick up above it a little. Haw has a role of “underwater glasses”, permitting monitor lizard to see normally under water. Nostrils of crocodile monitor lizard open at the end of muzzle that allows the reptile to breathe, only minimally displaying itself for catch. Edges of nostrils can close automatically at diving. Under water this monitor lizard finds possible catch with the help of sight and strongly advanced chemical feeling: the reptile from time to time analyzes water by tongue like snake.
Paws of crocodile monitor lizard are well advanced, animal easily moves on the ground. On toes claws, with which help monitor lizard tears apart large catch, are advanced. Palamas between toes of reptile are not present. The main swimming organ at the crocodile monitor lizard is long tail (its length is about half of general length of reptile). On tail the skinny edge is advanced, stretching up to middle of back. The skin of this monitor lizard is colored greenish-grey with pattern of longitudinal lines of darkly-green spots. Stomach, chest and throat are covered with soft yellowish-white skin.
Crocodile monitor lizard is active predator and scavenger. Its basic forage includes fishes, but the reptile equally willingly eats ground animals, for any reasons got in water, and during river floods searches corpses of sunk animals. Teeth of this reptile, as against to crocodile’s ones, resemble more teeth of shark: they are leaf-shaped with sharp saw-toothed edges. Attacking large animal, reptile puts to it deep cut wounds by teeth.
These reptiles are rather tolerant to each other, and frequently it is possible to see, as they gather on riverbank by small even-aged groups. The most part of day adult crocodile monitor lizards bask at the sun. If they become hot, huge lizards slip in water, wet skin and creep out to riverbank again, or hide in shadow of trees, or wallow in dirt. But such picture can be observed only when reptiles are full. Hungry crocodile monitor lizard is dangerous creature. It arranges ambush on shallow, near to favorite watering places of ground animals. Usually this reptile lays at the bottom, occasionally putting out from water tip of muzzle to breathe. Through river bottom monitor lizard feels steps of animals going to watering place. When the catch is located, monitor lizard cautiously creeps up in bottom as close as it is possible to animals drinking water, and makes sharp throw, trying to seize the chosen prey to the muzzle. If the attack is successful, reptile jerkily fells catch and drags it in water to drown. Thus it strongly grips it by jaws, not giving to prey any chance to escape.
Young crocodile monitor lizards eat at first insects, and then pass to more essential catch: frogs, small fishes, birds and animals had fallen in water. Crocodile monitor lizard eats exterminated catch alone when it is not so large. But if carcass is too large, it should hasten: the successful hunter is immediately surrounded by hungry neighbours, and everyone strives to bite off from another's catch richer piece. Sometimes near catch serious fight springs up. But teeth are not used, in other case after each such conflict the population promptly would decrease. Monitor lizards fight, pushing away opponents by all body, striking impacts by head and scratching by claws. Teeth are used only for demonstration of force: driving away neighbours from lawful catch, crocodile monitor lizard widely opens mouth, showing lines of sharp teeth, but does not try to bite the contender.
Being adapted to life in water, the crocodile monitor lizard confidently feels on land. It easily walks, and can even run to small distances. Sometimes it hunts on land, hiding near track of large animals. Here excellent masking colouring helps reptile. It attacks nothing suspecting prey when it walks beside. Sharply having turned around, monitor lizard strikes blow of tail on legs of prey, and then, having turned to it by head and rushes on animal trying to rise, seizing its neck or thorax. Even if the prey will escape, it is practically doomed: teeth of crocodile monitor lizard put to prey such wounds, that it quickly perishes from loss of blood. And the reptile easily finds wounded prey by blood trace. As against water turtles, the crocodile monitor lizard easily can swallow catch outside of water, and teeth with which it is possible to bite off suitable piece easily, favorably distinguish it from crocodiles. Crocodile is compelled to snap for its any sticking outside part and to turned around axis to dismember large catch. And such trick succeeds only in water.
The crocodile monitor lizard is very enduring, and it can even stay short time in sea water. Sometimes on “rafts” of floating trees these reptiles can be carried away far to the ocean, receiving an opportunity of settle at islands. They had crossed this way Tanganyika passage and have occupied the East-African subcontinent, and also had settled in Southern Arabia. At the East-African subcontinent (Zinj Land) this species had formed the separate dwarf form (Pseudosuchus varanoides carcinivorus) up to 3 meters long. The dwarf crocodile monitor lizard eats mainly fishes and freshwater crabs.
The breeding season at these reptiles stretches almost for all year, except for dry season at edges of natural habitat. Usually the male (on the average it is about meter longer than the female) begins caring: it chases female ready to pairing, seizing by paws for the basis of her tail (usually males of lizards keep females by teeth, but teeth of crocodile monitor lizard can put painful wounds). If the female is not ready to accept caring of the male, it can shake him from herself, having swept by the ground or having swam through driftwood.
If some males try to care to one female, there can be severe fights between them: contenders push each other away from the female, strike impacts by head and scratch by claws. If the competition becomes especially sharp, teeth are used and then fight may terminate in heavy traumas. In colonies of crocodile monitor lizards it is quite often possible to see animals with bitten off toes, injured skin and knocked out eyes, crippled during courtship tournaments.
Caring for the female, male pays to her signs of attention: it rubs against her head and throat. On riverbank male lays near to female, driving away from her probable competitors and when the female leaves in water, follows her. Pairing of reptiles takes place in water and repeats some times. After pairing male some time stays near to the female. Pregnancy at crocodile monitor lizard lasts about three weeks. When the female feels, that there comes time to lay eggs, she leaves riverbank and searches for secluded place in forest. In moisturized and friable wood ground she digs out by hinder leg hole about half meter depth, and lays in it about two tens eggs by size like goose ones. When all eggs are laid, female digs nest in and by bottom jaw rakes up atop leaves and branches of it. The care of posterity at this species of reptiles comes to an end at this moment, and female leaves nest.
The incubating lasts about two months. The length of just hatched young retile is only about 25 cm. By colouring it differs from adults: its skin is emerald-green with faltering cross strips of black color. Fin plica on tail is well advanced, and the young growth is able to swim and dive since the first day of life. But the first day of life is the hardest for the future river tyrant.
Young monitor lizards should fulfill very hard task: to dig independently the exit to the surface, and then to find way to water. It succeeds not to all ones: if the place for nest is chosen unsuccessfully, the overflow after rain river may simply inundate nest. A part of clutches may be founded and dug out by predatory animals, they destroy part of young monitors. In the river both predatory fishes and adult neighbours hunt young crocodile monitor lizards. Therefore the just hatched young monitor lizards searches shelter from cannibal neighbours in thickets of marsh plants where adult crocodile monitor lizard is not able to creep through. In total only posterity from one third of laid eggs survive up to monthly age. But at two-year-old age they reach one-and-a-half-meter length, and many of former enemies easily can turn to catch. And the eight-year reptile being about four meters long has practically no enemies. At the same age crocodile monitor lizards can breed. Life expectancy of this reptile can reach 70 years.