Real dinosaur fossil tooth  from the fossil beds of the Atlas mountains,nothern Africa.Found in hard sand rock,these teeth are left in the sandstone and jawbone mix,which includes other fossil remains.Real fossil tooth from a late Cretaceous age marine giant lizard better know as a Mosasaurus (from Latin Mosa meaning the 'Meuse river', and Greek saurus meaning 'lizard') were serpentine marine reptiles. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. These ferocious marine predators are now considered to be the closest relatives of snakes, due to similarities in jaw and skull.Mosasaursu were  lepidosaurus, reptiles with overlapping scales. These predators evolved from semi-aquatic squamates known as the aigialosaurus, close relatives of modern-day monitor lizards, in the Early Cretaceous Period. During the last 20 million years of the Cretaceous Period (Turonian-Maastrichtian), with the extinction of the ichthyosaurus and pliosaurus, mosasaurs became the dominant marine predators.Mosasaurus breathed air and were powerful swimmers that were well-adapted to living in the warm, shallow epicontinental seas prevalent during the Late Cretaceous Period. Mosasaurus were so well adapted to this environment that they gave birth to live young, rather than return to the shore to lay eggs, as sea turtles do.
The smallest-known Mosasaurus was Carinodens belgicus, which was about 3.0 to 3.5 m long and probably lived in shallow waters near shore, cracking mollusks and sea urchins with its bulbous teeth. Larger Mosasaurus were more typical: Mosasaurs ranged in size up to 17 meters or well over 50 feet Hainosaurus holds the record for longest mosasaurus, at 17.5 m.Mosasaurus had a body shape similar to that of modern-day monitor lizards (varanids), but were more elongated and streamlined for swimming. Their limb bones were reduced in length and their paddles were formed by webbing between their elongated digit-bones. Their tails were broad and supplied the locomotive power. This method of locomotion may have been similar to that used by the conger eel or sea snakes today. The animal may have lurked and pounced rapidly and powerfully on passing prey, rather than hunting for it.
Skeletal drawings of three types of Mosasaurus had a double-hinged jaw and flexible skull (much like that of a snake), which enabled them to gulp down their prey almost whole, a snakelike habit that has helped identify the unmasticated gut contents fossilized within mosasaurus skeletons. A skeleton of Tylosaurus proriger from South Dakota included remains of the diving seabird Hesperornis, a marine bony fish, a possible shark and another, smaller mosasaur (Clidastes). Mosasaurus bones have also been found with shark teeth embedded in them.
96 to 66 million years ago this marine lizard lived on the flesh of other weaker animals much like a crocodile does today.