In a late Cretaceous period 70 – 68 millions of years ago on territory of modern North America and Mongolia ( probably, in other areas of the world too ) lived duck billed dinosaurssaurolophus with small crest located at 45 degrees on the back of the head. They were herbivorous and were able to eat plants on ground level and up to 4 m above it; they moved on 2 and 4 legs; their maximal length was 12 m and maximal mass was 1.9 tons. Crest may had many functions : thermoregulation, gender determination and as basement of skin flaps, as modern basilisk lizards have.
Skull of saurolophus allowed to perform chew-like movements and grind food with large amount of teeth, which were replaced as they wear; on the sides of jaws they had cheeks, that helped them to keep food in mouth. Juvenile saurolophus had much smaller crests, then adults animals had, and it reached as they grow approximately 20% of a skull length. For the first time dinosaurs of this species were found in 1912 year by paleontologist Barnum Brown in Canada; also large amount of complete skeletons and their fragments were discovered in Gobi desert area in 1946 – 1949 years by expedition of Russian and Mongolian scientists, which later were described by Anatoly Rozhdestvenskiy.
One of the first discovered and scientifically described dinosaurs is an iguanodon, which was first described by fossilized teeth, that look like iguana‘s, but much larger, in 1820ies in England by Gideon Mantell. First it were reconstructed as massive animal, that looks like iguana with elephant size and spike on a nose, later findings showed, that spike located not on the nose, but on the hands of reptile, on a thumbs, and was used for protection from predators and food gathering. Also, findings showed, that iguanodons are not so massive and they were placed in upright vertical position, with basement on back paws and tile. Researches of 20th century made it clear, that this reconstruction is also not right, because at such position tile would be broken; and now animal is shown with horizontal body position and straight tile, which mainly moves on 4 legs and sometimes goes to running on 2 back paws.
Iguanodons reached 12 m in length and 3 tons mass; wherein their maximal running speed was 24 km/h on back limbs; they lived at the beginning of a Cretaceous period 140 – 120 millions of years ago. Animal ate plants, in mouths they had 2 rows of teeth, which replaced each other, with which they chewed food; teeth located deeply in mouths, this tells, that they had some kinds of cheeks : muscular or completely from skin. For now there are no undoubted data on whether these animals lived in large herds or in small families; adult animals preferred to move on all 4 legs, when they obtained size and weight ( by this time length of their arms reached 70% of the back legs length ), while light-weighted juveniles ran mostly on back paws ( their hands was only 60% of legs length ). By this time lots of iguanodons fossils were found in Europe, North America and presumably in Africa and Asia; many of the subspecies, initially placed in relation to iguanodons, now are moved into separate species, part of the others changed their location inside iguanodons genera. To date iguanodons are one of the most studied dinosaurs species and, together with megalosaurus and hylaeosaurus initially formed this genera of ancient reptiles.
Among hadrosauriddinosaurs, living on Earth in Mesozoic era, were Parasaurolophus – large herbivore animals 9.5 m in length and with 2.5 tons mass, which lived in areas, which currently form North America, in late Cretaceous period 76.5 – 66 millions of years ago. Their name means “before” or “near” “saurolophus” – another hadrosaurid dinosaur, and tells about their close relationship. Their notable feature is the crest, growing from the back of the head and reaching 90 cm in length; it was used for many purposes : loud sounds generation ( in support of this its hollowness speak, as well as adult’s animals brain orientation on hearing of high-pitch sounds, which their juveniles with smaller crests were producing ), thermoregulation ( crest was full of blood vessels and helped to warm up on Sun and cool in the shadow ) and gender and species identification. Parasaurolophus were able to move on 4 and 2 legs, probably, they ate grass on 4 legs and ran on 2 of them. They had large and strong bones, which helped them to carry large body mass and stay on 2 legs to reach high trees’ branches with large and juicy leafs.
Jaws of Parasaurolophus resembled beak of a duck; in a mouth they had lots of teeth, oriented for plants chewing and constantly replacing each other, as they wear off; between jaws there was semblance of checks, which helped to keep food in the mouth. Dinosaurs’ skin had scales of middle size without large formations; no complete skeletons of Parasaurolophus were found, only partially preserved on territory of USA, Canada and Mexico. Among their natural enemies there were large carnivore dinosaurs of that time, from which they protected themselves by living in large herds, signaling each other in case of danger and by fast running. First bones of this dinosaurs species were found in 1920 in Alberta, Canada, by scientists group from Toronto University; species was first described by William Parks in 1922.
Allosaurus ( “strange dinosaur” ) are carnivorous dinosaurs from theropod family, they lived in Jurassic Period 155 – 145 millions years ago. They was named so, because their vertebrae was very different from vertebrae of other dinosaurs, that was know at that time. Allosaurus reached 11 – 12 m in length and 2,5 – 3 m in height ; their maximal weight was 1 – 2 tons. They were biggest predators of their time and hunted on plant-eating dinosaurs, like stegosaurus and iguanodons. Fossils of allosaurus were found in North America, Europe, Africa and Australia; in total there were found 60 fossilized skeletons of allosaurus. First almost complete skeleton of allosaurus was found by farmer M. P. Felch in 1883 year in Colorado, USA. Dinosaur was described first time by paleontologist O. C. Marsh in 1877 year.
They moved on their 2 legs, their forelegs was small and mainly used for hunting. They were able to run fast on their legs, despite their big size and weight, because there were found lots of allosaurus skeletons with ribs, that were broken during falls at high speed running. Also, their vertebrae had special holes, that allowed them to breath through skin at high physical exercise; modern birds also has such adaptations in their skeletons. Probably, allosaurus lived and hunted in groups, because there are lots of their fossilized footprints found together. Their brain was big relative to their body size; and allosaurus was able to perform social interactions and care about their youth. Their inner ear was relatively big and they was able to perceive low frequencies; but they had problems in perceiving high frequencies. Their smelling was developed to high level and they was able to use it for hunting and to determine other animals of their kind.