Dinosaurs were the largest post-triassic creatures in Earth's history 250 million years ago, appearing in the Late Triassic 16 million years after the cataclysm. In the 16 million years before the advent of the dinosaurs, reptiles had begun to gradually dominate the land and sea.
Dinosaur restoration
After the Great Extinction, land reptiles were mainly single-bowed diplodonts, canines, and diptychs.
At the end of the Early Triassic period and the beginning of the Middle Triassic, all marine reptiles - Hubei crocodiles, finnosaurs, sea dragons, ichthyosaurs and long-necked dragons appeared in the ocean. They reached the peak of their radiant development in the Middle Triassic, and most of the taxa declined in the Late Triassic, with only plesiosaurs, descendants of ichthyosaurs and plesiosaurs, surviving until the end of the Cretaceous period.
Plesiosaur restoration
Hubei crocodiles have distinct endemic characteristics and are currently only found in the Lower Triassic in Nanzhang County, Hubei Province. Like ichthyosaurs, the body is flattened spindle-shaped, and unlike the large ichthyosaurs, the Hubei crocodile is only 33-85 cm long and is a small marine reptile. Its skull has an elongated but not toothless snout and jaw. There are longitudinal membranous plates on the neck and above the body. The limbs are paddle-shaped, but still retain many of the characteristics of terrestrial ancestors. They use the lateral swing of the body and tail to propel the body forward. At present, only two genera of Nanzhanghu Crocodile and Sun's Nanzhanglong are described.
Hu's Guizhou dragon is the first Triassic marine reptile found in China. It was a group of individuals living in the Middle Triassic with smaller ribostorans, with a short snout and a small temporal foramen, a long, flexible neck, and its forelimbs longer than its hindlimbs. Studies have shown that Unlike other swollen ribosaurs, Hu Guizhou Dragon did not completely rely on the tail and the lateral swing of the body to push the body forward, and its forelimbs played a very important role in movement. Because its limb structure is suitable for water movement, the elbow of the ulna is not ossified, it is difficult to imagine that it can climb up the coast to lay eggs with difficulty, and the fossils of pregnancy show that Hu's Guizhou dragon was egg-born.
Guizhou dragon fossil
" Plesiosaurs were very peculiar Mesozoic marine reptiles , especially the " Beantooth " in this group , which not only had bean-shaped teeth that grew on the jaw and palate , but also had turtle shell-like dorsal carapace. The jaw muscles of the plesiosaurs were strong and could crush solid objects, feeding mainly on marine mesozoans. They are not fast swimmers, and can only move slowly forward in shallow seas, paddling their bodies in the water with their four legs.
Ichthyosaurs are highly adapted reptiles to marine life, their bodies are streamlined, the back of the skull is connected to the trunk, and the appearance is not strictly visible neck, this long spindle-shaped body shape is an adaptation to the high-speed swimming lifestyle. As a result of supporting the body with the buoyancy of water, the spine has lost its twisted joints and is reduced to a flattened disc-shaped body with myeloids. The limbs have been transformed into copepods. The caudal fin is large and half-moon-shaped. It is speculated that it is like a fish that pushes the body forward with the rhythmic swing of the body. The four copepods act as a balance. The nostrils are located at the back, similar to modern whales, at the top of the forehead, making it easy to breathe on the surface of the water. Unable to walk on land, Ichthyosaurs are born of eggs. Its long snout has many cone-shaped teeth, and its food may be ammonites or fish, wandering around in the vast oceans of the Mesozoic Era, hunting for food. The sudden appearance of ichthyosaurs in the Early Triassic, even the most primitive species, has become so specialized that people are still uncertain about their ancestors. During the Jurassic period, ichthyosaurs reached the greatest differentiation, with more genera appearing in Europe and North America, and after the Cretaceous period, these reptiles active in the Mesozoic ocean suddenly disappeared from the earth just like their appearance.
Ichthyosaur restoration
Ichthyosaur fossils
Sea dragons are a monophyletic group of marine reptiles. They can reach a length of more than 3 meters. It has a narrow and long snout consisting mainly of the anterior maxilla, a narrowed or even completely closed upper temporal foramen, anteriorly concave occipital surface. The skeleton behind the head still retains the original characteristics of terrestrial tetrapods, with little adaptation to changes in aquatic life. This suggests that they do not have a wide-sea habit, and the range of activities may be limited to shallow surface seas and nearshore continental sea basins. Sea dragons have a long tail and move forward in the water by the lateral swing of their bodies. The mouth has pointed teeth, and some species also have button-like palate teeth, which may feed on fish and bivalves. There are 7 genera and 8 species of sea dragons in Europe and North America, but most of the fossils are incomplete. The Middle-Upper Triassic system in Guanling and southwestern Guizhou in China is extremely rich in sea dragon fossils, with a large number and exquisite preservation.