The Mesozoic Era – Triassic Period

The Mesozoic Era – Triassic Period (251-199.6 million years ago), Well time travellers, after the disruption to travel plans caused by the Permian extinction, evolution has gone into overdrive in an effort to provide some alternative attractions. The lizards are starting to take over the land, but as usual the crucible of life is in the sea. During the Mesozoic, new fauna arose including new species of sea urchins, crustaceans, and fish. The Mesozoic also witnessed the advent of marine reptiles. On the seabed, the void left behind by the demise of crinoids, blastoids, bryozoans and horn corals was filled by molluscs such as bivalves (clams) and gastropods (snails). The mid water area is home to a variety of swimming ammonites (nautilus-like animals) and fish. Feeding on the fish and ammonites were different kinds of marine reptiles ranging from short-legged, shortnecked varieties resembling seals to long-necked plesiosaurs with whale-like bodies and broad, paddle-shaped fins. The neck-span of pleisosaurs could reach 17 meters in length. The ichthyosaurs, or “fish lizards”, had dolphin-like bodies, welldeveloped paddles, and a long bill with teeth for catching fish. Most ichthyosaurs were less than 3 to 5 meters long, but some reached 15 meters in length. They first appeared approximately 250 million years ago during the early Triassic Period. Ichthyosaurs evolved from a group of, as yet unidentified land reptiles that had returned to the sea. They resembled but are not related to dolphins and whales. In the later Jurassic Period they were replaced as the top aquatic predators. Mosasaurs, related to modern monitor lizards, had a flattened tail for underwater propulsion, large flippers, and nostrils located on the top of their heads in order to breath while swimming. The largest mosasaurs grew more than 14 meters in length. The earliest dinosaurs appeared in the Triassic Period of the Mesozoic Era and were small, bipedal animals less than 1 meter in length. By late Triassic time, primitive archosaurs were replaced by a great radiation of dinosaurs. Flying reptiles included the pterosaurs, a close relative of the dinosaurs. Early pterosaurs were the size of birds, later ones, scarily enormous. Travel suggestions, go earlier in the era before the big predators really get going. Hitching a ride on a turtles (there are no other humans looking) can be fun, but not if spoiled by an encounter with an early crocodile. Flying Fish With predators getting bigger and better, prey had to adapt. An evolutionary strategy that appeared in the Triassic was the ability of fish prey to leap out of the water when threatened. Soon fish specialised in this strategy and evolved increasingly larger fins that could double as wings. A near-complete skeleton found in China has been identified as the oldest known gliding fish. Potanichthys is related to a nowextinct family of over-water glider known as thoracopterids. The fossils suggest that Potanichthys was squat, almost as wide as it was tall. Fish of that era usually aren’t very aerodynamic, being heavily built, so finding a flying fish this ancient was a surprise. If Potanichthys were anything like modern flying fishes, glides of tens of metres are not out of the realm of possibility. Flying fish possibly moved between what is now Asia and Europe, avoiding deep water. They instead travelled close to the shoreline that extended from what is now China to what is now Europe. Turtles The first proto-turtles are believed to have existed in the late Triassic Period, about 220 million years ago. They are thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell. Fossils of the freshwater Odontochelys semitestacea or “half-shelled turtle with teeth”, from China display a complete bony plastron and an incomplete carapace. A molecular analysis of genes from 16 vertebrate taxa suggests that turtles are a sister group to birds and crocodiles. The date of separation of turtles and birds and crocodiles was estimated to be 255 million years ago. The earliest known fully shelled turtle is the late-Triassic Proganochelys. This genus already possessed many advanced turtle traits, and thus probably indicates many millions of years of preceding turtle evolution. It lacked the ability to pull its head into its shell, had a long neck, and had a long, spiked tail ending in a club.