The Triassic Period - 251 to 205 MY - Tectonics and climate Life in the Oceans Jarðsaga 1 - Saga Lífs og Lands – -Ólafur Ingólfsson The Triassic Period The first period of the Mesozoic Era is the Triassic Period, which lasted from 251 to 205 million years ago. The name Triassic comes from Germany where it was originally named the Trias in 1834 by Friedrich August Von Alberti (1795- 1878) because it is represented by a three-part division of rock types in Germany. Triassic tectonic development In many ways, the Triassic was a time of transition. Pangea was fully assembled and remained so through the Triassic, affecting global climate and ocean circulation... Early Triassic climate The Triassic was a greenhouse world, with no evidence of ice at the poles. The interior of Pangea was hot and dry, and warm, temperate climates extended to the Poles. Pangea starts breaking up towards the end of the Triassic Towards the end of the Triassic, a rift develops between Gondwana and Laurasia The first chapter in the formation of the Atlantic Ocean... Late Triassic climate Global climate was warm during the Late Triassic. There was no ice at either North or South Poles. More pronounced climate zonation than during the Early Triassic, less extension of arid areas. Warm temperate conditions extended towards the poles. Space for new life forms to develop The Triassic followed the largest extinction event in the history of life, when 75-90% of all marine species vanished at the end of the Permian. This provided an opportunity for new lifeforms... Triassic marine deposits rather rare Sea level was fairly constant through the Triassic; lack of transgressions makes marine deposits rather rare in the geological record. Recovery from the Pemian extinction was slow for many groups. It has been suggested that increased salinity of shallow sea areas caused problems for many marine organisms. Slow start in the seas The survivors of the Permian mass extinction: - Geographically widespread - From temperate areas (not tropical) - Opportunistic ecologic generalists (meaning they can live in many ways/settings) - Tend to be mobile (not sessile) These features suggest the survivors were those who were suited to large changes in the physical environment...not competitively superior groups. Pelagic life Planktonic organisms are at the base of the food chain in the Oceans, but most kinds leave little or no fossil record. In Triassic times, dinoflagellates (skorusvipungar) were one very important group of plankton. Pherhaps the slow early Triassic recovery of marine life was caused by a mass-extinction crisis of pelagic life? Dinoflagellates are microscopic, unicellular, often photosynthetic protists, commonly regarded as "algae" (Division Dinoflagellata). They form a significant part of primary planktonic production in oceans and lakes. A gradual diversification of marine life through the Triassic Early Triassic: Bivalves (samlokur), ammonoids, a few brachiopods (armfætlur) – other groups very rare. Diversity is low. Stromatolites (strýtuþörungar) briefly return – can live where grazing animals are excluded. Middle Triassic: Gastropods (sniglar) radiate. Echinoids (íguldýr) become more common First appearance of scleractinians (stein- kórallar) – modern reef-building corals. Marine conditions are returning to normal from high salinity conditions. Late Triassic: Molluscs, echinoids, bony fish, and large marine reptiles diversify. By the end of the Triassic, the modern marine fauna is taking off. Modern molluscs originate during Triassic Bivalves and gastropods re-expanded Molluscs are a to become more diverse than in very diverse Paleozoic. They filled many of the groups of animals. niches previously occupied by the They first brachiopods. evolved in the Cambrian. There are about 60,000 living species, and at least 35,000 known fossil species. Two of the most impor- tant groups are bivalves and cephalopods Triassic ammonides expanded rapidly The ammonides just barely es- caped extinction in the Permian mass-extinction. One genera, the Ophiceras gave rise to an enormous Triassic expansion. Adaptive radiation of ammonoids from 2 to 100 genera. Belemnides (álfasmokkar) also had a great success The belemnites had a straight, chambered shell, similar to that of the nautiloids. The strong, massive, projectile-like calcareous shell, called the rostrum, is what usually is found fossilised. The hard-parts were internal in the living animal. The belemnites are known from the late Carboniferous until the latest Cretaceous. They were marine animals, who developed strongly during the Triassic. They were very abundant during the Jurassic and Cretaceous periods. The modern reef builders stem from the Triassic Modern reef-building corals appeared in mid-Triassic times (Hexacorals or scleractinian corals – sexukóralar, steinkóralar). They are probably not closely related to the extinct tabulate or rugose corals (pípukóralar, hrukkukóralar) , but arose independently from a sea anemone (sæfífill) ancestor. Bony-fishes continue to develop Paleozoic ray-finned fishes gave rise to forms that were successful in early Mesozoic times, but were still primi- tive compared to most modern-day fishes. They had partly cartillageous skeletons, primitive jaws and assymmetrical tails. Cleithrolepsis minor, a Triassic Lissodus africanus, another bony-fish from South Africa Triassic fish from South Africa The sharks Sharks were numerous in the early Mesozoic. Most lived in near-shore or freshwater habitats. Helicoprion, 2-3 m. Carbon-Triassic shark, probably lived off shellfish. Marine reptiles Reptiles increasingly took to the sea during the Triassic. The placodonts (broteðlur, 1-3 m) were blunt-toothed shell crushers, with a broad, armoured body that made them look like large turtles. Placodonts evolved during 35 MY. They were never fully adapted to the open sea, but lived in the shallow coastal waters of the Tethys Sea. Others tried to have the best of both worlds... The characteristic long neck of a Triassic protorosaur (frumeðla) reached its extreme in Tanystropheus -its neck was longer than body and tail combined, but with only 10 neck vertebrae. The length of the neck suggested that it may have lived in water, but there are no obvious water adaptations. It may have lived on the seashore and eaten shellfish or fish. Length: 6 m; weight: 300 kg The Nothosaurs (slóðeðlur) The Nothosaurs were 3-4 m long aquatic reptiles with a long neck, a long low skull with sharp teeth and a long, narrow tail. Its limbs were paddle-shaped. Nothosaurus probably ate fish and shellfish. The Plesiosaurs (svaneðlur) The placodonts (broteðlur) and and the nothosaurs (slóðeðlur), which were probably not completely aquatic, did not survive the Triassic Period. Their descendants, the Plesiosaurs, developed to a major group of predatory marine reptiles. The plesiosaurs, which appeared in the mid-Triassic, played an important role through the Mesozoic The Plesiosaurs - svaneðlur Plesiosaurs were an important Mesozoic group of marine reptiles.They were very well adapted for life in the oceans. One group of plesiosaurs, the elasmosaurs, had short tails and long necks. The longest neck in the Ocean The large Triassic elasmosaur (svaneðla -Thalassomedon hanningtoni) was about 14 m long. The “Head-on-tail” plesiosaur It is well known in the history of paleontology that Edward Cope of Philadelphia, who first described the E. Platyurus, initially reconstructed the skeleton with the head on the wrong end, that is, on the end of the tail. His error was pointed out by Othniel C. Marsh, thus precipitating a life-long feud, and a mortified Cope attempted to buy up the plates with the erroneous reconstruction and replace them with correct versions. Ancestors of Plesiosaurs (?) Paleontologists are uncertain what the ancestors of the first plesiosaurs looked like but it is probable that they came from primitive aquatic reptiles found in China (Keichousaurus hui). In these animals, the limbs were probably used as paddles to some extent, but could also still move the animal on land. The long neck and small head are also early plesiosaur traits. A complete Plesiosaur skeleton The first nearly complete plesiosaur was discovered in the Jurassic rocks of Lyme Regis, England in the winter of 1820-21. The name Plesiosaurus means "near-reptile", a reference to the view of the time that plesiosaurs were closer to reptiles than were the more fish-like ichthyosaurs. How did they swim? The plesiosaur limbs were very large and modified into well developed, paddles which were the main means of propulsion. Recent studies the limbs were 'flapped' up and down much like the wings of a bird or the paddles of a turtle. The plesiosaur, in effect, 'flew' through the water like a modern penguin. How did they reproduce? There is still some controversy about if they laid eggs or not, but the evidence seems to point toward plesiosaurs giving live birth like ichthyosaurs. It is hard to imagine a 14 m plesiosaur struggling up on a beach to lay eggs like a sea turtle. Besides having limbs that were unsuitable for travel on land, there are several good reasons (such as over-heating, and not being able to breathe) why egg laying would not be possible for plesiosaurs... What did they eat? Plesiosaurs ate fish, ammonites and other invertebrates - many specimens have been discovered with stomach stones in their abdomens. Gastrolites - magasteinar For digestion and buyoancy The Ichthyosaurs The most fish-like reptiles of the Mesozoic seas were the ichthyosaurs – fiskeðlur. Superficially the ichthyosaurs bear a close resemblance to modern dolphins (höfrungur = sjávarspendýr) . Development of the Ichthyosaurs Ichthyosaur = fiskeðla The most obvious transformation for aquatic life is the one from feet to flippers. What were the ichthyosaurs like? Ichthyosaurs were stream-lined in form, and ranged in size from 4-23 m. They had sharp teeth in long jaws, and big eyes. They had four crescent-shaped fins, a stabilizing dorsal fin, and a fish-like tail with two lobes. They breathed air with lungs through nostrils which were close to the eyes near the top of the snout.