Triassic
The Triassic (/traɪˈæsɪk/ try-ASS-ik; sometimes symbolized 🝈)[8] is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.4 Mya.[9] The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.[10] The Triassic Period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic.
Triassic
Formal
Global (ICS)
ICS Time Scale
Formal
First appearance of the conodont Hindeodus parvus
2001[6]
First appearance of the ammonite Psiloceras spelae tirolicum
Kuhjoch section, Karwendel mountains, Northern Calcareous Alps, Austria
47°29′02″N 11°31′50″E / 47.4839°N 11.5306°E
2010[7]
The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Three categories of organisms can be distinguished in the Triassic record: survivors from the extinction event, new groups that flourished briefly, and other new groups that went on to dominate the Mesozoic Era. Reptiles, especially archosaurs, were the chief terrestrial vertebrates during this time. A specialized group of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.[11] Archosaurs that became dominant in this period were primarily pseudosuchians, relatives and ancestors of modern crocodilians, while some archosaurs specialized in flight, the first time among vertebrates, becoming the pterosaurs.
Therapsids, the dominant vertebrates of the preceding Permian period, declined throughout the period. The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period. The vast supercontinent of Pangaea dominated the globe during the Triassic, but in the following Jurassic period it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
The global climate during the Triassic was mostly hot and dry,[12] with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups, including most pseudosuchians, and allowed dinosaurs to assume dominance in the Jurassic.
The Triassic was named in 1834 by Friedrich August von Alberti, after a succession of three distinct rock layers (Greek triás meaning 'triad') that are widespread in southern Germany: the lower Buntsandstein (colourful sandstone), the middle Muschelkalk (shell-bearing limestone) and the upper Keuper (coloured clay).[13]
Plateosaurus was one of the largest of early sauropodomorphs, or "prosauropods", of the Late Triassic
Lagerstätten[edit]
Two Early Triassic lagerstätten (high-quality fossil beds), the Dienerian aged Guiyang biota[66] and the earliest Spathian aged Paris biota[67] stand out due to their exceptional preservation and diversity. They represent the earliest lagerstätten of the Mesozoic era and provide insight into the biotic recovery from the Permian-Triassic mass extinction event.
The Monte San Giorgio lagerstätte, now in the Lake Lugano region of northern Italy and southern Switzerland, was in Middle Triassic times a lagoon behind reefs with an anoxic bottom layer, so there were no scavengers and little turbulence to disturb fossilization, a situation that can be compared to the better-known Jurassic Solnhofen Limestone lagerstätte. The remains of fish and various marine reptiles (including the common pachypleurosaur Neusticosaurus, and the bizarre long-necked archosauromorph Tanystropheus), along with some terrestrial forms like Ticinosuchus and Macrocnemus, have been recovered from this locality. All these fossils date from the Anisian and Ladinian ages (about 242 Ma ago).