Triassic
Friedrich August von Alberti stood in southern Germany during 1834 and examined three distinct rock layers. He named this geological period the Triassic after observing these specific formations. The lower layer was known as Buntsandstein, a colorful sandstone that covered vast areas. Above it lay Muschelkalk, a shell-bearing limestone rich with ancient marine fossils. The uppermost section consisted of Keuper, a colored clay deposit that capped the sequence. Alberti published his findings in Stuttgart and Tübingen within a monograph titled Beitrag zu einer Monographie des bunten Sandsteins. On page 324 of that work, he wrote about joining these structures into one formation which he would call Trias. This term derived from the Greek word for triad or group of three. His classification system replaced earlier descriptions that treated these rocks as separate entities.
The supercontinent Pangaea dominated global geography at the start of the Triassic Period. It stretched from the north to south polar regions while centered on the equator. Laurussia occupied the northern sector while Gondwana held the southern position. The Paleo- and Neo-Tethys oceans lay within the arc of the supercontinent. Panthalassa Ocean extended beyond the continental mass to the east. North China and Amuria remained separated from Pangea by the Paleoasian Ocean during early stages. This ocean closed by the Late Triassic era. The Cimmerian terranes drifted northwards through the period after rifting from Gondwana in the Permian. Their movement caused the Paleo-Tethys to close in front while the Neotethys opened behind them. By the Carnian stage around 230 million years ago, tectonic motion shifted from westward drift to counterclockwise rotation. Later movements resumed westward direction again. Major rift basins formed along the eastern North American margin from Florida to Newfoundland. These included Newark Supergroup basins filled with continental deposits from regional river systems. The Moroccan and Iberian basins developed similarly along the Europe-African margin. Rifting ended with emplacement of the Central Atlantic Magmatic Province around 201 million years ago.
Global temperatures fluctuated between extreme heat following volcanic eruptions and humid pluvial events that punctuated the arid continental interior. The Early Triassic was the hottest portion of the entire Phanerozoic eon. Titantic volumes of greenhouse gases discharged from the Siberian Traps Large Igneous Province. Temperatures cooled briefly during the Dienerian Cooling phase from 251 to 249 million years ago. A Latest Smithian Thermal Maximum occurred around 249 to 248 Ma before cooling returned. The Ladinian-Carnian Cooling period lasted from 242 to 233 million years ago. Eruption of the Wrangellia Large Igneous Province around 234 Ma caused abrupt global warming. This triggered the Carnian Pluvial Event which brought widespread humidity across tropical latitudes. The Mid-Carnian Warm Interval followed from 234 to 227 million years ago. An Early Norian Cool Interval existed between 227 and 217 million years ago. The Manicouagan impact event around 214 Ma may have caused brief cooling. The Rhaetian Cool Interval lasted from 209 to 201 million years ago. At the end of the period, an extreme warming event called the End-Triassic Thermal Event occurred. Bubbles of carbon dioxide in basaltic rocks indicate volcanic activity from the Central Atlantic Magmatic Province helped trigger this change.
Life rebounded slowly after the Permian extinction with early archosauromorphs and marine reptiles diversifying over thirty million years. Diverse communities with complex food-web structures took that long to reestablish following devastation. Two Early Triassic lagerstätten stand out due to exceptional preservation and diversity. The Dienerian aged Guiyang biota represents one such site while the earliest Spathian aged Paris biota offers another view. These locations provide insight into biotic recovery from the mass extinction event. Marine environments saw new modern types of corals appear in the Early Triassic forming small patches of reefs. Serpulids appeared in the Middle Triassic while Microconchids became abundant. Shelled cephalopods called ammonites recovered by diversifying from a single line that survived the Permian extinction. Bivalves began to rapidly diversify during the Middle Triassic becoming highly abundant in oceans. Aquatic insects diversified quickly during the Middle Triassic representing crucial development for Holometabola clade. Coelacanths showed their highest post-Devonian diversity in the Early Triassic period. Ray-finned fishes underwent remarkable diversification leading to peak diversity during the Middle Triassic era. First stem-group teleosts appeared during the Triassic becoming far more diverse than any other fish group today.
Pseudosuchians ruled terrestrial ecosystems while dinosaurs first appeared as minor predators before the period ended. True archosaurs split into two branches: Avemetatarsalia ancestors to birds and Pseudosuchia ancestors to crocodilians. Archosauriforms were distinguished by active predatory lifestyle with serrated teeth and upright limb postures. Large-headed erythrosuchids dominated carnivore niches in early Triassic times. Phytosaurs prospered during Late Triassic as long-snouted semiaquatic predators resembling living crocodiles. Tanystropheids elevated neck size to extremes with largest genus having neck longer than body. Rhynchosaurs thrived only short time becoming extinct about 220 million years ago despite exceptional abundance in middle Triassic. Allokotosaurs included Trilophosaurus common Late Triassic reptile with three-crowned teeth. Aetosaurs were heavily-armored reptiles common during last 30 million years of Late Triassic until extinction at boundary. Rauisuchians served as keystone predators occupying large-predator niche later filled by theropods. Over 25 species found including giant quadrupedal hunters and sleek bipedal omnivores. Early pterosaurs appeared in Norian spreading worldwide quickly. Triassic dinosaurs evolved in Carnian including early sauropodomorphs and theropods. Most Triassic dinosaurs were small predators with few common examples like Coelophysis which measured around 3 meters long.
Mass extinctions at both beginning and end of period were likely triggered by massive volcanic activity from large igneous provinces. The Permian-Triassic extinction event reduced biosphere significantly before the Triassic began. Siberian Traps Large Igneous Province erupted persisting into Early Triassic causing thermal maximum conditions. End-Triassic mass extinction wiped out many groups including most pseudosuchians allowing dinosaurs to assume dominance in Jurassic. Conodonts disappeared while all marine reptiles except ichthyosaurs and plesiosaurs vanished from oceans. Invertebrates like brachiopods and molluscs suffered severe losses. Twenty-two percent of marine families possibly half of marine genera went missing during oceanic crisis. Several important clades of crurotarsans disappeared along with most large labyrinthodont amphibians. Groups of small reptiles and most synapsids also perished. Some primitive dinosaurs became extinct but adaptive ones survived evolving into Jurassic forms. Huge volcanic eruptions occurred as supercontinent Pangaea broke apart about 202 to 191 million years ago forming Central Atlantic Magmatic Province. This represents one of largest known inland volcanic events since planet cooled and stabilized. Evidence suggests Manicouagan impact preceded end of Triassic by approximately 10±2 Ma making it unlikely immediate cause.
Common questions
Who named the Triassic period and when did he publish his findings?
Friedrich August von Alberti named the Triassic period in 1834. He published his findings in Stuttgart and Tübingen within a monograph titled Beitrag zu einer Monographie des bunten Sandsteins.
What were the three rock layers Friedrich August von Alberti identified in southern Germany?
The lower layer was known as Buntsandstein, a colorful sandstone that covered vast areas. Above it lay Muschelkalk, a shell-bearing limestone rich with ancient marine fossils. The uppermost section consisted of Keuper, a colored clay deposit that capped the sequence.
When did the Early Triassic occur and what caused its extreme heat conditions?
The Early Triassic occurred from 251 to 249 million years ago during the Dienerian Cooling phase. Titantic volumes of greenhouse gases discharged from the Siberian Traps Large Igneous Province created these thermal maximum conditions.
Which major supercontinent dominated global geography at the start of the Triassic Period?
The supercontinent Pangaea dominated global geography at the start of the Triassic Period. It stretched from the north to south polar regions while centered on the equator.
How many species of early pterosaurs appeared during the Norian stage of the Triassic period?
Early pterosaurs appeared in Norian spreading worldwide quickly. Over 25 species found including giant quadrupedal hunters and sleek bipedal omnivores existed alongside them.