The Lower Triassic series is coeval with the Scythian Stage, which is today not included in the official timescales but can be found in older literature. In Europe, most of the Lower Triassic is composed of Buntsandstein, a lithostratigraphic unit of continental red beds.[citation needed]
The climate during the Early Triassic Epoch (especially in the interior of the supercontinent Pangaea) was generally arid, rainless and dry and deserts were widespread; however the poles possessed a temperate climate. The pole-to-equator temperature gradient was temporally flat during the Early Triassic and may have allowed tropical species to extend their distribution poleward. This is evidenced by the global distribution of ammonoids.[13] The extremely hot ocean temperatures facilitated extremely powerful hurricanes that frequently hit the coast of North China.[14]
The mostly hot climate of the Early Triassic may have been caused by late volcanic eruptions of the Siberian Traps,[15][8] which had probably triggered the Permian-Triassic extinction event and accelerated the rate of global warming into the Triassic.[16] Studies suggest that Early Triassic climate was very volatile, punctuated by a number of relatively rapid global temperature changes, marine anoxic events, and carbon cycle disturbances,[17][18][19] which led to subsequent extinction events in the aftermath of the Permian-Triassic extinction event.[20][21][22] On the other hand, an alternative hypothesis proposes these Early Triassic climatic perturbations and biotic upheavals that inhibited the recovery of life following the P-T mass extinction to have been linked to forcing driven by changes in the Earth's obliquity defined by a roughly 32.8 thousand year periodicity with strong 1.2 million year modulations. According to proponents of this hypothesis, radiometric dating indicates that major activity from the Siberian Traps ended very shortly after the end-Permian extinction and did not span the entire Early Triassic epoch, thus not being the primary culprit for the climatic changes throughout this epoch.[23]
The Early Triassic Epoch saw the biotic recovery of life after the biggest mass extinction event of the past, which took millions of years due to the severity of the event and the harsh Early Triassic climate.[24] Many types of corals, brachiopods, molluscs, echinoderms, and other invertebrates had disappeared. The Permian vegetation, which was dominated by Glossopteris in the Southern Hemisphere, ceased to exist.[25] Other groups, such as Actinopterygii, appear to have been less affected by this extinction event[26] and body size was not a selective factor during the extinction event.[27][28] Animals that were most successful in the Early Triassic were those with high metabolisms.[29] Different patterns of recovery are evident on land and in the sea. Early Triassic faunas lacked biodiversity and were relatively homogeneous due to the effects of the extinction. The ecological recovery on land took 30 million years, well into the Late Triassic.[30] Two Early Triassic lagerstätten stand out due to their exceptionally high biodiversity, the Dienerian aged Guiyang biota[31] and the earliest Spathian aged Paris biota.[32]
The flora was gymnosperm-dominated at the onset of the Triassic, but changed rapidly and became lycopod-dominated (e.g. Pleuromeia) during the Griesbachian-Dienerian ecological crisis. This change coincided with the extinction of the Permian Glossopteris flora.[25] In the Spathian subage, the flora changed back to gymnosperm and pteridophyte dominated.[37] These shifts reflect global changes in precipitation and temperature.[25][20] Floral diversity was overall very low during the Early Triassic, as plant life had yet to fully recover from the Permian-Triassic extinction.[38]
Microbially induced sedimentary structures (MISS) are common in the fossil record of North China in the immediate aftermath of the Permian-Triassic extinction, indicating that microbial mats dominated local terrestrial ecosystems following the Permian-Triassic boundary. The regional prevalence of MISS is attributable to a decrease in bioturbation and grazing pressure as a result of aridification and temperature increase.[39] MISS have also been reported from Early Triassic fossil deposits in Arctic Canada.[40] The disappearance of MISS later in the Early Triassic has been interpreted as a signal of increased bioturbation and recovery of terrestrial ecosystems.[39]
Aquatic biota
In the oceans, the most common Early Triassic hard-shelled marine invertebrates were bivalves, gastropods, ammonoids, echinoids, and a few articulate brachiopods. Conodonts experienced a revival in diversity following a nadir during the Permian.[41] The first oysters (Liostrea) appeared in the Early Triassic. They grew on the shells of living ammonoids as epizoans.[42]Microbial reefs were common, possibly due to lack of competition with metazoan reef builders as a result of the extinction.[43] However, transient metazoan reefs reoccurred during the Olenekian wherever permitted by environmental conditions.[44]Ammonoids show blooms followed by extinctions during the Early Triassic.[45]
Aquatic vertebrates diversified after the extinction:
McElwain, J. C.; Punyasena, S. W. (2007). "Mass extinction events and the plant fossil record". Trends in Ecology & Evolution. 22 (10): 548–557. doi:10.1016/j.tree.2007.09.003. PMID17919771.
Cavin, L.; Argyriou, T.; Romano, C.; Grădinaru, E. (2024). "Large durophagous fish from the Spathian (late Early Triassic) of Romania hints at earlier onset of the Triassic actinopterygian revolution". Papers in Palaeontology. 10 (2). e1553. doi:10.1002/spp2.1553.
Mutter, Raoul J.; Neuman, Andrew G. (2008). "New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada". In Cavin, L.; Longbottom, A.; Richter, M. (eds.). Fishes and the Break-up of Pangaea. Geological Society of London, Special Publications. Vol.295. London: Geological Society of London. pp.9–41. doi:10.1144/sp295.3. S2CID130268582.
Martinetto, Edoardo; Tschopp, Emanuel; Gastaldo, Robert, eds. (2020). Nature through Time: Virtual field trips through the Nature of the past. Springer International Publishing. ISBN978-3-030-35057-4.
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