Early Triassic Epoch
251.902–247.2 million years ago
Ages in the Early/Lower Triassic
-252 —
-251.5 —
-251 —
-250.5 —
-250 —
-249.5 —
-249 —
-248.5 —
-248 —
-247.5 —
-247 —
Triassic
E a r l y
Middle T
Induan
Olenekian
 
 
 
 
 
Ages of the Early/Lower Triassic.
Axis scale: millions of years ago.
System/
Period
Series/
Epoch
Stage/
Age
Age (Ma)
Jurassic Lower/
Early
Hettangian younger
Triassic Upper/
Late
Rhaetian 201.3 ~208.5
Norian ~208.5 ~227
Carnian ~227 ~237
Middle Ladinian ~237 ~242
Anisian ~242 247.2
Lower/
Early
Olenekian 247.2 251.2
Induan 251.2 251.902
Permian Lopingian Changhsingian older
Subdivision of the Triassic system
according to the ICS, as of 2018.[1]

The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.902 Ma and 247.2 Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic series, which is a unit in chronostratigraphy.

Sandstone from the Early Triassic Epoch

The Early Triassic is the oldest epoch of the Mesozoic Era. It is preceded by the Lopingian epoch (late Permian, Paleozoic Era) and followed by the Middle Triassic epoch. The Early Triassic is divided into the Induan and Olenekian ages. The Induan is subdivided into the Griesbachian and Dienerian subages and the Olenekian is subdivided into the Smithian and Spathian subages.[2]

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.




Early Triassic life

Fauna and Flora

Early Triassic brittle stars (echinoderms)

The Permian-Triassic extinction event spawned the Triassic period. The massive extinctions that ended the Permian period and Paleozoic era caused extreme hardships for the surviving species.

The Early Triassic epoch saw the 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.[3] Many types of corals, brachiopods, molluscs, echinoderms, and other invertebrates had disappeared. The Permian vegetation dominated by Glossopteris in the southern hemisphere ceased to exist.[4] Other groups, such as Actinopterygii, appear to have been less affected by this extinction event[5] and body size was not a selective factor during the extinction event.[6][7]

Different patterns of recovery are evident on land and in the sea. The most common land vertebrate was the small herbivorous synapsid Lystrosaurus interpreted as a disaster taxon. First archosauriforms appeared, such as Erythrosuchus (Olenekian-Ladinian).[8] This group includes the ancestors of crocodiles, dinosaurs and birds. Fossilized foot prints of dinosauromorphs are known from the Olenekian.[9] The flora became lycopod dominated (e.g. Pleuromeia) and changed back to gymnosperm and pteridophyte dominated in the Spathian subage.[10] These shifts reflect global changes in precipitation and temperature.[11]

Skull of Erythrosuchus
The Putorana plateau is composed of basalt rocks of the Siberian Traps.

In the oceans, the most common Early Triassic hard-shelled marine invertebrates were bivalves, gastropods, ammonites, echinoids, and a few articulate brachiopods. First oysters appeared in the Early Triassic. They grew on the shells of living ammonoids.[12] Microbial reefs were common, possibly due to lack of competition with metazoan reef builders as a result of the extinction.[13] However, transient metazoan reefs reoccurred during the Olenekian wherever permitted by environmental conditions.[14] Ammonoids show blooms followed by extinctions during the Early Triassic.[15]

Aquatic vertebrates diversified after the extinction.

Fishes: Typical Triassic ray-finned fishes, such as Australosomus, Birgeria, Bobasatrania, Boreosomus, Pteronisculus, Parasemionotidae and Saurichthys appeared close to the Permian-Triassic boundary, whereas neopterygians diversified later during the Triassic.[16] Many species of fish had a global distribution during the Early Triassic. Coelacanths show a peak in their diversity and new modes of life (Rebellatrix). Chondrichthyes are represented by Hybodontiformes like Palaeobates, Omanoselache, Lissodus, some Neoselachii, as well as last survivors of Eugeneodontida (Caseodus, Fadenia).

Amphibians: Relatively large, marine temnospondyl amphibians, such as Aphaneramma or Wantzosaurus, were geographically widespread during the Induan and Olenekian ages. The fossils of these crocodile-shaped amphibians were found in Greenland, Spitsbergen, Pakistan and Madagascar.

Reptiles: In the oceans, first marine reptiles appeared during the Early Triassic.[17] Their descendants ruled the oceans during the Mesozoic. Hupehsuchia, Ichthyopterygia and sauropterygians are among the first marine reptiles to enter the scene in the Olenekian (e.g. Cartorhynchus, Chaohusaurus, Utatsusaurus, Hupehsuchus, Grippia, Omphalosaurus, Corosaurus). Other marine reptiles such as Tanystropheus, Helveticosaurus, Atopodentatus, placodonts or the thalattosaurs followed later in the Middle Triassic.[18] The Anisian aged ichthyosaur Thalattoarchon was one of the first marine macropredators capable of eating prey that was similar in size to itself, an ecological role that can be compared to that of modern orcas.[19]

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.[20] 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.[21]

The mostly hot climate of the Early Triassic may have been caused by late volcanic eruptions of the Siberian Traps, which had probably triggered the Permian-Triassic extinction event and accelerated the rate of global warming into the Triassic. Studies suggest that Early Triassic climate was volatile, with relatively rapid and large temperature changes.[22][23][24]

Smithian-Spathian boundary extinction

Early Triassic and Anisian marine predators[25]: 1. Wantzosaurus, 2. Fadenia, 3. Saurichthys, 4. Rebellatrix, 5. Hovasaurus, 6. Birgeria, 7. Aphaneramma, 8. Bobasatrania, 9. Hybodontiformes, 10. Mylacanthus, 11. Tanystropheus, 12. Corosaurus, 13. Ticinepomis, 14. Mixosaurus, 15. Cymbospondylidae, 16. Neoselachii, 17. Omphalosaurus skeleton, 18. Placodus

An important extinction event occurred during the Olenekian age of the Early Triassic, near the Smithian and Spathian substage boundary. The main victims of this Smithian-Spathian boundary extinction event[26] were ammonoids and conodonts. Until recently the existence of this extinction event about 2 million years following the end-Permian mass extinction was not recognised.[27]

The Smithian-Spathian boundary extinction was linked to late eruptions of the Siberian Traps, which resulted in climate change.[28] Oxygen isotope studies on conodonts have revealed that temperatures rose in the first 2 million years of the Triassic, ultimately reaching sea surface temperatures of up to 40 °C (104 °F) in the tropics around 249 million years ago.[29]

Large and mobile species disappeared from the tropics, and amongst the immobile species such as molluscs, only the ones that could cope with the heat survived; half the bivalves disappeared.[30] On land, the tropics were practically devoid of life.[31] Big, active animals only returned to the tropics, and plants recolonised on land when temperatures returned to normal around 247 million years ago in the Anisian age of the Middle Triassic.

There is evidence that life had recovered earlier during the Early Triassic, at least locally. This is indicated by sites that show exceptionally high biodiversity (e.g. the Paris Biota)[32][33] and by the occurrences of large predators, which suggest that food webs were complex and comprised several trophic levels.[34] A recent study indicated that temperature alone cannot account for the Smithian-Spathian boundary extinction, but that several factors were at play.[35]

See also

References

  1. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. 2018.
  2. ^ Tozer E. T. (1965): Lower Triassic stages and ammonoid zones of Arctic Canada: Paper of the Geological Survey of Canada 65:1–14.
  3. ^ Chen, Z.-Q. and Benton, M.J. (2012): The timing and pattern of biotic recovery following the end-Permian mass extinction. Nature Geoscience 5,:375–383 https://doi.org/10.1038/ngeo1475
  4. ^ Hochuli et al. (2016): Severest crisis overlooked—Worst disruption of terrestrial environments postdates the Permian–Triassic mass extinction. Scientific Reports 6:28372 https://doi.org/10.1038/srep28372
  5. ^ Smithwick F.M., and Stubbs T.L. (2018): Phanerozoic survivors: Actinopterygian evolution through the Permo‐Triassic and Triassic‐Jurassic mass extinction events. Evolution 72:348-362. https://doi.org/10.1111/evo.13421<
  6. ^ Romano et al. (2016): Permian–Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolutionBiological Reviews 91:106-147 https://doi.org/10.1111/brv.12161
  7. ^ Puttick et al. (2017): Body length of bony fishes was not a selective factor during the biggest mass extinction of all time. Palaeontology 60:727-741 https://doi.org/10.1111/pala.12309
  8. ^ Foth et al. (2016): Unappreciated diversification of stem archosaurs during the Middle Triassic predated the dominance of dinosaurs. BMC Evolutionary Biology volume 16:188 https://doi.org/10.1186/s12862-016-0761-6
  9. ^ Brusatte et al. (2010): Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B 278 https://doi.org/10.1098/rspb.2010.1746
  10. ^ Schneebeli-Hermann et al. (2015): Vegetation history across the Permian–Triassic boundary in Pakistan (Amb section, Salt Range). Gondwana Research 27:911-924 http://dx.doi.org/10.1016/j.gr.2013.11.007
  11. ^ Hochuli et al. (2016): Severest crisis overlooked—Worst disruption of terrestrial environments postdates the Permian–Triassic mass extinction. Scientific Reports 6:28372 https://doi.org/10.1038/srep28372
  12. ^ Hautmann et al. (2017): Geologically oldest oysters were epizoans on Early Triassic ammonoids. Journal of Molluscan Studies 83:253-260 https://doi.org/10.1093/mollus/eyx018
  13. ^ Foster et al. (2020): Suppressed competitive exclusion enabled the proliferation of Permian/Triassic boundary microbialites. The Depositional record 6. 1–13. https ://doi.org/10.1002/dep2.97
  14. ^ Brayard et al. (2011): Transient metazoan reefs in the aftermath of the end-Permian mass extinction. Nature Geoscience 4:693–697 https://doi.org/10.1038/ngeo1264
  15. ^ Brayard et al. (2009): Good genes and good luck: ammonoid diversity and the end-Permian mass extinction. Science 325:1118-1121 DOI: 10.1126/science.1174638
  16. ^ Romano et al. (2016): Permian–Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolutionBiological Reviews 91:106-147 https://doi.org/10.1111/brv.12161
  17. ^ Scheyer et al. (2014): Early Triassic Marine Biotic Recovery: The Predators' Perspective. PLoS ONE https://doi.org/10.1371/journal.pone.0088987
  18. ^ Scheyer et al. (2014): Early Triassic Marine Biotic Recovery: The Predators' Perspective. PLoS ONE https://doi.org/10.1371/journal.pone.0088987
  19. ^ N.B. Fröbisch, J. Fröbisch, P.M. Sander, L. Schmitz, and O. Rieppel. Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1216750110
  20. ^ Sahney, S.; Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time". Proceedings of the Royal Society B: Biological Sciences. 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148.
  21. ^ Brayard et al. (2006): The Early Triassic ammonoid recovery: Paleoclimatic significanceof diversity gradients. Palaeogeography, Palaeoclimatology, Palaeoecology 239:374–395 https://www.researchgate.net/profile/Arnaud_Brayard/publication/222227655_The_Early_Triassic_ammonoid_recovery_Paleoclimatic_significance_of_diversity_gradients/links/5be303f8a6fdcc3a8dc50b2d/The-Early-Triassic-ammonoid-recovery-Paleoclimatic-significance-of-diversity-gradients.pdf
  22. ^ Romano et al. (2013): Climatic and biotic upheavals following the end-Permian mass extinction. Nature Geoscience 6 (1): 57-60; https://doi.org/10.1038/ngeo1667
  23. ^ Sun et al. (2012): Lethally Hot Temperatures During the Early Triassic Greenhouse. Science 338:366-370 DOI: 10.1126/science.1224126
  24. ^ Goudemand et al. (2019): Dynamic interplay between climate and marine biodiversity upheavals during the early Triassic Smithian -Spathian biotic crisis. Earth-Science Reviews 195:169-178 https://doi.org/10.1016/j.earscirev.2019.01.013
  25. ^ Scheyer et al. (2014): Early Triassic Marine Biotic Recovery: The Predators' Perspective. PLoS ONE https://doi.org/10.1371/journal.pone.0088987
  26. ^ Galfetti et al. 2007, Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis, Geology 35 (4): 291–294. https://doi.org/10.1130/G23117A.1
  27. ^ Hallam, Anthony and P.B. Wignall 1997. Mass Extinctions and Their Aftermath, "Extinctions with and at the close of the Tiassic" p143f.
  28. ^ Romano et al. (2013): Climatic and biotic upheavals following the end-Permian mass extinction. Nature Geoscience 6 (1): 57-60; https://doi.org/10.1038/ngeo1667
  29. ^ Michael Marshall (2012). "Roasting Triassic heat exterminated tropical life". New Scientist.
  30. ^ Hallam and Wignall 1997:144.
  31. ^ Sun et al. (2012): Lethally Hot Temperatures During the Early Triassic Greenhouse. Science 338:366-370 DOI: 10.1126/science.1224126
  32. ^ Brayard et al. (2017): Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna. Science Advances 3 (2):e1602159; doi:10.1126/sciadv.1602159 https://advances.sciencemag.org/content/3/2/e1602159/tab-pdf
  33. ^ Special issue on Paris Biota: https://www.sciencedirect.com/journal/geobios/vol/54
  34. ^ Romano et al. (2017): Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): implications for the Smithian equatorial vertebrate eclipse. Journal of Paleontology 91:1025-1046
  35. ^ Goudemand et al. (2019): Dynamic interplay between climate and marine biodiversity upheavals during the early Triassic Smithian -Spathian biotic crisis. Earth-Science Reviews 195:169-178 https://doi.org/10.1016/j.earscirev.2019.01.013

Further reading

  • Martinetto et al. (2020): Nature through Time. Virtual field trips through the Nature of the past. Springer Textbooks in Earth Sciences, Geography and Environment. [1]

External links

  • GeoWhen Database - Early Triassic
  • Palaeos
  • scotese