Late Triassic
End of the Triassic
The Late Triassic (237–201 Ma) is the last epoch of the Triassic, occuring before the Hettangian of the Early Jurassic, and after the Ladinian of the Middle Triassic
What happened during this period?
Geophysical
The Triassic-Jurassic boundary marks a major animal mass extinction, but records of accompanying environmental changes are limited.
Central Atlantic Magmatic Province (CAMP), the Earth's largest igneous province, covered 11 million km² of central Pangaea
Paleobotanical evidence indicates a fourfold increase in atmospheric carbon dioxide concentration and suggests an associated 3° to 4°C “greenhouse” warming across the boundary.
These environmental conditions are calculated to have raised leaf temperatures above a highly conserved lethal limit, perhaps contributing to the >95 percent species-level turnover of Triassic-Jurassic megaflora (McElwain, Beerling, and Woodward 1999)
Climate extremes went back and forth unpredictably, making equatorial environments difficult for new species to establish
Evidence also indicates that high levels of volcanic mercury lead to mutagenesis in land plants, and may have caused the collapse of ecosystems during this time (Lindström et al., 2019).
Carnian Pluvial Event, occurs around 234-232 Ma (early Late Triassic), and is a time when the arid climate of the early Late Triassic changed to more humid conditions with increased rainfall.
Biological
Flora
Caytoniales, a possible sister group to the angiosperms, appear on the landscape.
Obscure seed plant groups, Iraniales and Czekanowskiales, appear during this time.
Also on the landscape are Ferns, Horsetails, Conifers, Cycads, Bennettitaleans, Ginkgoes, Peltasperms, and Corystosperms
Conifers in the Late Triassic include Voltziaceae, Majoniacaceae, Araucariaceae, and Podocarpaceae as well as some of the earliest evidence of the Pinaceae, Cupressaceae, Taxaceae, and Cheirolepidiaceae
Ferns in the Late Triassic include the ancient tree ferns, Marattiales, and the modern tree ferns, Dicksoniaceae, as well as the Osmundaceae, Gleicheniaceae, Matoniaceae, Dipteridaceae, and Hymenophyllaceae.
There is a "burst" of amber during the middle Carnian during the Carnian Pluvial Event
Palynological analysis indicated a lowland fern flora and a warm and humid climate in the Late Triassic (Norian to Rhaetian), which was interrupted by a cooler interval at the Norian-Rhaetian transition, and followed by a mixed mid-storey forest under cooler and drier conditions in the latest Rhaetian (Li et al. 2020)
The end-Triassic mass extinction (~201.6 million years ago) led to dramatic changes in terrestrial ecosystems including the extinction of several seed-plant groups, and the dominance of the peculiar pollen, Ricciisporites tuberculatus, across large areas of the Northern Hemisphere immediately prior to and during the extinction event (Vajda et al. 2023)
The peltasperm, Lepidopteris ottonis, produced R. tuberculatus in permanent tetrads.
Vajda et al. (2023) demonstrate that R. tuberculatus is a large, abnormal form of the small smooth-walled monosulcate pollen traditionally associated with Lepidopteris ottonis,
That pollen disappeared at the extinction, when volcanism induced cold-spells followed by global warming.
Aberrant R. tuberculatus resulted from ecological pressure in stressed environments that favored asexual reproduction in peltasperms
The expansion of dry environments led to the dominance of drought-tolerant plants in the Early Jurassic of northern middle latitudes
Fauna
During the Late Triassic, the dicynodonts mostly disappear at the end of the Carnian
The diversity of conodonts, ammonoids, and bryzoans were severely impacted by the Carnian Pluvial Event
Dinosaurs, crocodylomorphs, phytosaurs, sphenodontians, and "stem" turtles probably appear in the Middle Triassic and increase in diversity during the Late Triassic.
Eoraptor and Herrerasaurus are some of the earliest known dinosaurs, that appear around 231 Ma (Carnian) from northwestern Argentina
Nyasasaurus from the Middle Triassic [243 Ma] is the oldest known dinosaur (Nesbitt et al. 2013)
Mammals appear in both North American and European sediments during the Late Triassic
Additional Information
The Petrified Forest National Park is composed mostly of Late Triassic tree
The New Yorker: Rocks, Paper, Sinners - a story about people who have stolen and returned petrified wood
Late Triassic (Palaeos web page)