TRIASSIC PERIOD
The Triassic began in the wake of the Permian–Triassic
extinction event, which left the Earth's biosphere impoverished; it would take
well into the middle of the period for life to recover its former diversity.
Therapsids and archosaurs were the chief terrestrial vertebrates during this
time. A specialized subgroup of archosaurs, dinosaurs, first appeared in the
Late Triassic but did not become dominant until the succeeding Jurassic. The
first true mammals, themselves a specialized subgroup of Therapsids also
evolved during this period, as well as the first flying vertebrates, the
pterosaurs, who like the dinosaurs were a specialized subgroup of archosaurs.
The vast supercontinent of Pangaea existed until the mid-Triassic, after which
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, 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, wiping out many
groups and allowing dinosaurs to assume dominance in the Jurassic.
On land, the holdover plants included the lycophytes, the
dominant cycads, ginkgophyta (represented in modern times by Ginkgo biloba) and
glossopterids. The spermatophytes, or seed plants came to dominate the
terrestrial flora: in the northern hemisphere, conifers flourished.
Glossopteris (a seed fern) was the dominant southern hemisphere tree during the
Early Triassic period.
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