Triassic Period Part 2

 Now let's take a look at the inhabitants of the Triassic Period.

Three categories of organisms can be distinguished in the Triassic record: survivors from the Permian–Triassic extinction event, new groups which flourished briefly, and other new groups which went on to dominate the Mesozoic Era.

To go back to the beginning, after the extinction event just before the Triassic Period began, the Earth's biosphere was impoverished. It was well into the middle of the Triassic before life recovered its former diversity. Therapsids (including what would become mammals) and archosaurs (including crocodilian reptiles) were the chief terrestrial vertebrates of this period. A specialized subgroup of archosaurs, called dinosaurs, first appeared late in the Triassic, but did not become dominant until the succeeding Jurassic Period.

The first true mammals also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who were a specialized subgroup of archosaurs.

In marine environments, new types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of modern times. The shelled ammonites (whose shell resembled that of the modern nautilus, but is not an ancestor) recovered, diversifying from a single line that survived the Permian-Triassic extinction.

The fish fauna was remarkably uniform, with many families and genera exhibiting a global distribution in the wake of the mass extinction event. There were also many types of marine reptiles. The first of the lizard-like animals appeared in the Early Triassic seas and soon diversified, and some developed to huge size during the Late Triassic.

On land, the surviving plants included ginkos, ferns, and horsetails, among others. Seed plants came to dominate the terrestrial flora. In the northern hemisphere, conifers and ferns flourished. A seed fern genus would dominate Gondwana throughout the period.

Many groups of terrestrial fauna appeared in the Triassic period or achieved a new level of evolutionary success during it. They include lungfish, Temnospondyls (early amphibians that had mostly been replaced by reptiles, they made a come-back in this period), Rhynchosaurs (the primary large herbivores in many Triassic ecosystems), Phytosaurs (looked like crocodiles, but unrelated), Aetosaurs (heavily armored and mostly herbivorous), Rauisuchians (the keystone predators of most Triassic terrestrial ecosystems), Theropods (dinosaurs but not the large kind that would come later; most were 1-2 meters long), and Cynodonts (a large group that includes true mammals, complete with hair and a large brain).

Some amphibians were among those groups that survived the Permian-Triassic extinction event. The first ancestors of frogs are known from the Early Triassic, but did not become common until the Jurassic (which comes next).

Among reptiles, the earliest turtles appeared during the Late Triassic Period.

During the Triassic, archosaurs displaced therapsids as the dominant amniotes. This may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammalia-form successors to live as small, mainly nocturnal insectivores. Nocturnal life may have forced the mammaliaforms to develop fur and a higher metabolic rate.

Though the end-Triassic extinction event was not equally devastating in all terrestrial ecosystems, several important clades of large reptiles disappeared, as did most of the amphibians, groups of small reptiles, and others (except for the proto-mammals). Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived into the Jurassic. Surviving plants that went on to dominate the Mesozoic Era included modern conifers.

The cause of the Late Triassic extinction in uncertain. It was accompanied by huge volcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago, forming one of the largest known inland volcanic events since the planet had first cooled and stabilized. Another possible but less likely cause for the extinction event might be global cooling.

 

 

https://en.wikipedia.org/wiki/Triassic