Triassic Period

Other Life During the Triassic

What were the major groups of land organisms during the Triassic?

The true numbers, types, names, and evolutionary events of the Triassic land animals is often highly debated, which is typical when we try to interpret our ancient past. The following list gives a general synopsis of only some of the larger animals; however, not everyone agrees on these interpretations. Fossils are subject to various explanations that sometimes vary from scientist to scientist—often making it difficult to arrive at any definitive statements about these animals. Below are brief descriptions of the other animals living during this time:


Primitive amphibians: Only a few large, primitive amphibians (labyrinthodonts), survived into the Mesozoic era after the Permian period extinctions; they gradually declined in abundance and diversity during the Mesozoic; most of them were aquatic, the majority living in freshwater environments.

Primitive frogs and toads: First links to these modern amphibians (or lissamphibians) evolve during the Early Triassic; the oldest member of the frog group was the Triadobatrachus, the only known link between the true frogs with jumping motion and the primitive ancestors of frogs.

Land Reptiles (Anapsids, Diapsids, and Euryapsids)

First turtles: Of the several Paleozoic groups of anapsids, only turtles and procolophonids survived into the Mesozoic; the oldest subgroup, proganochelydians, were moderately large, but the animal could not pull its head inside its shell; disagreement exists as to whether turtles are truly diapsids, not anapsids.

Procolophonids: Lizard-like in their overall habits and shape; they probably ate insects, smaller animals, and some plant material; even though they looked like lizards, the true lizards did not appear until the Late Jurassic.

Rhynchosaurs: Short-lived diapsid reptiles of the group Archosauromorpha; they were herbivorous, walked on all fours, and had huge beaks that helped them bite off vegetation; they are so widespread during the Triassic that their fossils are often used to correlate deposits on different continents.

Tanystropheids: Very short-lived diapsid reptiles of the group Archosauromorpha; they lived near (and sometimes in) marine waters; they had an oddly-shaped body, with a tiny head on an extremely long neck, and a short, medium-sized body; the reason for such a long neck is unknown, but one theory suggests that it helped the tanystropheid stretch its neck low over the water in order to catch fish.

Archosaurs: Part of the diapsid reptile group Archosauromorpha, and the dominant tetrapods on the continents during most of the Mesozoic; the archosaurs (“ruling reptiles”) were the precursors to dinosaurs; they are characterized by their better adaptation of legs, feet, and hips, giving them agility on land; others categorize the archosaurs by the openings in their skull; the earliest archosaurs were relatively large and carnivorous, and either lived on land, or led a semi-aquatic existence.

Aetosaurs: Heavily armored, herbivorous archosaurs.

Phytosaurs: lived during the Late Triassic only, and looked very much like modern crocodiles.

Crocodylomorphs: A group that includes crocodiles, alligators, caimans, and gavlals, known to exist from the Late Triassic to the present; not all survived to the present, including the fast-running saltoposuchians.

Rauischians: the creature’s upright front and hind legs were under the trunk of the body, making them the dominant land predator during the Triassic.

Ornithosuchian: Relatively large (10 feet [3 meters]), land predators that may have walked on all fours, but ran fast only on its hind legs; they were the most dinosaur-like of the non-dinosaur archosaurs.

Small rodent-sized mammals similar to this mouse first appeared as early as the Triassic period (iStock).

Ornithodira: The Middle and Late Triassic group of archosaurs to which the dinosaurs belong; it also includes the pterosaurs, birds, and some early forms of creatures that appear to be closely related to dinosaurs and pterosaurs.

Aerial Reptiles (Diapsids)

Gliding reptiles: The three main Late Triassic gliding reptiles used either skin membranes on the wings and legs (such as the Sharovipteryx), scales (Longisquama), or fan-like wings (Kuehneosaurus)—all of which acted as an airfoil, allowing the reptiles to glide through the air; they probably did not flap their “wings” for powered flight.

Flying reptiles: The pterosaurs (they are also called pterodactyls, but that is only one subgroup of pterosaurs); the front legs (or arms) were modified into true wings by the elongation of the fourth finger, which supported a skin membrane stretching to the body; they probably flapped their wings occasionally for powered flight; they lived from the ocean shores and inland, eating fish, insects, and other small animals; they evolved during the Late Triassic period.

Mammals and Their Reptile-like Relatives (Synapsids)

Therapsids: More advanced synapsids; varied group of mammal-like reptiles that apparently evolved from the pelycosaurs, the earliest known mammal-like reptile that evolved in the Late Carboniferous period, about 290 million years ago, and went extinct in the Late Permian period; the biggest change was their ability to walk more efficiently with their limbs tucked beneath their body, whereas pelycosaurs walked with their limbs in a sprawled position; one group of therapsids gave rise to mammals, known from the Late Triassic to today.

Anomodonts: The most common subgroup were the dicynodonts, large, herbivorous, mammal-like reptiles; it includes the Lystrosaurus, a three-to six-foot(one-to two-meter-) long, pig-like animal that has been found as fossils in Australia, South Africa, India, China, and Antarctica, and hippopotamus-like Kannemeyeria, a 10-foot-(3-meter-) long animal with two big canine-like teeth in the upper jaw; they died out during the Late Triassic period.

The Elasmosaurus was one of the largest plesiosaur species to swim through Earth’s oceans. Today, some people believe that the Loch Ness monster in Scotland is a type of plesiosaur that survived the extinction of the dinosaurs (Big Stock Photo).

Cynodonts: Carnivorous, mammal-like therapsid reptiles; they walked more upright, with limbs held more underneath their bodies; some were probably wolf-like animals, and some seem to have had whiskers, pointing to the possibility of having fur, and thus, may have been warm-blooded; they evolved during the Late Permian to the Middle Jurassic; at least one group of cynodonts evolved into mammals.

Therocephalians: Existed from the Late Permian to Middle Triassic period, these therapsid reptiles had their peak during the Late Paleozoic era; they were small to medium sized, walked on all fours, and ate insects or small animals.

True mammals: Small, about the size of a rat or mouse, with the largest about the size of a cat; they were probably nocturnal; they probably ate insects or small mammals, and at least one group ate plants; they evolved in the latter part of the Triassic, at the same time as the dinosaurs first appeared. Triconodonts: Late Triassic to Late Cretaceous mammals; one of the oldest fossil mammals; three cusps of teeth in a straight row give them their name.

Haramyoids: Late Triassic to Middle Jurassic mammals; one of the oldest fossil mammals; their teeth had many cusps in at least two parallel rows.

Other Creatures

Insects: Very common; included the first species to undergo complete metamorphosis from larva through pupa to adult.

Spiders: Very common; spiders had been around for millions of years already, showing up in fossils dating back to the Cambrian period. Earthworms: Very common; earthworms had been around for millions of years already, showing up in fossils dating back to the Cambrian period.


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