The Handy Dinosaur Answer Book. Patricia Barnes-Svarney

with sharp teeth. As it walked on two legs, Coelophysis used its long, slender tail for balance. Its feet were narrow, with only three prominent toes, a distinctive characteristic of the theropods. The Coelophysis were part of a carnivorous dinosaur group that later included the Tyrannosaurus rex and Velociraptor.

      What were the smallest dinosaurs known to have existed during the Triassic period?

      At present, the smallest Triassic period dinosaurs known to have existed were the early, carnivorous bipeds Eoraptor and Herrerasaurus. The Eoraptor was about 3 feet (1 meter) long, whereas the Herrerasaurus was about 10 to 18 feet (3 to 6 meters) in length.

      Were there other reptiles in the Middle to Late Triassic period that may have been early dinosaurs?

      Yes, the Herrerasaurus may have had some other dinosaur relatives in North and South America during the Middle to Late Triassic periods. Some scientists believe the Staurikosaurus pricei from southern Brazil and northwestern Argentina, and the Chindesaurus bryansmalli from the Chinle formation in North America, were close relatives. But disagreements still exists as to where to put these dinosaurs on the overall family tree. One thing is certain: this important group gives us some idea of the time that dinosaurs first appeared—and what these early creatures looked like.

      What was the largest dinosaur known to have existed during the Triassic period?

      At present, the largest dinosaur known to have existed during the Triassic was the herbivorous Plateosaurus, with a length of up to 20 to 33 feet (6 to 10 meters). The creature had a long neck, large stocky body, and a pear-shaped trunk. Its skull was deeper than that of Coelophysis, though still small and narrow compared to the size of its body. The reptile’s teeth were set in sockets, and were small, peg-like, and leaf-shaped, with coarse serrations. The eyes were directed to the sides, rather than to the front, which reduced its depth perception, but gave the Plateosaurus a wider field of view to detect predators.

      The foot of the Plateosaurus was very similar to that of Herrerasaurus and the structure of the legs indicates that this dinosaur was not a fast runner. A unique feature of Plateosaurus was its broad, apron-shaped pubis, forming a “shelf” that may have provided support for its huge gut. The animal’s tail could be bent sharply upward near its base—a good characteristic to have when rearing up against trees.

OTHER LIFE DURING THE TRIASSIC

      If the dinosaurs were just evolving, which land and marine animals dominated the Triassic period?

      On land, the true dominant species of the Triassic period, even after the dinosaurs started to evolve during the Late Triassic, were the non-dinosaurian predators, the archosaurs; the main herbivores were the dicynodont (synapsids). In the oceans, many types of reptiles and fishes dominated.

      What are the tetrapods?

      All the approximately 5,000 species of frogs known today are skilled jumpers, and they are all apparently descended from Triadobatrachus, which lived during the Triassic (iStock).

      Tetrapods (“four feet”) is a term used to describe the four-legged creatures that left the water to live on land. The first tetrapods were the amphibians; dinosaurs were also tetrapods. In fact, all modern amphibians, reptiles, birds, and mammals are tetrapods. (Interestingly, some scientists say humans can be considered tetrapods, as they are descendants of the original tetrapods; we have four limbs, though we use two of them as arms instead of for walking.)

      Where did tetrapods live on Pangea during the Late Triassic period?

      The distribution of the tetrapods was not uniform during the late Triassic period—even though Pangea was a huge connected landmass. The major reason for this non-uniform distribution was the very pronounced climate zones over the very large continental landmass. The equator had a narrow, humid zone; humid temperate climates existed from around 50 degrees north and south latitudes to the poles. In between, at approximately 30 degrees north and south latitude, were wide arid zones.

      The distribution of tetrapods followed these climatic variations. For example, the prosauropods, a group of dinosaurs that included the Plateosaurus, had a range roughly corresponding to the temperate zones in both hemispheres; prosauropods shared this area with large amphibians. Phytosaurs, distant relatives of the crocodiles, were limited to the Northern Hemisphere and the coastal regions of the Southern Hemisphere. And some tetrapods, such as rauisuchians, crocodylomorphs, and aetosaurs, were distributed over all of Pangea.

      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:

      Amphibians

      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: