POSTOSUCHUS. Dinosaurs ruled the earth for 160 million years. At their very beginnings, they were small and suppressed by their rival rauisuchians. The latter were the largest terrestrial carnivores during the Middle and Late Triassic, and had cosmopolitan distribution. One of the unusual and interesting rauisuchians discovered in recent times is Postosuchus, from the Triassic Dockum Formation of Texas. Postosuchus and its contemporary animals were found near Post, in Garza county. The Post quarry has rapidly come into prominence as one of the richest paleontological sites for that period ever discovered in the world. Among them are the world's oldest bird, the oldest pterosaur, the earliest plant-eating dinosaur, various armored archosaurs, labyrinthodonts, lizards, mammal-like reptiles, and possibly a mammal. The geological and social evidence indicates that these diverse animals perished in a flash flood. Though it is a rocky, dry, and forbidding place today, the South Plains was lush with vegetation and water during the Triassic period, 225 million years ago.
Postosuchus was the arch-predator in the Triassic forest of the American Southwest. It was about fifteen feet long and eight feet high, and walked on two powerful legs, balancing its body on its strong tail. The skull is very large, equipped with sharp, serrated teeth for cutting flesh. The hands with sharp claws were used for seizing and manipulating food. The animal was a smaller version of Tyrannosaurus rex but was not as fully developed for hunting and killing as this cruel king of the Cretaceous. Its crocodile-like ankle joint discouraged fast running. Postosuchus was probably an ambush predator that captured its prey by stealth and surprise like the modern komodo dragon of Indonesia. In contrast, the dinosaurs acquired refined locomotion and cursorial adaptations and could run faster with longer strides than the contemporary rauisuchians.
At the end of the Triassic there was a drastic change in the global climate. Many of the Triassic forests gave rise to more open prairie with a shift to more dry and arid habitats. This is reflected by the occurrence of dune sands over a large area of the southwestern United States. In an open country, the great speed and endurance of dinosaurs became more advantageous. The ambush hunting strategy of Postosuchus and other rauisuchians became less effective in this new environment, where they could not compete with dinosaurs. They began to decline and soon became extinct at the end of the Triassic, while the dinosaurs proliferated.
S. Chatterjee, "Postosuchus, a New Thecodontian Reptile from the Triassic of Texas and the Origin of Tyrannosaurs," Philosophical Transactions of the Royal Society of London, Series B, Vol. 309 (1985).
The following, adapted from the Chicago Manual of Style, 15th edition, is the preferred citation for this article.Sankar Chatterjee, "POSTOSUCHUS," Handbook of Texas Online (http://www.tshaonline.org/handbook/online/articles/bcp03), accessed December 09, 2013. Published by the Texas State Historical Association.