Texas  Triassic Dinosaurs



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Triassic Period

By Late Triassic, as the formation of Pangea was complete, Pangea began to break apart along rift basins that were forming along the modern East Coast of North America.  The basins filled with sediment and lava flows.  During the rifting, regions that once were part of Africa remained attached to North America, including parts of the Atlantic Coastal Plain and most of Florida.  The elevated land mass along the Appalachian Mountains eroded large amounts of sediment into the lower areas of the central part of the continent.  Shallow seas covered most of the continent west of the modern Rocky Mountains and north into Canada, but subduction along the continental margin generated small volcanic landmasses that began to form the core of the ancestral Sierra Nevada.  A subduction zone was located off the west coast of future Mexico.  The large emergent landmass and rain shadows from several high mountain belts created a hot and arid climate causing desert-like conditions and large seasonal temperature variations over most of the supercontinent.  There were seasonal heavy rains however, forming rivers and lakes during the wet season.  The Polar Regions were moist and mild.

The Triassic Period was a time when life on Earth was recovering from the great mass extinction that ended the Paleozoic Era, at the end of the Permian Period (Great Dying) that ended the Paleozoic Era, at the end of the Permian Period..  There were no dinosaurs at the start of the Triassic period, but there were many amphibians and some reptiles such as ichthyosaurs and plesiosaurs as well as invertebrate survivors of the Permian extinction, such as a few ammonites, brachiopods and molluscs.  In the seas, corals appeared and ammonites reappeared.

Triassic Period Scene - From Smithsonian Collection


On land, the plants were mainly seed plants, conifers and cycads.  The Triassic also saw the development of forked-frond seed ferns.

Triassic Araucariad Forest

From Petrified Forest National Park Museum

The dinosaurs made their first appearance in the Late Triassic, and diversified to dominate the terrestrial faunas for the next 180 million years.  The Triassic dinosaurs were small, and most were very similar in appearance.  Another vertebrate group evolved in the Triassic at about the same time as the dinosaurs, the mammals.  The first mammals were tiny, about the size of the modern shrew or mouse.  The first turtles also appeared, as well as frogs, salamanders, lizards and snakes.

The end of the Triassic period is marked by another mass extinction.  Pangaea was beginning to break apart, there were huge volcanic eruptions and about 35 percent of animal species died out.  Most of the Late Triassic early dinosaurs became extinct, but some were able to adapt and evolved further during the following Jurassic period.  Based on evidence of elevated atmospheric CO2 levels retrieved from near the Triassic–Jurassic boundary, some researchers have suggested that the cause of this rise, and of the mass extinction itself, could have been a combination of volcanic CO2 outgassing and catastrophic dissociation of gas hydrate. 

Texas Dinosaurs

Texas Dinosaurs are only found in the Late Triassic Dockum Group of the Pan Handel Area of Texas.  The Dockum Group was deposited in an environment of lakes and rivers confined to a large basin that received sand, silt and clay sediments from adjacent highlands. The first Texas dinosaurs are dated at 220 millions years.  Examples of Late Triassic Texas reptiles are as follows:

Caseosaurus Paratypothorax Spinosuchus
Chindesaurus Phytosaur Shuvosaurus
Coahomasuchus Placerias Technosaurus
Desmatosuchus Protoavis Tecavasuchus
Eudimorphodon Postosuchus Trithelodontids
Pachygenelus Revueltosaurus Typothorax

The most populous suite of dinosaurs and reptiles was found in the Post Quarry, near Post, Texas. 

Caseosaurus/Chindesaurus (a theropod) is the most primitive dinosaur identified and is between 6,and 12 ft (1.8 and 3.7 m) long and walked on its two hind legs.  It was an herbivore (plant-eater). Caseosaurus and Chindesaurus may be two different theropods.  Both were found in the Tecovas Member of the Dockum Group in the Post Quarry, Crosby, Texas..



Technosaurus  was a small, primitive saurischians dinosaur.  It was originally thought to be an ornithischian dinosaur, but based on other discoveries its classification was changed.  This dinosaur is poorly known; only a partial jaw bone (with many ridged teeth) was found.  Of similar shape as the Coelophysis, but an herbivore, it may have been about 4 ft (1.2 m) long, weighing about 25 lb (1.3 kg) and ran on two legs. It was found in the Dockum Group at the Post Quarry in Garza County, Texas.

Revueltosaurus was originally thought to be an ornithischian dinosaur, but discovery of bones in the Petrified Forest in Arizona, suggest that it is a crocodile ancestor.

Shuvosaurus was initially classified as an ornithomimosaur (ostrich dinosaurs).  Later investigators considered it a saurischians dinosaur, a basal theropod or an ancestor to the crocodile.  However, there is still a group thinking it might be an ostrich mimic, although the following rendition doesn’t suggest that.  If so, time wise it is out of place, not in the Cretaceous Period with the others.  It is a beaked herbivore reptile and was 10 ft (3.0 m) long and walked on its two hind legs.  Some of the traits shared with the ostrich dinosaurs include large eyes, a beak, a long tail, and no teeth.  Also, both walked on two feet, not four as living crocodiles do.


Protoavis is not a dinosaur, but disserves discussion because it appears to be one of the first birds found, some 70 million years prior to the Archaeopteryx in the Late Jurassic. Protoavis is believed to have been a foot-tall bird and its skeletal structure is a bird-like carnivorous bird that had teeth.  Based on the tip of its jaws and eyes in the front of the skull, suggests that it may have hunted at twilight or in the dark.  It is believed to have little flying ability but could have flown up a tree.  


The fossils were found in a jumbled cache, which may have lead to misidentification.  If in fact a bird, Protoavis raises the questions about when birds began to diverge from the dinosaurs.  Until there is better proof, the animal's status will remain uncertain.

Postosuchus was the top carnivorous predator, and not a dinosaur.  It was a basal archosaur, closely related to dinosaurs and a cousin of crocodiles.  It was up to 18 ft (5.5 m) long and had a wide head 2 ft (0.6m)long, larger than the small dinosaur predators of the Triassic.  Postosuchus was a quadrupedal reptile that could walk/attack on its hind legs.  It had a crocodile-like snout that was filled with many large-sized dagger-like teeth and rows of protective plates covering its back.


Postosuchus Skeleton


Placerias was a synapdia (a group of mammal-like reptiles) and not a dinosaur.  This animal was the biggest herbivore in Texas during the Triassic Period, measuring up to 1.1 ft (3.5 m) long and weighing 1 to 2 tons 907 to 1,814 (kg) with a powerful neck, strong legs, and a barrel-shaped body.  There are possible ecological and evolutionary similarities with the modern hippopotamus as it spent time during the wet season in the water.



Phytosaurs were a group of large (6.6 to 3.7 ft (2 to 12 m) long - average size 0.9 to 1.2 ft (3 to 4 m)) semi-aquatic predatory archosaurs.  These long snouted and heavily armored archosaurs e resembled the modern crocodile in size, appearance, and (clearly) lifestyle, an example of convergence or parallel evolution.  The name "phytosaur" (plant reptile) is very misleading, and their snapping jaws clearly show that phytosaurs were predators. The person who first described them mistakenly thought the specimens he was working with were plant-eaters.  Although phytosaurs were not true crocodilians, they were related to the crocodilians, as both phytosaurs and proto-crocodiles share a common ancestor.  Crocodiles did not become 'phytosaur'-like until the Early Jurassic.  At least four genera of phytosaurs were found in the Dockum Group, Paleorhinus, Angistorhinus, Rutiodon and Nicrosaurus.

Phytosaur Skull


Rhynchosaurs and specifically the otischalkia, were a group of unusual Triassic diapsid reptiles related to the archosaurs found in the Post quarry.  They were herbivores, and at times abundant; in some fossil localities accounting for 40 to 60% of specimens found. They had stocky bodies and powerful down-curving bony beaks that overhung the lower jaws.  Their skulls were very broad and had massive jaw muscles that opened and closed the jaws rather like a pair of tongs with rows of crushing toothplates in the cheeks. Rhynchosaurs were up to about 6.6 ft (2 m) long with short legs and barrel-like bodies that had room for a large gut to digest bulky plant food.  They were four-legged and the feet of their hind legs were equipped with sharp claws.


Rhynchosaurs Skull


Pachygenelus, and Trithelodontids or Tritheledon, were small to medium-sized highly advanced carnivorous cynodonts, a close relative to the mammal.  The extremely small mammal-like cynodont, had many of the mammal traits but retained a very few reptilian anatomical traits such as laying eggs. They were mainly carnivorous or insectivorous, though some species may have developed omnivorous traits.  The pachygenelus evolutionally cousins were one of the longest lived non-mammalian that may have given rise to primitive mammals.  It is believed they became extinct in the Jurassic period, possible due to competition with prehistoric mammals.


Pachygenelus - (Trithelodontids, or Ictidosaurs)

Coahomasuchus, Desmatosuchus, Tecavasuchus, Typothorax and Paratypothorax are all similar genera in the Steganolepididae Family. They were a heavily armored, medium- to large-sized  herbivorous archosaurs.  The head is small relative to the large body, and quite distinctive in shape, being flat and blunt at the front, like the snout of a pig. The chisel-shaped teeth are small and leaf-likeAll were found in the Dockum Group, Coahomasuchus in the Colorado City Formation in Howard County, Texas and the others in the Bull Canyon Formation at the Post Quarry in Garza County, Texas.


Desmatosuchus Skeleton


Spinosuchus is a genus of extinct reptile of uncertain affinities that has been classified differently since it was found in 1912 north of Cedar Mountain in Crosby County, Texas  Its identification is based on one vertebra and is considered it to be about 8.5 ft ( 2.6 m ) long.

Eudimorphodon is one of the earliest genus of flying reptiles, Pterosaurs.  It had a wingspan of about 3.2 ft (1.0 m) and at the end of its long bony tail may have been a diamond-shaped flap to help it steer while maneuvering in the air.  It had a total of 114  densely packed teeth into a jaw only 0.2 ft (0.06 m) long.  The front of the jaw was filled with a few fangs that gradually gave way to a line of smaller multipointed teeth some of which had more than five cusps.  It was found in the Tecovas Formation of the Dockum Group in West Texas.

Eudimorphodon Skeleton




Texas Dinosaurs    Post Triassic Period    Triassic Period     Jurassic Period


Cretaceous Period


Central Hill Country &  Prairies and Lakes Areas Cretaceous    Big Bend Country Area Cretaceous