Cretaceous Period

Big Bend Country Area

The period of uplift and erosion of pre-Cretaceous rocks in the Big Bend area of Texas ended with the transgression of the sea, forming the Interior Seaway during the Early Cretaceous.  These marine conditions depositing limestones to shales, would only be favorable for the preservation of marine vertebrates such as Plesiosaurs and Mosasaurs.  As the Interior Seaway was forming the Pacific and North American tectonic plates collided, causing the Rocky Mountains to form in western North America.  This resulted in the marine shelf formed in the Early to Middle Cretaceous in the Big Bend Country Area to emerge, depositing the non-marine Aguja and Javeline formations in Late Cretaceous over the marine shale of the Pen Formation.  The coastal swamp and deltaic deposits formed a suitable habitat for the Late Cretaceous dinosaurs that were preserved in the Big Bend Country of Texas.

Big Bend Country Area Dinosaurs and Reptiles

	Agujaceratops	Goniopholus	Stegoceras
	Alamosaurus	Halisaurus	Torosaurus
	Deinosuchus	Ricardoestesia	Tupuxara
	Edmontonia	Quetzalcoatlus	Tyrannosaurs
		Saurornitholestes

Agujaceratops is a four-legged, herbivorous, beaked dinosaur with a relatively short, bony frill rear of the skull and three horns on its skull.  It had rows of shearing teeth in the back of the jaw.  It is estimated to have reached about 26–29.5 ft (7.9 to 9.0 m) in length, 9.5 ft (2.9 m) in height and 6 to 12 tons (5,443 to 10,886 kg) in weight.  It has some similarities with the modern rhinoceros. It bore a single horn on the snout, above the nostrils and a pair of horns approximately 3 ft (0.9 m) long, with one above each eye.  Agujaceratops was reclassified as a new genus of Ceratopsian dinosaur in 2006, previously it was identified as Chasmosaurus, which is considered to be older.  Agujaceratops is in the same subfamily, Ceratopsinae, as the better known genus Triceratops.  Originally the Texas specimen was thought to be a subadult Triceratops.  The frill of the Agujaceratops had two large fenestraes (openings surrounded by the boney frill), while the frills of Triceratops were solid.  Agujaceratops lived during the Late Cretaceous and several individuals were found in bone beds in the Agua Formation in Big Bend Park in Texas.

	Agujaceratops Skull  (Fenestrae Frill)	Triceratops Shull (Solid Frill)

  

Agujaceratops

Alamosaurus was a large quadrupedal herbivore, measuring in at 100 ft (30.5 m) in length and probably weighing over 50 tons (45,360 kg).  It was a genus of titanosaurian sauropod dinosaur and like other sauropods, had a long neck and a long tail, which may have ended in a 'whiplash' structure.  No skull material is known, except for a few slender teeth.  The Teas specimens are from are from the Javelina Formation where possibly three individuals, one adult and two juveniles, (half the adult size) were found.  The Alamosaurus is believed to be a re-entrant" into North America from South America.

Alamosaurus

Deinosuchus was one of the largest extinct crocodiles having been estimated to be over 45 ft (13.7 m) in length, extrapolated from 6.5 ft (2.0 m) skull size (largest recent crocodile is around 33 ft (10.0 m)).  Recent discoveries indicate that it was 27 to 30 ft (8.2 to 9.1 m) long and had a body mass of 2.7 to 5.5 tons (2,449 to 4,990 kg), three to five times more than the largest crocodiles alive today.  Deinosuchus was a carnivore and may have preyed on smaller dinosaurs.  Deinosuchus may have lived for up to 50 years, growing at a similar rate to that of modern crocodilians.  Reasonably well-preserved skull specimen discovered in Late Cretaceous upper Aguja Formation in the Big Bend area of Texas, indicated that the animal's head measured about 4.30 ft (1.31 m), and from this the calculated a body length of 32.2 ft (9.8 m).

Deinosuchus

Edmontonia was part of the nodosaur family from the Late Cretaceous Period.  The 3 ton (2,721 kg) quadruped herbivore, Edmontonia, had a low-slung body; sharp spikes on shoulders of its bulky and tank-like body at roughly 19-20 ft (5.8 to 6.1 m) long and 6 ft (1.8 m) high.  It had small, ridged bony plates on its back and head and many sharp spikes along its back and tail. The four largest spikes jutted out from the shoulders on each side, two of which were split into subspines in some specimens.  Its skull had a pear-like shape when viewed from above.  It is reported from the Aguja Formation in Texas.

	Edmontonia Skeleton	Edmontonia

Goniopholus, a crocodyliform, ranged from 6 to 13 ft (1.8 to 3.9 m) in length, and would have had a very similar lifestyle to the American alligator or Nile crocodile.  It was found in the Aguja Formation in the Big Bend area of Texas.

	Goniopholus Skeleton	Goniopholus

Halisaurus is a mosasaur with a length of 10-13 ft (3.0 to 4.0 m).   The Texas specimen consisted of a dorsal vertebrae from the Upper Cretaceous Pen Formation.

	Halisaurus Skull	Halisaurus

Quetzalcoatlus skeletal remains of two species have been recovered from the Big Bend Region of Texas in the Javelina Formation; the larger of the two had an estimated wingspan of up to 39 ft (11.9 m).  This would rank it as the larges flying animal to ever exist.  There is still considerable debate as to the upper limit of Quetzalcoatlus wingspans, its long neck vertebrae and long toothless jaws it might have fed on fish like a heron, or perhaps it scavenged on the ground or in shallows; others maintain that it fed like modern-day skimmers.  It is believed that Quetzalcoatlus could take off under its own power, but once aloft it soared for a long time. It may have weighed close to 200 lb (90.8 kg).  On the ground, Quetzalcoatlus probably walked on all fours.

	Quetzalcoatlus

Ricardoestesia cf. gilmorei and R. isosceles, is a medium sized, approximately 220 lb (100 kg), roughly 6.5 ft (2.0 m) long, carnivorous theropod dinosaur from the late Cretaceous Period.  It is known from a single pair of lower jaw bones and a large number of isolated teeth.  The jaws are slender and rather long but the teeth are small and finely serrated. Ricardoestesia was a raptor and it has been suggested that it was a fish eater, like a heron.  Evidence of the two species of Ricardoestesia is from teeth found in the Aguja Formation of the Big Bend Area, Texas.

Ricardoestesia

Saurornitholestes is a carnivorous dromaeosaurids dinosaur genus from the Upper Cretaceous that was about 5 ft (1.5 m) long and weighed 30 lb (13.6 kg).  Several incomplete skeletons, dozens of isolated bones, and scores of teeth are known.  Like other theropods in the family, Saurornitholestes was more long-legged and flippantly built than other dromaeosaurids and had an extended, curving, bladelike claw on the second toe.  It resembles the more known Velociraptor in having large, fanglike teeth in the face of the jaws and probably feathers.  It resembled Velociraptor, although the precise relationships is not well understood.  Little is known about what it ate and how it lived, but a tooth of Saurornitholestes has been found entrenched in the wing bone of the pterosaur Quetzalcoatlus.  Whether it in fact killed the pterosaur or merely scavenged an already dead animal is unknown.

	Saurornitholestes Skeleton	Saurornitholestes

Stegoceras, herbivorous dinosaur, was about 6 feet (1.8 m) long and 120 lb (54.4 kg) with a well-developed thick domed skull roof.  Male Stegoceras having thicker skulls may have had head-butting contests to win females or territory.  The structure of their braincase, back of the skull, and backbone indicate that forces from the head-butting would be transmitted from the dome through the head, around the braincase, and down the backbone to the limbs.  In this way, animals like Stegoceras could survive the stress of head-to-head combat, much the same way as goats and sheep of today.  Stegoceras teeth found in Texas are from the San Carlos Formation and Aguja Formation.

	Stegoceras Skeleton	Stegoceras

Torosaurus, belongs to the same subfamily, Ceratopsinae, as Agujaceratops, were 25 ft (7.6 m)  in length and weighed an estimated 4.4 to 6.6 tons (3,992 to 5,988 kg).  It had one of the largest skulls of any land animal known.  It has some similarities with the modern rhinoceros.  It bore a single horn on the snout, above the nostrils and a pair of horns approximately 3 ft (0.9 m) long, with one above each eye.  Similar to the Agujaceratops, it had two fenestraes in its boney frill.  It had one of the largest skulls of any land animal known, reaching 8.5 ft (2.6 m) in length.  A 2 ft (0.6 m) long Torosaurus horn, has been found in the lower third of the Late Cretaceous Tornillo Group (probably Javelina Formation)  in Brewster County, the Big Bend Region of Texas along with  the of a maxilla (upper jaw) with teeth of Tyrannosaurus rex.  The lack of fossil evidence suggests it may have been uncommon.

	Torosaurus Skull	Torosaurus

Tupuxara a large, crested, toothless pterosaur, measured a length of  3 ft (0.9 m), the length of the entire body was 8 ft (2.4 m), and had a wingspan of 17.7 ft (5.4 m).  Its crest was swept back, arising from the snout; making it larger and more pronounced than other pterosauus. The skull of the Tupuxuara Among pterosaurs, it was only of moderate size, probably had the same habits as other, a fish eater and livind near the coasts.  A partial skull was found in the Javelina Formation of west Texas and was previously referred to Quetzalcoatlus sp., but on further investigation has been reassigned to the Tupuxara related genus.

	Tupuxara Skeleton	Tupuxara

Tyrannosaurs rex was one of the largest known Tyrannosaurid  and land predators, measuring over 43 ft (13.1 m) in length, 13 ft (4.0 m) tall at the hips  and weighing as much as an elephant (7.5 tons, 14,991 lb, 6.8 kg).  It was a bipedal carnivore with a massive skull with serrated teeth, balanced by a long, heavy tail.  Relative to its large, powerful hindlimbs, Tyrannosaurus forelimbs were small, though powerful with two clawed digits.  Tyrannosaurs rex has been called an apex predator, preying upon hadrosaurs and ceratopsians, although some experts have suggested it was primarily a scavenger.  A Tyrannosaurus maxilla (upper jaw) with teeth, was found in the lower third of the Late Cretaceous Tornillo Group (probably Javelina Formation) along with a 2 ft (0.6 m) long Torosaurus horn in Brewster County, the Big Bend Region of Texas.

	Tyrannosaurus Skeleton	Tyrannosaurus

 

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