Student project submitted June 2000

What do fossils tell us about the history of Big Bend National Park?

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What do fossils tell us about the history of Big Bend National Park?

Big Bend Fossils

J.A. Udden gathered the first collection of dinosaur remains in Big Bend. In 1907 he wrote a report on the geology of the Big Bend, in which he included a letter from Samuel Wendell Williston of the University of Chicago. Williston identified at least three different species of dinosaurs, as well as a turtle and a crocodile that he said were new to science. In 1936 Ross A. Maxwell, a geologist, discovered the greatest amount of remains for the National Park Service and was the first superintendent of the Big Bend National Park. Paleontologists from the University of Oklahoma began to use workers from the Civilian Conservation Corps and others who were developing a state park in the Chisos Mountains. These bones were assembled and placed in a wood-frame barrack located in what is now called the Basin, high in the Chisos. On Christmas Eve, 1941, a fire destroyed the building and the bones that were inside. They were the bones of a duck-billed hadrosaurs and horned ceratopsian dinosaurs.

Taken from Lone Star Dinosaurs page 14. These are the bones that burned in the fire on Christmas Eve 1941. (Photo courtesy of Wann Langston, Jr.)

There are three areas in Texas that contains dinosaur bones. Dinosaur deposits in the Panhandle are the oldest, dating back 200 million years ago to the beginning of the Age of Reptiles, or Mesozoic Era. In Central Texas, the dinosaur’s age is around 100 million years. Big Bend has the youngest of all Texas dinosaurs, dating to the end of the Mesozoic, 66 million years ago. The differences in species can be determined by restructuring the ecology of the community.

This is our group at a dig site.

If fossils are found in one place similar to those in another, then, we can say the rocks surrounding them are of similar age. Most fossils are discovered on or near the surface of the ground where they have been exposed by erosion.

Fossil found in Big Bend include:

-Ripple marks, fossil shells, and current structures

-Two skulls of crocodile-like monster, Phobosuchus riograndensis

One skull and jaws of a fifty foot-long crocodile were found in the upper Aguja Formation near Glenn Springs. It is on display at the American Museum of Natural History in New York, NY. The other is on display at the University of Texas at Austin.

Ripple marks at the Tornillo Flats.

This was taken from Guidebook 7 of The Big Bend of the Rio Grande page 21. It is a six-foot skull of a Phobusuchus riograndensis. This was taken form the upper Aguja Formation. (Photograph by American Museum of Natural History.)

-Skeletal remains of a duckbilled dinosaur

-Ceratopsiam bones similar to Triceratops

-Some large carnivorous types

-Few bird-like reptiles

-Jawbone fragments and teeth of swimming reptiles

Upper Cretaceous formation fossils include:

-Fossilized stumps of agatized wood, roots in sandy lagoon deposits, fossil turtles and wood suggest the ancient environment was similar to our present East Texas and Louisiana environments.

Trace fossils at the Hot Springs site.

Dinosaur fossils in the Big Bend have been found in shallow marine and non-marine deposits, late Cretaceous in age, which accumulated in a warm, swampy, coastal environment. In 1971 a student at UT, Douglas Lawson, found wing bones and other fragments from pterosaurs (a flying reptile). He found a large radius bone of giant pterosaur, which became known as the “Big Bend Pterodactyl”.

The Big Bend Pterodactyl is estimated to have a wingspan of thirty-eight feet. They are not sure if it was a glider or how it hunted. At the end of the Cretaceous period, the pterosaurs, which dominated the skies for millions of years, died along with the other dinosaurs

Pterodactyl bones

Early in the Triassic Period, some 248 million years ago, the ruling reptiles appeared. Dinosaurs, pterosaurs and crocodiles were the dominant life form on land during the Mesozoic Era. Mammals appeared later in the Triassic period.

There are two groups of dinosaurs distinguished by their hipbones, the Orinithischians, or bird-hipped dinosaur, and the Saurischians, or lizard-hipped dinosaurs. The Orinithischians were herbivores and the Saurischians, included both herbivores and carnivores. Dinosaurs evolved rapidly during the Late Triassic and Early Jurassic, attaining their greatest numbers during the Late Jurassic and Cretaceous times about 140 million years ago.

Dinosaur remains are found in the non-marine Aguja and Javelina Formations in Big Bend.

In Big Bend dinosaurs walked the tidal flats of much of the northeastern shore of the Glen Rose Sea. In the southwest, the water extended over the area of Big Bend toward the mountain that ultimately became the Sierra Madre Occidental in Mexico. As the sea reached the region that is now the border between the US and Mexico, the platform dropped off and the waters deepened drastically. Superimposed was the platform bottom of the shallow sea as it dove into the deeper ocean trough that is now known as Big Bend. Big Bend lies between both, not as high but twisted, broken and crumbled, forming the Chisos Mountains.

Our group on the way to a dinosaur site

There are two suborders of pterosaurs or flying reptiles: Rhamphorhynchoidea and the Pterodactyyloidea. They could fly, but differently than today’s birds and bats. The Rhamphorhynchoidea were the first to appear in late Triassic Period. They had long tails and became extinct in the Jurassic Period. The Pterodactyyloidea appeared in the Jurassic Period and lived through the Cretaceous Period. They had stubby tails, long beaks, and a large crest that extended backward often making the skulls longer. Later in the Cretaceous Period, the Pterodactyyloidea developed toothless jaws. They, along with the dinosaurs, became extinct at the end of the Cretaceous Period.

This was taken from Guidebook 7 of The Big Bend of the Rio Grande page 20.

As the species changed, they developed specialized wings and hind limbs that may have limited their ability to adapt to changing environments. Absence of tails or other stabilizing features on Pterodactyyloidea made them poor fliers compared to birds. Their wings were similar to bats with four fingers and leathery membranes extending from the sides of the body to the thigh. An elongated finger, forming a long spar-like structure along the leading edge of the wing, lent the only structural support to the wing membrane. Three other fingers, also appearing on the leading edge of the wing, were short and claw-like, but offered no structural support. A tear in the wing membrane of a Pterodactyyloidea would result in a serious injury. Instead of feathers, short hair covered the body to prevent heat loss.

In 1971, a radius was found in the Javelina formation. It had been previously known as Quetzalcoaatlus northropi for Quetzalcoatlus, the Aztec god who took the form of a feathered serpent. Seventy-five percent of the wing skeleton was recovered. The rocks containing Quetzalcoaatlus were formed far from the sea. The fossils are on display at the Texas Memorial Museum at the University of Texas at Austin. Flight tests show that it was primarily a soaring creature controlling its direction by turning its head, flexing the 3 fingers on the wing’s leading edge, and by warping the wing tip. They were able to climb and dive by changing the wing sweep, but were unstable in gusty winds.

Environmental Change over Geologic Time

Basin view at sunset

The big divisions of the geologic time scale of vertebrate animals are the Paleozoic Era, or the Age of Ancient Life (Age of Fishes); the Mesozoic Era, or Age of Middle Life (Age of Reptiles); and Cenozoic Era, or the Age of Modern Life (Age of Mammals). The Mesozoic is composed of three parts: from oldest to youngest, the Triassic, Jurassic and Cretaceous periods. Dinosaurs have their origin in the Triassic. The extinction that brought about their demise marks the end of the Cretaceous Period.

This was taken from A Road Guide of the Geology of Big Bend National Park page 6.

Paleozoic Era

The Cambrian Period contained the oldest animals that included floating, crawling, swimming creatures of the sea, later flying creatures of the air, dinosaurs, trees, shrubs were on land, mammals, grasses and flowering plants. Three great sea troughs bordered the interior of continental platform in Big Bend-Ouachita system.

This was taken from Guidebook 7 of The Big Bend of the Rio Grande page 11. This represents an outline of North America showing general location of the most persistent Paleozoic troughs.

Mesozoic Era

Most of North America was covered by sea.

Late Cretaceous

Marine reptile ichthyosaur, mosasaur, and plesiosaur were known.

Dinosaurs lived 100 million years.

Strawberry cactus is an example of an angiosperm.

The Aguja Formation is the older of the two major dinosaur-bearing rock units in Big Bend. The Cretaceous extends from 144 million years to 66 million years ago, about 80 million years-nearly half of the total time of the Mesozoic when dinosaurs ruled the Earth. The Cretaceous is officially divided into two parts-Early and Late. The boundary lies at 97.5 million years ago. The dinosaurs of the Early Cretaceous, just before the boundary and those of the Late Cretaceous just after it are particularly poorly known or understood. The end of the Cretaceous and the end of the Mesozoic is recorded in the rock record of Big Bend. There are no Jurassic dinosaurs known from Texas, their occurrence near the Early Cretaceous-Late Cretaceous boundary in the middle portion of the Mesozoic helps document the important botanical changes of life on land at that time.

The Aguja Formation is a rock unit deposited in the deltas, marshes, streams, and lagoons 80 million years ago. It provides a record to show that dinosaurs wandered back to Texas. They came in from the North and had been gone from the state since the time of the Woodbine Formation. Fifteen million years ago, there was dry land and no ocean. The Aguja sediments represent the environment when the sea first receded and exposed land in the Big Bend area. Between 84 million years and 74 million years ago, the Western Interior Seaway was complete. The Aguja was deposited in the southern part of the western American peninsula landmass, on the western shore of the seaway.

Rudis clam trace fossils.

The second formation is called the Javelina and is on top of the Aguja. The rock resulting from the deposition of river sand and muds in channels and on the floodplains is called the Javelina Formation. It ranges from about 74 million years in age to the end of the Mesozoic at 66 million. The Javelina Formation is a sequence of purple, red, gray, and green mudstone layers. The mudstones contain nodule sand and are interbedded with mudstones and lenses of sand. The sand lenses are remnants of ancient stream channels, and the colorful bands of mudstone represent overbank floodplain deposits on which soils were repeatedly developed.

The Aguja and Javelina formations were formed under different environmental conditions and in different geological settings. A distinct and separate animal community inhabited the environment in which they were deposited, and that community was replaced by the fauna of the Javelina.

A rare horn toad is an example of today’s ancient reptiles.

The oldest Big Bend dinosaur formations are found in the Aguja and were deposited as the ocean withdrew. There are tons of fossils, but complete skeletons are never found. Partial skeletons and scattered bones usually are arranged as if they came to rest in a depression, like a shallow pool of water that is gone. Vertebrae of the backbone seem to stay together longer than the rest of the skeleton, at least in the Aguja. The Aguja Formation is drab in color, with black layers that were formed from the remains of plants that accumulated in swamps near the coast. Rivers and streams deposited sandy layers as they formed deltas into the sea. Between the stream and river channels, the land remained low and marshy. Water-loving plants covered the low areas, providing a rich source of food for the plant-eating dinosaurs. The low areas were frequented by horned certopsians and duck-billed hadrosaurs, by less-common armored ankylosaurs, therapods, and others. The most common Aguja dinosaur is a horned dinosaur Chasmosaurus mariscalensis. Remains of ten to fifteen individuals were recovered from just one single bone bed.

The ceratopsid from the Javelina Formation is Torosaurus utttahensis. It belongs to the same group of ceratopsids as Triceratops and Chasmosaurus. The difference between the Big Bend horned dinosaurs is the brow horns of Torosaurus curve downward and forward towards the nose rather than backward and upward as in Chamosaurus. The largest of Big Bend dinosaur is Alamosaurus and is only from the Javelina Formation. The name comes from a trading post because it was in those same badlands where Alamosaurus bones were first found. They were found in Utah and Wyoming and were herbivores. Tyrannosaurus rex also lived in Big Bend. A piece of an upper jawbone with teeth was found in the Javelina Formation.

In the Aguja Formation there are large number of cartilaginous fish: the sharks and rays. None are known from the Javelina. Bony fish are present in each of the formations but are more diverse in the Aguja. Bowfins and gars are common to both. Amphibians and salamanders are present in the Aguja but not in the Javelina, and frogs are known from neither. Eight species of turtles are known from Aguja, while three have been reported in Javelina. Snakes and crocodiles are found in both. Pterosaurs are found the in Javelina, and mammals are found in both. The Big Bend giant crocodile is Deinosuchus riogranensis.

Cenozoic Era

North America is above sea level with only the edges of the continents being covered by seas.

Excavation Permits

Procedure for acquiring a dig permit:

1. Find something.

2. Apply for a site permit.

Park officials and/or federal government officials will check your credentials and check their database to make sure the area has not been claimed. They want to make sure you are associated with a university or a museum. The specimens must be on display. You must show where and how they are to be kept.

3. The Park will, then, send out an archeologist, botanist and environmentalist to conduct an Environmental Assessment. The archeologist will make sure no native bones or artifacts will be disturbed. The botanist will make sure no endangered plants will be damaged. A watershed study will be conducted to see how the water flow will be altered during excavation.

4. The Park will, then, send out a paper to the public explaining the intent of the curator.

5. Permits are issued for a specific period of time and only for what you have asked to study. Least impact on the environment rules must be followed: No wheeled vehicles; ten people per team; use of helicopter to remove large bones-no landing of helicopter though; the group must enter and leave a different way each time.

6. Constant monitoring must occur. Bones must be on display. Permits must be with you at all times. You must follow the Federal Antiquities statutes.

7. The federal government owns the bones; the scientists are the curators.

See also: Big Bend National Park Research Information, http://www.nps.gov/bibe/resrchpg.htm.

Sources used:

Jacobs, Louis. Lone Star Dinosuars. Texas A & M University Press. College Station, Texas.1995

Maxwell, Ross. The Big Bend of the Rio Grande. Guidebook 7. Bureau of Economic Geology, The University of Texas at Austin. 1998.

Montgomery, Homer. Personal interview June 26, 2000. Dallas, TX.

Moore, Dr. Wayne. Dinosaur, Pterosaurs, and Crocodile Brochure. National Park Service U.S. Department of the Interior. 1996.

Nelson, Kerri. A Road Guide of the Geology of Big Bend National Park. Big Bend Natural History Association. 1992.

Tuttle, Sherwood D. Big Bend National Park. University of Iowa.

| Geology | Ecology | Man |

| Environment |

This page is a part of the Big Bend Virtual Field Trip available at www.utdallas.edu/dept/sci_ed

and was produced for the GLOBAL ENVIRONMENTAL CHANGE program funded by a grant from the National Science Foundation and the Woodrow Wilson National Fellowship Foundation; sponsored by the University of Texas at Dallas - Science Education Department with support from Duncanville Independent School District.