Inland Floodplain Environment
Choose an Environment to Explore
Julius Csotonyi & Alexandra Lefort
Wann Langston with the femur of Alamosaurus (UT Austin VPL)
UT Dallas crew excavating the gigantic articulated neck of Alamosaurus
Hadrosaur skin impressions
North America 65 Million Years Ago / Ron Blakey
Texas Brazos River: modern analogue for Javelina Fm
Gastropods, bivalves, and crustacean burrows from Lehman, 2010
In The Beginning…
During the Early Cretaceous (130 million years ago), Big Bend National Park was underwater. The warm, shallow sea that covered Big Bend and most of Texas is called the Western Interior Seaway. This sea supported a magnificent assemblage of marine organisms including the mighty mosasaur and the monstrous fish, Xiphactinus. Alongside these “monsters of the sea” lived ammonites, turtles, sharks, sea urchins, oysters, and snails. The rocks from this time period yield many scientific treasures. For example, the oldest North American mosasaur was discovered in the limestones at Big Bend National Park.
Geological Setting
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North American Compression
As the Rocky Mountains rose higher and higher to the west, the compression of North America caused the land here in Big Bend to be warped downward, creating a broad, river-filled basin. This forested floodplain supplied many slow-moving meandering rivers that carried lots of mud, sand and silt. The landscape resembled today’s Brazos River valley in southeast Texas.
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Javelina and Black Peaks
Over millions of years, the sediments carried by the rivers filled up the basins, creating the Javelina and Black Peaks rock formations. The layers of mud and sand surrounded and preserved the skeletons to create fossils. Today the Javelina and Black Peaks Formations are represented by thick, fluvial channel sandstones, floodplain mudstones as well as colorful paleosol (ancient soils that resemble badlands) horizons in reds, blacks, and purples.
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Invertebrate and Vertebrate Fossils
Fossils are not as numerous in the Javelina and Black Peaks Formations as they are in the underlying Aguja Formation. Invertebrate fossils are rare but include fresh water snails and crustacean burrows. Vertebrate fossils include those from fish, turtles, pterosaurs, dinosaurs as well as small mammals. Plant fossils are also present in the Javelina Formation, including fan palms as well as conifers and flowering plants.
Featured Fossils
1 Bravoceratops
One of the largest of the horned dinosaurs and discovered in Big Bend in 2013. Bravoceratops would have lived along the riverbanks, searching out plants to eat and keeping watch for its giant predator, Tyrannosaurus.
2 Tyrannosaurus
Known for its massive size, powerful jaws, and sharp teeth, the Tyrannosaurus was the top of the ecosystem. It possessed strong hind limbs for running and relatively small, yet functional, forelimbs that have continued to captivate scientists and the public alike.
3 Alamosaurus
Another giant unearthed in Big Bend National Park. Alamosaurus’ limb bones indicate that the long-necked dinosaurs were one of the largest dinosaurs to ever exist: 80 ft (25 m) long and up to 65,000 pounds (29,000 kg).
4 Quetzalcoatlus
Soaring overhead, this creature likely migrated across the globe with fossils of this found from Texas to Romania. The gigantic creature had an impressive wingspan estimated to be up to 36 feet.
5 Gryposaurus
This is most common dinosaur in Big Bend. A duck-billed (or hadrosaur) dinosaur had a plant-based diet. Unlike most plant-eaters of their time, hadrosaurs are unique because they stood on two legs (bipedal) instead of four and lived in large, social herds.
6 Brachychampsa
Known for its broad, robust skull and strong jaws, Brachychampsa was a formidable predator in its ecosystem. Its existence alongside dinosaurs and survival into the early Paleocene highlights its adaptability and resilience during a time of significant environmental changes.
7 Baena
Notable for its distinctive shell morphology, the Baena provides important insights into the diversity and evolution of ancient turtles. Fossils of this species have helped us understand that Big Bend was a much wetter place 72 – 55 million years ago.
8 Meniscoessus
A member of the multituberculates group, this dinosaur was known for its intricate and distinctive crowns of their teeth. The diversity of tooth shapes allowed Meniscoessus to feed on many different plants and animals and thrive alongside the giant dinosaurs.
Significance
Javelina & Black Peaks
One of the most unique features of the Javelina & Black Peaks Formations of Big Bend National Park is that they preserve the most well known extinction event of all time, the end of the dinosaurs. At 65.5 million years ago the dinosaurs go extinct, a time called the K-Pg (Cretaceous - Paleogene) boundary. This extinction event was triggered by a giant meteor hitting Earth, leaving behind the huge Chicxulub crater along the Yucantan Peninsula in Mexico. By 63 million years ago (Paleocene time) the dinosaurs were gone (except the avian dinosaurs, which evolved into birds) but the ancient mammals that managed to survive the vast extinction event began to flourish.
Alamosaurus
The long-necked sauropod dinosaur Alamosaurus was discovered in Big Bend in 1940 by famous paleontologist Barnum Brown. It was thought that sauropods went extinct at the end of the Jurassic period 145 million years ago, but the Alamosaurus fossils found in Big Bend were from the Late Cretaceous Javelina Formation (72 million years ago). This helped prove otherwise. More specimens of Alamosaurus have been discovered in Big Bend National Park than anywhere else in the world. A full-size skeleton replica of Alamosaurus can be seen at the Perot Museum of Nature and Science in Dallas, TX.
Quetzalcoatlus
Quetzalcoatlus, the largest flying creature to ever be discovered, was found in the Javelina Formation of Big Bend National Park. This giant flying reptile, or pterosaur, was found in 1971 by Douglas Lawson (above), a graduate student from the University of Texas at Austin. The wingspan of Quetzalcoatlus is estimated to be almost 40 feet wide. This fossil is named after the Aztec feathered serpent god, Quetzalcoatl.
Where to See The Rocks
The Javelina Formation
The Javelina Formation can be seen to the west of the park entrance sign near the Maverick Entrance Station (the western park entrance) along highway 118. As you drive south from Study Butte towards the park, the outcrops straight ahead preserve the Javelina Formation. Along the western portion of the Chimneys Trail more Javelina Formation can be seen up close. For those folks who enjoy the less-maintained roads, check out the Glenn Spring Road around Chilicotal Mountain for a chance to see the Javelina Formation. As you travel south on the Glenn Spring Road from the northern entrance, keep your eyes out for the Camp Chilicotal campsite, approx. 3.6 miles down the road. This site offers views of the Javelina Formation to the east, which continues as you drive further south on Glenn Spring road. On the road between mile 3.6 and 7.1 check out views of the Javelina Formation to the east, at the base of the Chilicotal Mountain. If you continue on south, the Javelina Formation continues to outcrop on the right (west) between the turn-off for the Black Gap Road (mile 8.6) and where the Glenn Spring Road meets the River Road (mile 8.5).
The Black Peaks Formation
The Black Peaks Formation can be best seen from the Fossil Discovery Exhibit, where a sighting scope has been installed to point directly at the hills for which the Black Peaks were named (Check out our page about Where to see the K-Pg Boundary in Big Bend). The Glenn Springs 4-wheel drive road also reveals outcrops of the Black Peaks Formation south of the Robber’s Roost backcountry campsite. To get to this section of the park, enter the Glenn Spring road from the northen entrance and travel 7.1 miles south. Then turn right (west) on to the Juniper Canyon Road. Follow this road for 2.9 miles until you reach the Robber's Roost campground. The rocks outcroping to the south are Black Peaks Formation.