Ancient Environments and Fossil Plants of Big Bend National Park

Article by Renee Cace, University of Texas
for Park Paleontology Newsletter, Fall 2024

Introduction

Big Bend National Park was officially established on June 12, 1944. Before then, the land was used for ranching, farming, mining, and military activities throughout the 18th and 19th centuries. By the 1930s, however, a growing appreciation for the unique beauty and ecological significance of the area led to its protection. In 1976, the United Nations Educational, Scientific and Cultural Organization (UNESCO) designated Big Bend as an International Biosphere Reserve. This title highlights the park's significance in preserving the Chihuahuan Desert ecosystem and fostering international collaboration in research and environmental monitoring. Beyond the undeniable value of Big Bend’s current ecosystems lies a deep history preserved in its rocks.

Figure 1. Big Bend National Park’s location along the Western Interior Seaway during the Middle Campanian, ~77.0 Ma.

Image copyright R. Blakey, Colorado Plateau Geosystems, Inc., 2014. Used with permission

Big Bend’s rich fossil record has captivated paleontologists for over a century. The initial spark for paleontological exploration in the west Texas region can be traced back to the early 1900s. These early expeditions, often funded by museums or universities, aimed to collect spectacular dinosaur remains. The ventures were often characterized by a focus on quantity over meticulous excavation and documentation. The earliest published report of (vertebrate) fossils in Big Bend was from 1907, written by J.A. Udden from the University of Texas at Austin (Udden 1907). The collected specimens from those early years played a crucial role in establishing Big Bend's reputation as an important dinosaur locality. Beyond dinosaur discoveries, additional studies of the geology, invertebrate fossils, and plant fossils have been key to reconstructing paleoenvironments of this region that was located along the Western Interior Seaway during the Cretaceous (Figure 1).

Collecting History

As the 20th century progressed, paleontological collecting at Big Bend entered a phase of increased scientific rigor. Researchers began to move beyond simply collecting large dinosaur bones and placed greater emphasis on documenting the broader ecological picture. This shift involved collecting and studying a wider variety of fossils, including smaller vertebrates, invertebrates, and plant remains. In the 1930s, plant macrofossils were described in detail for the first time within Big Bend’s Cretaceous Aguja Formation. These included an impression of a palm leaf and a compression belonging to a Sequoia-like plant, the genus to which redwoods belong (Dorf 1939).

A pivotal figure in this era was Dr. Wann Langston Jr., who conducted extensive fieldwork in Big Bend as Director of the Vertebrate Paleontology Laboratory at the University of Texas at Austin. Langston's meticulous collecting and documentation practices throughout the mid-1900s significantly broadened our knowledge of paleofaunas and their environments in the Big Bend region. However, paleobotany was not a focus of Big Bend research until decades later. Analysis of petrified wood from the Cretaceous–Paleocene Black Peaks Formation was started in an unpublished Master’s thesis by Chao-wu Chang and by the late Dr. Maxine Abbott (Chang 1973; Abbott 1986; Wheeler 1991). Dr. Elisabeth Wheeler, continuing the work the previous researchers started, narrowed the abundant petrified wood present in a massive “log-jam” dating to the Paleocene down to two species, naming Paraphyllanthoxylon abbottii and cf. Plataninium haydeni (Wheeler 1991). These taxa were some of the first named from the Paleocene of North America.

Figure 2. Petrified wood in the Javelina Formation of BIBE.

NPS photo.

From there, interest in the fossil flora found in Big Bend grew. More collecting trips focused on petrified wood, which is relatively abundant within park boundaries (Figure 2). In 1994, the first paper on petrified wood of the Javelina Formation was published (Wheeler et al. 1994). Since then, in situ petrified wood stumps have been found in both the Aguja and Javelina Formations, with detailed paleoenvironmental reconstructions possible due to the well-preserved stumps and the paleosols they are rooted in (Lehman & Wheeler 2001; Lehman & Shiller 2020). Moreover, leaf fossils originally collected and thought to be from the Javelina Formation found by Langston and his graduate student Douglas Lawson were later determined to be from the Eocene Canoe Formation, notably increasing the span of time across which plant fossils can be found in Big Bend (Lawson 1972).

Other leaf compression fossils were collected and studied by Nina Baghai-Riding from the Aguja Formation southwest of Rattlesnake Mountain (Baghai 1998). Then, in the 2010s, a study on palm leaves, stems, and reproductive structures collected in Big Bend played a role in describing ecological co-occurrence of plants and dinosaurs (Manchester et al. 2010).

The National Park Service has been part of a growing awareness of the ethical implications of fossil collecting. This has led to stricter regulations to protect these irreplaceable resources. The NPS Paleontology Program plays a crucial role in monitoring and documenting paleontological resources in the National Park System, allowing for the discovery of new fossil localities, the recovery of lost ones, and ensuring the future of paleontological study and research. In Big Bend National Park, knowing what plant fossils are present is important for understanding the park's ancient ecosystems and how they have changed over time.

The Floral Record, Cretaceous to Eocene

Figure 3. Transverse section slide image of Javelinoxylon multiporosum, an angiosperm tree from the Javelina Formation of BIBE. Slides and images like this can be used to help identify fossil trees down to species level.

Photo by E.A. Wheeler, NC State University.

The record of fossil plants from Big Bend ranges in age from the Late Cretaceous Aguja, Javelina, and Black Peak Formations (late Campanian, ~76 Ma [million years ago] to the late Maastrichtian, ~66 Ma) to the middle Eocene Canoe Formation, and finally to the Early Oligocene Chisos Formation. A range of fossil plants are preserved within these rocks. Compressed leaves from the Aguja represent plants reminiscient of modern taxodiaceous trees, palms, and other flowering plants (Figure 3). The Javelina Formation contains petrified wood resembling modern woody vines , as well as larger trees (Figure 4).

Figure 4. Leaves collected by N. Baghai-Riding from the Aguja Formation southwest of Rattlesnake Mountain. A: Taxodiaceous leaf, B: Palm leaf, C: Lauraceous leaf. Scale bar = 1 cm.

Big Bend also contains a record of Cretaceous-Paleocene transition in the Black Peaks Formation, containing petrified wood on both sides of the K-Pg impact boundary. As the Mesozoic Era came to a close and the Cenozoic took its place, some of the depositional settings in this region continued to bury plant remains, preserving some of the floral history. The Eocene Canoe Formation contains leaf compressions and pollen that provide evidence of plant community composition (Figure 5). Lastly, the Chisos Formation is the most recent geological formation to preserve fossil plants—in this case, petrified wood was reported (Maxwell et al. 1967).

Figure 5. Leaf collected and identified by D. Lawson as “Ficus.” Scale bar = 1 cm.

Late Cretaceous floras in Big Bend have provided researchers a glimpse of the types of plants making up the forests preserved in southern North America in both the understory and the tree canopy. Studying these fossils allows researchers to examine the diversity and abundance of plants living along different parts of the landscape. In the ecosystems found within the Cretaceous of Big Bend, angiosperms and other plant groups occupy the understory, with most wood assemblages still dominated by larger gymnospermous (coniferous, in this case) trees. The pollen and spore record, reflecting a more regional signal, shows that angiosperms in the understory of the plant community were highly diverse in this region by the end of the Cretaceous (Baghai 1996). Further study of the floras have also found evidence of plant-insect interactions, for example termite frass found within logs of the Javelina Formation (Rohr et al. 1986).

The distribution and abundance of different plant types, including angiosperms and conifers, have helped researchers reconstruct past climates and environmental conditions during the Late Cretaceous of Big Bend. Their presence and characteristics can be indicative of temperature, rainfall patterns, and other environmental factors. In the case of Big Bend, presence of certain species of plants (such as laurels, mangroves, palms, and others) support the idea of a subtropical climate with plentiful rain. However, other sources of information such as growth rings within petrified wood suggest there may have been periods of time where water may have been scarce, or perhaps the flora and fauna faced other natural disturbances such as floods, sediment inundation, and volcanism associated with the geographic location of Big Bend at that time. Fossils found within Big Bend provide valuable evidence of the composition of plant communities at a lower paleolatitude during a key period of shifting ecosystems, climate, and biota. By researching these fossils, we gain a deeper understanding of the incredible diversity and dynamic hitory of life on Earth.

Conclusion

Museums often collaborate with the Park Service to create educational exhibits featuring replicas and casts of Big Bend's fossils, allowing the public to experience the wonders of the park's prehistoric past. The dedication of paleontologists, past and present, has been instrumental in transforming Big Bend National Park into a treasure trove of knowledge about our planet's deep history, especially along the southern Western Interior Seaway. As research continues with responsible practices at its core, Big Bend's fossils will undoubtedly continue to unlock new information about the park's prehistoric past.

References

• Abbott, M.L. 1985. Petrified wood from the Paleocene, Black Peaks Formation, Big Bend National Park, Texas. Unpublished manuscript, Big Bend National Park archives, 61 pp.

• Baghai N.L. 1996. An analysis of palynomorphs from Upper Cretaceous sedimentary rocks with emphasis on the Aguja Formation, Big Bend National Park, Brewster County, Texas. PhD diss. University of Texas, Austin, 519 p.

• Blakey, R. C. 2014. Paleogeography and paleotectonics of the Western Interior Seaway, Jurassic-Cretaceous of North America. American Association of Petroleum Geologists, Search and Discovery Article 30392. 72 pp.

• Chang, S.W. 1973. Petrified wood from the Paleocene, Black Peaks Formation, Big Bend National Park, Texas. Master’s Thesis, Sul Ross State University, Alpine, Texas.

• Dorf, E. 1939. Fossil Plants from the Upper Cretaceous Aguja Formation of Texas. American Museum Novitates 1015: 1–9.

• Lawson, D.A. 1972. Paleoecology of the Tornillo Formation, Big Bend National Park, Brewster County, Texas. M.A. thesis, University of Texas, Austin, 182p.

• Lehman TM, Shiller II T. 2020. An angiosperm woodland in the Javelina Formation (Upper Cretaceous), Big Bend National Park, Texas, USA. Cretaceous Research. 115: 104569. DOI: 10.1016/j.cretres.2020.104569.

• Lehman, T. & Wheeler, E. 2001. A fossil dicotyledonous woodland/forest from the Upper Cretaceous of Big Bend National Park, Texas. Palaios. [Online] 16 (1), 102–108.

• Manchester, S. R., Lehman, T.M., Wheeler, E.A. 2010. Fossil palms (Arecaceae, Coryphoideae) associated with juvenile herbivorous dinosaurs in the Upper Cretaceous Aguja Formation, Big Bend National Park, Texas. International journal of plant sciences. [Online] 171 (6), 679–689.

• Maxwell, R. A., Lonsdale, J.T., Hazzard, R.T.; and Wilson, J.A. 1967. Geology of Big Bend National Park, Brewster County, Texas: Univ. Texas Bur. Econ. Geol. Pub. 6711, 320 p.

• Rohr, D. M., Boucot, A.J., Miller, J., Abbott, M. 1986. Oldest termite nest from the Upper Cretaceous of West Texas. Geology (Boulder), 14 (1), 87–88.

• Udden, J.A. 1907. A sketch of the Geology of the Chisos country, Brewster County, Texas, University of Texas Bulletin, 93: 101pp.

• Wheeler, E.A. 1991. Paleocene Dicotyledonous Trees from Big Bend National Park, Texas: Variability in wood types common in the Late Cretaceous and Early Tertiary, and Ecological Inferences. American Journal of Botany, 78(5), 658–671. https://doi.org/10.2307/2445087

• Wheeler, E. A. Lehman, T.M., Gasson, P.E. 1994. Javelinoxylon, an Upper Cretaceous dicotyledonous tree from Big Bend National Park, Texas, with presumed malvalean affinities. American journal of botany. [Online] 81 (6), 703–710.

Related Links

• Big Bend National Park (BIBE), Texas—[BIBE Geodiversity Atlas] [BIBE Park Home] [BIBE npshistory.com]

• NPS—Geologic Time

Fossils and Paleontology