Sister Parks: Petrified Forest and Ischigualasto, Across the Equator

By Dr. Adam Marsh, lead paleontologist, Petrified Forest National Park.

The Triassic Period was a time of evolutionary experiment worldwide. Crocodile ancestors that walked on two legs, the first flying vertebrates, several groups of armoured reptiles, and early dinosaurs and their closest relatives shared ecosystems across the supercontinent Pangea — before one of Earth's most severe ecological disasters closed the period ahead of the Jurassic. The fossil record is incomplete everywhere, so telling the story means combining evidence from distant places with a shared geological and biological past. Many countries protect such places, among them Petrified Forest National Park in the United States and Ischigualasto Provincial Park in Argentina.

Two fossil parks

Even in the Late Triassic the two lay on opposite sides of the Equator, and each adds something the other lacks. Both have the armoured reptiles called aetosaurs and the puzzling shuvosaurids — two-legged relatives of crocodiles that, when first found in western Texas, were taken for Triassic ornithomimid dinosaurs. The Late Triassic story begins at Ischigualasto and ends at Petrified Forest.

The Talampaya (Lower Triassic) and Tarjados (Middle Triassic) Formations form a long slot canyon in Talampaya National Park. Image from the National Park Service's page.

Becoming sister parks

The resemblance is so close that nearly two decades ago Dr. William Parker of Petrified Forest began exploring a sister-park arrangement. With help from the province of San Juan and the U.S. State Department, the two parks signed it on July 31, 2023, at a sunset ceremony at a well-known overlook in Ischigualasto.

Ischigualasto park coordinator Emilio Fernandez and Petrified Forest park manager Jeannine McElveen sign the sister-park agreement. Image from the National Park Service's page.

An Albright-Wirth grant took Petrified Forest staff to northern Argentina: park manager Jeannine McElveen, chief of interpretation Sarah Herve, resource stewardship and science programme manager Dr. William Parker, and lead paleontologist Dr. Adam Marsh. They met Ischigualasto's administration, rangers and scientists to share ideas and problems and to start working together on interpretation, park policy, museum exhibits and science. Their hosts included park coordinator Emilio Fernandez, deputy coordinator "Richard" Burgoa, rangers Angie Elizondo and Edén Melián, Dr. Oscar Alcober of the Museum of Natural Science at the National University of San Juan, Marcelo Fretes, San Juan's secretary of institutional relations, and Angeles Coscolla of the U.S. Embassy in Buenos Aires.

The visit

• Getting there took two days, through Phoenix, Houston, Buenos Aires and San Juan.
• Talampaya National Park (one day): Early and Middle Triassic rocks in a tall canyon, guanacos (relatives of llamas), maras (jackrabbit-sized relatives of capybaras), and petroglyphs made by local Indigenous peoples.
• Ischigualasto (two days): museum exhibits, guided circuits through the fossil-rich badlands, an interpretive centre built over a dig, and an area soon to open to tours with striking rock art left by Argentina's historic cattle drivers.
• A high point was a night hike through the "Valley of the Moon" under a full moon, ending with empanadas in the badlands.

"El Hongo" (the Mushroom), a balanced sandstone block in the Ischigualasto Formation (Upper Triassic); the red cliffs behind are the Los Colorados Formation (Upper Triassic to Lower Jurassic). Image from the National Park Service's page.

A string of vertebrae eroding out of the Ischigualasto Formation, probably from a rhynchosaur or a cynodont. Image from the National Park Service's page.

A sandstone boulder at Ischigualasto with inscriptions left by historic cattle drives. Image from the National Park Service's page.

What comes next

Petrified Forest looks forward to hosting Ischigualasto's staff in Arizona, and early talks have begun on a second sister-park arrangement with Talampaya, which borders Ischigualasto and shares its rich geology and fossils. The parks have much to learn from each other: how today's animal lineages survived the mass extinction at the end of the Triassic, how to limit damage and theft, how to turn complex research into clear exhibits and programmes, and what it means to be a "fossil park".

Sources

• National Park Service, "Sister Parks: Triassic reflections across the Equator at Petrified Forest and Ischigualasto," by Dr. Adam Marsh. https://www.nps.gov/articles/000/sister-parks-triassic-reflections-across-the-equator-at-petrified-forest-and-ischigualasto.htm
• The original cites the scientific literature for its ages and fossil lists, including Colombi et al. (2021) for the Ischigualasto Formation and Rasmussen et al. (2020) for Petrified Forest.
• Rewritten in hubnx's own words.