Discovery of Lystrosaurus and a Scientific Revolution

Saturday, December 1, 2018

Lystrosaurus hedini skeleton at the Museum of Paleontology, Tübingen

Fifty years ago, as astronauts trained for the Apollo 11 moon mission, Earth-bound geologists at the Museum of Northern Arizona trained for an expedition that would rock the world of paleontology.

Geology was in the throes of a revolution — from fixed continents and fixed oceans to continents that split apart in slow motion, drifted, collided, fragmented, and realigned. As they drifted, these landmasses uplifted mountains, opened new oceans and destroyed older oceans, isolated animals and plants, then reunited in different continental configurations. This concept was so revolutionary many scientists refused to accept the mounting evidence for the theory of plate tectonics and continental drift. Many paleontologists were among the Resistance.

In December of 1967, New Zealand geologists mapping 240-million-year-old Triassic rocks in the desolate interior of Antarctica stumbled upon some fragmentary bones. A few months later they brought the fragments to paleontologist Edwin H. Colbert for identification. Colbert was in the process of retiring after 40 years as Curator of Paleontology at the American Museum of Natural History in New York City and relocating to the Museum of Northern Arizona in Flagstaff. He wasn’t ready for this surprise.

Colbert recognized the bones as an extinct labyrinthodont amphibian, so named for details in their characteristic teeth. Like modern frogs and salamanders, these distant relatives from the Permian and Triassic Periods could never have swum across the cold, salty water of the Antarctic Sea from other southern continents, nor survived the frozen landscape of Antarctica.

Colbert and other paleontologists had struggled with the new ideas of drifting continents, but he knew instantly this discovery would be a decisive, paleontological blow to the long-held theory of fixed continents. He and two New Zealand paleontologists published an article in Science the following year entitled “Triassic Amphibian from Antarctica.” The paper drew immediate attention, including from the Office of Polar Studies at the National Science Foundation.

At the retirement age of 63 years, Colbert hadn’t considered the possibility that he, himself, would be the one to return to Antarctica – that would be the work of younger, more physically fit geologists. Other paleontologists and officials in the National Science Foundation declared otherwise: if Colbert could pass the physical exams and fitness training, he would be their first choice to lead a return expedition. Simultaneously thrilled and reluctant, he agreed to this ultimate challenge. Astronauts must have felt the same way.

Colbert and his wife, Margaret, completed their move to Flagstaff in the summer of 1968, and then his supreme adventure began. The austral spring in Christchurch, New Zealand, was resplendent with flowers and fresh greenery, as he and his crew made ready for their flight to the all-white, frozen continent. He had invited MNA Curator of Geology Bill Breed, paleontologist James Jensen from Brigham Young University and geologist Jon Powell from the University of Arizona for his own field crew. An international team of 16 scientists and their assistants accompanied them.

Once they reached McMurdo Station, the U.S. headquarters located on Ross Island, they also had support of three Navy helicopters, five pilots, and more than a dozen mechanics and other personnel.

They pushed to the interior of the continent toward the Transantarctic Mountains, with some dramatic side stories, one involving the crash of a companion helicopter and death of two occupants from New Zealand.

Despite this terrifying crash and the ensuing rescue of others in the field party, Colbert’s team continued. First they discovered the fernlike plant, Dicroidium, widely known from Triassic sediments of other continents, stimulating considerable excitement again for the implications related to continental drift (Colbert simply wrote “Drift” in his notes). Soon thereafter, others in their field party explored the slopes of a remote exposure called Coalsack Bluff and found bone fragments.

Colbert’s team followed and discovered another animal, which became the centerpiece of this epic expedition. It was Lystrosaurus, a rather squat, dog-sized primitive reptile with very characteristic skull and jaws, furnished only with two tusk-like teeth and no other dentition. Lystrosaurus was strictly terrestrial, known from many sites in Triassic rocks in southern Africa, and in peninsular India. Relatives were known from other continents as well, including in North America a large oxen-sized form from the Chinle Formation of northern Arizona.

Coalsack Bluff, one of the most remote fossil sites ever encountered on our planet, had yielded a direct link to the supercontinent called Gondwana (also “Gondwanaland”). This was the southern supercontinent, containing Africa, peninsular India, Australia, South America and Antarctica before they split apart and separated.

Those land connections were the routes taken by populations of Lystrosaurus, the labyrinthodont amphibians, and the fernlike Dicroidium before Gondwana fragmented in the Triassic, soon to be separated by the deep, cold, southern ocean and rendered utterly impassable to land-bound animals and plants. This was remarkable evidence of continental drift, even to those paleontologists who resisted all previous discoveries.

The Resistance crumbled, and the world of geology became united in this revolution-in-slow-motion, not as spectacular as the moon, perhaps, but every bit as arresting for the utter joy of discovery.

Colbert and Breed returned to Flagstaff and the Museum of Northern Arizona, and other members went their respective ways, but the fundamental importance of their work continues today. Fifty years later, Flagstaff can celebrate two anniversaries during the year we recognize here as Lunar Legacy.

Source: https://azdailysun.com

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