Reveals Climate Clues

Jason Head, UNL assistant professor of earth and atmospheric sciences and curator of vertebrate paleontology at the University of Nebraska State Museum of Natural History, led a team of U.S. paleontologists that analyzed the creature’s fossils for the first time. He found it is one of the biggest known lizards. Fittingly, he named his discovery after Morrison.

At nearly 6 feet long and weighing more than 60 pounds, the giant lizard provides new, important clues on the evolution of plant-eating reptiles and their relationship to global climate and competition with mammals.

Today, plant-eating lizards are much smaller than mammal herbivores. The largest lizards, like the carnivorous Komodo dragon, are limited to islands with few mammal predators. But it’s not known whether lizards’ size is limited by competition with mammals or by modern climates.

But B. morrisoni lived in an ecosystem with many herbivorous and carnivorous mammals during a warm age when carbon dioxide levels were very high. The creature was larger than most of the mammals with which it lived, suggesting that competition or predation by mammals did not restrict its evolution into a giant.

“You can’t fully understand the evolution of ecosystems in the modern world without looking at the ones that preceded them,” Head said. “We would’ve never known this by looking at lizards today. By going back in time using the fossil record, we can find unique information on the origin of modern ecosystems.”

The discovery raises other questions: How long did these giant lizards walk the earth? How far and wide did they move? What does their evolution and time on Earth tell us about global temperature change throughout history?

“That becomes very important in modeling what temperature change will be like across the surface of the planet in the future,” Head said. “That, obviously, bears directly on our own health.”

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