Barbaturex morrisoni: Lizard King of the Paleogene

Some 40 million years before rock and roll singer Jim Morrison's lyrics earned him the moniker "the Lizard King," an actual king lizard roamed the hot tropical forests of Southeast Asia, competing with mammals for food and other resources.

A team of U.S. paleontologists, led by Jason Head of the University of Nebraska-Lincoln, describes fossils of the giant lizard from Myanmar this week in the scientific journal Proceedings of the Royal Society B. Their analysis shows that it is one of the biggest known lizards ever to have lived on land.

Fittingly, it's been named for the aforementioned Doors singer: The creature's official name is Barbaturex morrisoni.

At almost six feet long and weighing upwards of 60 pounds, the lizard provides new and important clues on the evolution of plant-eating reptiles and their relationship to global climate and competition with mammals.

In today's world, plant-eating lizards like iguanas and agamids are much smaller than large mammal herbivores. The largest lizards, like the giant, carnivorous Komodo Dragon, are limited to islands that are light on mammal predators. It's not known, however, if lizards are limited in size by competition with mammals, or by temperatures of modern climates, Head said.

But B. morrisoni lived in an ecosystem with a diversity of both herbivorous and carnivorous mammals during a warm age in the earth's history -- 36 to 40 million years ago -- when there was no ice at the poles and atmospheric 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.

"We think the warm climate during that period of time allowed the evolution of a large body size and the ability of plant-eating lizards to successfully compete in mammal faunas," Head said.