Utah Badlands May Have Harbored Oldest Marsupial : Fossil: An animal’s jaw deemed to be 100 million years old and measuring less than an inch long is recovered. The discovery reinforces the theory that such pouched creatures, now identified with Australia, originated in North America.

The fossilized jaw of a chipmunk-size, 100 million-year-old animal recovered from the rocky badlands of Utah belongs to the world’s oldest marsupial.

The find reinforces the theory that marsupials--those pouched creatures identified today with Australia--originated in North America.

The earliest previous marsupial fossil, a smaller portion of a 90-million-year-old jaw with three teeth, was also found in Utah, about a decade ago.

Spectacularly complete, the new three-quarter-inch-long jaw contains six teeth, including four molars that are characteristic of marsupials.

“The specimen represents an extremely primitive marsupial, or it could be the ancestor of all marsupials,” said Richard L. Cifelli, the University of Oklahoma paleontologist who led the 1992 summer expedition that made the find in central Utah.

Cifelli named the fossil “Kokopellia” after the flute-playing mythical figure of Southwest Indian lore that is a frequent theme on petroglyphs in the region. The jaw was discovered and hand-quarried from a rocky outcrop by William J. May, a paleontologist from the Oklahoma Museum of Natural History.

The expedition also found well-preserved 100-million-year-old fossils of frogs, salamanders, snakes, crocodiles, a diversity of dinosaurs and a “top-of-the-notch” carnivorous lizard.

The animals browsed and hunted in a lush, flat landscape watered by wide, slow-moving streams and bedecked with evergreens, ferns and flowering plants. The process of mountain-making had not yet begun.

Of all the fossils, the marsupial jaw has elicited the most interest. “This covers a new stage in marsupial evolution and fills a gap in our knowledge of how they evolved,” commented Louis L. Jacobs, professor of geological sciences at Southern Methodist University in Dallas.

“Cifelli has pushed them back close to the origin of modern groups of mammals, when they were living in the shadows and footprints of the dinosaurs,” he added.

“It’s pretty important. We’re tracing their roots.”

Marsupials--mammals seemingly forgotten by time--use their pouches to shelter, carry and nurse their tiny, helpless young. They include kangaroos, koalas, pouched mice and possums.

Most of today’s marsupials roam Australia and South America, but scientists still debate their place of origin.

One recent theory even suggested Asia, although none are left there.

“The age and primitiveness of Kokopellia, a suitable ancestor for all later marsupials, are important new pieces of evidence suggesting that the group originated in North America,” said Cifelli, whose fieldwork was supported by the National Geographic Society.

According to this scenario, marsupials would have spread to South America at the end of the Cretaceous period about 65 million years ago, and from there to Australia via Antarctica.

The three southern continents were connected until about 40 million years ago.

Some scientists don’t think the new jaw proves anything one way or another.

“I’ve favored a North American origin for marsupials since the ‘60s,” said Jason A. Lillegraven, a paleontologist and vertebrate-fossil expert at the University of Wyoming.

“But I don’t think the case is proven from a practical point of view. How do you know for sure? You need a terribly good fossil record, probably better than we’re ever likely to have, to be really sure.”

Jacobs thinks that the age and location of the jaw make a good case for North American origin. “If the geography of fossils speaks to the geography of where things actually originated, then this supports it,” he said.

Scientists still debate the reasons why placental mammals--named for the placenta, a membrane that nourishes the embryo in the womb--ousted the marsupials in North America and now dominate its animal life.

The only remaining North American marsupial is the possum, which still shelters its young in a pouch long after birth.

This ancient beast has not only survived among the continent’s competing placentals, but has extended its range in recent years, spreading north to southern Canada.

Perhaps it has been successful, scientists say, because it will eat anything, live almost anywhere, multiply prolifically and treat its young so casually that all but the fittest are weeded out.