SALT LAKE CITY — Scientists say dinosaur fossils unearthed in northeastern Utah back in 1990 are the oldest Allosaurus fossils ever found in the state, dating back 155 million years.. The discovery, they say, also shows there were only two Allosaurus species that existed in North America.

Their findings of the new species — dubbed Allosaurus jimmadseni — were released Friday in the science journal PeerJ.. The study not only identified a second Allosaurus species — the other being Allosaurus fragilis — but it found that the upward of 12 Allosaurus species named in North America were actually misidentified as anything other than the Allosaurus fragilis. The discovery, researchers say, helps understand how the ecosystem changed over the course of millions of years.

“We’re starting to understand this animal — Allosaurus fragilis — it’s one of the five iconic dinosaurs. Every plastic bag of toy dinosaurs you get has this animal in it,” said Mark Loewen, a research associate at the Natural History Museum of Utah and associate professor in the Department of Geology & Geophysics at the University of Utah, while pointing at a dinosaur fossil on display Friday. “This new dinosaur lived before it. … We’re actually looking at changes in the ecosystem as this ecosystem turns into a (another) ecosystem — the iconic one we think about.”

Loewen co-led the study along with Daniel Chure, a retired paleontologist at Dinosaur National Monument. The findings came after years of work between researchers at the National Park Service, the Bureau of Land Management and the Natural History Museum of Utah, where the largest collection of Allosaurus fossils in the world is kept.

Understanding Allosaurus jimmadseni

The Allosaurus jimmadseni was a carnivorous dinosaur that existed during the Late Jurassic Period, 157 to 152 million years ago, according to the findings released Friday. Researchers say the species was about 26 to 29 feet long and weighed 4,000 pounds. It’s believed to have been the top predator in its ecosystem at the time, and had long arms and legs with a tail and three sharp claws.

A display of an Allosaurus jimmadseni skull, left, next to an Allosaurus fragilis skull inside the Natural History Museum of Utah collections room on Friday, Jan. 24, 2020. (Photo: Carter Williams, KSL.com)

Its range of existence means the bones predate the Allosaurus fragilis, which was first named in 1877. The Allosaurus fragilis was believed to have existed about 150 million years ago, according to the Natural History Museum of Utah.

Researchers say the newly discovered species had a slender skull with a short nasal crest, compared to the previously known species. There were also changes in the body of the two species, but those weren’t as significantly different as the skull.

An artist rendering of what it may have looked like when an Allosaurus jimmadseni attacked a juvenile sauropod. (Photo: Todd Marshall)

The new dinosaur species is believed to have lived in a semi-arid inland basin that would have been filled with lakes, floodplains and other water sources along the western portion of the continent, according to researchers.

How the study came about

The findings are something nearly 30 years in the making. In 1990, a paleontologist from the University of Nebraska Omaha discovered the bones of the new species at Dinosaur National Monument in Uintah County. Most of the dinosaur was unearthed at that time.

Scientists struggled to figure out a way to move the skeleton from the rock, so crews had to use a helicopter to fly the large block of rock to a lab to be studied, Chure said. The prehistoric creature’s skull was discovered by a University of Utah radiologist six years after the other bones were discovered. It’s the only dinosaur skull found from radioactivity, as far as Loewen knows.

The fossil that helped lead to the discovery of the Allosaurus jimmadseni inside the Natural History Museum of Utah collections room on Friday, Jan. 24, 2020. Researchers say the dinosaur lived about 155 million years ago. (Photo: Carter Williams, KSL.com)

After the discovery, researchers began analyzing thousands upon thousands of Allosaurus fossils across the world. They concluded there were two species of the creature in North America.

“It just, ultimately, took a very long time. But we were trying to be very thorough and give a very detailed description — not a very cursory one that would establish the name but not really be of a lot of use for other researchers who are studying meat-eating dinosaurs,” Chure said.

Loewen added the 70-page paper was written for researchers 200 years from now, so they would know where the dinosaurs were discovered and how they were excavated. The paper also details how most of the previously reported species were actually just Allosaurus fragilis.

The dinosaur unearthed in Utah was the first but not the only Allosaurus jimmadseni that has been discovered, researchers say. Tthey say “Big Al,” a dinosaur discovered in Wyoming in 1991 was erroneously identified as an Allosaurus fragilis. The dinosaur was featured on a BBC special in 2001. There are at least a half-dozen other samples identified from museums across the U.S. and even Switzerland, researchers say.

“This exciting new study illustrates the importance of continued paleontological investigations on public lands in the West,” said Brent Breithaupt, a regional paleontologist for the BLM, in a prepared statement. “Discovery of this new taxon of dinosaur will provide important information about the life and times of Jurassic dinosaurs and represents another unique component of America’s Heritage.”

Honoring a paleontology legend

Chure and Loewen described their findings at the Natural History Museum of Utah just feet from a plaque in the Past Worlds Gallery that honors James Madsen Jr., a late Utah paleontologist. Madsen was the first state paleontologist for Utah and uncovered thousands of Allosaurus bones during his lifetime.

In many ways, Madsen was in the room with them. Not only was his name there with the other researchers, several members of his surviving family attended the meeting, and many of the bones — including some in a display underneath the podium — were dug up by Madsen. That’s why researchers didn’t struggle finding a name for the new species, which pays homage to him.

According to the researchers, the name Allosaurus breaks down to “other”, “strange” or “different” and “lizard.” However, “jimmadseni” honors Madsen.

An undated photo of paleontologist James Madsen Jr. as he assembles a composite skeleton of Allosaurus from the Clevland Lloyd Dinosaur Quarry. The Allosaurus jimmadseni was named in honor of Madsen, who died in 2009. (Photo: J. Willard Marriot Library)

“Jim Madsen was really famous as the authority of the Allosaurus,” Chure said, adding that Madsen’s work at the Cleveland-Lloyd Dinosaur Quarry in the San Rafael Swell played an instrumental role in the discovery announced Friday. “Being able to name a new species of Allosaurus, the very animal that he dedicated so much of his life to studying and understanding, was and is really a no-brainer.”

It’s an honor Madsen’s daughter, Lisa, said her father would enjoy. He was even told that it would be named after him prior to his death in 2009; however, it took many years to confirm the findings.

She said her father loved paleontology and discovering dinosaurs, especially the Allosaurus. That’s why the Madsen family was touched that this new finding honors his work.

“To have him celebrated today, and then from now on, it’s very sweet. We’re just very proud and grateful,” Lisa Madsen said. “He was really special, and this was his thing. We are just really lucky that we can come up here and visit something that he loved. We’re just very lucky.”

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