Fossil Find Suggests Dinosaurs Crossed North America Before Extinction

A single dinosaur tooth is helping paleontologists better understand what North America looked like right before non-avian dinosaurs went extinct.

Prior to 68–66 million years ago, hefty horned dinosaurs migrated from western North America to the east. One such animal died sometime after the lengthy journey, perhaps falling victim to a bloodthirsty tyrannosaur. The unfortunate dinosaur’s body then fell into bay water, where it turned into a bloated, floating carcass. Scavengers of all shapes and sizes feasted on the remains, leaving behind only inedible items, like the dinosaur’s teeth.

As time went on, non-avian dinosaurs became extinct and mammals rose to the top of the terrestrial food chain, yet one of the horned dinosaur’s teeth still remained entombed not too far from where the animal had died in what is now Mississippi.

George Phillips, who is the paleontology curator at the Mississippi Department of Wildlife, Fisheries, and Parks’ Museum of Natural Science, was excavating the Owl Creek Formation in the northern part of the state when he spotted the quarter-sized tooth. He then did what many of us do when we find something interesting: He posted a photo of the tooth at Facebook.

“Quite a few, although not all, of my colleagues use social media,” explained Phillips. “I was fairly confident one of them would chime in to the conversation and have some idea of the tooth’s owner.”

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Sure enough, in about 10 minutes he was in contact with his soon-to-be co-author Andrew Farke, a paleontologist at the Raymond M. Alf Museum of Paleontology at The Webb Schools. Farke confirmed the suspicions of their mutual friend, Lynn Harrell of the University of Alabama, that the tooth was from a horned dinosaur. The dino looked a lot like Triceratops, they agreed, and might have even been this iconic species.

The tooth, described in a new Peer J paper, provides the first direct evidence of a horned dinosaur in eastern North America.

Additionally, the location of the tooth and its ancestry suggest that the two halves of North America, formerly separated by a giant seaway, were connected before the Dinosaur Age came to a dramatic close. Phillips explained that the tooth has a distinctive double root, which is unique to western North American horned dinosaurs known as ceratopsids.

Although paleontologists have suspected for a while that horned dinosaurs once lived in what are now Maryland and North Carolina, based on fossil fragments, those possible remains belonged to more primitive species that likely lived in the area before the Western Interior Seaway separated it from western North America. Farke therefore believes that it is "highly unlikely" that the Mississippi animal belonged to a unique eastern evolutionary group.

The researchers instead propose that the ancestors of the Triceratops-like dinosaur came from western North America.

The Western Interior Seaway that once split North America was estimated at its largest to have been 2,500 feet deep, 600 miles wide, and over 2,000 miles long. Such a massive barrier probably would have prevented a terrestrial animal — and particularly one with little or no water navigation skills — to have swum across it.

The Western Interior Seaway is long gone, but exactly when it receded has been a mystery. The dinosaur tooth shows that the seaway must have done so before dinosaurs went extinct 66 million years ago.

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“The Western Interior Seaway receded from the continent in either a southerly and/or northerly direction as a result of an actively growing Rocky Mountains, which were the size of mere foothills when the last of the dinosaurs were roaming the earth,” Phillips said. “Evidence for this retreat of the seaway lies in the types of sediments deposited and stacked in the ancient basin once occupied by the seaway and are now exposed at higher elevations with the growth of the Rockies.”

Since the Triceratops-like animal wound up in bay water — not the seaway — after its death, the dinosaur’s tooth fossil was found alongside the remains of water dwellers, such as ancient clams, crabs, fishes, and giant marine lizards. During the dinosaur’s lifetime, these animals were all in the large bay, which was about the size of today’s Mobile Bay in Alabama.

Farke and Phillips suspect that the aforementioned tyrannosaur, or possibly a large crocodile, killed the horned dinosaur.

“Such a predation event would have had to have happened on land, prior to the ceratopsid tooth washing into and becoming buried in the bay,” Phillips said.

The horned dinosaur’s tooth, now housed at the Mississippi Museum of Natural Sciences, provides a reminder that many different dinosaur species once lived, and apparently traveled, across North America. They did so before 66 million years ago, when two incredible disasters happened.

One was a meteoroid or asteroid strike in what is now the Yucatán Peninsula of Mexico. “It is postulated to have incinerated everything within a certain sizable radius of ground zero," Phillips said, "and the voluminous fine, aerosolized debris blast from this location, having become airborne and distributed widely, would have certainly induced short-term and possibly significant long-term climate change.”

The second disaster involved prolonged, large scale volcanic eruptions centered in India. The eruptions would have spewed toxic and greenhouse gases far into the atmosphere, further making life challenging for animals lucky enough to have survived the asteroid strike.

Together, the one-two punch wiped out as much as 75 percent of all species inhabiting the earth at that time, including Triceratops and all other non-avian dinosaurs.  

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