Giant Gar from Cretaceous–Palaeogene

One for the books! An astonishing discovery by Denver Museum of Nature & Science Scientist

By Julio Poletti

It is scorching hot in the middle of July 2016, temperatures surpassing the 3-digit mark. Location: Southwestern North Dakota, aka middle of nowhere. Sweat is dripping from every pore of Denver Museum of Nature & Science Scientist Tyler Lyson and Director of the Smithsonian’s National Museum of Natural History Kirk Johnson. They were the only two brave souls in this part of the Hell Creek badlands roasting under the summer sun, hiking along the outcrop in search of amazing plant and animal fossils... and [hopefully] new discoveries.

“When we’re out prospecting, it's incredibly exciting because anything is possible. We could find amazing fossils like a completely articulated T. rex skeleton, mummified dinosaurs or even a new species of animal. These possibilities make it all worth it, regardless of what mother nature throws at us — extreme temperature, rattlesnakes, scorpions and the unknown,” said Lyson.

For Lyson and Johnson, mother nature was not a limiting factor that year, though. In fact, all the sweating and hundreds of miles of hiking and non-stop digging turned out to be quite the opposite: a truly remarkable discovery. One that wouldn’t be known to the public until now.

For over 100 years, teams of scientists from all over the world, including Denver Museum of Nature & Science scientists, have been working in this area. Historically, scientists have worked in this area to collect dinosaur skeletons, such as T. rex, Triceratops, Edmontosaurus or Ankylosaurus to display in their museums worldwide. Within the past 50 years or so, scientists have been studying this area looking for answers to what caused Earth’s last mass extinction, the extinction of the dinosaurs. It’s the last dinosaur ecosystem on the planet and it’s also one of the most spectacular.

But that day, they found more than just dinosaurs. Right as Lyson and Johnson were headed back to a much-deserved cold beer, Lyson spotted an area he wanted to explore some more.

“ seemed out of place”

The team stopped to dig through the Cretaceous/Paleogene (K/Pg) boundary, a thin band of rock containing much more iridium than other rock units and marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. In other words, this geological boundary separates two worlds, the one before the asteroid that hit Earth and extinguished 75% of life on Earth (including all dinosaurs, except birds) to the mammal-dominated world we know today.

“I saw some fish vertebrae and scales sticking out of the side of a hill, just above the K/Pg boundary line that we had been mapping. The large size of the vertebrae suggested a noticeably big fish, and given the size of the fish, it seemed out of place,” said Lyson.

A four and a half-foot fish? Sticking out of a rock on top of a hill in southwestern North Dakota? And sitting just above the K/Pg boundary, meaning awfully close to the time when dinosaurs were extinct? This... was something special.

Turns out, Lyson and Johnson had just found a new species of fossil fish — an alligator gar. But this is not just any kind of skeleton. We’re talking an approximately 66-million-year-old species related to the modern-day alligator gar found in the southeastern US. These fish can breathe air, live in many types of waters and are generalist predators – features that undoubtedly helped them persist and flourish in the wake of the destruction caused by the massive asteroid impact.

“The fossil speaks to how quickly life rebounded in freshwater ecosystems after the giant dinosaur-killing asteroid struck Earth, which was the single worst day for multicellular life on Earth. This discovery suggests that freshwater life rebounded very quickly, within thousands of years, and not hundreds of thousands or millions of years as we had previously assumed,” said Lyson.

No other large vertebrate fossil had ever been found this close to the actual K/Pg boundary, making this a discovery that will go in the books.

In 2022, Lyson’s discovery was published in the peer-reviewed scientific journal Biology Letters by The Royal Society Publishing and lead by Yale undergraduate Chase Doran Brownstein. To have a publication in a peer-reviewed journal is a rigorous process wherein the authors' scholarly work is subjected to the scrutiny of other experts in the same field to check its validity and evaluate its suitability for publication.

The article “Giant gar from directly above the K/Pg boundary suggests healthy freshwater ecosystems existed within thousands of years of the asteroid impact” is now public and universally accessible by libraries, universities, scientists, scholars and students. This publication expands our collective knowledge of how life rebounded after the mass extinction that wiped out the dinosaurs.

Why did it take so long to get the fossil published into a journal?

According to Lyson, the fossil first needed to be meticulously extracted from the rock using small pneumatic air scribes and sand blasters, a process that can take months. Once the fossil was cleaned, it was shipped to the University of Texas to get CT (computed tomography) scanned to look at internal details. After that, it was time for a team of scientists to study the data. Analyzing 66 million-year-old data simply takes time.

This alligator gar fossil is stored in the collections at the Denver Museum of Nature & Science, where it’s kept safely for scientists, scholars and future generations to study and learn about.

“I’m just really thrilled and fulfilled to have this amazing fossil published and available to scientists and the public worldwide,” said Lyson. “To make the discovery, to oversee the cleaning and the scanning, and to work with an undergraduate student to get it published, is a remarkable feeling. It’s the full circle of a field paleontologist.”

All that sweating, hiking, dusting, cleaning and analyzing the data for the past six years sure paid off. To know that some life on Earth rebounded just thousands of years after the asteroid that extinguished the dinosaurs hit, and not millions of years after, is a remarkable discovery. Earth found a way.

Making the world a better place through the process of scientific discovery

The Denver Museum of Nature & Science has teams of scientists out in the field every year looking for new and important fossils. They are the reason these discoveries happen. Thanks to our community’s support, the Museum can fund these costly expeditions and discoveries that allow us to better understand our past, present and future.

Tyler Lyson is a vertebrate paleontologist who studies the extinction of dinosaurs, the rise of placental mammals and the evolutionary origin of various reptiles, particularly turtles. Lyson currently works as a curator of vertebrate paleontology at the Denver Museum of Nature & Science. He combines developmental, genetic and fossil data with high-resolution chronostratigraphic data to address his research questions. Lyson has conducted fieldwork throughout the American West and has active field sites in North Dakota, Montana and Colorado. Lyson was born in North Dakota and has been doing paleontology fieldwork since he was in middle school. He received his bachelor’s from Swarthmore College and his Ph.D. from Yale University. Tyler joined the Museum in 2014 after a postdoctoral position at the Smithsonian Institution.


Tyler R. Lyson, PhD

Associate Curator of Vertebrate Paleontology

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