Dinosaurs in New Mexico thrived until the very end, study shows
Study challenges long-held assumptions, finding late-surviving dinosaurs lived in vibrant, regionally distinct communities
Baylor University
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Researchers analyzed fossils of the Alamosaurus found in northwestern New Mexico and discovered these dinosaurs were very different but the same age as dinosaurs found further north in Wyoming and Montana. (Dinosaur image credit: Natalia Jagielska)
view moreCredit: Natalia Jagielska
For decades, many scientists believed dinosaurs were already dwindling in number and variety long before an asteroid strike sealed their fate 66 million years ago. But new research in the journal Science from Baylor University, New Mexico State University, The Smithsonian Institution and an international team is rewriting that story.
The dinosaurs, it turns out, were not fading away. They were flourishing.
A final flourish in the San Juan Basin
In northwestern New Mexico, layers of rock preserve a hidden chapter of Earth’s history. In the Naashoibito Member of the Kirtland Formation, researchers uncovered evidence of vibrant dinosaur ecosystems that thrived until just before the asteroid impact.
High-precision dating techniques revealed that fossils from these rocks are between 66.4 and 66 million years old – placing them in the catastrophic Cretaceous-Paleogene boundary.
“The Naashoibito dinosaurs lived at the same time as the famous Hell Creek species in Montana and the Dakotas,” said Daniel Peppe, Ph.D., associate professor of geosciences at Baylor University. “They were not in decline – these were vibrant, diverse communities.”
Dinosaurs in their prime
The New Mexico fossils tell a different story than originally thought. Far from being uniform and weakened, dinosaur communities across North America were regionally distinct and thriving. Using ecological and biogeographic analyses, the researchers discovered that dinosaurs in western North America lived in separate “bioprovinces,” divided not by mountains or rivers, but by temperature differences across regions.
“What our new research shows is that dinosaurs are not on their way out going into the mass extinction,” said first author Andrew Flynn, Ph.D. ‘20, assistant professor of geological sciences at New Mexico State University. “They're doing great, they're thriving and that the asteroid impact seems to knock them out. This counters a long-held idea that there was this long-term decline in dinosaur diversity leading up to the mass extinction making them more prone to extinction.”
Life after impact
The asteroid impact ended the age of dinosaurs in an instant – but the ecosystems they left behind set the stage for what came next, the researchers said. Within 300,000 years of their extinction, mammals began to diversify rapidly, exploring new diets, body sizes and ecological roles.
The same temperature-driven patterns that shaped dinosaur communities continued into the Paleocene, showing how climate guided life’s rebound after catastrophe.
“The surviving mammals still retain the same north and south bio provinces,” Flynn said. “Mammals in the north and the south are very different from each other, which is different than other mass extinctions where it seems to be much more uniform.”
Why the discovery matters today
The discovery is more than a window into the past – it’s a reminder of the resilience and vulnerability of life on Earth. Conducted on public lands managed by the U.S. Bureau of Land Management, the research highlights how carefully protected landscapes can yield profound insights into how ecosystems respond to sudden global change.
With a clearer understanding of the timeline of the dinosaurs’ final days, the study reveals not a slow fade into extinction but a dramatic ending to a story of flourishing diversity cut short by cosmic chance.
About the authors
In addition to Peppe and Flynn, the research team included scientists from Baylor University, New Mexico State University, the Smithsonian Institution, the University of Edinburgh, University College London and multiple U.S. and international institutions.
- Stephen L. Brusatte, Ph.D., The University of Edinburgh
- Alfio Alessandro Chiarenza, Ph.D., Royal Society Newton International Fellow, University College London
- Jorge Garcia-Giron, Ph.D., University of Leon
- Adam J. Davis, Ph.D., WSP USA Inc.
- C. Will Fenley, Ph.D., Valle Exploration
- Caitlin E. Leslie, Ph.D., ExxonMobil
- Ross Secord, Ph.D., University of Nebraska-Lincoln
- Sarah Shelley, Ph.D., Carnegie Museum of Natural History
- Anne Weil, Ph.D., Oklahoma State University
- Matthew T. Heizler, Ph.D., New Mexico Institute of Mining and Technology
- Thomas E. Williamson, Ph.D., New Mexico Museum of Natural History and Science
Funding
This research was supported by the National Science Foundation, European Research Council, Royal Newton International Fellowship, Geologic Society of America Graduate Research Grant, Baylor University James Dixon Undergraduate Fieldwork Fellowship (AGF), the European Union Next Generation, the British Ecological Society and the American Chemical Society – Petroleum Research Fund.
The researchers would like to thank the Bureau of Land Management for providing collecting permits and supporting the research.
ABOUT BAYLOR UNIVERSITY
Baylor University is a private Christian University and a nationally ranked Research 1 institution. The University provides a vibrant campus community for 20,000 students by blending interdisciplinary research with an international reputation for educational excellence and a faculty commitment to teaching and scholarship. Chartered in 1845 by the Republic of Texas through the efforts of Baptist pioneers, Baylor is the oldest continually operating University in Texas. Located in Waco, Baylor welcomes students from all 50 states and more than 100 countries to study a broad range of degrees among its 12 nationally recognized academic divisions. Learn more about Baylor University at www.baylor.edu.
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The College of Arts & Sciences is Baylor University’s largest academic division, consisting of 25 academic departments in the sciences, humanities, fine arts and social sciences, as well as 11 academic centers and institutes. The more than 5,000 courses taught in the College span topics from art and theatre to religion, philosophy, sociology and the natural sciences. The College’s undergraduate Unified Core Curriculum, which routinely receives top grades in national assessments, emphasizes a liberal education characterized by critical thinking, communication, civic engagement and Christian commitment. Arts & Sciences faculty conduct research around the world, and research on the undergraduate and graduate level is prevalent throughout all disciplines. Visit the College of Arts & Sciences website.
Journal
Science
Method of Research
Content analysis
Subject of Research
Animals
Article Title
Late-surviving New Mexican dinosaurs illuminate high end-Cretaceous diversity and provinciality
Article Publication Date
23-Oct-2025
Dinosaur ‘mummies’ unlock secrets of life appearance
UChicago paleontologists unveil fossil duck-billed dinosaur specimens collected in Wyoming and carefully prepared in the Fossil Lab that preserve their fleshy external anatomy with sufficient detail to depict how this large-bodied dinosaur looked in life.
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Some 66 million years ago, just before the great extinction, the duck-billed dinosaur Edmontosaurus annectens walks in the soft mud of a coastline passing the sun-dried a carcass of another individual and leaving a set of footprints — before spotting its nemesis, the great predator Tyrannosaurus rex, and turning to run. Floodwaters would bury carcasses of the duckbill preserving its fleshy surface detail as a clay mask over skeletons of its fossilized bones in a small area located today in the badlands of east-central Wyoming. (artwork by Dani Navarro; storyboard by Jonathan Metzker; animation by Davide la Torre)
view moreCredit: Artwork by Dani Navarro; storyboard by Jonathan Metzker; animation by Davide la Torre
In a new paper in Science, experts from the University of Chicago describe steps that took place some 66 million years ago to transform carcasses of a duck-billed dinosaur, Edmontosaurus annectens, into dinosaur “mummies” preserving fine details of scales and hooves. Called clay templating, the external fleshy surface of the dinosaur was preserved over the skeleton after burial by a thin clay mask no more than 1/100th of an inch thick. Using an array of imaging techniques, the scientists reconstructed the fleshy appearance of the animal in life, from a tall crest over the neck and trunk to a spike row over its tail and hooves sheathing its toes. Combined with fossilized footprints, the appearance of a duck-billed dinosaur — long guessed at but never demonstrated in this detail — is now at hand.
“It’s the first time we’ve had a complete, fleshed-out view of a large dinosaur that we can really feel confident about,” said senior author Paul Sereno, PhD, Professor of Organismal Biology and Anatomy at UChicago. “The badlands in Wyoming where the finds were made is a unique ‘mummy zone’ that has more surprises in store from fossils collected over years of visits by teams of university undergrads.”
From field puzzle to full profile
Using historical photos and field sleuthing, Sereno and his team relocated the sites in east-central Wyoming where several famous dinosaur mummies were discovered in the early 20th century, mapping out a compact “mummy zone.” In those stacked river sands, they excavated two new Edmontosaurus mummies — a late juvenile and an early adult — with large continuous areas of preserved external skin surface.
Sereno is quick to explain that his dinosaur mummies are not like the human-prepared mummies in Egyptian tombs; no organic material remains. Across both newly described specimens and previous ones labeled mummies (including those found at the same site in the 20th century), the skin, spikes, and hooves were preserved not as tissue, but as a sub-millimeter clay film that formed on the carcass surface soon after burial.
“This is a mask, a template, a clay layer so thin you could blow it away,” Sereno said. “It was attracted to the outside of the carcass in a fluke event of preservation.”
The team used several imaging tools, including hospital and micro-CT scans, thin sections, X-ray spectroscopy, clay analyses, and examination of the discovery site, all of which pointed to how this unique preservation occurred. After each sun-dried dinosaur carcass was covered up suddenly in a flash flood, a biofilm on the carcass surface electrostatically pulled clay out of the wet sediment to congeal a wafer-thin template layer, capturing the true surface in three dimensions, after which the organic material decayed away and the skeleton below fossilized over longer timescales.
Exposing such a soft, paper-thin clay boundary required hours of careful cleaning led by Fossil Lab manager Tyler Keillor, a co-author of the paper. Other researchers led by postdoctoral scholar Evan Saitta used 3D surface imaging, CT scans and contemporary footprints to follow the soft anatomy, characterize the sediment inside and outside the mummy, and fit the hooves back into a footprint. Digital artists then joined the science team to reconstruct the fleshy appearance and movement of the duckbill, walking on soft mud near the very end of the dinosaur era.
“I believe it’s worth taking the time to assemble a dream team in order to generate science that can be appreciated by the general public,” Sereno said. “We’ve never been able to look at the appearance of a large prehistoric reptile like this — and just in time for Halloween.”
Crests, spikes, and scales
Working with the two new mummies, the researchers reconstructed a complete, fleshy profile of Edmontosaurus annectens.
“The two specimens complemented each other beautifully,” Sereno said. “For the first time, we could see the whole profile rather than scattered patches.”
They identified a continuous midline feature that began as a fleshy crest along the neck and trunk and transitioned over the hips into a single row of spikes running down the tail — each spike positioned over a single vertebra and fitted to each other.
The lower body and tail had the largest polygonal scales, although most were tiny pebble-like scales just 1–4 millimeters across, surprisingly small for a dinosaur growing to over 40 feet in length. Wrinkles preserved over the ribcage suggest the skin of this duckbill was thin.
A hoofed dinosaur
The hind feet of the larger mummy held the biggest surprise: hooves. The tip of each of the three hind toes were encased in a wedge-shaped hoof with a flat bottom like that of a horse. The team used CT scans of the mummy’s feet and 3D images of the best-preserved duckbill footprint from the same time period, fitting the former into the latter. Using information from both sources, they accurately reconstructed the appearance of the hind foot. Unlike the forefoot that touches the ground only with its hooves, the hind feet have a fleshy heel pad behind the hooves.
“There are so many amazing ‘firsts’ preserved in these duck-billed mummies — the earliest hooves documented in a land vertebrate, the first confirmed hooved reptile, and the first hooved four-legged animal with different forelimb and hindlimb posture,” Sereno said.
Shaping the future of the field
Beyond the anatomical revelations, the study offers a toolkit for future research on dinosaur soft anatomy: new preparation methods, a clear lexicon for soft structures and scales, an imaging workflow from fossil to a flesh model, and a recipe for generating a dinosaur mummy. More than standalone discoveries, the team’s mummy research offers a new model for dinosaur mummification involving clay templating to test on future finds.
The authors also point to what comes next: targeted searches for similarly preserved specimens in the same Wyoming strata and elsewhere; biomechanical models that now have reliable external boundaries; and companion analyses that probe when and where clay templating takes hold.
“This may be the single best paper I’ve released,” Sereno said. “From field to lab to 3D reconstructions along with a suite of useful terms defined, it’s a tour de force, and it tells a coherent story about how these remarkable fossils come to be and what we can learn from them.”
Journal
Science
Article Publication Date
23-Oct-2025
THE HADROSAURUS IS THE OFFICIAL DINOSAUR OF ALBERTA
Mummy zone drone footage [VIDEO]
Drone footage of the “mummy zone” in east-central Wyoming, where a half a dozen dinosaur mummies have been discovered including the two new mummies of the duck-billed dinosaur Edmontosaurus annectens.
Credit
University of Chicago Fossil Lab
Scene painting some 66 million years ago showing the duck-billed dinosaur as it appeared in life based on mummies discovered in east-central Wyoming which document its scaly skin and hooves. It had a fleshy crest over neck and trunk, a fleshy spike row over hips and tail and hooves capping the toes of the hind feet. (artwork by Dani Navarro)
Credit
Artwork by Dani Navarro
Mummy of the juvenile duck-billed dinosaur Edmontosaurus annectens with fossil preparator Tyler Keillor of the University of Chicago. The dinosaur mummy nicknamed “Ed Jr.,” was covered by floodwaters some 66 million years ago, preserving its fossilized skeleton and, in a thin clay layer, large areas of scaly, wrinkled skin and a tall fleshy crest over its back.
Credit
Photograph courtesy of University of Chicago Fossil Lab
The scaly skin of a crest over the back of the juvenile duck-billed dinosaur Edmontosaurus annectens, nicknamed “Ed Jr.” The juvenile duckbill, estimated to be about two years old at the time it died, is the only juvenile dinosaur mummy ever discovered.
Credit
Photograph courtesy of Tyler Keillor/Fossil Lab
The hoof, preserved in section as a very thin clay layer, caps the end toe bone in the foot of an adult mummy of the adult duck-billed dinosaur Edmontosaurus annectens.
Credit
Photograph courtesy of Tyler Keillor/UChicago Fossil Lab
Professor Paul Sereno of the University of Chicago marvels at the preserved hooves on the foot of an adult mummy of the duck-billed dinosaur Edmontosaurus annectens nicknamed “Ed Sr.”.
Credit
Photo by Kieth Ladzinski


