Fossils from embryo to adult suggest how enigmatic, bird-like troodontid dinosaur grew

Study of Montana hip and leg bone fossils might support designation as primary example of Troodon formosus

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Geologic context and preserved material for Troodon described here. Chronologic placement of Two Medicine Troodon specimens after Rogers et al. (A). Graphical representation of preserved pelvic and hindlimb material, with silhouettes reflecting relative size of the individuals preserved (B). Abbreviation: Ma, millions of years ago. Troodon silhouettes made with reference to work by Scott Hartman (https://creativecommons.org/licenses/by-nc-sa/3.0/). 

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Credit: Varricchio, Caldwell et al., 2026, PLOS One, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

Analysis of fossilized remains from dinosaurs known as troodontids reveals how one species’ hip and leg bones may have developed over its lifespan, from embryo to adult—with potential implications for resolving longstanding taxonomic challenges. David Varricchio of Montana State University, US, and Heath Caldwell of North Carolina State University, US, present their findings in the open access journal PLOS One on September 9, 2026.

Troodontids were a family of bird-like dinosaurs with long legs, large brains and eyes, and feathers. Fossils indicate they lived in North America in the late Cretaceous period. For decades, a limited amount of fossilized remains hampered understanding of troodontids, but recent new fossil discoveries are advancing the field.

To help fill in the blanks, Varricchio and Caldwell analyzed pelvic and hindlimb fossils collected in western Montana, US, in an area thought to have been a coastal plain when the dinosaurs lived there between about 75 to 78 million years ago. The fossils are thought to represent individuals of the species Troodon formosus at various stages of its lifespan, from embryo to adult, enabling the researchers to reconstruct how a typical individual’s hip and leg bones may have developed over time.

The analysis suggests that, during its lifetime, T. formosus underwent specific changes in the texture, shape, and relative proportions of different parts of these bones. For instance, the ratio of femur to tibia length was higher in adult fossils than in juveniles. These changes appear to have occurred at consistent growth stages, suggesting a limited influence of environmental factors. The analysis also suggests that adults varied distinctly in size and, in line with prior research, suggests foot problems may have been common in the species.

The researchers say these findings support designation of a specific subset of the remains—a collection of pelvic and hindlimb fossils from juveniles and adults—as the primary representative, or “type specimen,” of T. formosus. This would replace a single tooth that has been the type specimen for decades and could help resolve longstanding concerns about the validity of the Troodon genus. The authors note that this assignment would depend on a decision that is currently pending from the International Commission of Zoological Nomenclature.

Further research could help deepen understanding of the lifestyle of Troodons, such as how they walked or ran.

The authors add: “In this study, we investigated the morphology of the hindlimb and pelvic skeleton for the bird-like dinosaur Troodon formosus from a relatively large sample of embryonic to skeletally mature individuals. Analysis of these bones provided an unprecedented opportunity for understanding the biology of a historically enigmatic group of animals and will serve as a valuable resource for paleontologists for years to come.”

 

 

The "killing claw" (pedal ungual II) from Troodon from a juvenile (top) and adult (bottom).

 

Embryonic pelvis and femur of Troodon formosus. Embryonic pelvic elements for Troodon (MOR 246−11) in lateral view. Abbreviations: fe, femur; il, ilium; isp, ischiadic peduncle; pp, pubic peduncle; ps, pubis.

Credit

Varricchio, Caldwell, 2026, PLOS One, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

  

Reconstruction of Troodon formosus by Clarissa Koos (hi-resolution image available upon request from article authors).

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Clarissa Koos, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

Author interview: https://plos.io/4yCXHXB

In your coverage, please use this URL to provide access to the freely available article in PLOS One: https://plos.io/4wRUe65

Citation: Varricchio DJ, Caldwell HR (2026) Pelvic and hindlimb osteology and ontogeny of a troodontid from the upper member of the Two Medicine Formation (Cretaceous) of Montana. PLoS One 21(9): e0356249. https://doi.org/10.1371/journal.pone.0356249

Author countries: USA.

Funding: The author(s) received no specific funding for this work.

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Journal

PLOS One

DOI

10.1371/journal.pone.0356249 

Method of Research

Observational study

Subject of Research

Animals

Article Title

Pelvic and hindlimb osteology and ontogeny of a troodontid from the upper member of the Two Medicine Formation (Cretaceous) of Montana

Article Publication Date

9-Sep-2026

 

Ice Age origins of one of humanity’s oldest drug habits

Griffith University

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The CPL-2a skeleton in the trench.

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Credit: Fakhri

A team of Griffith University archaeologists has uncovered evidence that humans were using mind-altering substances much earlier in time than previously supposed.

Led by Professor Adam Brumm from Griffith’s Australian Research Centre for Human Evolution (ARCHE), and involving ARCHE colleagues Associate Professors Carney Matheson and Michelle Langley, the team combined biochemical and archaeological evidence to trace the prehistoric roots of one of the world’s most popular addictive stimulants, “betel nut”, an ancient drug used throughout much of the Asia-Pacific region.

The group’s research, conducted in collaboration with Indonesian archaeologists from Makassar’s University of Hasanuddin and the National Research and Innovation Agency (BRIN), shows that the use of betel nut as a drug emerged among some Indonesian communities by up to 25,000 years ago, moving beyond the previously suggested Neolithic or Bronze Age (~3500 years ago) start times.

Current theories on the earliest history of drug-taking 

Presently, it is thought the world’s first traditions of psychoactive drug use arose after the Neolithic advent of farming, beginning with the innovation of fermented alcoholic drinks (barley beer) about 13,000 years ago in Israel.

“However, this theory fails to account for the possibility that very ancient drug-taking lies at the roots of our most commonly used psychoactive substances,” Professor Brumm said.

Professor Brumm’s investigation focused on the origins of betel nut usage, a near-universal tradition among hundreds of millions of people between India and the South Pacific (about one in 10 of the modern global population).

Consuming betel nut induces a sense of mild euphoria and heightened alertness, among other effects.

“Although poorly known in western societies, it is the world’s fourth most widely used psychoactive substance, after alcohol, caffeine and nicotine,” Professor Brumm said.

Modern users take the betel drug by mixing a processed seed of the Areca catechu palm (the betel “nut”) with slaked lime – commonly made by grinding burnt shells into a fine powder – and other ingredients to form a “quid”, which is then chewed to get high.

“Slaked lime is an essential ingredient because it causes a chemical reaction that releases the nut’s psychoactive compounds into the bloodstream more rapidly,” Professor Brumm said.

The early history of this drug use practice had remained uncertain, largely because areca seeds were rarely preserved at archaeological sites.

Discovery reveals prehistoric drug use 

In the new study, published in Science Advances, the Griffith team reports the discovery of extremely rare skeletal remains of two early human foragers from the Indonesian island of Sulawesi, one dating to 25,000-16,000 years ago, the other to 7600-6300 years ago.

Both hunter-gatherers display a highly unusual dental-wear pattern (deep, rounded tooth grooves), a novel bioarchaeological marker the researchers established was caused by a previously unknown drug-use behaviour: habitual sucking of whole betel nuts.

Previous reports suggested the main neuroactive alkaloid in betel nut (arecoline) was released by chewing the processed nut in a prepared quid with slaked lime, with the latter converting arecoline into a free base form, thereby increasing its bioavailability.

"But our team conducted experiments in which we soaked betel nuts in artificial saliva and tested the resultant broths against a panel of cloned human receptors expressed in frog egg cells, including specialised proteins that act as molecular switches, regulating neural activity,” Professor Brumm said.

“This showed that just sucking on intact betel nuts will release arecoline in sufficient amounts to have a physiological effect, altering brain function.”

In addition, biochemical analyses carried out by Associate Professor Carney Matheson detected the presence of arecoline in the dental tissues of the foragers, providing strong evidence for betel nut ingestion.

Taken together, the findings suggest early foragers in Sulawesi engaged in an ancient and longstanding practice of habitually sucking betel nuts, resulting in dramatic alterations to their teeth.

Bad medicine 

While the psychoactive “high” of sucking betel nuts may have been milder than modern quid chewing, the team suggested the habit was significant enough to cause severe periodontal disease.

Ancient foragers on this island generally had bad teeth, and arecoline is a natural analgesic (“painkiller”), so the team suspected one reason for betel nut-sucking was to alleviate the discomfort of toothache.

“Over time, however, sucking these hard, abrasive seeds wore down the foragers’ teeth so badly that in some cases the inner pulp chamber became completely exposed – this would have been extremely painful, caused difficulty eating, and greatly increased the rate of chronic tooth infection,” Professor Brumm said.

“So while this habit may have been a remedy for toothache, years of prolonged nut-sucking eventually caused much worse dental health problems, creating a cycle of continued habitual use.”

Earliest evidence for drug use 

This finding marks a significant shift in our understanding of human drug history, as the practice of using betel nut can now be traced to the Late Pleistocene period.

“Emerging by up to 25,000 years ago in Sulawesi, thus long preceding the onset of agriculture, betel nut-sucking may be the earliest evidence for drug use anywhere in the world,” Professor Brumm said.

“By identifying the ancient practice underlying betel-nut chewing as we know it, the study implies that some modern drug-taking behaviours are deeply rooted in forager traditions.”

The findings also suggest habitual psychoactive substance use, and its associated health costs, were already present among hunter-gatherers tens of thousands of years before agriculture.

The study ‘Betel nut sucking is the earliest recorded evidence for the habitual use of a neuroactive plant drug’ has been published in Science Advances.

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Journal

Science Advances

DOI

10.1126/sciadv.aei1901 

 

Researchers find Asian elephants can resist impulsive behavior

Study provides new evidence of inhibitory control in elephants, offering insights into how they make decisions and adapt to changing environments.

The Graduate Center, CUNY

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An Asian elephant reaches for a treat during a study of inhibitory control conducted by researchers from the CUNY Graduate Center and Hunter College in Thailand.

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Credit: Sydney Hope

NEW YORK, September 9, 2026 — Researchers at the CUNY Graduate Center and Hunter College have found that Asian elephants can suppress impulsive behaviors and adjust their actions when circumstances change—a cognitive ability that may help explain the animals’ sophisticated problem-solving skills and social behavior.

The study, led by CUNY Graduate Center and Hunter College Psychology Professor Joshua Plotnik and postdoctoral researcher Sydney Hope, provides the first evidence that Asian elephants demonstrate this form of inhibitory control, an important component of decision-making and cognitive flexibility in humans and other animals. The research was published in PLOS ONE.

The findings could ultimately contribute to conservation strategies aimed at reducing conflict between elephants and people, particularly in areas of Asia where elephants and human communities increasingly share the same landscapes.

“We found that, when elephants were faced with a situation in which they needed to suppress an impulsive behavior, either the impulse to reach directly toward a food reward behind a transparent barrier or the impulse to continue using a previously effective technique, they were generally able to suppress the impulse,” Hope said. “This ability may be important for elephants' social interactions or for other aspects of cognition, such as problem-solving.”

Testing elephants’ ability to change course

The researchers tested 16 Asian elephants at the National Elephant Institute in Thailand. The elephants were presented with a transparent box containing fruit. Although the animals could see and smell the food through small holes in the box, they learned to resist the impulse to reach directly toward the reward. Instead, they used an opening on the side of the box to access the food.

The researchers then rotated the box, changing the location of the opening. Initially, the elephants reached toward the location where the opening had previously been. But they were able to suppress that impulse and adjust their behavior, quickly learning to use the opening in its new location.

The researchers found that older elephants took longer to adapt to the change. The result could point to age-related changes in cognitive flexibility, although the researchers caution that additional research is needed to determine whether the difference reflects cognitive decline.

The study adds to growing evidence that elephants possess sophisticated cognitive abilities. Inhibitory control—the ability to suppress an automatic or previously learned response in favor of a more appropriate action—is particularly important when animals must navigate changing or unpredictable environments.

From animal cognition to conservation

For nearly two decades, Plotnik has studied elephant intelligence, personality, and social behavior in Thailand, combining experimental research with conservation efforts. His work examines not only what elephants can do, but also how their cognitive abilities and individual behavioral differences may influence interactions with people.

Research from Plotnik and his collaborators has shown that elephants can recognize themselves in mirrors, console distressed companions, coordinate actions with partners, and solve novel problems. The team has also found that elephants living near human communities tend to be more willing to take risks and explore unfamiliar situations—behaviors that could help explain why some elephants repeatedly enter agricultural areas and come into conflict with people.

Understanding how elephants respond to obstacles, make decisions, and adapt to changing circumstances may help researchers better predict their behavior in human-dominated environments.

“The more we understand about how elephants think, make decisions about risk, and adapt to human-driven environmental change, the better we can predict ‘what they’ll do next’ and the better designed our strategies for human-elephant coexistence can be,” Plotnik said.

 

About the CUNY Graduate Center

The CUNY Graduate Center is a leader in public graduate education devoted to enhancing the public good through pioneering research, serious learning, and reasoned debate. The Graduate Center offers ambitious students nearly 50 doctoral and master’s programs of the highest caliber, taught by top faculty from throughout CUNY, the nation’s largest urban public university. Through its nearly 40 centers, institutes, initiatives, and the Advanced Science Research Center, the Graduate Center influences public policy and discourse and shapes innovation.

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Journal

PLOS One

DOI

10.1317/journal.pone.0356549 

Method of Research

Observational study

Subject of Research

Animals

Article Title

Asian elephants (Elephas maximus) demonstrate inhibitory control in a detour task

Article Publication Date

9-Sep-2026

Clever elephants can think before they act

Experiments show Asian elephants can resist an impulsive approach in favor of the more effective route to problem solving

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Experiment Setup. (A) An elephant enters the “over” opening to gain access to food in a familiarization trial. (B) An elephant enters the “under” opening to gain access to food (apple) in a test trial. Photos were cropped to remove extraneous background material; the left image was mirrored. Photos by Sangpa Dittakul.

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Credit: Hope et al., 2026, PLOS One, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

Asian elephants can resist their impulses and choose a more rational course of action, according to a study published September 9, 2026 in the open access journal PLOS One by Sydney Hope of Hunter College, New York and colleagues.

Inhibitory control – the ability to resist an impulse in favor of more effective behavior – is an important part of decision-making and cognitive flexibility in humans and other animals. This feature has been demonstrated in various species of birds and mammals, often using a detour test in which subjects must ignore an obvious but ineffective path to a treat in favor of an indirect route. In this study, Hope and colleagues document the first such demonstration with elephants.

Sixteen Asian elephants were tested at the National Elephant Institute in Thailand. When presented with a transparent box with small holes through which they could see and smell fruit inside, the elephants consistently were able to resist the temptation to try to reach directly for the food and instead used an opening on the side of the box as they had been taught earlier. When the box was later rotated, the elephants at first succumbed to the impulse to reach for the previous position of the opening before quickly correcting their behavior. This adjustment was slower in older individuals, with one possible explanation being cognitive decline with age, although the researchers note that more study will be needed to confirm this.

Overall, these trials demonstrate the ability of elephants to resist impulsive but ineffective action in favor of indirect effective behaviors, even when it requires them to adjust a previously effective approach. The authors note that this inhibitory control might be a key part of elephants’ famed problem-solving and socializing skills. Understanding how elephants respond to barriers might also help with the development of more effective mitigation strategies to avoid human-elephant conflict.

The authors add: “We found that, when elephants were faced with a situation where they needed to suppress an impulsive behavior—either the impulse to reach directly toward a food reward behind a transparent and perforated barrier, or the impulse to continue using a previously (but no longer) effective technique—they were generally able to suppress the impulse. This ability may be important for elephants' social interactions or for other aspects of cognition, such as problem-solving.”

 

 

In your coverage, please use this URL to provide access to the freely available article in PLOS One: https://plos.io/4d4YaZZ

Citation: Hope SF, Jacobson SL, Dittakul S, Schmitt G, Pla-ard M, Yindee M, et al. (2026) Asian elephants (Elephas maximus) demonstrate inhibitory control in a detour task. PLoS One 21(9): e0356549. https://doi.org/10.1371/journal.pone.0356549

Author countries: USA, Thailand.

Funding: This research was funded in whole or in part by Templeton World Charity Foundation (funder DOI 501100011730, grant TWCF-2022-30066 to J.M.P.; https://doi.org/10.54224/30066). This research was also supported by Hunter College through the Research Foundation of the City University of New York. G.S. received funding support from the Animal Behavior and Conservation Program at Hunter College. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Asian elephants (Elephas maximus) demonstrate inhibitory control in a detour task [VIDEO] 

Familiarization Trial. An elephant (ThongChai) interacting with the familiarization (opaque) box. The box is in the “under” orientation and the reward is half of an apple. Video was taken on a Sony FDR-AX100 camcorder.

Asian elephants (Elephas maximus) demonstrate inhibitory control in a detour task [VIDEO]

Testing the Knowing/Acting Mismatch. An elephant (ThongChai) interacting with the test (transparent) box. The box is in the “under” orientation and the reward is half of an apple. Note that this is the same elephant as in Video 1, and this test trial occurred immediately after familiarization trials with the “under” orientation. Video was taken on a Sony FDR-AX100 camcorder.

Asian elephants (Elephas maximus) demonstrate inhibitory control in a detour task [VIDEO] 

Testing Inhibition of a Previously Learned Behavior. An elephant (Malini) interacting with the test box positioned in the “left” orientation. Note that this is her first interaction with the box in this orientation. This trial immediately follows four trials of the box in the “right” orientation. The reward is half of an apple. Video was taken on a Sony FDR-AX100 camcorder.

Credit

Hope et al., 2026, PLOS One, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

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Journal

PLOS One

DOI

10.1371/journal.pone.0356549 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

Asian elephants (Elephas maximus) demonstrate inhibitory control in a detour task

Article Publication Date

9-Sep-2026

COI Statement

J.M.P. is the president of Think Elephants International, Inc., a charity dedicated to elephant conservation. The authors have no other competing interests to declare that are relevant to the content of this article.