An extraordinary trace fossil probably a Tyrannosaurus rex trackway has been discovered in North Dakota. It provides a rare glimpse of a giant theropod walking through the Late Cretaceous landscape. The four huge footprints date to approximately 66.5 million years ago (Maastrichtian faunal stage).

Scientists from the Denver Museum of Nature & Science and Liverpool John Moores University studied the trackway. Their research has been published in the Journal of Vertebrate Paleontology.

An aerial view of the tridactyl trackway excavation. Picture credit: Kent Hups.

Picture credit: Kent Hups

Dinosaur tracks, particularly those associated with large theropods are extremely rare within the Hell Creek Formation. The trackway exceeds seven metres in length and consists of four large three-toed prints. It represents two left and two right footprints – a walking sequence. Each print is around a metre in length. The size and tridactyl nature of the tracks is consistent with an adult T. rex trackmaker. Moreover, numerous Tyrannosaurus rex bones have been found in this locality. These body fossil finds support the hypothesis that these tracks were indeed produced by an adult T. rex.

An isolated tridactyl track from the probable Tyrannosaurus rex trackway. Picture credit: Tyler Lyson.

Picture credit: Tyler Lyson

Studying Theropod Locomotion

Stride lengths and foot dimensions indicate a walking speed in the region of 1.5 to 2 metres per second. This is roughly comparable to a brisk human walking pace. The velocity estimate is consistent with the walking speeds calculated for other large theropod tracks.

Each track in the sequence is preserved as fine-grained sandstone concretions cemented with calcium carbonate. They nucleated around footprint depressions and the resultant footprint casts are harder than the surrounding rock. However, the surfaces of the footprint casts are heavily fractured and retain little anatomical detail beyond size and number of digits. Nevertheless, this is an important data point that marks the first report of a trackway that is likely attributable to an adult Tyrannosaurus rex.

A reconstruction of an adult Tyrannosaurus rex leaving tracks in the soft substrate. Picture credit: Andrey Atuchin.

Picture credit: Andrey Atuchin

Is This a Tyrannosaurus rex Trackway?

The researchers identified an adult Tyrannosaurus rex as the most likely trackmaker. They based this conclusion on several lines of evidence. These include the enormous size of the prints and the relatively narrow toes. Furthermore, T. rex fossils are abundant in the surrounding area.

Individual footprints have previously been attributed to adult T. rex. However, this discovery represents the first described sequence of tracks probably made by an adult tyrannosaur.

For example, back in 2007 we wrote about the discovery of a single, large theropod print in the Hell Creek Formation.  It could represent a T. rex footprint.

To read about this trace fossil discovery: The Mystery Tyrannosaur Footprint.

Co-author of the study Tyler Lyson (Denver Museum of Nature & Science) commented:

“Bones tell us an enormous amount about these animals, but footprints capture a moment of behaviour. With a trackway, we can actually follow an animal as it moved across the landscape. That is incredibly rare for T. rex.”

Co-author of the scientific paper Tyler Lyson next to one of the tridactyl tracks. Picture credit: Natalie Toth.

Picture credit: Natalie Toth

Following the Footprints of a Theropod Dinosaur

Whilst the weathered nature of the tracks hinders extensive study, the researchers propose that the trackway records a stride length of approximately four metres. The heavily weathered footprints prevent a more detailed assessment.

The trackway was discovered in 2025 on federal land administered by the U.S. Forest Service near Marmarth, North Dakota. The team used high-resolution 3D surface scanning to document each footprint and the full trackway. The resulting digital models allow scientists to examine the tracks in detail and create physical 3D reproductions.

A computer-generated relief map of one of the large tridactyl prints. Picture credit: Antoine Bercovici.

Picture credit: Antoine Bercovici

Peter Falkingham, a professor of palaeobiology at Liverpool John Moores University and a dinosaur track expert, was lead author of the study, despite never having seen the tracks in person.

Professor Falkingham explained:

“The technology we’re able to apply in the digital age means my colleagues could scan the tracks in the field and then send the 3D information over to me to visualise on my computer and in VR, enabling me to take as close a look as they did in person.”

Fossilised bones reveal the anatomy of extinct animals. In contrast, footprints preserve fleeting moments in their lives. These remarkable tracks may therefore record several seconds in the life of an adult Tyrannosaurus rex some 66.5 million years ago.

Everything Dinosaur acknowledges the assistance of a media release from the Denver Museum of Nature & Science in the compilation of this article.

The scientific paper: “A large tridactyl trackway from the Upper Cretaceous Hell Creek Formation of North Dakota, likely attributable to an adult Tyrannosaurus rex” by Peter L. Falkingham, Kent M. Hups, Evan M. Tamez-Galvan, Antoine D. Bercovici and Tyler R. Lyson published in the Journal of Vertebrate Paleontology.

The Everything Dinosaur website: Models of Tyrannosaurs and Other Dinosaurs.

A remarkable new species of Jurassic squid-like animal has been described from Wyoming. The bizarre belemnite, named Wyoteuthis linsterorum, lived around 160 million years ago (Oxfordian faunal stage). Furthermore, it had an extraordinarily thick and barrel-shaped internal skeleton.

An international research team studied two exceptionally rare fossils from the famous Sundance Formation. The scientists concluded that they represented a new genus and species of prehistoric cephalopod.

The Remarkable Wyoteuthis linsterorum

Belemnites were distant relatives of living squid and cuttlefish. Their fossils are extremely common in some marine deposits. Typically, the most frequently preserved part is a hard, bullet-shaped internal structure called the rostrum or guard.

Millions of belemnite fossils occur in Wyoming’s Sundance Formation. These rocks represent an ancient inland sea that once covered parts of western North America. However, Wyoteuthis linsterorum was very different from the more familiar belemnites found in these rocks. Most complete Wyoming belemnite rostra measure around 5–10 cm long. They are generally no more than 1–2 cm in diameter. In contrast, the rostrum of Wyoteuthis reached approximately 10 cm long but was around 6 cm thick at its broadest point.

Wyoteuthis linsterorum paratype with common Pachyteuthis belemnite guard provided for size comparison. Picture credit: Courtesy of Jessica Lippincott.

Picture credit: Courtesy of Jessica Lippincott

Consequently, the researchers describe it as the thickest belemnite rostrum known to science.

The complete animal, including its arms, could have measured approximately 60 cm long. Therefore, this was a surprisingly substantial cephalopod swimming in the Jurassic Sundance Sea.

Honouring the Linster Family

The genus name Wyoteuthis essentially means “Wyoming squid”. Meanwhile, the species name honours Cliff Linster and the Linster family. Cliff discovered one of the fossil specimens northwest of Ten Sleep, Wyoming. He subsequently donated it to the Wyoming Dinosaur Center in 2019 so that scientists could study it.

Cliff Linster, the discoverer of one of the Wyoteuthis linsterorum specimens, hunting for fossils. Picture credit: The Linster Family.

Picture credit: The Linster Family

The Linster family has a long association with fossil hunting. Indeed, Cliff’s son Wes discovered the fossil material that ultimately led to the naming of the dinosaur Bambiraptor.

Wes Linster recalled a childhood dominated by family fossil-hunting adventures:

“Our whole family has taken vacations into the Badlands looking for one treasure or another. The fun was in the search.”

Sadly, Cliff Linster passed away in June. However, he knew that scientists were studying his unusual discovery.

Speaking about the decision to honour the family, Wes added:

“It may not be a new species of T. rex, but I’m honoured to have an extinct giant squid bear our family name.”

He explained that his father remained passionate about searching for fossils throughout his life. Indeed, Cliff had been visiting the ridge where the specimen was discovered shortly before his death.

Dr Dean Lomax Remembers Cliff Linster

British palaeontologist and study co-author Dr Dean Lomax knew Cliff and Sandy Linster personally. Dean first met them in 2009. As a teenager, he spent time excavating a dinosaur bonebed on their property in northern Montana.

Dr Lomax commented:

“I have fond memories of that dig, listening to Cliff share his passion for fossils, including this belemnite. I’m honoured to help name this fossil after Cliff.”

Dr Lomax added:

“It’s bittersweet that he didn’t get to see it published, but it’s wonderful that we can immortalise him and his family name in the history of palaeontology.”

Cliff Linster looking for fossils northwest of the town of Ten Sleep (Wyoming) discovered a super-sized belemnite guard. Picture credit: The Linster Family.

Picture credit: The Linster Family

Dr Lomax is an 1851 Research Fellow at the University of Bristol and an Honorary Research Fellow at the University of Manchester.

A Belemnite That “Stuck Out Like a Sore Thumb”

Wyoming palaeontologist and study co-author Bill Wahl helped bring the research team together. He immediately recognised that the extraordinary fossil deserved further investigation. According to the media release, the strange belemnite “stuck out like a sore thumb”.

The specimen was brought to the attention of belemnite specialist Alexey Ippolitov of Victoria University of Wellington (New Zealand).

The researcher was deeply surprised by its unusual morphology. After more than two centuries of palaeontological discoveries, finding something so different within a well-studied fossil group is exceptional. The scientists used computed tomography (CT) scanning to examine the fossil’s internal structure. Crucially, this technique enabled them to investigate the specimen without damaging it.

Their research placed Wyoteuthis linsterorum within the family Megateuthididae. This group includes enormous belemnites known from older geological deposits. The discovery therefore provides important new evidence concerning the evolutionary history and persistence of these cephalopods.

Wyoteuthis linsterorum paratype (left) and holotype (right) with scale bar. Picture credit: Courtesy of Jessica Lippincott.

Picture credit: Courtesy of Jessica Lippincott

A Hunter of Other Jurassic Cephalopods?

Why Wyoteuthis evolved such a robust body remains uncertain. However, the researchers have proposed an intriguing possibility.

Alexey Ippolitov explained:

“A possible explanation is that their relatively large size gave them an advantage when hunting co-occurring smaller belemnites of the genus Pachyteuthis.”

He pointed out that living squid readily hunt other cephalopods. Some even prey upon members of their own species. Perhaps the unusually chunky Wyoteuthis was therefore an active predator of smaller belemnites sharing the Sundance Sea.

Illustration of Wyoteuthis linsterorum attacking a smaller belemnite (artwork by Jason Poole). Picture credit: Courtesy of Jessica Lippincott.

Picture credit: Courtesy of Jessica Lippincott (artwork by Jason Poole)

A Discovery Decades in the Making

The story actually began during the late 1990s. Dr Burkhard Pohl, founder of the Wyoming Dinosaur Center, discovered an unusually large belemnite in Hot Springs County.

The specimen remained unstudied in a collection drawer for many years. Around two decades later, Cliff Linster discovered another example. Eventually, researchers recognised that the two remarkable fossils represented something entirely new.

The fossils have now been formally described as Wyoteuthis linsterorum. Both specimens are displayed at the Wyoming Dinosaur Center in Thermopolis (Wyoming). The scientific paper has been published in the journal “Papers in Palaeontology”.

Photo of the research team including Dr Dean Lomax (left) Jessica Lippincott (centre), and Bill Wahl (right), at the Wyoming Dinosaur Center. Picture credit: Courtesy of Dr Dean Lomax.

Picture credit: Dr Dean Lomax

The Secret Lives of Prehistoric Animals

Dr Dean Lomax has spent considerable time exploring Wyoming’s remarkable fossil record. His work has included collecting fossils and excavating plesiosaurs and ichthyosaurs from the Sundance Formation.

Readers interested in how fossils reveal extraordinary details about prehistoric animals might also enjoy Dean’s recent book “The Secret Lives of Dinosaurs – Unearthing the Real Behaviors of Prehistoric Animals”.

The front cover of the recently published book “The Secret Lives of Dinosaurs – Unearthing the Real Behaviors of Prehistoric Animals” written by Dr Dean Lomax and illustrated by Bob Nicholls. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Illustrated by renowned palaeoartist Bob Nicholls, the book examines exceptional fossils that provide evidence about the lives and behaviours of long-extinct creatures. From predator-prey interactions to reproduction and prehistoric parenting, these remarkable fossils provide snapshots of events that occurred millions of years ago.

To read Everything Dinosaur’s review of this amazing book: “The Secret Lives of Dinosaurs” Reviewed.

We recommend this book. It can be purchased from Columbia University Press (search for Dr Dean Lomax): Columbia University Press.

The scientific paper: “The Big Chunky Belemnite’: A new relict megateuthidid from the Oxfordian (Late Jurassic) of Wyoming, USA, and its place in the evolutionary history of the group” by Ippolitov, A., Lippincott, J., Lomax, D. R., Wahl, W. 2026 published in Papers in Palaeontology.

Scientists have described an exceptional fossil of the long-necked, Triassic marine reptile Austronaga minuta. The specimen comes from China and is around 245 million years old. Remarkably, much of the animal’s digestive system has been preserved. The almost complete fossil provides scientists with an unprecedented view of the skeleton and internal anatomy of an archosauromorph. Researchers identified traces of several organs, including the stomach, liver and intestines.

Furthermore, the specimen represents the oldest known example of a largely complete reptile digestive system.

The study has been published in the scientific journal “Science Advances”.

An Early Marine Reptile Adapted to Life in Water

Named and described in 2023 (Wang, Lei and Li), from a single but beautifully preserved fossil specimen, Austronaga demonstrates significant adaptations to a fully marine existence.  For example, it had elongated, flipper-like forelimbs and a long tail that probably provided locomotion.  The rear limbs were reduced and probably played little role in locomotion.  The long neck helped it to catch prey. The teeth were sharp and interlocking, an adaptation for catching fish.  It measured around sixty centimetres in length.

This small reptile evolved not long after the end-Permian mass extinction event, which led to the extinction of around ninety-five percent of all life on Earth.  The discovery of Austronaga and other vertebrates from the Guanling Formation of China hints at the recovery of ecosystems following this dramatic chapter in our planet’s history.

The adaptations are particularly interesting because Austronaga taxonomically is close to the evolutionary lineage leading to archosaurs. This important reptile group includes crocodilians, pterosaurs and dinosaurs. Most marine reptiles displaying comparable swimming adaptations belonged to very different evolutionary lineages. Examples include ichthyosaurs and the much later Mosasauridae.

Co-author of the study, Dr Spiekman (Staatliches Museum für Naturkunde, Stuttgart), explained that archosaurs and their ancestors became extremely diverse on land. However, scientists had generally considered their adaptations for marine life to have been relatively limited. The discovery of Austronaga challenges this view. Early members of this evolutionary lineage developed sophisticated adaptations for living in the sea.

A life reconstruction of Austronaga minuta, a dinocephalosaurid archosauromorph marine reptile from the Middle Triassic of China. Picture credit: Gabriel Ugueto.

Picture credit: Gabriel Ugueto

A Remarkable Look Inside Austronaga minuta

The researchers noticed dark patches preserved between the fossil’s ribs. Further investigation revealed something extraordinary. These patches represented remnants of the digestive tract. The team used several analytical techniques to examine them. These included ultraviolet-light photography and mass spectrometry. As a result, scientists could confidently identify several internal organs. For example, a substantial, sack-like stomach occupied the front portion of the digestive system. Behind it lay the liver, which has a distinctive reddish colour in the fossil.

Remarkably, analysis of the liver revealed chemical traces associated with haemoglobin, the oxygen-carrying pigment found in blood. Behind the liver, the researchers identified a long and relatively simple intestinal tract. This structure represented the small and large intestines.

The evidence suggests that Austronaga possessed a comparatively unsophisticated digestive system.

Lead author of the research Dr Wei Wang of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, described the specimen as the oldest known reptile fossil preserving a largely complete digestive system.

Austronaga has been classified as the sister taxon to the coeval Dinocephalosaurus. Dinocephalosaurus also demonstrates some remarkable marine adaptations, including viviparity.

To read our blog post from 2017 about viviparity in Dinocephalosaurus: Dinocephalosaurus – The Only Known Viviparous Archosauromorph.

Constructing the long neck of Dinocephalosaurus: Dinocephalosaurus and the Year of the Dragon.

Clues to the Evolution of the Archosaur Digestive System

The fossil also provides evidence concerning digestive evolution. Living birds and crocodilians have a stomach divided into two specialised regions. However, Austronaga possessed only a single stomach chamber. This difference could provide an important evolutionary clue.

Co-author Dr Nick Fraser (National Museums Scotland) explained that early archosaur relatives probably possessed relatively simple stomachs. More complex arrangements subsequently evolved within the lineage. In addition, Austronaga had a comparatively short and uncomplicated digestive tract.

Interestingly, similar digestive systems occur in living reptiles that primarily eat fish. Therefore, its internal anatomy could provide additional evidence about the animal’s diet and ecology.

The stunning Austronaga minuta fossil specimen (IVPP V18579) from the Middle Triassic sediments of the Guanling Formation (Member II) Yunnan Province, China. Picture credit: Wei Wang.

Picture credit: Wei Wang

An Exceptional Middle Triassic Fossil from Yunnan Province

The discovery highlights how exceptional fossil preservation can reveal much more than bones. Soft tissues and internal organs normally decompose rapidly after death. Consequently, their preservation requires unusual environmental and chemical conditions. The Austronaga minuta specimen provides palaeontologists with a rare opportunity to examine both skeletal and internal anatomy in a Triassic marine reptile.

Researchers from several institutions collaborated on the study. These included the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and National Museums Scotland. Scientists from the State Museum of Natural History Stuttgart and the University of Hohenheim also participated. Furthermore, researchers from the Field Museum in Chicago, Luoping Biota National Geopark and the University of Zurich contributed.

The research forms part of a wider investigation into the early evolutionary history of modern reptile groups. Scientists are also examining their remarkable diversity in Triassic marine ecosystems.

Further discoveries could reveal more about the transition from terrestrial ancestors to highly specialised marine reptiles. The extraordinary Austronaga minuta fossil specimen is housed in Beijing.

Commenting on this recent study, Mike from Everything Dinosaur stated:

“Austronaga is one of the earliest stem archosauromorphs to evolve adaptations to a marine existence. Moreover, the remarkable fossil preserves the oldest known liver, stomach and intestines in the Reptilia. This discovery provides evidence of the transition from terrestrial to marine forms within the Triassic Archosauromorpha.”

Everything Dinosaur acknowledges the assistance of a media release from the Staatliches Museum für Naturkunde, Stuttgart in the compilation of this article. Permission to write an article about this research was granted by the Communications Department at the Staatliches Museum für Naturkunde, Stuttgart.

The scientific paper: “Highly aquatic marine stem archosaur with soft tissue preservation” by Wei Wang, Nicholas C. Fraser, Stephan N.F. Spiekman, Zhiheng Li, Olivier Rieppel, Hong Lei, Torsten M. Scheyer and Chun Li published in Science Advances.

For models of marine reptiles and other prehistoric animal figures: Marine Reptile Figures and Other Prehistoric Animal Models.

Scientists studying the newly described ichthyosaur Jabalisaurus tethyensis have gained a remarkable insight into its diet. A beautifully preserved fossil from southern Germany contains evidence of the animal’s last meals. In addition, the specimen preserves important details of the skeleton and body outline.

The fossil, specimen number JME-SOS-08369, was previously assigned to Aegirosaurus. However, researchers have now referred it to Jabalisaurus tethyensis. This specimen helps palaeontologists understand how this Late Jurassic ichthyosaur lived.

To read our recent article outlining the reassessment of Aegirosaurus fossil material to J. tethyensis: A New Species of Jabalisaurus Links Germany to Mexico.

Evidence of the Jabalisaurus Diet

JME-SOS-08369 preserves material interpreted as gastric contents. A small concentration of ganoid scales occurs in the anterior dorsal region of the body. The researchers interpret these remains as the partially digested remains of small ray-finned fishes. Therefore, scientists have direct evidence of the Jabalisaurus diet. This ichthyosaur consumed relatively small fishes.

The evidence also agrees with the anatomy of the skull. Jabalisaurus tethyensis had a slender skull armed with numerous relatively small teeth. Such jaws were well suited to catching small, active prey.

Jabalisaurus tethyensis, referred specimen JME-SOS-08369. A, overview photograph, box ‘G’ indicates the location of the preserved gastric contents, arrowhead indicates location of ischiopubis (not easily visible under natural light); B, close-up of skull; C, close-up of dentition. Picture credit: Maxwell, Neumann and Serafini.

Picture credit: Maxwell, Neumann and Serafini

The photograph of JME-SOS-08369 (above) shows the position of the preserved gastric contents. Close-up images also reveal details of the skull and dentition.

A Late Jurassic Hunter of Fish

The gastric contents provide rare direct evidence concerning the diet of a Late Jurassic ichthyosaur. Although ichthyosaurs have an extensive fossil record, direct evidence of what Late Jurassic species ate is surprisingly scarce. Other specimens have yielded fish remains and cephalopod hooklets. However, the gastric contents of JME-SOS-08369 add important information about the feeding ecology of Jabalisaurus tethyensis.

The researchers conclude that its diet included small ganoid-scaled actinopterygian fishes. These are ray-finned fishes characterised by distinctive scales covered with a hard, enamel-like substance.

A new life reconstruction (below) depicts Jabalisaurus tethyensis swimming close to the surface and pursuing halecomorph fishes. These are common Late Jurassic ray-finned fishes.

Artistic reconstruction of Jabalisaurus tethyensis, depicted in the water column close to the surface while pursuing halecomorph fishes. Picture credit: Giovanni Serafini.

Picture credit: Giovanni Serafini

The illustration provides a glimpse of this small ichthyosaur hunting in the warm waters associated with the ancient Tethys Ocean.

Examining the Jabalisaurus Skeleton

JME-SOS-08369 provides other important anatomical information. For example, the forelimbs preserve polygonal phalanges. These small bones formed part of the animal’s paddle-like limbs.

Both the right and left forelimbs preserve this distinctive polygonal morphology. Furthermore, ultraviolet light helped the researchers examine the ischiopubis, part of the pelvic region that is difficult to distinguish under natural light.

Jabalisaurus tethyensis, referred specimen JME-SOS-08369. A, phalanges from the right forelimb, with arrow indicating polygonal morphology; B, phalanges from the left forelimb, also showing polygonal form. C, ischiopubis, photographed under UV-light. Picture credit: Maxwell, Neumann and Serafini.

Picture credit: Maxwell, Neumann and Serafini

These anatomical characteristics helped the researchers compare JME-SOS-08369 with other Late Jurassic ichthyosaurs.

An Exceptionally Important Ichthyosaur Fossil

This specimen has already played an important role in studies of ichthyosaur soft tissues. Previous research examined its exceptionally complete body outline. The fossil even contributed to research suggesting that ichthyosaurs possessed an insulating layer of blubber. Now, JME-SOS-08369 has helped scientists investigate the anatomy, taxonomy and feeding behaviour of Jabalisaurus tethyensis.

To read more about this research: Ichthyosaurus Had Blubber According to New Research.

The fossil demonstrates how much information can be preserved in the fine-grained deposits of southern Germany. Bones reveal the animal’s anatomy, while traces of soft tissues help reconstruct its body. Remarkably, the contents of its digestive system provide evidence of what it ate.

Learning More About Jabalisaurus tethyensis

Everything Dinosaur recently reported the formal description of Jabalisaurus tethyensis (see link in this article). Fossils assigned to this species had previously been included within Aegirosaurus. Their reassessment has increased the known diversity of Late Jurassic ichthyosaurs from the German Plattenkalk deposits.

The discovery of Jabalisaurus in Europe is significant for another reason. Before this research, the genus was known only from Mexico. Its presence on both sides of the ancient Tethys region supports the idea of a distinctive Peri-Tethyan ichthyosaur fauna.

However, JME-SOS-08369 tells a more intimate story. Around 149 million years ago, this marine reptile hunted small fishes in a tropical sea. Thanks to exceptional fossil preservation, evidence of its prey has survived to the present day.

Everything Dinosaur acknowledges the assistance of one of the study’s authors in the compilation of this article.

The scientific paper: “Late Jurassic ichthyosaurs from southern Germany” by Erin E. Maxwell, Jule Neumann and Giovanni Serafini published in Palaeontologia Electronica.

The award-winning Everything Dinosaur website: Models of Ichthyosaurs and Other Marine Reptiles.

Palaeontologists have named a new species of theropod dinosaur from New Mexico. The dinosaur, Dinevenator robustus, lived around 73 million years ago (Campanian faunal stage of the Late Cretaceous). Researchers identified the dinosaur from a fossil skull bone (a frontal) found in north-western New Mexico. It represents a new genus and species of troodontid.

Troodontids were lightly built, theropod dinosaurs closely related to birds. They also possessed relatively large brains compared to many other dinosaurs. The discovery of Dinevenator robustus provides new information about troodontid diversity in Late Cretaceous North America.

The research was undertaken by Dr Steven E. Jasinski and Dr Robert Sullivan. Their study was published in the scientific journal “Fossil Studies” earlier this month.

Dinevenator robustus life reconstruction. The newly described, large troodontid has caught a mammal. Whilst rare, the De-na-zin Member of the Kirtland Formation has recorded fragmentary remains of metatherian mammals. Picture credit: Sergey Krasovskiy.

Picture credit: Sergey Krasovskiy

A Large Troodontid Theropod Dinosaur

Although scientists have found very little fossil material, Dinevenator (pronounced Din-ee-ven-nay-tor), may have been surprisingly large for a troodontid. Comparisons with the skull bones of related dinosaurs suggest a body length of around 2.4 to 3 metres. Researchers estimate that it weighed approximately 68 to 136 kilograms. Therefore, Dinevenator robustus ranks amongst the larger troodontids currently known.

Palaeontologist Dr Steven Jaskinski, from the New Mexico Museum of Natural History and Science (NMMNHS) and corresponding author of the study commented:

“This really helps us get a clearer picture of the diversity in this family of dinosaurs during the Late Cretaceous in North America, and it adds to our knowledge of dinosaurs that once roamed New Mexico.”

The discovery of this new dinosaur helps clarify troodontid diversity during the Late Cretaceous. Furthermore, it increases our knowledge of New Mexico’s dinosaur biota.

Dinosaurs of the Kirtland Formation

Dinevenator robustus lived on a subtropical floodplain approximately 73 million years ago. It shared this environment with a remarkable variety of dinosaurs. For example, the crested lambeosaurine hadrosaur Parasaurolophus tubicen inhabited the same ecosystem. Armoured ankylosaurs and horned ceratopsians also roamed the region.

To read a recent blog post about the discovery of new lambeosaurine from Alberta, Canada: A New Lambeosaurine Hadrosaur from Alberta.

In addition, dome-headed pachycephalosaurs lived alongside agile dromaeosaurids. Huge tyrannosaurs represented some of the ecosystem’s largest predators. Consequently, the discovery adds another dinosaur to an already diverse Late Cretaceous fauna.

The left frontal of Dinevenator robustus (holotype) specimen number SMP VP-1955 shown in dorsal view (left) and ventral view (right). Picture credit: Sullivan (New Mexico Museum of Natural History and Science).

Picture credit: Sullivan (New Mexico Museum of Natural History and Science)

A Fossil Discovered in 2005

The fossil that eventually led to the new dinosaur’s identification was discovered more than twenty years ago. Dr Robert Sullivan found the specimen during the summer of 2005. He was collecting Cretaceous fossils in New Mexico’s San Juan Basin. The fossil came from the De-na-zin Member of the Kirtland Formation. Sullivan had discovered part of the skull of a relatively small theropod dinosaur. Initially, researchers thought the bone belonged to a dromaeosaur.

Dromaeosaurids include famous dinosaurs such as Velociraptor. However, subsequent research demonstrated that the specimen belonged to a troodontid.

Scientists have recently learned much more about North American troodontids. For instance, studies of Albertavenator from Alberta provided important comparative information. Research into Xenovenator from northern Mexico also helped scientists reassess the New Mexico fossil.

A phylogenetic analysis was conducted on a modified dataset, recovering Dinevenator robustus in a clade of robust troodontins (Troodontini) as the basal-most taxon and as the sister taxon to (Albertavenator curriei and Xenovenator espinosai). The recognition of a distinct, large, robust-skulled troodontid also increases the known diversity of theropod dinosaurs from the southern United States and provides further evidence for dinosaurs that are unique to the Kirtlandian faunas of New Mexico during the Late Cretaceous.

To read Everything Dinosaur’s blog post from 2017 about the discovery of Albertavenator: Albertavenator – Something to Get Your Teeth into.

Identifying Dinevenator robustus

Scientists have named this dinosaur from just one fossil skull bone (frontal). This bone forms part of the upper surface of the skull. Despite the limited material, the fossil preserves distinctive anatomical characteristics. Most notably, the frontal is thicker than equivalent bones in many related troodontids. Researchers also identified other features that distinguish the specimen.

These anatomical differences supported the establishment of a new genus and species. The fossil currently resides at the State Museum of Pennsylvania. However, plans are being made to transfer it to the New Mexico Museum of Natural History and Science.

Understanding Troodontid Diversity

The discovery of D. robustus increases the known dinosaur diversity of New Mexico. More importantly, it provides another piece of the complex troodontid evolutionary puzzle.

Palaeontologists continue to reassess fragmentary fossils as new discoveries provide additional comparative material. As a result, specimens collected decades ago can reveal entirely new dinosaur species.

Dr Anthony Fiorillo, Executive Director of the New Mexico Museum of Natural History and Science, highlighted this dynamic process stating:

“This new work illustrates the dynamic nature of dinosaur studies as we continue to test what we think we know. Furthermore, it demonstrates that New Mexico clearly has a prominent place in those global conversations.”

Everything Dinosaur acknowledges the assistance of a media release from the New Mexico Museum of Natural History and Science in the compilation of this article.

The scientific paper: “Dinevenator, a New Genus of Troodontid Dinosaur from the Late Cretaceous of New Mexico” by Steven E. Jasinski and Robert M. Sullivan published in Fossil Studies.

The award-winning Everything Dinosaur website: Models of Troodontids and Other Dinosaurs.