Dueling Dinosaurs

The Dueling Dinosaurs were unearthed in August 2006 on the Murray Ranch in Garfield County, Montana, within exposures of the Hell Creek Formation located southwest of Jordan. The discovery was made by Clayton Phipps, a rancher and commercial fossil collector sometimes known as the 'Dinosaur Cowboy,' along with fellow collectors Mark Eatman and Chad O'Connor. The fossil block, weighing approximately 30,000 pounds (roughly 13,600 kg), contained the articulated skeletons of a small-bodied tyrannosauroid and an adult Triceratops preserved in close physical contact, with evidence of injuries on both individuals suggestive of a lethal encounter.

The tyrannosaur specimen was nicknamed 'Bloody Mary' (later also referred to as 'Manteo'), while the Triceratops was less formally designated. Both skeletons exhibited an extraordinarily high degree of completeness and articulation. The fossil also preserved soft-tissue impressions, including scale patterns on the Triceratops skull—described as a first-of-its-kind find—and a patch of skin on the tyrannosaur's foot.

Following excavation, the Dueling Dinosaurs became mired in a protracted legal dispute over ownership. The fossils were found on land where surface rights were owned by ranchers Lige and Mary Ann Murray, while subsurface mineral rights were held by other parties. The legal question of whether fossils constitute 'minerals' under Montana law led to years of litigation. The U.S. Ninth Circuit Court of Appeals ultimately ruled in 2018 that fossils are not minerals, confirming that the surface landowners held rights to the specimen.

In 2013, the fossils were consigned to Bonhams auction house in New York City. They attracted a bid of $5.5 million but failed to reach the $6 million reserve price, leaving them unsold. The specimens subsequently remained in storage and inaccessible to the scientific community for years. In November 2020, the Friends of the North Carolina Museum of Natural Sciences announced that they had acquired the Dueling Dinosaurs for approximately $6 million through a combination of private donations and institutional fundraising. The fossils were transported to the museum in Raleigh, North Carolina, and formal accession occurred in 2024.

The North Carolina Museum of Natural Sciences opened its Dueling Dinosaurs exhibit to the public on April 27, 2024. The exhibit includes an open-access paleontology laboratory where visitors can observe the ongoing preparation and study of the fossils. Relief sculptures of the two skeletons at 50% scale serve as centerpieces, while the actual fossil elements are displayed in nearby preparation facilities. Admission to the museum and the Dueling Dinosaurs exhibit is free.

A companion study by Roberts et al. (2025), published as a bioRxiv preprint, established the first high-precision radioisotopic dates for the lower portion of the Hell Creek Formation at the Dueling Dinosaurs locality. Using CA-ID-TIMS U-Pb zircon geochronology on two newly discovered bentonite beds—the 'Dueling Bentonite' (66.929 ± 0.020 Ma) and the 'Ingomar Bentonite' (66.850 ± 0.026 Ma)—the team bracketed the fossil locality. Bayesian age-stratigraphic modelling placed the Dueling Dinosaurs at approximately 66.897 +0.023/−0.028 Ma, confirming that the specimen dates to the lower third of the Hell Creek Formation, approximately one million years before the end-Cretaceous extinction event at approximately 66.05 Ma. This was significant because no radioisotopic ages had previously been reported for this stratigraphic interval anywhere in the Hell Creek Formation.

Palynological analysis of the surrounding strata confirmed a late to latest Maastrichtian age. Magnetostratigraphic data from the measured sections were correlated with the broader Hell Creek Formation stratigraphic framework. The study further suggested that the base of the Hell Creek Formation in this area is approximately 67.1 Ma or older, offering new constraints on the total duration of the formation.

The scientific significance of the Dueling Dinosaurs peaked with the publication of a landmark paper in Nature on October 30, 2025, authored by Lindsay E. Zanno (North Carolina State University and NCSM) and James G. Napoli (Stony Brook University). The study focused on the tyrannosaur skeleton NCSM 40000 and provided multiple independent lines of evidence that the specimen represents a somatically mature individual of Nanotyrannus lancensis, not a juvenile Tyrannosaurus rex.

Key anatomical evidence included:

• Growth rings and bone histology: Analysis of growth rings in the long bones demonstrated that NCSM 40000 was approximately 20 years old at the time of death. The bone histology showed mature bone tissue with slowing growth, indicating near somatic maturity.
• Spinal fusion: The vertebral column exhibited fusing spinal sutures consistent with an adult individual.
• Tooth count: NCSM 40000 possessed more maxillary tooth positions than any known T. rex specimen, a feature that is developmentally fixed and does not change with ontogeny.
• Fewer tail vertebrae: The tail contained fewer caudal vertebrae than T. rex—a meristic trait determined early in embryonic development and invariant during growth.
• Proportionally larger forelimbs: The arms of NCSM 40000 were proportionally much larger relative to body size than those of T. rex at any ontogenetic stage.
• Distinct skull nerve and sinus patterns: The internal cranial anatomy, including nerve pathways and sinus configurations, followed developmental pathways distinct from those documented in T. rex.

The researchers argued that these features are 'ontogenetically invariant'—they are established early in development and do not change as an animal grows. For NCSM 40000 to be a juvenile T. rex, it would need to gain tail vertebrae, lose teeth, and drastically alter its cranial nerve pathways during growth—changes that are biologically impossible in vertebrates.

Phylogenetic analysis using a novel dataset placed Nanotyrannus outside Tyrannosauridae proper—more distantly related to T. rex than previously assumed. The study demonstrated that Nanotyrannus was an early-diverging tyrannosauroid rather than a close relative within the tyrannosaurid family.

In the course of their research, Zanno and Napoli examined over 200 tyrannosaur fossils. They identified that one previously known skeleton, formerly classified as a juvenile T. rex, differed subtly from NCSM 40000. This specimen was designated as the holotype of a new species, Nanotyrannus lethaeus sp. nov. The species epithet 'lethaeus' references the River Lethe from Greek mythology—the river of forgetfulness—alluding to how the species had been overlooked and misidentified for decades.

The genus Nanotyrannus thus contains two recognized species as of the 2025 study: N. lancensis (based on the Cleveland holotype skull CMNH 7541, originally collected in 1942 and described by Gilmore in 1946, later reassigned by Bakker, Williams, and Currie in 1988) and N. lethaeus (Zanno & Napoli, 2025). NCSM 40000 was referred to N. lancensis.

At skeletal maturity, Nanotyrannus reached approximately half the body length and one-tenth the body mass of an adult T. rex. Where T. rex was a massive, robustly built apex predator, Nanotyrannus was lighter, more gracile, and presumably more agile. The researchers characterized Nanotyrannus as a 'leaner, swifter, and more agile hunter,' ecomorphologically distinct from the heavyweight T. rex.

The confirmation of Nanotyrannus as a separate genus coexisting with T. rex in the same ecosystems during the final million years of the Cretaceous significantly revises the picture of Late Cretaceous predator diversity. Rather than T. rex reigning as the sole large tyrannosaur predator, at least two ecomorphologically distinct tyrannosauroid genera shared the Hell Creek ecosystem.

The validation of Nanotyrannus has far-reaching consequences for the study of tyrannosaur biology. For decades, numerous smaller tyrannosaur specimens from the Hell Creek and Lance Formations had been assumed to represent juvenile or subadult T. rex individuals. These specimens had been incorporated into growth curves, life history models, ontogenetic niche partitioning hypotheses, bite force analyses, and locomotor biomechanics studies for T. rex. The 2025 study demonstrated that many of these specimens likely belong to Nanotyrannus rather than T. rex, meaning that existing T. rex growth models may conflate data from two distinct taxa.

As Zanno stated: 'This fossil doesn't just settle the debate. It flips decades of T. rex research on its head.' The study necessitates a re-evaluation of dozens of published hypotheses about T. rex ontogeny, ecology, and behavior that were based on what are now potentially misidentified specimens.

From a taphonomic perspective, the Dueling Dinosaurs is among the most remarkable fossil preservations in the paleontological record. Both skeletons are nearly complete and largely articulated—a rarity for large dinosaur specimens, which are more commonly found disarticulated or partially scattered. The close physical association of a predator and prey individual, both bearing evidence of injuries, provides a rare snapshot of interspecific interaction frozen in the fossil record. The preservation of soft-tissue impressions, including skin with scale patterns, adds an additional dimension of information that is unavailable from skeletal remains alone.

The taphonomic scenario is interpreted as a rapid burial event, likely involving floodplain sedimentation that entombed both animals together shortly after or during their fatal encounter. The lower Hell Creek Formation depositional environment has been interpreted as an extensive floodplain with meandering river systems and ephemeral backwater deposits, consistent with conditions that could produce rapid burial and exceptional preservation.

While the Zanno and Napoli (2025) study represents the most comprehensive analysis to date, some paleontologists have urged caution, noting that larger sample sizes would further strengthen the case. The debate surrounding Nanotyrannus had persisted for approximately four decades, with influential studies on both sides. Notably, Woodward et al. (2020) had argued in Science Advances that bone histology supported Nanotyrannus being a juvenile T. rex, while Longrich and Saitta (2024) had provided earlier support for the validity of Nanotyrannus as a distinct taxon.

The December 2025 analysis of the Cleveland holotype skull (CMNH 7541) by the Cleveland Museum of Natural History added further support, demonstrating that the original holotype skull was itself from a fully grown individual. Ongoing preparation and study of the Dueling Dinosaurs specimen at the NCSM open laboratory continues, and additional publications on the Triceratops skeleton (NCSM 40001) and taphonomic details of the specimen are anticipated.