「決闘けっとうする恐竜きょうりゅう」化石かせきが示しめす新知見しんちけん――ティラノサウルス幼体ようたい説せつの再考さいこうと分類学的ぶんるいがくてき再評価さいひょうか

This specimen, known as the legendary fossil Dueling Dinosaurs, is housed at the North Carolina Museum of Natural Sciences in Raleigh, North Carolina, USA. It contains the skeletons of two dinosaurs that are believed to have become fossilized while entwined after a fierce prehistoric battle.

So far, paleontologists believe that this is evidence documenting the epic confrontation between two world-famous dinosaurs: Triceratops and Tyrannosaurus rex.

However, detailed research findings from the past five years have made it necessary to significantly revise this traditional understanding.

According to the latest research, the small dinosaurs included in this fossil group are more likely to be adult specimens of a separate species, Nanotyrannus lancensis, which has been debated for many years, rather than juvenile Tyrannosaurus rex.

From the microstructure of the bone, it is indicated that this individual is already an adult.

This indicates that it is inevitable that many fossils previously misidentified as juvenile Tyrannosaurus rex will need to be re-evaluated.

Nanotyrannus, although similar in appearance to Tyrannosaurus rex, was much smaller at about 5.5 meters in length, and is thought to have been an agile predator with long legs and powerful arms.

On the other hand, Tyrannosaurus rex reached a total length of 12.8 meters, hunted large prey with its powerful bite, and moved slowly.

Notably, the forelimbs of Nanotyrannus are larger than those of an adult Tyrannosaurus rex, and since the bones do not shrink during growth, this further supports the view that they are different species.

Associate Professor Zanno of North Carolina State University pointed out that for the past 30 years, data on Nanotyrannus had been mistakenly mixed into biological studies of Tyrannosaurus rex, and stated that this discovery means existing knowledge needs to be re-examined.

The fossil of the Dueling Dinosaurs, discovered in the Hell Creek Formation in Montana, USA in 2006, is about 65.5 million years old.

Nanotyrannus lancensis was first described based on specimens excavated from the same stratum in the 1940s, but later, the prevailing view became that this small tyrannosaurid is actually a juvenile Tyrannosaurus rex.

The opinion supporting the existence of a separate species has gradually decreased, but scientific debate still continues.

In a new study comparing more than 200 fossils from the Tyrannosauridae family, it was shown that fossils of young Tyrannosaurus rex individuals may not be as common as previously thought.

This discovery raises new questions about how different predators were involved in the ecosystems at the end of the Cretaceous period.

Professor Witmer of Ohio University points out that the research results not only resolve the controversy over classification, but also require a fundamental review of related studies and papers from the past several decades.

Professor Brusatte of the University of Edinburgh also emphasized the need to reassess the classification and evolution of tyrannosaurids.

Professor Brusatte is cautious about concluding that all small tyrannosaurs are Nanotyrannus, but he believes that distinguishing between adult or nearly adult Nanotyrannus and juvenile Tyrannosaurus rex will become an increasingly important issue in future paleontological research.

Currently, some parts of the Dueling Dinosaurs fossils are still encased in rock, and the reason why the two dinosaurs became fossilized while intertwined remains unknown.