Tyrannosaurus rex Evolved in North America, but Its Ancestors Came from Asia, New Study Reveals

A recent study led by Cassius Morrison, a doctoral student in paleontology at University College London, has brought forth new insights regarding the origin of the formidable Tyrannosaurus rex. The research indicates that the direct ancestors of T. rex likely migrated from Asia to North America via a land bridge approximately 70 million years ago. This finding builds on previous theories that had sparked robust discussions among paleontologists over the geographic origins of this iconic dinosaur. Morrison's study employs sophisticated mathematical modeling, inclusive of fossil data, the evolutionary tree of tyrannosaurids, and the prevailing climate conditions of the time. This model suggests that the ancestors of T. rex could have traversed what is today known as the Bering Strait, which was once a temperate rainforest mirroring contemporary British Columbia's climate. This places T. rex’s evolutionary roots in Asia—specifically relating it closer to the large Asian carnivore Tarbosaurus than to other North American predators like Daspletosaurus. Moreover, the timing of the T. rex's evolution correlates significantly with shifts in global temperatures. The study highlights a rapid increase in the size of both tyrannosaurids and megaraptors, coinciding with a cooling climate following the Cretaceous Thermal Maximum, around 92 million years ago. Such adaptations to cooler climates may have included features similar to feathers or a warm-blooded physiology, which would have better positioned them in the harsh ecological environments of the Late Cretaceous. Paleontologist Steve Brusatte commended this research, noting it provides a detailed understanding of how climate influenced the evolutionary trajectory and size of these apex predators. He asserted that the T. rex, while often viewed as the quintessential American dinosaur, was in fact an immigrant that crossed continents in search of new ecological niches. This revelation adds depth to our understanding of how geographical migrations and climatic factors can shape the evolution of species. Additionally, the implications of this study extend beyond T. rex to broader questions regarding the evolutionary dynamics among dinosaur lineages in response to changing environments. The study not only reinforces the theory of migration from Asia but also addresses prior findings suggesting North American ancestry based on a particular fossil—Tyrannosaurus mcraeensis. Morrison and his team challenge this assumption, arguing that the dating of this fossil is unreliable, thus reaffirming their conclusions about T. rex's origins. Overall, Morrison’s research paves the way for further exploration into the potential undiscovered fossils of T. rex’s ancestors in Asia, while emphasizing the interconnectedness of climate change and evolutionary adaptability among dinosaurs. This pivotal work thus stands not only as a significant contribution to paleontology but also underscores the essential role of environmental changes in the evolution of life on Earth.