70 million years ago, during a cooling climate after Earth’s hottest period, there was a significant increase in the population of predatory dinosaurs such as Tyrannosaurus rex and megaraptors. Recent discoveries shed light on why these dinosaurs grew to gigantic sizes. It is believed that the key to their immense proportions may be linked to the shift in climate following a period of extreme warmth.
Around 92 million years ago, the Earth went through the Cretaceous Thermal Maximum, a phase characterized by peak global temperatures. As temperatures gradually dropped thereafter, it created favorable conditions for certain dinosaurs to grow to massive sizes. Scientists now hypothesize that dinosaurs like tyrannosaurs and megaraptors expanded in size as the climate became cooler, filling a void left by previously extinct giants.
Lead author Cassius Morrison from University College London (UCL) explains that their research provides insights into the emergence of the largest tyrannosaurs in North and South America during the Cretaceous period and the reasons behind their substantial growth by the end of the dinosaur era.
Unlike the T. rex with its powerful jaws, megaraptors were agile hunters with slender heads, lightweight bones, and notably long arms ending in giant claws. These creatures, with claws measuring up to 35 centimeters, are considered enigmatic predators due to the scarcity of fossils found. Originally believed to inhabit primarily southern continents like South America and Australia, recent evidence suggests a wider distribution. It is now thought that megaraptors first evolved in Asia around 120 million years ago, spreading across Europe and eventually throughout Gondwana — comprising present-day South America, Africa, and Antarctica.
Researchers speculate that megaraptors may have roamed regions such as Europe and Africa where their remains have not yet been discovered, attributing the limited fossil record to the difficulty in piecing together their history. This paucity of fossils has made it challenging to understand how their distinct anatomy evolved, likely influenced by different prey and environmental factors that set them apart from other dinosaurs.
While the origins of tyrannosaurs were believed to be solely in North America, recent studies from UCL suggest that their early ancestors originated outside of the continent. Through comprehensive analyses of fossils and geographical data, researchers have traced the evolutionary path of tyrannosaurs back to regions far from North America.
In studying the histories and environments of the past, the team uncovered that the predecessors of T. rex actually originated from Asia. The team’s research suggests that the ancestors of T. rex likely migrated to North America from Asia, traversing the Bering Strait between present-day Siberia and Alaska. They dispute earlier claims suggesting that a different North American dinosaur, Tyrannosaurus mcraeensis, was an older relative of T. rex due to unreliable fossil dating. Instead, they propose a strong connection to Asian species like Tarbosaurus rather than solely North American tyrannosaurs.
The study also delved into the movement of megaraptorans and tyrannosaurs across the world during the Late Cretaceous period. Despite originating from similar regions, these groups evolved differently. Tyrannosaurs developed robust jaws for crushing bones, while megaraptorans evolved long arms and sharp claws, suited for hunting smaller, agile prey such as juvenile sauropods.
As the ancient supercontinent Laurasia fragmented, tyrannosaurs expanded across Asia and North America, while megaraptorans diversified in southern regions following the split of Gondwana from Laurasia. The researchers suggest that these movements were shaped more by rapid ecological changes, localized extinctions, and the emergence of new habitats rather than geographic barriers.
Morrison’s team found no direct correlation between gigantism and cooler temperatures, although the overall trend towards cooler conditions appeared to benefit both dinosaur groups. The researchers proposed that feathers or a warm-blooded physiology might have enabled tyrannosaurs and megaraptorans to better adapt to the cooling climate, giving them an edge over other less adaptable dinosaur species.
At their peak, T. rex and other tyrannosaurs reached weights close to that of a large African elephant, while megaraptorans stretched up to lengths of 10 meters. These sizes represented a significant increase from their smaller ancestors, signifying a crucial evolutionary step prompted by ecological opportunities and changes in climate.
Despite many unanswered questions, this research sheds light on the origins and evolutionary paths of these fascinating dinosaurs and their adaptations to changing environments.
New research has shed light on dinosaur evolution in the Late Cretaceous period. The widespread presence of megaraptors and tyrannosaurs indicates how rapidly dinosaurs adapted to new environments following extinction events and changing climates. This study highlights the differences in evolution between the Northern and Southern hemispheres of the Earth after the Cretaceous Thermal Maximum. The findings emphasize the intricate connection between climate change and evolution. According to Scherer, the disappearance of large predators created opportunities for tyrannosaurs and megaraptors to flourish. Researchers are optimistic that further fossil discoveries, particularly in less-explored areas such as Europe, Africa, and Asia, will unveil more insights into how these ancient predators evolved and dominated their ecosystems. The study has been published in the journal Royal Society Open Science. For more uplifting stories like this, subscribe to The Brighter Side of News newsletter.
