No, Dinosaurs Did Not Roam Through Dense Rainforests

Rainforests did not exist during the age of the Tyrannosaurus rex and Triceratops. These iconic dinosaurs, often depicted in lush, jungle-like settings in films, actually lived in environments that were quite different from today’s rainforests. The lush, dense forests we now recognize as rainforests began to develop only after the mass extinction event that wiped out the non-avian dinosaurs.

Paleobotanists have discovered that Earth’s earliest rainforests emerged after the asteroid impact that marked the end of the Cretaceous period. This extinction event not only wiped out the large dinosaurs but also allowed a new type of plant—angiosperms, or flowering plants—to thrive. These plants, which included palms and legumes, contributed to the formation of dense, warm, and humid rainforests. The disappearance of large herbivorous dinosaurs like Edmontosaurus meant that the landscapes, previously kept open and dominated by conifers, could close into dense forests where new species, including early primates, could evolve.

Tracking the history of these ancient rainforests has been challenging due to the incomplete fossil record. However, in 2009, researchers from the Smithsonian Tropical Research Institute, led by Carlos Jaramillo, identified evidence of an early neotropical rainforest in Colombia’s Cerrejón Formation. Fossils from this site, dated to around 58 million years ago, revealed a rich forest filled with palm and legume species, similar to modern rainforests. These findings confirm that the rainforest environment could only develop after the asteroid impact, which set the stage for the proliferation of angiosperms.

The Cerrejón fossils show a forest with diverse leaf shapes, mostly from angiosperms, and indicate conditions like high temperatures and abundant rainfall. The variety of plant-eating insects also points to a thriving ecosystem. This contrasts sharply with the earlier, less dense forests that existed before the mass extinction.

According to University of Wyoming paleobotanist Ellen Currano, imagining large dinosaurs like T. rex navigating a dense rainforest is unrealistic. The presence of such enormous herbivores would have prevented the growth of thick, closed-canopy forests, as their feeding habits and movement kept landscapes more open.

Before the asteroid impact, the world was populated by large herbivorous dinosaurs that altered their environment significantly. These megaherbivores, similar to today’s elephants and rhinos, kept the landscape open and prevented the dense growth of forests. As these dinosaurs disappeared, angiosperms had the opportunity to flourish and form the dense canopies associated with modern rainforests.

The asteroid impact also played a crucial role by enriching the soil with minerals and iron, which favored the growth of angiosperms. The spread of legumes increased nitrogen levels in the soil, further supporting the growth of these plants. As angiosperms grew rapidly, they created dense canopies that shaded the forest floor, preventing other plant species from competing.

The new, dense rainforests that emerged after the extinction event provided diverse habitats and ecological niches. This complexity allowed mammals and other survivors to explore new ways of life, leading to increased biodiversity. The closed-canopy rainforests of today support a wide range of species, a legacy of the Paleocene forests that followed the extinction of the dinosaurs.

In summary, the development of rainforests was a direct result of the mass extinction that ended the age of the dinosaurs. The extinction event allowed flowering plants to dominate, leading to the dense, diverse rainforests we see today, which have significantly shaped the evolution of many species.