Dinosaurs dominated Earth’s terrestrial ecosystems for over 165 million years, appearing approximately 245 million years ago and diversifying across Pangea. Their long reign in the Mesozoic Era leads to a question: what was the last dinosaur on Earth? The answer involves understanding their world just before their disappearance and the event that ended their era.
The Dinosaurs of the Late Cretaceous
The Late Cretaceous period (100 to 66 million years ago) saw non-avian dinosaurs thrive across continents that were drifting apart. Iconic species like Tyrannosaurus rex roamed North America, primarily in the western United States and Canada. This predator, reaching up to 12 meters and weighing around 9 tons, hunted large herbivores in subtropical forests, river valleys, and coastal plains.
Coexisting with T. rex was the armored Ankylosaurus, a herbivore known for its bony plates and club-like tail. This “fused lizard” lived in warm climates with lush vegetation, feeding on low-growing plants like ferns. Triceratops, another herbivore, was recognized by its large bony frill and three horns. This massive creature, up to 9 meters long and weighing up to 12 tons, inhabited lush plains and river valleys, grazing on ferns, palms, and cycads. These specialized dinosaurs represented a thriving ecosystem until the end of the Cretaceous period.
The Extinction Event
The reign of non-avian dinosaurs abruptly ended 66 million years ago with the Cretaceous-Paleogene (K-Pg) extinction event. The leading scientific theory attributes this mass extinction to an asteroid impact. An asteroid, estimated at 10 to 15 kilometers (6 to 9 miles) in diameter, struck the Earth in what is now Mexico’s Yucatán Peninsula, creating the Chicxulub crater. The impact released immense energy, equivalent to about 100 million megatons of TNT.
The immediate aftermath was catastrophic, with superheated winds, shockwaves, and megatsunamis over 100 meters tall scouring coastlines. The impact ejected trillions of metric tons of material into the atmosphere, which heated the Earth’s surface upon re-entry, igniting widespread wildfires across nearly 70% of the planet’s forests. Long-term consequences were equally devastating: dust, soot, and sulfur aerosols blocked sunlight for years, leading to a global blackout and freezing temperatures, known as “impact winter.” This disruption halted photosynthesis, collapsed food chains, and caused acid rain, leading to the extinction of approximately 75% of all species, including all non-avian dinosaurs. Evidence supporting this theory includes a worldwide layer of iridium, a metal rare on Earth but common in asteroids, found at the K-Pg boundary.
The Dinosaurs Among Us Today
While large non-avian dinosaurs vanished, not all dinosaurs perished in the K-Pg extinction event. A lineage of small, feathered dinosaurs, known as avian dinosaurs, survived and continued to evolve. These survivors are the direct ancestors of all modern birds, considered living dinosaurs carrying the legacy of their ancient relatives.
Several factors contributed to avian dinosaur survival. Their smaller body size required less food, allowing adaptation to diminished resources after the impact. The ability to fly enabled them to escape devastated areas and seek new food sources or more hospitable environments. Their varied diets, including a reliance on seeds, proved advantageous when plant life was scarce. Modern birds, with their diverse forms and behaviors, represent the enduring continuation of the dinosaur lineage, demonstrating resilience through one of Earth’s most significant extinction events.