As of November 2026, most scientists accept that an asteroid impact was the main cause of the end-Cretaceous mass extinction. Volcanoes and slow climate change may also have played a part. They still disagree about exactly how the extinction unfolded and how long it took, and many details are unknown.

Some think volcanoes and climate change had already stressed life before the asteroid struck.

As of November 2026, the Deccan Traps, a huge lava field in western India, erupted close in time to the end-Cretaceous extinction, so scientists argue about its role, and the answer depends on pinning down exactly when the eruptions happened.

Some evidence suggests dinosaurs were already in a slow decline late in the Cretaceous. But the rocks cannot show this precisely, so it is still debated. As of November 2026, a 2025 study that re-dated fossil rocks in New Mexico suggests that dinosaurs there were still flourishing not long before the asteroid hit, adding evidence to a long debate over whether they were already in decline.

Carbon dating only works on things from the past 50,000 years or so, which is far too recent for dinosaur fossils.

Most fossils found are of sea animals such as shellfish, so a fossil of a big land animal is unusual.

As of November 2026, a 2016 hypothesis holds that bird ancestors lived through the end-Cretaceous extinction because their toothless beaks let them eat seeds, which stayed available when most other food sources were lost.

As of November 2026, a 2021 study led by Charles Marshall estimated that the total number of Tyrannosaurus rex that ever lived could be anywhere from 140 million to 42 billion, a very wide range because so many of the numbers behind it are uncertain.

As of November 2026, in 2010 scientists reconstructed the colours of the feathered dinosaur Anchiornis. They studied the shapes of fossil pigment particles, called melanosomes, in its feathers under a microscope. They compared them with pigment from modern birds. As of November 2026, they said the result supports the idea that feathers first evolved for display, camouflage or signalling, not only for flight.

Surprisingly, birds belong to the lizard-hipped group of dinosaurs, not the bird-hipped group. The bird-like hip, with the pubis bone pointing backward, evolved twice. It happened once in the bird-hipped dinosaurs and once in the line leading to birds.

Words to know

• hypothesis: testable idea
• camouflage: hiding colours
• pubis: hip bone
• signalling: sending signals