‘If it weren’t for that asteroid, they might still share this planet’: Dinosaurs weren’t doomed before the asteroid hit, new study suggests

The dinosaurs were not in decline before the asteroid hit, a new study finds. Instead, poor fossilization conditions and unexposed late Cretaceous rock layers mean they’re either not preserved or hard to find.

🦖 Dinosaurs Were Thriving — Until the Asteroid Hit

For decades, scientists debated whether dinosaurs were already on the decline before a massive asteroid wiped them out 66 million years ago. Now, a new study published April 8 in Current Biology says: Nope, they were doing just fine — and the idea that they were fading out before the impact is likely a misread of the fossil record.

🦴 Fossils: Misleading at First Glance?

At first glance, fossil records suggest dinosaur diversity peaked around 76 million years ago, then began to decline, especially during the final 6 million years of the Cretaceous. But researchers now believe that this drop isn’t real — it’s just that the fossils from that time are harder to find, thanks to how Earth’s geology shifted.

“There’s no sign of environmental or ecological stress that would explain a pre-asteroid extinction,” said lead author Chris Dean, paleontologist at University College London.

🧪 What the Study Actually Looked At

• Analyzed ~8,000 dinosaur fossils from North America.
• Focused on four major families:
  • Tyrannosauridae (like T. rex)
  • Hadrosauridae (duck-billed dinos)
  • Ceratopsidae (like Triceratops)
  • Ankylosauridae (armored dinos)
• Compared fossils from two time periods:
  • Campanian (83.6–72.1 million years ago)
  • Maastrichtian (72.1–66 million years ago)

While raw fossil counts suggested diversity declined in the Maastrichtian, the researchers say this is more about where and how fossils were preserved, not actual extinction trends.

🏔️ Blame It on Mountains and Mud

Two big Earth changes likely messed with fossil preservation:

1. Retreat of the Western Interior Seaway – This massive inland sea split North America but began to disappear toward the end of the Cretaceous.
2. Rise of the Rocky Mountains – As these mountains formed, they caused erosion and geological upheaval, disturbing areas where fossils might have formed.

This combination made it much harder for fossils to form or survive — and even harder for paleontologists to dig them up today.

“Some key fossil-rich rock layers are covered by vegetation or just not exposed,” said Dean. “So we’re simply not seeing the full picture.”

🧬 A Few Fossil Fun Facts From the Study

• Ceratopsians (like Triceratops) were the most common fossils — likely because they lived in open plains, which preserved fossils better.
• Hadrosaurians were underrepresented — possibly because they liked river environments, and reduced river flow in the Maastrichtian led to fewer sediment deposits and worse fossil conditions.

🦕 What If the Asteroid Had Missed?

“Dinosaurs were probably not inevitably doomed to extinction,” said co-author Alfio Alessandro Chiarenza. “If it weren’t for that asteroid, they might still share this planet with mammals, lizards — and birds.”

So, the asteroid wasn’t just a nail in the coffin — it was the whole coffin. Without it, dinosaurs might have kept evolving and thriving alongside other life on Earth.

🌍 Why This Matters

Because half of the known Maastrichtian fossils come from North America, and the same geological factors may have affected fossilization elsewhere, these findings could reframe our understanding of global dinosaur diversity before the extinction event.

So, next time someone tells you dinosaurs were already on the way out, you can hit them with some fossil science:
They weren’t declining — we just haven’t found all their bones yet.