Science Friday

Were Dinos On Their Way Out Before The Asteroid Hit? Maybe Not

November 7, 2025

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  • New fossil evidence from New Mexico suggests that dinosaurs were diverse and thriving right up until the asteroid impact, challenging the idea that they were already in decline. 
  • Reanalysis of a juvenile T. rex fossil, using bone growth ring data, indicates it is likely a separate, smaller, mature species named *Nanotyrannus*, increasing predator diversity estimates in the Hell Creek Formation. 
  • Understanding the health and diversity of dinosaur ecosystems immediately preceding the end-Cretaceous extinction provides relevant lessons for understanding how modern life responds to rapid environmental change. 

Segments

Dinosaur Extinction Debate Origins
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(00:01:25)
  • Key Takeaway: The debate over dinosaur decline before the asteroid centers on evidence interpretation since the 1980 Alvarez impact theory.
  • Summary: The long-standing argument in paleontology questions whether dinosaurs were already declining due to climate change or if the asteroid impact was the sole cause of extinction. This debate intensified after the 1980 Alvarez theory proposed an asteroid impact 66 million years ago. New evidence is continually brought forward to support either the decline hypothesis or the sudden extinction hypothesis.
New Mexico Fossil Evidence
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(00:04:43)
  • Key Takeaway: Accurately dated New Mexico fossils show large dinosaurs, including Alamosaurus, were present right before the asteroid impact.
  • Summary: New dating of fossils from the Four Corners region of New Mexico confirms the presence of diverse dinosaurs, including giant sauropods like Alamosaurus, within a few hundred thousand years of the asteroid strike. This suggests these animals were at the top of their game when the extinction event occurred. Further well-dated fossils globally are needed to confirm if this thriving state was a worldwide phenomenon.
Tyrannosaur Diversity Reassessment
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(00:06:58)
  • Key Takeaway: A complete small tyrannosaur skeleton confirms Nanotyrannus is a distinct species, not a juvenile T. rex.
  • Summary: Research on the Hell Creek Formation re-examined small tyrannosaur fossils, long debated as juvenile T. rex. Analysis of a complete specimen, including counting bone growth rings, showed it was a mature, smaller-bodied animal, likely Nanotyrannus. This finding increases the known predator diversity in that ecosystem immediately before the mass extinction.
Relevance of Extinction Studies
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(00:14:36)
  • Key Takeaway: Studying the end-Cretaceous extinction provides crucial wisdom on how ecosystems respond to rapid environmental change, relevant to current global shifts.
  • Summary: Fossil studies inform how life evolves and responds to massive environmental shifts, which is relevant as the Earth changes significantly today, partly due to human activity. The end-Cretaceous event, involving an asteroid, volcanism, and sea-level changes, serves as the most recent mass extinction benchmark for understanding ecological vulnerability. Dinosaurs’ failure to adapt to the sudden change allowed smaller, adaptable mammals to eventually prosper.
Costume Contest Results
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(00:18:57)
  • Key Takeaway: Denise won the Spooky Science Halloween costume contest with a Weatherman and Tornado costume set.
  • Summary: The first annual spooky science Halloween costume contest winner was Denise, who created costumes for her grandkids: a Weatherman and an accompanying tornado. The tornado costume featured objects like a house and a cow suspended within the vortex structure. The runners-up were the ‘Western Blots,’ a science-themed cowboy mashup.