Short Wave

What crocodile bones teach us about dinosaurs

March 9, 2026

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  • The traditional method of aging dinosaurs by counting one growth ring per year in their bones may be inaccurate, as research on crocodiles (close living relatives of dinosaurs) shows they can form more than one growth ring annually. 
  • Scientists studied Nile crocodiles at Le Bonnier Reptiles and Adventures near Cape Town, injecting them with an antibiotic to create time markers in their bones, revealing up to five growth marks in two-year-old individuals. 
  • The findings suggest that dinosaur growth marks might be better understood as 'cycles of growth' rather than strictly annual markers, potentially meaning some dinosaurs were younger when they died than previously estimated. 

Segments

Introduction to Dinosaur Aging
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(00:00:21)
  • Key Takeaway: Traditional dinosaur aging relies on counting bone growth rings, assuming one ring equals one year.
  • Summary: Regina Barber introduces science reporter Ari Daniel to discuss dinosaur aging. The traditional method involves counting growth rings in fossilized bones, similar to counting tree rings, to estimate age annually. This method was used to estimate that a T-Rex took about 20 years to reach adulthood.
Crocodile Study Location
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(00:02:29)
  • Key Takeaway: The research validating new aging theories is being conducted at Le Bonnier Reptiles and Adventures near Cape Town.
  • Summary: The reporting takes place at Le Bonnier Reptiles and Adventures, an outdoor recreation and education center outside Cape Town. The center houses approximately 170 Nile crocodiles, which are considered among the closest living relatives to dinosaurs. This location is central to studying modern reptile growth patterns.
Antibiotic Bone Marking Method
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(00:05:08)
  • Key Takeaway: Researchers injected young crocodiles with an antibiotic to create visible time markers within their developing bone tissue.
  • Summary: The initial goal of the research was to see how a crocodile’s environment impacts its skeletal growth. Scientists injected year-old crocodiles with an antibiotic over several months, which left a signal in the bone development. This technique allowed researchers to track growth trajectories over time, even as individuals grew differently.
Unexpected Growth Ring Findings
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(00:07:46)
  • Key Takeaway: Two-year-old crocodiles exhibited up to five growth marks, contradicting the one-ring-per-year assumption.
  • Summary: Upon microscopic analysis of the thin bone cross-sections, researchers found more growth marks than anticipated in the two-year-old crocodiles. In many cases, up to five growth marks were visible in bones from animals that were only two years old. This suggests that growth marks may not correspond strictly to annual periods.
Expert Reaction to Findings
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(00:08:58)
  • Key Takeaway: Other paleontologists view the crocodile study as important ‘ground truthing’ but caution against immediately discarding the annual ring assumption.
  • Summary: Paleohistologist Holly Woodward noted that studies like this are vital for confirming the reliability of growth rings using modern animals. However, she stated that the cause for variable ring formation is not yet understood, possibly relating to hormones or day-night cycles. Christy Curry Rogers added that this serves as a cautionary tale against overinterpreting bone tissue data.
Implications for Dinosaur Age Estimates
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(00:10:20)
  • Key Takeaway: Dinosaur age estimates based on bone rings should now be treated as rough estimations rather than definitive ages.
  • Summary: Anusia agrees that more work is necessary to fully understand the implications of the findings. The research means that while bone rings still provide a rough estimate of dinosaur age, scientists must acknowledge this is an estimation. The answers regarding growth patterns are believed to be discoverable within the bones themselves.
Human Bone Rings Inquiry
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(00:11:26)
  • Key Takeaway: Humans also possess growth rings in their bones, but they are often destroyed by bone remodeling processes later in life.
  • Summary: The hosts briefly address whether human bones also contain growth rings. Holly Woodward confirmed that humans do have them, but they are rarely reported because bone tissue examined often comes from older individuals. In older adults, bone remodeling destroys the presence of previously formed rings.