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2w ago

Study Confirms Teeth Originated as Sensory Structures in Ancient Fish Armor

High-resolution CT scans reveal dentin-filled tubules in Ordovician fossils and reclassify Anatolepis as an invertebrate, supporting the outside-in hypothesis of tooth evolution.

This artist's illustration depicts Astraspis being attacked by the sea-scorpion Megalograptus in dark shallow waters. The glow of the animals' interacting exoskeletons represent how both would have sensed the world around them.
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Overview

  • New research shows that dentin, the sensory tissue inside teeth, first evolved in the armored exoskeletons of ancient fish around 465 million years ago.
  • High-resolution CT imaging confirmed dentin-filled tubules in Ordovician fish like Eriptychius, demonstrating their sensory capabilities.
  • Anatolepis, previously thought to be an early vertebrate, has been reclassified as an invertebrate arthropod with sensory structures similar to modern crustaceans.
  • Modern fish such as sharks and catfish possess skin denticles connected to nerves, mirroring the sensory function of ancient odontodes.
  • These findings strongly support the outside-in hypothesis, suggesting that external sensory armor evolved before and gave rise to vertebrate teeth.