Paleohistology (WHY TEETH EXIST) with Yara Haridy

What It Covers

Paleohistologist Dr. Yara Haridy explains how vertebrate teeth evolved from sensory structures called odontodes covering ancient fish exteriors 455 million years ago. Her 2025 Nature paper reveals teeth originated as external sensory organs before migrating into mouths, challenging century-old assumptions about skeletal evolution and proving modern catfish retain innervated odontodes across their bodies.

Key Questions Answered

• •Tooth tissue origins: Vertebrate teeth evolved from odontodes, tooth-like structures made of enamel and dentine that covered the exterior of jawless fish 455 million years ago in the middle Ordovician period. These external bumps appeared before jaws existed and predated internal teeth by millions of years, fundamentally changing understanding of skeletal evolution. Modern sharks retain this ancestral pattern with dermal denticles creating their sandpaper texture.
• •Sensory function discovery: Dr. Haridy bred aquarium plecos and used clarity imaging with fluorescent antibodies to prove odontodes contain nerve innervation, demonstrating they function as sensory organs. This explains why human teeth remain sensitive despite being used for chewing, an inherited complexity from their original sensory purpose. Elephants and narwhals still use their teeth primarily for environmental sensing rather than eating.
• •Synchrotron scanning method: Particle accelerators generate x-rays 100 billion times stronger than medical imaging, penetrating rock to reveal 480-million-year-old tissue structures including blood vessels, cell spaces, and growth patterns. This paleohistology technique allows researchers to determine animal age, growth rate, seasonal stress markers, and whether specimens experienced hard winters, all preserved in fossilized bone and dentine despite extreme age.
• •Tooth replacement patterns: Constant tooth replacement represents the ancestral vertebrate condition, retained by sharks losing one tooth weekly, crocodiles, and dinosaurs. Mammals uniquely reduced this to two sets due to precise occlusion requirements where molars must fit together exactly for effective chewing. Researchers now grow mouse teeth from stem cell implants, working toward human tooth regeneration to replace crowns and implants.
• •Fossil misidentification correction: A supposed late Cambrian vertebrate studied since the 1970s proved to be an arthropod with sensory structures mimicking odontodes, eliminating the transitional fossil between soft-bodied ancestors and armored fish. This leaves a 50-million-year gap in the fossil record and demonstrates how comparative scanning of modern arthropods reveals ancient sensory networks previously mistaken for vertebrate dental tissues.
• •Field work accessibility: Paleontology fieldwork costs approximately $2,000-3,000 per week-long expedition, less than a used car, covering multiple researchers excavating sites before construction destroys them. Fragmentary specimens smaller than rice grains yield significant data through microscopy and scanning. Museums need preparation funding for skilled technicians spending hours on manual labor, making donor support critical for natural history research.