Evolutionary origins of the vertebrate dentition: phylogenetic patterns and developmental evolution

Area of Science:

• Paleontology
• Evolutionary Biology
• Vertebrate Zoology

Background:

• The traditional theory linking tooth evolution to dermal denticles and jaw origin is increasingly challenged by new fossil data.
• Understanding the primitive oropharyngeal dental patterns in early vertebrates is crucial for determining evolutionary polarity.
• Divergence between teeth and denticles may have occurred early in vertebrate phylogeny, despite shared developmental systems.

Purpose of the Study:

• To review oropharyngeal dental patterns across fossil early vertebrate groups.
• To establish the primitive condition of dental structures and understand evolutionary changes.
• To investigate the hypothesis that teeth evolved from specialized oropharyngeal denticles.

Main Methods:

• Comprehensive review of oropharyngeal dental patterns in fossil early vertebrates.
• Analysis of fossil record data to establish primitive conditions and evolutionary polarity.
• Comparative analysis of developmental systems (odontodes) and their regulatory changes.

Main Results:

• The evolutionary precedence of dermal denticles before teeth is less likely; they may represent alternative expressions of a common morphogenetic system.
• Teeth are characterized by regulated growth, size, position, developmental timing, and replacement mechanisms, distinguishing them from denticles.
• Tooth whorls in oropharyngeal denticles suggest a preadaptation for the tooth replacement mechanism.
• New fossil evidence indicates teeth may have originated from specialized oropharyngeal denticles in agnathan vertebrates.

Conclusions:

• The origin of jaws and teeth is more complex than previously thought, with a common morphogenetic system potentially underlying both dermal denticles and teeth.
• Teeth evolved unique regulatory mechanisms for growth and replacement, possibly preadapted by features like tooth whorls found in specialized denticles.
• The study supports the evolution of teeth from specialized oropharyngeal denticles in early jawless vertebrates (agnathans).