Investigating the Morphogenesis and Replacement of Lamprey Toothlets Using Synchrotron Imaging

Area of Science:

• Evolutionary developmental biology
• Comparative anatomy
• Vertebrate paleontology

Background:

• Teeth are crucial for jawed vertebrate evolution, with origins potentially in jawless vertebrates.
• Lamprey and hagfish toothlets, though unmineralized, may be precursors to vertebrate teeth.
• Previous research overlooked extant jawless vertebrates, focusing instead on extinct stem-gnathostomes.

Purpose of the Study:

• To synthesize literature on cyclostome toothlet structure and development.
• To provide new insights into lamprey toothlet replacement mechanisms using X-ray microtomography.
• To lay the foundation for molecular studies on the evolution of teeth.

Main Methods:

• Literature synthesis on cyclostome toothlet morphology and development.
• X-ray microtomography of three parasitic lamprey species.
• Detailed morphological analysis of toothlet replacement at the tissue level.

Main Results:

• Described the toothlet replacement mechanism in lampreys at the tissue level.
• Uncovered a relationship between toothlet size and the number of replacement cones.
• Confirmed the presence of replacement toothlets in all examined lamprey species, indicating a conserved feature.

Conclusions:

• Toothlet replacement is a conserved, symplesiomorphic trait in cyclostomes (lampreys and hagfish).
• This study provides a foundation for understanding the evolution of teeth and tooth-like structures across vertebrates.
• Lamprey toothlet development and replacement offer insights into the evolutionary origins of vertebrate teeth.