Like many reptiles and insects Chelydridae hasn't evolved as drastically as other species. The main distinguishable difference would be size.

Family Chelydridae

• • Genus Acherontemys (extinct)
  • Genus Chelydrops (extinct)
  • Genus Chelydropsis (extinct)
  • Genus Emarginachelys (extinct)
  • Genus Macrocephalochelys (extinct)
  • Genus Planiplastron (extinct)
• Subfamily Chelydrinae
  • Genus Protochelydra (extinct)
  • Genus Macrochelys (alligator)
  • Genus Chelydra (common)