Amphibious. The archelon can breathe air and water.
Multiattack. The archelon makes two Bite attacks.
Bite. Melee Attack Roll: +6, reach 5 ft. Hit:14 (3d6 + 4) Piercing damage.
Use these stat blocks to represent the creatures they're named for or other similar creatures. For example, the Panther stat block can also represent a mountain lion, while the Giant Goat stat block might represent a buffalo. Any of these stat blocks might also serve as fantastical animals with distinctive names and cosmetic details unique to your D&D adventures.