From the Super Mario Wiki
Stompin' Chomps are Chomps from Yoshi's Island DS that jump up and down with a loud bang. Although not as large as giant Chomps such as Chomp Sharks and the Chomps, Stompin' Chomps are larger than the original Chain Chomps. Some Stompin' Chomps can jump straight up and down, while others can bounce left and right as well.
In the Island Museum, Stompin' Chomps are part of the Giant Enemy Exhibit, despite the fact that they're not exactly giants. They are prominently featured in the level Rompin', Stompin' Chomps.