Simplify the following text for a Grade 10 native English-speaking person.
Original: Axolotls should not be confused with waterdogs , the larval stage of the closely related Tiger Salamanders ( Ambystoma tigrinum and Ambystoma mavortium ) , which are widespread in much of North America and also occasionally become neotenic , nor with mudpuppies ( Necturus spp . )
Simplified: Axolotls are closely related to waterdogs , the larval stage of the closely related Tiger Salamanders Ambystoma tigrinum and Ambystoma mavortium . These are common in much of North America and also sometimes become neotenic .