Marapets haven't always looked the same. The most well-known of the redraws were launched from January-November 2017, but there have been others before that. To begin browsing, start by choosing any combination of species and color.
There is a trend of MaraPets re-releasing old costumes to either revamp them or replace them with completely new ones. For Account Upgrades, some revamped costumes retire sooner than normal (usually 2 weeks).
This trend first emerged in 2012 when the Underwater AU was re-released but wouldn't go into full swing until 2015 when the Killer pets were revamped.