* Dragons are mythical creatures, often depicted as large, winged, fire-breathing reptiles. They exist only in stories and legends.
* Marsupials are mammals that give birth to relatively undeveloped young, which then complete their development in a pouch on the mother's abdomen. Examples include kangaroos, koalas, and wombats.
Therefore, combining these two concepts doesn't make biological sense. It's possible that you've encountered this term in a fictional context, such as a fantasy book or video game. If you could provide more information about where you heard the term, I might be able to give you a more specific answer.