Is the mridangam related to the pakhawaj?

Yes, the pakhawaj of Hindustani music is a close relative of the mridangam. Darbar calls the mridangam its prototype and describes the pakhawaj as larger, with a different playing technique. The maddale of Yakshagana and the khol of Bengal are related double-headed drums, though the maddale differs in structure and acoustics from the Carnatic mridangam.