Dimetrodon is a synapsids, which means it belong to a group directly ancestral to all living mammals like you and me. Dinosaurs is an entirely different lineage, and belong to a group that is ancestral to birds. They are on separate lineages and neither is an ancestor to the other. Last common ancestor of both synapsids and dinosaurs probably lived 50 million years before dimetrodon and 100 million years before the first dinosaurs.
As to stamps, I know there are professional stamp appraisers. The charge a fee and advise you on how much you collection is worth and where and how to sell it.
As to stamps, I know there are professional stamp appraisers. The charge a fee and advise you on how much you collection is worth and where and how to sell it.
