Mastids

Mastids refer to a group of extinct mammals that were part of the order Artiodactyla, which includes modern-day even-toothed ungulates like pigs, deer, and whales. The term "mastid" is not a formally recognized taxonomic group but is sometimes used colloquially or in older literature to describe certain lineages within Artiodactyla that share similarities in skull structure, particularly the presence of a prominent "mast" or ridge on the skull, often associated with large, robust teeth.

One of the most well-known groups often loosely referred to as mastids are the **Chalicotheriidae**, a family of extinct ungulates that lived from the Eocene to the Pleistocene epochs. Chalicotheres were distinctive for their long, curved claws, which they likely used for digging and climbing. They were not closely related to modern elephants, despite superficial similarities in body shape, but shared a similar ecological niche in some cases.

Another group sometimes associated with the term "mastid" is the **Entelodontidae**, commonly known as "entelodonts" or "terror pigs." These large, robust mammals thrived during the Eocene and Oligocene epochs and were among the largest land mammals of their time. Entelodonts had a powerful build, short legs, and a skull resembling that of a boar, though they were not directly related to modern pigs.

The term "mastid" is not widely used in modern taxonomy, as phylogenetic studies have refined the classification of these animals into more specific families and genera. Many of these extinct groups were once thought to be closely related but are now recognized as part of diverse evolutionary lineages within Artiodactyla. Their study provides valuable insights into the evolutionary history of hoofed mammals and their adaptations to various environments.