Macromerion (Macro- is Greek/Latin for “large”) is an extinct genus of non-mammalian synapsids, specifically Pelycosaurs, in the family Sphenacodontidae from Late Carboniferous deposits in the Czech Republic.

[4] Macromerion was one of the moderate to large-sized Spenacodontids and represented the most dominant terrestrial predators from the Late Carboniferous and Early Permian, which means they lived about 300 million years ago.

This taxon was first found among three other Pelycosaurs in Upper Carboniferous deposits, which shows that it must have originated from Middle Pennsylvanian times.

During the Carboniferous Period, Bohemia is a part of the major landmass of Laurussia, which was made-up of present-day North America, western Europe through the Urals, and Balto-Scandinavia.

The sail along their back is made up of hyperelongate vertebral neural spinous processes, which at the time was covered with thick skin and blood vessels.

Some of the common skull autopomorphies of the Sphenacodontidae clade include a nasal longer than parietal and a narrow posterior process of the postorbital, both being compared to the features of other Synapsids.

The large size of Macromerion, especially compared to other Sphenacodontids, suggested that they represented some of the most dominant terrestrial predators of the Late Carboniferous.