Edaphosaurus- One of the ‘sail-backs’. Not a dinosaur!Mounted specimen on display at the

Edaphosaurus- One of the ‘sail-backs’. Not a dinosaur!Mounted specimen on display at the American Museum of Natural History, NYCReconstruction by Karen Carr, for the Sam Nobel Museum of Natural HistoryWhen: Early Permian ~ 300-265 million years ago  Where: North America and Europe. What: This tiny headed taxon looks very reptilian, but it’s more closely related to mammals than to lizards. Edaphosaurus was a one of many basal synapsids or 'mammal like reptiles’. This latter term has really fallen out of favor in recent years, however, as it implies a kinship between modern reptiles and these primitive synapsids.  The clade Synapsida (which includes modern mammals) first appears in the fossil record ~ 320 mya, so these 'sail backs’ were very early members. It is theorized that the sails seen on these taxa aided in thermoregulation -keeping the animal warm when it was cold and cooling it off when it was hot- and that once the synapsid lineage became more adapt at controlling their body temperature they were not needed anymore.  Edaphosaurus was one of the first large terrestrial herbivores, and dominated the landscape during it’s time - they grew to roughly 12 feet (3.7 meters) and their weight is estimated at over 600lbs (~270 kg).  Their major predator was their much more famous relative, Dimetrodon, whose predatory niche was much more typical of the basal synapsids.  Despite the close resemblance between these two 'sail backs’, Dimentrodon is actually our closer relative. This early experiment in large herbivores left no living descendants. And yes it has a very tiny head. It is not the most extreme case of 'tiny head’ seen in basal synapsids either! I find the reduction of the head in these animals very interesting, as most of their meat eating relatives (like Dimetrodon) have what we would consider very large heads for their body size.  -- source link

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