Dimetrodon, the name of which meaning, "Two measures of teeth", was the top predator on land, during the Early-Early Mid Permian Period, 285-265 Million Years Ago.
They are Pelycosaur Synapsids, of the strange and iconic looking 'sailbacks', that are often incorrectly referred to as Dinosaurs. Fossils of them are known from North America and Europe.
They were the largest predatory Pelycosaurs ever, at 3.5 Metres Long, and probably weighed a third of a tonne. They were formidable carnivores in their day, preying on even their 'own kind' - as in other Pelycosaurs such as Edaphosaurus. It is most likely they were even cannibals, not being above preying on newly hatched infants of their own species when given the chance to.
Description[]
They were well adapted to life in the Early-early Mid Permian, with their 'sails', used for thermo-regulation, in an increasingly arid climate. Seasons would bring different conditions, and winter in the time of Dimetrodon, surprisingly may have brought ice and snow.
The ability to absorb every bit of energy and heat from the sun upon the large surface area of their sails, would have been a great advantage over other reptiles. They preyed on anything they could catch, including smaller amphibians such as Seymouria. These types of animals seem to have given risen to the ancestors of mammals, evolving eventually into the Therapsids (true mammal like reptiles, though Dimetrodon is essentially analogous to a mammal like reptile) which in turn developed into true mammals. The Pelycosaurs as a whole disappeared as they were super-ceded by Gorgonopsids and such other large Therapsids.
Walking With Monsters[]
Dimetrodon appears as the apex predator of the early Permian in Walking With Monsters, during the second episode. There is a female Dimetrodon, who kills a young Edaphosaurus. She has to eat lots of food in order to care for her eggs; though she is injured in the process, while fighting with another female Dimetrodon to defend her nest site and her eggs. Her nest is also stalked by a Seymouria but she drives it away. Eventually, she abandons the nest when the eggs hatch, and leaves them to fend for themselves. Dimetrodon was then shown evolving into Gorgonops.
However, it is highly important to note that this was not a literal evolution from species to species, but a representative and illustrative evolution portrayal for groups in general; as with most if not all shown in the series, being done thematically, to demonstrate the changes between the groups, not the species themselves as such. In a way, this was to the detriment of the series, mainly because this is never explained at all to the audience, and could be considered a poor choice on the part of the makers of Walking With Monsters. This is because some people who don't know much about the subject, could literally believe the series is saying Gorgonops came directly from Dimetrodon, which it certainly did not (and the series was not trying to literally say so either, but sadly they weren't very clear about this, leading to some confusion and criticism they could have easily avoided)