Non-mammal synapsids and therapsid

The first vertebrates on land were amphibians descended from fish, and during the Carboniferous Period one branch of these amphibians became the amniotes – vertebrates that laid eggs specially built to survive on land. This was kind of a big deal.
Very quickly, the amniotes split in two. One branch, the sauropsids, would ultimately give rise to snakes, crocs, turtles, dinosaurs, ichthyosaurs, and all the other critters we call reptiles. The other branch were the synapsids.

The defining trait of synapsids is the construction of the skull, specifically a lateral temporal fenestra. That is, a hole. On either side of the head, situated between several bones behind the eye socket, this lone fenestra differentiates synapsids from, for example, the two-holed diapsid reptiles.
This simple difference laid the groundwork for the evolution of one of the most successful groups of animals in Earth history.
The earliest synapsids in the fossil record come from the Late Carboniferous, just over 300 million years ago. Like other early amniotes, they are small and lizard-like, possibly insectivores. These are animals like Archaeothyris and Echinerpeton.
Several early branches of the synapsid family tree are collectively called the “pelycosaurs.” Though they started small and same-y, they evolved into a huge variety of carnivores and herbivores of all different shapes and sizes. In the Early Permian Period, they dominated ecosystems on land.
In general, pelycosaurs have sprawling limbs (like reptiles and amphibians) and often prominent canine-like teeth. Many, like the famous Dimetrodon (perhaps the least dinosaur-like animal commonly mistaken for a dinosaur), had dorsal sails – they were the first animals to evolve this feature!
One branch of pelycosaurs ultimately gave rise to the therapsids. As the Permian wore on, these newcomers would take over most of the major niches from their pelycosaur ancestors. Among the therapsids, a new selection of carnivores and herbivores, big and small, took to the scene.

A. Tetraceratops by Nobu Tamura; B. Diictodon by Nkansahrexford; C. Gorgonops by Dmitry Bogdanov; D. Moschops by Robert Broom; E. Placerias by Petrified Forest
These Permian therapsids aren’t mammals, but they’re a bit closer, standing more erect (like mammals do) and with a greater variety of teeth (also a mammal trait).
The therapsids included the largest terrestrial animals in the Middle and Late Permian. They included herbivores and carnivores, ranging from small animals the size of a rat (e.g.: Robertia), to large, bulky herbivores a ton or more in weight (e.g.: Moschops). After flourishing for many millions of years, these successful animals were all but wiped out by the Permian-Triassic mass extinction about 250 mya, the largest known extinction in Earth"s history, possibly related to the Siberian Traps volcanic event. Lystrosaurus was the most common synapsid shortly after the Permian–Triassic extinction event.
Only a few therapsids went on to be successful in the new early Triassic landscape; they include Lystrosaurus and Cynognathus, the latter of which appeared later in the early Triassic. Now, however, they were accompanied by the early archosaurs (soon to give rise to the dinosaurs). Some of these, such as Euparkeria, were small and lightly built, while others, such as Erythrosuchus, were as big as or bigger than the largest therapsids.
After the Permian extinction, the synapsids did not count more than three surviving clades. The first comprised the therocephalians, which only lasted the first 20 million years of the Triassic period. The second were specialised, beaked herbivores known as dicynodonts (such as the Kannemeyeriidae), which contained some members that reached large size (up to a tonne or more). And finally there were the increasingly mammal-like carnivorous, herbivorous, and insectivorous cynodonts, including the eucynodonts from the Olenekian age, an early representative of which was Cynognathus.
Unlike the dicynodonts, which were large, the cynodonts became progressively smaller and more mammal-like as the Triassic progressed, though some forms like Trucidocynodon remained large. The first mammaliaforms evolved from the cynodonts during the early Norian age of the Late Triassic, about 225 mya. During the evolutionary succession from early therapsid to cynodont to eucynodont to mammal, the main lower jaw bone, the dentary, replaced the adjacent bones. Thus, the lower jaw gradually became just one large bone, with several of the smaller jaw bones migrating into the inner ear and allowing sophisticated hearing.

Whether through climate change, vegetation change, ecological competition, or a combination of factors, most of the remaining large cynodonts (belonging to the Traversodontidae) and dicynodonts (of the family Kannemeyeriidae) had disappeared by the Rhaetian age, even before the Triassic-Jurassic extinction event that killed off most of the large nondinosaurian archosaurs. The remaining Mesozoic synapsids were small, ranging from the size of a shrew to the badger-like mammal Repenomamus.
During the Jurassic and Cretaceous, the remaining nonmammalian cynodonts were small, such as Tritylodon. No cynodont grew larger than a cat. Most Jurassic and Cretaceous cynodonts were herbivorous, though some were carnivorous. The family Tritheledontidae, that first appeared near the end of the Triassic, was carnivorous and persisted well into the Middle Jurassic. The other, Tritylodontidae, first appeared at the same time as the tritheledonts, but was herbivorous. This group became extinct at the end of the Early Cretaceous epoch. Dicynodonts are thought to have become extinct near the end of the Triassic period, but there is evidence this group survived. New fossil finds have been found in the Cretaceous rocks of Gondwana.
Today, the 5,500 species of living synapsids, known as the mammals, include both aquatic (whales) and flying (bats) species, and the largest animal ever known to have existed (the blue whale). Humans are synapsids, as well. Most mammals are viviparous and give birth to live young rather than laying eggs with the exception being the monotremes.
Triassic and Jurassic ancestors of living mammals, along with their close relatives, had high metabolic rates. This meant consuming food (generally thought to be insects) in much greater quantity. To facilitate rapid digestion, these synapsids evolved mastication (chewing) and specialized teeth that aided chewing. Limbs also evolved to move under the body instead of to the side, allowing them to breathe more efficiently during locomotion.This helped make it possible to support their higher metabolic demands.

Lisowicia bojani,a newly discovered Triassic mammal cousin probably was the largest of all non-mammal synapsids

Lisowicia bojani,a newly discovered Triassic mammal cousin that had a body shaped like a rhinoceros, a beak like a turtle, and weighed as much as an African elephant, about 9 tons.

at 20 feet (6.1 meters) and 2 tonnes.

Cotylorhynchus was a very large

Therapsida

Moschops was the largest therapsid, with a weight of 700–1000 kg, and a length of about 5 meters. Moschops (Greek for "calf face") is an extinct genus of therapsid that lived in the Guadalupian epoch, around 265–260 million years ago. Therapsids are synapsids, which were at one time the dominant land animals. Its remains were found in the Karoo region of South Africa.
Moschops was a roughly 2.7-metre-long (9 ft), massively built dinocephalian. It had a short, thick and massive head, which was broad across the orbits. The occiput was broad and deep, but the skull was more narrow in the dorsal border. Furthermore, the pterygoid arches and the angular region of the jaw were quite heavy, allowing the insertion of strong jaw muscles. Due to that and because it possessed long-crowned, stout teeth, it is believed that Moschops was a herbivore feeding on nutrient-poor and tough vegetation, like cycad stems. Due to the presumably nutrient-poor food, it very likely had to feed for a very long time. Its anatomy allowed Moschops to open its elbow joint more widely, enabling it to move in a more mammal-like way than the other crawlers in its time. That might have helped it to carry its massive body more easily while feeding.Very likely, most dinocephalians were rather slow-moving animals, but capable of raising themselves, for short bursts. It is also possible that Moschops and other dinocephalians were semiaquatic, given the heavy build and the limbs with their spreading hands and feet. The heavy head could have been useful for diving after food.
Moschops had a thick skull, prompting speculation that individuals competed with one another by head-butting.Some doubt whether the Moschops were born with thick skulls. If they were, then Moschops" short, heavy tail may have counterbalanced the weight of its head. Its main enemies were very likely titanosuchids and the larger therocephalians.
Moschops material was discovered for the first time by Robert Broom in the Ecca Group (part of the Karoo Supergroup) in South Africa. The geological horizon dubious, it was referred to that group on the basis of Pareiasaurus remains in the near. The material includes a holotype (AMNH 5550) and seven topotypes (AMNH 5551-5557). The degree of pachyostosis varies within the skulls of the specimens. According to Broom, it is because of gender and age variation within the discovered specimens. In 1910, the material was sent to the American Museum of Natural History in New York and it was described in 1911.
Moschops is characterized by a strongly pachyostosed skull with a broad intertemporal region and greatly reduced temporal fossae. Two species are known from good fossil record, M. capensis and M. koupensis. Two other species were assigned (M. whaitsi and M. oweni), but the validity is doubtful.
Genera regarded as synonyms are Moschoides, Agnosaurus, Moschognathus and Pnigalion.
Another taxon, Delphinognathus conocephalus, could have been a synonym also, as it could represent a juvenile Moschops. This taxon is known from a single, moderately pachyostosed skull. It has a conical boss on the parietal surrounding the pineal foramen.

Pareiasaurs (Pareiasauridae)

The largest is Scutosaurus, up to 3 metres (9.8 ft) in length, with bony armor, and a number of spikes decorating its skull Scutosaurus was a massively built reptile, up to 3 metres (9.8 ft) in length, with bony armor, and a number of spikes decorating its skull.Despite its relatively small size, Scutosaurus was heavy, and its short legs meant that it could not move at speed for long periods of time, which made it vulnerable to attack by large predators. To defend itself Scutosaurus had a thick skeleton covered with powerful muscles, especially in the neck region. Underneath the skin were rows of hard, bony plates (scutes) that acted like a form of chain mail.
As a plant-eater living in a semi-arid climate, Scutosaurus would have wandered widely in order to find fresh foliage to eat. It may have stuck closely to the riverbanks and floodplains where plant life would have been more abundant, straying further afield only during times of drought. Its teeth were flattened and could grind away at the leaves and young branches before digesting them at length in its large gut. Given that it needed to eat constantly, Scutosaurus probably lived alone, or in very small herds, so as to avoid denuding large areas of their edible plants.
The skull is about 50 cm wide.It is very broad, flat, and strongly sculptured, and bears bony protuberances in the jugal (cheek) and rear regions. As with some species of Pareiasaurus, with which it is clearly related, the quadrato-jugal or cheekbones extend outwards and forwards, makings an angle of about 120° with the maxillary border.With its large cheekbones, Scutosaurus may have been able to make a loud bellowing sound

Jonkeria