Dinosaurs aren't the only group of giant reptiles that inhabit Tapiri.

During the onset of the Pliocene, a large number of the continent's native dinosaur species suddenly died out for as-yet unknown reasons, leaving a wealth of niches open for megafauna. These niches would quickly be filled, not by mammals as they would have in most other parts of the world, but by notosuchians, quickly diversifying into a group that could no longer be reasonably considered crocodilians. So began the rise of a new dynasty, one whose descendants's footsteps would shake the very earth the world over: the retrosaurs.

A battle between an agathaumid and a tyrannoverum, two of the most well-known varieties of retrosaurs.

Most retrosaurs have digitigrade limbs that stand mostly erect, rather than sprawling out like the limbs of typical crocodilians, giving them a considerable advantage over their relatives when it comes to endurance running. Strangely enough, unlike their notosuchian ancestors, retrosaurs are typically endothermic, meaning that they rely on their environment to provide them with heat rather than producing it themselves, although a few species have redeveloped a form of endothermy. As a result of this, retrosaurs are on average more resistant to diseases than dinosaurs are, and generally eat quite a bit less than a similarly-sized dinosaur would. In colder climes, the enormous size and thick hide of most retrosaurs keeps them warm, but smaller species are known to have trouble in such weather.

In terms of diversity, retrosaurs are neck and neck with their cousins the dinosaurs, even rivaling dragons in the sheer variety within their group: species range from predators of all shapes and sizes to tiny scavengers no bigger than a sparrow to enormous armor-plated herbivorous giants to titanic ocean-dwellers to blood-drinking flyers.

"Advanced" Carnivorous Retrosaurs are split into four groups: Paleo Tyrants, Transitional Tyrants, Flying Tyrants, and Sea Tyrants.

Bipedal creatures with digitigrade legs, the Paleo Tyrants are remarkably fast despite their reptilian metabolisms, and are armed with saber fangs and razor sharp claws on their hands and feet. Many Paleo Tyrants have short, thin arms, which border on being vestigial in a few species. The Paleo Tyrant clade is split into three subclades: True Tyrants, Tiny Tyrants, and Egg Thieves.

While most Retrosaurs are large, Tiny Tyrants are exceptions to this rule. Few are larger than a dog, with some species being little larger than a chicken. They were not nearly as successful in their evolutionary history as their larger cousins, as they were in direct competition with small Coelurasaurids and Maniraptorans.

However, one group- the Pithecusaurs or "Ape Lizards"- began converging on a more primate-like body plan (interestingly, this was a route also being taken by the unrelated Chameleoniforme lizards known as the Sauropithecines at roughly the same time in Zebrica).

Common Pithecusaur

Highly intelligent, these reptiles, while non-sapient, are capable of advanced tool use similar to the habits found within non-sapient primates like the Capuchin Monkey.

Unlike many Tiny Tyrants, they are omnivorous, and the majority of their diet consists of small animals and fruit. The fruit part of their diet may be a key as to why they are so intelligent, as finding fruit involves remembering both where the fruit trees are and when they come into season.

Sickle-Foot

A solitary hunter found from the Pampas of Tapiri to the plains of Concordia, this beast lacks the endurance of many true dinosaur predators, and so prefers to set ambushes via simple traps.

Dire Pithecusaur

A native of a Tepui chain to the south of Kaku Hidi, the Dire Pithecusaur is the undisputed apex predator of its home

Prairie Lizard

A burrowing, social species that is essentially a reptilian meerkat

Ape-Raptor

Pack-hunting, baboon-sized predators who roam the mountain forests of Tapiri in groups led by a single alpha male.

The alpha uses pheromones to suppress the hormones of the subordinate males, ensuring he stays in charge.