Paramammalia

These are a new clade of animals, which evolved from a specialized group of archosaurs informally known as "mammalsaurs", during the Triassic. The mammalsaurs were all small, homeothermic archosaurs, which had rings of feather like integument around their ears and fur like integument covering their entire body. The first definitive paramammals were first found in the mid Jurassic, in Poland. The biggest difference between mammalsaurs and paramammals is that paramammals have modified their skull bones. Their quadrate, angular, and surangular skull bones have shrunk to be used as ear bones. The arrangement of these bones have allowed paramammals to have a much better degree of hearing than any archosaur. They are also all covered in unique integument, which are similar to feathers or fur.

These earliest paramammals were small, but still wildly diverse. Most were quadrupedal, although a few unique forms, like †Jerboamimus, were bipedal. They were mostly nocturnal, and they all had some form of hard keratinous beak. These early paramammals all laid eggs, which is something that is later modified by several different groups.

Later on, during the Cretaceous, paramammals rafted to Australia and Zealandia. They diversified into many different forms there. One family, the †Bubomimids, evolved extremely maniraptoran body shapes, including the type genus, †Bubomimus. Others were simply very tall, more bird like animals, like †Megalatrymimus. They diversified all across Zealandia and Australia, and were very successful. However, they, unlike other paramammals, were highly specialized and not adaptable, and ended up going extinct during the Maastrichtian.

However, during the Campanian, a new infraclass of paramammals arose; the Panserinia. They had evolved a new way of reproducing. They still laid eggs, but they had a special pouch, where they laid their eggs. The eggs, once laid, would remain in the pouch, which is sealed off by a special sticky oil produced in the skin, which it secretes and seals the pouch. This allows the mother to still hunt and feed and move around instead of having to look after a nest. The hatching time is also incredibly speeded, with the eggs hatching only after two weeks. These became the dominate paramammals of the southern hemisphere, spreading out across Antarctica, Africa, and South America. Today they are relatively common, although their range has slightly increased, now they can only be found in some parts of Argentina, but are particularly abundant in Antarctica and New Zealand. They are the most cold adapted of the paramammals.

The second infraclass of paramammals are the Petarsialia. They are unique in that they give birth to live young. They also exhibit less parental care, as their young are born able to walk, run, and jump. They are amongst the more common paramammals, and can be found in almost every continent, except Antarctica, Australia, and Zealandia.

The third infraclass known are the Australokipansonia. These are primitive paramammals found in New Zealand, which retain many primitive features, such as oviparity. They were remarkably diverse, but have since been outcompeted, to the point that only three species remain, two of which are critically endangered, and one that is vulnerable.

The fourth and as far as is known last living infraclass are the Xartchetia. These are very bizarre, poorly understood nocturnal paramammals endemic to Siberia. They have only recently been described, and only two definitively identified living species are known, though some taxonomists argue that there are five. Fossils have been found of them dating back to the latest Maastrichtian (65.5 million years ago), and appear to have once been very diverse and ranged all across Russia and Poland.

This group exhibits a diversity that surpasses that of birds and mammals (combined) in our world, and now are the dominant organisms on Earth.