Weird and wonderful world

Australia, 65 million years ago. Another place from which no Maastrichtian fossils are known and which is full of entirely fictional descendants of Early or Middle Cretaceous fauna. The climate changes have turned this place from a temperate forest into an open, more steppe-like habitat, where animals have to grow large, be fast or hide underground to survive. And what makes this still one of the most extraordinary locations during the Cretaceous is the fact that it features both hot summers with 24 hours of sunlight and cold winters in total darkness.
The most successful dinosaurs of Australia are the Hypsilophodonts. Multiple species are known from the Middle Cretaceous Dinosaur Cove like Atlascopcosaurus, Fulgurotherium and most notably Leaellynasaura. Leaellynasaura amicagraphica is noteworthy for its large eyes enabling it to find food during the dark winters and its freakish long flexible tail which was probably covered in some sort of fuzz (as the fluffy Ornithischian Tianyulong shows Coelurosaurs weren´t the only fuzzy dinosaurs) to wrap around the body and keep it warm. Its descendant has kept these traits and also spends more time in burrows. While they do have robust beaks and strong arms their burrows are mostly made by their cohabitant, another species of Hypsilophodont showing distinctly greater adaptations for digging like shovel-like hands and claws and a massive beak. The two species live in a mutual relationship – the short-legged species digs the burrows for its relative´s clan and in return the clan shares the food it collects with its lodger.
Most of the theropods here have evolved into cursorial omnivores which will eat anything they can find. Two fragmentary theropods known from Early Cretaceous Australia were Kakuru kujani and Timimus hermani. Their true relationships may stay a mystery forever, but in this scenario Timimus has evolved into an Ornithomimid-mimic or may actually be part of that family while Kakuru has evolved into an Oviraptor-mimic. They have found quite different solutions for the annual winters: The Kakuru descendant uses its strong beak and large claws to kill any small creature active during that time, mainly the Leaellynasaura descendants. As examination of Timimus´ bones show it stopped growing during the winter months likely because of hibernating and the same is true for its descendant. During hibernation it survives thanks to the energy it stores in the hump on its back (unlike Spinosaurids this hump isn´t supported by any tall neural spines).
Larger dinosaurs have to migrate north to survive the winters. The largest dinosaur of Maastrichtian Australia is a Macronarian sauropod, either descended from Wintonotitan or Diamantinasaurus. Their placement is still uncertain but they appear to be titanosaurs. They are hunted by the apex predators of Maastrichtian Australia, a giant Neovenatorid descended from Australovenator wintonensis. These polar predators are equipped with serrated teeth and massive talon-like claws on their hands. More familiar fauna are armored descendants of Minmi paravertebra and the honking ornithopods, descendants of Muttaburrasaurus langdoni. Because of the hard life conditions even these animals are not exclusively herbivorous and add grubs and carrion to their food supply.
But dinosaurs are not the only creatures inhabiting Australia. One of the weirdest animals of our own timeline, the platypus, is a common sight in the prehistoric rivers. Early Cretaceous Monotremes like Kollikodon were among the largest Mesozoic mammals known and their descendants are going to keep this title. Other creatures inhabiting the rivers are Temnospondyls, giant ancient amphibians often called “Labyrinthodonts”. The Early Cretaceous Koolasuchus cleelandi was the last species of these amphibians known and likely survived in Australia because the water was too cold for crocodiles. But with no fossils known from Maastrichtian Australia, why shouldn´t Temnospondyls have lasted till the end of the Cretaceous (when the water was still too cold)?
The sea around Australia and New Zealand is prowled by giant marine reptiles.