Imagine 20 million years into the future, when the Earth is barely recognizable and just a few million years prior the Earth went through a mass extinction larger than the ones caused by humans (which evidently also wiped those stinky mammals out too…). Due to a worldwide nuclear war millions of year ago, much of the world was brought into another impact winter. However unlike with the K-Pg extinction, a few large animals survived. Many larger reptiles like Pythonidae and Varanidae were capable of long term hibernation, along with crocodilians. Ratite birds were also another group to survive, although much less diverse than even what the Holocene had to offer. However most birds managed to survive and a few artificially bred or engineered organisms survived as well, but in sparse numbers.
Now millions of years after the human-created impact winter, lush green fertile valleys have sprang up across many regions across the world. Dense jungles and thick boreal forests cover much of North and South America, along with much of what used to be called sub-Saharan Africa. The polar icecaps only exist in small pockets, retreating to the very tips of the Artic Ocean and the Antarctic continent, further allowing colonization among those areas.
The Neotheropoda are an artificially created group that derived from Galliformes, ratites, Opisthocomus and Ardeotis. They are a result of the process of extreme backbreeding and the turning on of formally dormant genes. Although the first Neotheropoda were very similar to their ancestors, selective breeding for more primitive characteristics has drastically changed their appearances including colors, patterns, behaviors and basic morphology. All Neotheropoda possess teeth, which was turned on by humans and a long saurian-like tail, genetically lengthened from the adding of genes and prevention of the tail vertebrae from fusing during embryogenesis. The genes for the beak have been largely removed, allowing a crocodile-like snout with a hard keratin cover to replace the classic avian beaks that we most associate as birds having. In the process some strands of Neotheropoda were modified with the genes for the bone-infused plates that make up crocodilian skin and some lineages possesses bred features similar to those of Pachycephalosauria and Ornithomimosauria.
After the extinction of humanity, the diversity of these manmade corruptions of Aves almost went extinct. The long freezing temperatures drastically killed off most branches. However, a few were able to survive the cold temperatures, developing thicker feathers and new behaviors such as burrowing and huddling together for warmth. All in all, three branches descended from Galliformes, and a descendant branch of each of the terrestrial Opisthocomus and a cat-sized Ardeotis surprisingly beat the odds. These species would later heavily diversify in the continental regions they inhabited, which large included the now separated continents of what used to be North and South America. Though some species have diversified in more open-landscapes and herd animals outcompeting the few species of large mammalian herbivores that evolved from rodent and ungulate ancestors.
Paraxetheridea is the largest superfamily, of which some species can stand as tall as 4 meters (14 ft). The group is a distant descendant of Galliformes (possibly pheasants), and ranges among the lush mountainous areas of North America close to large bodies of water. Somewhat semi-aquatic, its omnivorous habits allow it to feed on most available food. Their multi-chamber stomachs allow them to digest and extract nutrients from otherwise non-nutritious food. Strangely, these birds lack significant plumage, with quilled feathers only appearing at the "wing" and back, making a somewhat mane-like appearance. This is something which is maximized on males to attract females, who are also extremely colorful. Color-wise, it is easy to draw their color as similar to Canada geese or even ostriches, with unique crests and facial patterns appearing on different genus and species.
There are two families which make up Paraxetheridea, Vonaxetheridae and Coxapantheridae, with the former being the larger and more aquatic group and the latter being a smaller rainforest-dwelling group that is significantly less widespread. Each family generally stays geographically separated from each other. The Vonaxetheridae possess thick-buoyant layers of fat similar to ducks and geese. These neotheropods are much more specialized for aquatic life and live on the edges of lake and rivers, possessing duck-like muzzles, which they forage with both above land and underwater.