Anseriformes is a diverse order of Neognathae. In the midst of avian domination, they were the most diverse order after the passerines. Anseriforms evolved somewhere during the late Maastrichian, with Vegavis as the first representative. They are characterized by the internal structure of their rostrum; their highly modified tongue cooperates with the bill to suck liquid inside. There are also lamellae within the bill. The anseriforms survived the K-Pg event, and radiated during the Cenozoic. Molecular studies show that the ancestors of the basal anseriforms and advance anseriforms diverged during the Cretaceous despite the lack of fossil specimens. Like all birds, they easily survived the Eocene glaciation. By now, they radiated once again and filled virtually the niches that are filled by large mammals in our timeline. And one of the reasons is the presence of a pecten, a comb-like structure whose function is to filter food, in this timeline they are broader and more robust, and serve the function of teeth. The next step was to masticate, so instead of moving the lower jaw, they move the upper jaw.
These are the basal anseriforms, probably ancestral to later anatoids in our timeline. In this timeline, the phoenicopterids never evolved and they radiated into a variety of forms. They divide into two distinct clades, Mastimornithidae and Sacrostridae. For the most part, they are filter-feeders, using their bristle-like pecten to scoop edible particles and small organisms into their mouth. There is a membrane between the toes, which helps paddle water during swimming.
Having to evolve during the late cretaceous, they are closely related to Vegavis and diverged from the main line somewhere during the early Paleocene. They acquired the niche of flamingos and at least in our timeline, became extinct during the Oligocene, at the same time as true flamingos started to appear. However, in this timeline they radiated. It is divided into two distinct clades, the more anatid-like basal Presbyornithinae and Paranatinae, the latter evolved during the Miocene. The former retain a broad duck-like bill and their pecten isn’t prominent. The latter live in large, closely knitted groups, especially during the breeding season. They have bills whose tip is pointing downwards and its tip is circular in shape. While its highly modified tongue suctions water within the mouth, the lamellae are vestigial and are nearly absent. The latter is much more diverse and is found throughout gondawana, and some even evolved into semiaquatic forms. During winter in polar and continental regions, they huddle in dense groups, which minimize heat loss by fifty percent.
They are the descendants of presbyornithids, and most species are the dominant herbivores in their ecosystem. A sagittal crest is present, and it is attached with muscles for mastication. The pecten is very broad, and they develop into high cusp-like crowns typical of a grazer. Then they store their food within the crop, were bacteria digests it. During the breeding season, the females and males produce crop milk and the skin around the sagittal crest in females become brighter, while the males roll around in mud and slow down (which allows algae to grow in their skin) to camouflage their plumage. In one subfamily, Iubarostrinae, the nasal bones face upwards and during the mating season, a piece of cartilage grows from the tip of the nasal bone and a dewlap develops there. Whenever a male breathes in, it produces a very deep, sound, and it is one of the few species which can control the rate of breathing. In both sexes, the crest becomes very colorful, and although the female lacks the nasal structure that males possess, they instead produce slightly lighter sounds by closing the nostrils with nasal muscles. Males are polygamous, and mate with a variety of females, and to do so they hit each other with their heads. In order to avoid brain damage, the cranium is really thick, in order to absorb the force. In one species the domish structure is the base of a singular, very large horn, which is attached to the nasal structures. The anterior pecten is shed every year and they form antler-like protrusions which are used as mating devices to signal their strength. Healthy males would send blood and the antler-like protrusions will turn bright red.
Their young are born almost fully developed, and their displaying organs are already developing. Once the mating season is over, the herd separates and they live a solitary life feeding on grass. However, during this time of plenty, they are willing to share land with non-relatives. Unlike the dentaves, they have a different birthing strategy, they take care of a fully developed, single or triple young until it is big enough to live a solitary life (the juveniles wean and escape from their mothers by the end of the mating season).
Dentaves, as they are called, are the dominant predators in every continent except for two, South America and Antarctica. The pecten is curved and is serrated and it continuously grows, as a result they gnaw in order to shorten their pecten. Like their nearest relatives (the mastimornithids) they have a very thick cranium to resist the force during rut. The most special trait is the presence of two glands, which are modified internal sebaceous glands carrying symbiotic, fatal bacteria that can cause infection. The glands secrete the liquid and dissolve it into their saliva, and once they tear a chunk of meat, they spit the bacteria. The bacteria not only poison the prey, but also release an enzyme which digests it. They have primitive nasal sacs too supported by a nasal bone. The membrane surrounds the nasal cavity and the male distinctively roars in order to attract mates or to frighten predators.
Dentaves have a short incubation period, as lengthy as a few weeks. Their young are born helpless, and they require a long ontogeny. This is their birthing strategy; they take care of a dozen young for a year extensively, so that mortality rates are very low.