Skycetaceans

Skycetaceans are a group of whales that, unlike any other life on earth, doesn't need wings to fly, instead, they have helium-filled organs in order for these whales to be completely airborne, even when born and even if they're much heavier than any other life forms native to earth. They fly by "swimming" with their strong flukes on their tails and use their flippers for steering while swimming in air. While aquatic cetaceans rule the seas, skycetaceans rule the skies alongside flying birds. Just like aquatic cetaceans, they range in size from the 1 m (3 ft 3 in) and 50 kg (110 lb) Maui's skydolphin to the 29.9 m (98 ft) and 190,000 kg (420,000 lb) blue skywhale, which is also the largest animal ever known to have existed.

Several species exhibit sexual dimorphism. They have streamlined bodies and two (external) limbs that are modified into flippers. Though not as flexible or agile as birds, skycetaceans can swim very quickly, with the killer skywhale able to travel at 56 kilometres per hour (35 mph) in short bursts and the fin skywhale able to cruise at 48 kilometres per hour (30 mph). Skydolphins are able to make very tight turns while swimming at high speeds. The hindlimbs of both cetaceans and skycetaceans are internal, and are thought to be vestigial. Baleen skywhales have short hairs on their mouth, unlike the toothed skywhales. Skycetaceans have well-developed senses—their eyesight and hearing are adapted for both air and water, and baleen skywhales have a tactile system in their vibrissae. They have a layer of fat, or blubber, under the skin to maintain body heat in cold environments. Some species are well adapted for flying to great heights, sperm skywhales, for example, can fly up close to earth's atmosphere without any harm to these whales. Skycetaceans produce a number of vocalizations, notably the clicks and whistles of skydolphins, the moaning songs of the humpback skywhale.

Skycetaceans are widespread across the entire planet, with many adapting to human settlements as all known skycetaceans are very friendly and seem "tame" towards humans, dylanus, and all land dwelling animals, but feeds only on small flying birds including starlings, swallows, etc. Male skycetaceans typically mate with more than one female (polygyny), although the degree of polygyny varies with the species. Skycetaceans are not shown to have pair bonds. Male skycetacean strategies for reproductive success vary between herding females, defending potential mates from other males, or whale song which attracts mates. Calves are typically born in the fall and winter months, and females bear almost all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively short period of time.

Evolution
During the Late Oligocene period in some of the world's oceans, prehistoric baleen whales and toothed whales were struggling due to an extreme food shortage, the biggest food shortage for whales in earth's history, so many had to adapt by becoming smarter, more predatory, smaller/larger, and or faster, leading into modern aquatic cetaceans, both marine and freshwater dwellers. But some early baleen whale and toothed whale species had evolved a helium-filled organ, they had left their ancestor's former homes, taking to the skies for the very first time, making them the first ever animals to fly on earth without wings of any kind.