Species: scp-3199
SCP-3199 is a monstrous humanoid hybrid species from the mythos of the SCP Foundation website. Their debut story, SCP-3199 — Humans, Refuted was posted in May 2017 by a writer known as bittermixin. The story and thusly SCP-3199 are loosely based off of an anecdote from the 4th century BC where the philosopher Plato of Athens laconically defined a human as a "featherless biped", to which the cynic Diogenes of Sinope presented a plucked chicken with the announcement "Behold! I've brought you a man," (both quotes a translation of course, as the anecdote originates from Ancient Greece.)
SCP-3199 are a Keter-class object contained by the SCP Foundation after their discovery in rural Ireland. They are a genetically-engineered species of large roughly humanoid and avian features, which a recovered journal indicates they were created by a mad scientist with the vision to eradicate and replace humanity. DNA testing of the creatures have identified genome portion from chickens (Gallus gallus domesticus, Silkie breed), chimpanzees (Pan troglodytes), stoats (Mustela erminea), freshwater pearl mussels (Margaritifera margaritifera), cross adders (Vipera berus), and of course humans (Homo sapiens). SCP-3199 instances are opportunistic hunters that will try to ambush and kill any animal that it encounters within a 0.6 kilometer radius of its nest, liquefying their victims' cadavers and feeding it to the adolescent chicks of their brood.
SCP-3199 are 2.9-meter-tall bipeds and flightless, but possess significant terrestrial movement and flexibility. The average specimen can run 25 kilometers an hour, just over three times as fast as the average human, and (due to cervical vertebrae composed of cartilage and not bone) can dislocate their necks and rotate their heads 340° left or right. SCP-3199 (both on average) weigh about 360 kilograms upon hatching and up to almost 800 kilograms upon maturity. As they are featherless and nearly hairless, their appearance is dominated by white skin coated in a thin film of an albumen (egg white)-like excretion.
On the subject of nests, SCP-3199 reproduce asexually. Specimens do so by screaming loudly and regurgitating eggs covered in highly corrosive structure superficially resembling placenta. These eggs are large and rubbery yet nearly indestructible, their durability and pliability attributable to their bivalve and viper DNA respectively. While they will eventually hatch normally, the process can be accelerated or decelerated by increasing or deceasing the heat of the surrounding environment. The most concerning aspect about SCP-3199's reproduction is the fact that SCP-3199 has the ability and instinctual desire to rapidly fill any and all available open space with its eggs. Additionally, every instance of SCP-3199, regardless of age, will contain at least one egg inside them at all times that is capable of surviving even upon death of parent, thus preventing the species from going extinct unless all eggs are managed to be destroyed before hatching.
Due to the difficulty to keep the population in check brought by their resilience, their rapid reproduction, and their predatory nature, SCP-3199 has the potential to cause an LK-Class Species Transmutation End of the World Scenario; meaning that they pose the risk to replace humankind as the dominant lifeform on the planet Earth.