Siren

The siren, known to the Teeth as the doppelganger, is the closest living relative of the leucrocottas. The ancestral leucrocotta and the siren diverged from each other no more than 5 million years ago, and together comprise their own genus of grassland-adapted forest unicorns. Of the two subgroups, the siren is the more derived, a fast-running, dog-like predator with extremely long legs for crossing over the vast and largely empty landscape of the central steppe. Both species are obligate carnivores, but of the two, sirens tend to have the wider diet, incorporating more very small vertebrate prey and large insects, and a small amount of plant material. Unlike the leucrocottas which are megafauna-hunting specialists, the siren hunts animals smaller than itself and lacks the strength to take on big game. But this does not mean they are no threat.

Sirens very closely resemble leucrocottas... to other species. To the Teeth, they represent the archetype of the uncanny valley - a creature indescribably wrong. Though the animals share a similar shape, sirens are much lankier. Though they always weigh less than leucrocottas (sometimes by almost half as much), they are about the same height. They are faster too, by at least ten miles per hour, which allows them to easily escape their more robust related rival during confrontations. There is only one hoof on the hind leg, in contrast to the three of the leucrocotta, which is related to its higher cursorial adaptation. Siren's facial structure is distinct from leucrocottas' in having a proportionally smaller skull with a narrower jaw, larger eyes (which are always an unnervingly bright gold, while leucrocottas ancestrally had dark eyes), and bigger, more upright ears. Their jaw shape relates to a diet much higher in small prey, while their eyes and ears relate to heightened senses due to a nocturnal lifestyle which differs from the more crepuscular nature of the leucrocotta. 

The crests of the siren are flatter and extend less distance above the eyes, and the nostrils open outwards rather than upwards, improving their ability to "throw their voice" in different directions to trick prey. The siren is so named for this trick; like its kelpie ancestor, sirens can mimic the voices of other animals to lure them from hiding. This ability extends to leucrocottas themselves, and the siren has a reputation as a thief of young children which it lures away in the night by mimicking the voice of a family member or close friend. Vocal mimicry is extraordinarily well-developed in this species, which can remember long conversations and play them back in the speaker's own voice, something the leucrocotta cannot do (though the whisperwing can.) But the siren is only pretending to be intelligent; it cannot use the words it picks up in context. It is only playing a ruse, and its intelligence is closer to that of a chimpanzee than a human being.

Unlike leucrocottas, which have become social predators in order to hunt bigger prey, the siren is largely solitary. Groups larger than a pair are very unusual, though couples are not that uncommon - they may be male/female, or a mother with a dependent young. Leucrocottas all but universally vilify the siren across their cultures and make active efforts to kill them wherever they meet, with varying success. Adults are mostly able to escape their pursuers, and smart enough to avoid traps and tricks, but their young are initially very vulnerable before they can quickly run; females hide them in caves and burrows, where leucrocottas can sometimes find and kill them. This has resulted in the functional extirpation of the species within Sanctuary Crater and the Fortune River Valley where leucrocottas are very numerous, though it is known to still occur along the unpopulated outer edges of civilization, and to occasionally venture into inhabited areas in the quiet of night to hunt. Outside these population centers, leucrocotta population density can be much lower, and so the siren survives in healthy numbers. It poses the greatest threat to more isolated outlying and nomadic leucrocotta communities, which have fewer eyes to spot the threat if it pops up in the night, and fewer technological defenses. 

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