Ursa

The Ursa are a genetically-modified species, created by the Skrel race and released onto Nova Prime. They were made to specifically hunt and kill Humans.

Biology
Ursa are large creatures, the latest generation (Ursa Maximus) growing around nine to ten feet tall (~ 2.7 to 3 meters). They are hairless, with their pale skin and muscle tissue exposed. As they are genetically modified and engineered, they've gone through numerous regenerations and differentiating forms thanks to the Skrel's attempts to make them a deadly predator against Human beings.

First generation (576 A.E.)
The first generation created by the Skrel were designed as a typical predatory creature: four appendages ending in sharp claws, and insatiable hunger, and no vision in order to rely on its sense of smell which is described as being 100 times stronger than a Human's. Three dozens were released, and this generation slaughtered Humans left and right until the rangers found weaknesses they exploited.

Second generation (651 A.E.)
The secondary generation were built more as a speed demon with a hollowed-out bone structure and an extra set of joints in their limbs for flexibility and locomotion. One of the back legs was removed, however, and made thicker for stability or use similar to a scorpion's tail. Three dozen were released, but the rangers were better prepared (albeit their success was slower), and prevailed.

Third generation (726 A.E.)
The third generation were reverted back to a four-legged anatomy. This generation was given an extra set of arm-like appendages, sharper claws, and their bony protuberances were covered in densely packed keratin. This is also the first generation to be using the species' iconic black venom, this type causing paralysis upon contact. Five dozen were released this time, and while Humans did prevail again, they determined the original purpose of the Ursa from this generation.

Fourth generation (801 A.E.)
The fourth generation didn't undergo any major physical altering, but this generation was given the ability to track down Humans by their scent from their fear. This is also the first generation to show signs of reproduction, indicating that the Skrel planned to have them as a permanent part of Nova Prime's ecosystem, making this generation self-perpetuating. Six dozen in two different releases were made, causing more destruction than the previous but were wiped out by Humans in fear of their reproduction.

Fifth generation (876 A.E.)
The fifth generation of Ursa had their venom turned from a paralyzing venom into a corrosive venom, capable of burning through flesh and bone upon contact, and their digestion system converting anything they eat into energy on a cellular level. The biggest alteration in this version was their ability to camouflage themselves thanks to added chromatophores placed under each layer of skin, with a transparent outer layer. This allowed them to remain almost invisible until their prey was right in front of them. A hundred were released and it took over a decade to wipe them all out.

Sixth generation (951 A.E.)
The sixth and latest generation (Ursa Maximus) was made the largest known generation of Ursa. They went through a major skeletal change, with metallic material bounded to the organic skeletal structure on a molecular level. A virtually indestructible carapace was the result of this alteration. Much of their behavior was also altered: they only require five one-hour sleeping periods over a full night's sleep, and are able to imprint on specific targets of interest. This generation, unlike the ones before, became more elusive and as such managed to better survive and made numerous attacks on the Human population.

Appearances

 * After Earth (2013)