Rampaging Dinosaur
First appearing to the entire Gantz team in Chapter 152: Unavoidable, the Brontosaurus Alien is a dinosaur behemoth that emerges from the Tokyo museum after the Gantz team had finished destroying its smaller dinosaur brethren. Initially, he is seen fighting with Izumi. It is a colossal creature, having the resemblance of a dinosaur, but with humanoid eyes and large tusks extending from above and below its head. This alien is considered the "boss" of the Jurassic mission.
After smashing its way out of the museum, it tells the Gantz team that it will "destroy the ones who have inflicted pain upon my children" in reference to the smaller dinosaur raptors that the team had annihilated earlier. Kurono decides to take the blame and tells the boss it was he who killed its children and tries to lure the alien away from the other Gantz members. With aid from Izumi, Kurono is able to kill the Brontosaurus Alien.
The alien (Due to its size) posesses incredible strength. It has two horns which make a cresent like shape on its head, these horns made of an extremely sharp material and act more like swords than horns, due to their slashing potential. The sharpness of the sword is comparable to that of the Gantz swords, it can cut clean through almost anything, suits included, it is also quite accurate considering the speed at which it swings its head, and how hard it must be to see when attached to ones head. Another one of this alien's traits, is the immense speed at which is can swing its "sword" adorned head, with even a skilled swordsmanship specialist such as Izumi struggling to keep up with the speed, and stated if not for the suit, he would die near instantly. Even the notoriously quick and agile Kurono has difficulty tracking its speed, although he didnt have a suit at the time. And finally, the alien is able to manifest "new" eyes at will nearly anywere on its body, most prominently making them appear on the underside of its belly, the one place many would think it cannot see. This prevents people exploiting its species seemingly only weak point.