The "1.2" means that there were three rhinoceroses, one male and two females. The number before the period stands for the number of males, and the number after the period stands for the number of females. If there is another period followed by a number, that third number will stand for the unknowns. That said, at this time the zoo has two Sumatran rhinoceroses, one male and one female (1.1), a father and his daughter.
