built in 1957, defining the zoo as a separate area but still within City Park. Automobile traffic in the zoo was finally eliminated completely in 1959. Pachyderm Habitat was opened the same year, and Cookie was joined by a second elephant, Candy. The zoo opened the Feline House in 1964, a Giraffe House in 1966, and an Animal Hospital in 1969. Bird World was opened in 1975, followed by the Mountain Sheep Habitat in 1979, Northern Shores for polar bears, Arctic foxes, North American river otters, and pinnipeds in 1987, and Wolf Pack Woods in 1988. The Marine Mammal Protection Act of 1972 made it impossible to keep the polar bears and sea lions in the Bear Mountain enclosure. This and its deteriorating condition lead to a $250,000 renovation of the exhibit starting in 1987 ($ in dollars ). The exhibit reopened in 1989 with grizzly bears and Asiatic black bears occupying the northern two exhibits and coatis in the southern tip. 1990s-present In 1993, the zoo opened the $11.5 million Tropical Discovery exhibit. Designed by the Denver architectural firm Anderson Mason Dale, this indoor tropical garden topped by glass pyramids is the aquarium and herpetarium of Denver Zoo, and its opening doubled both the number of species and the number of animals at the zoo. Along with the animals, 90% of which had never been on display at the zoo, there are over 250 species of plants represented in the exhibit. On November 6, 1994, twin polar bear cubs Klondike and Snow were born to a first-time mother named Ulu, who rejected the cubs. They were successfully raised by zoo staff and became a popular attraction. The bears were transferred to SeaWorld Orlando. In 2012 Snow was transferred from Sea World in Orlando, Florida to the Reid Park Zoo in Tucson, Arizona, where she died unexpectedly on September 2, 2012. Klondike died at SeaWorld Orlando on September 13, 2013. Their story is commemorated at Denver Zoo by a bronze sculpture located across from the main polar bear viewing area. On February 24, 2007, a jaguar mauled zookeeper Ashlee Pfaff inside the animal's enclosure. The jaguar was shot and killed by the zoo's emergency response team while rescuing Pfaff, who later died of her injuries at a local hospital. This event occurred despite zoo policy prohibiting direct contact between keepers and big cats. An investigation by the zoo concluded the