Because of melting ice caps about 120 million years ago, Bali and Lombok separated. The channel between these two islands marks the so-called 'Wallace Line', named after the great naturalist Sir Alfred Wallace. Sir Alfred observed, after 7 years of zoological and botanical research, that on all the island west of Lombok you find tropical vegetation, monkeys, elephants, Bengal Tigers, wild cattle, and straight-haired Asiatics, while on the islands east of Bali are thorny arid plants, cockatoos, parrots, giant lizards, marsupials, frizzy-haired Papuans, all typical of Australasia. The more advanced placental animals and flora which were beginning to evolve at that time in Asia proper were prevented entery over this turbulant 300 m deep strait. Thus, zoological Model T-Fords such as kangaroos and echidnas were allowed to proliferate on the islands east of Bali because of the absence of flesh-eating mammal predators.