Sahul

Sahul, paleocontinent made up of the present-day landmasses of Australia, Tasmania, and New Guinea and the land bridges (which were composed of nearby emergent sea basins) that connected them during the Pleistocene Epoch (2.6 million to 11,700 years ago). Sahul existed from the onset of the Pleistocene Ice Age, which lowered sea levels by about 131 metres (430 feet), to about 18,000 years ago, when rising waters from melting continental ice sheets reclaimed low-lying areas. Some researchers estimate that Sahul was about 30 percent larger than the collective area of present-day Australia, Tasmania, and New Guinea, which would mean that it measured 11,062,000 square km (4,271,200 square miles), making it slightly smaller than Antarctica.

Geographically, Sahul was located at the same latitude as present-day Australia and New Guinea. Cartographic depictions of Sahul often retain the basic shape of present-day Australia, with the size of the landmass enlarged to incorporate New Guinea and Tasmania as well as the nearby continental shelf—which included the dry emergent seafloor of the Arafura Sea, the Bass Strait, the Gulf of Carpentaria, and much of the Timor Sea. Some depictions also show the presence of large lakes in the low-lying areas between Australia and New Guinea (within the Carpentaria Basin), between Australia and Tasmania (within the Bass Basin), and within Sahul’s interior.

Sahul’s equatorial mountain regions were likely dominated by tropical rainforests, while the Timor, Arafura, and Carpentaria areas made up a large region of savanna and tropical dry forests. Areas farther south likely mirrored the biomes of modern Australia—that is, a large interior desert that extended from the continent’s western coast to the southern coast, which was separated from the northern forests by scrubland, with steppe and temperate forest habitats along the continent’s eastern coast. Sahul’s tallest mountains were the New Guinea Highlands, a ridge whose peaks topped 4,000 metres (13,000 feet).

Human beings (Homo sapiens) first reached Sahul from Sunda (a region made up of Southeast Asia, Java, Sumatra, Borneo, the Philippines, and the emergent parts of the Java Sea and South China Sea basins) and Wallacea (a region characterized by numerous archipelagos between Sahul and Sunda) sometime between 45,000 and 50,000 years ago, though some modeling studies suggest that humans may have arrived as early as 75,000 years ago. While the specific details of how humans reached Sahul from Asia remain unclear, modeling studies note that people could have made short sailing trips from one visible island on the horizon to the next across Wallacea before landing in Sahul.

Sahul’s vertebrate fauna was largely characterized by marsupials whose ancestors likely migrated to the Australian portion of Gondwana from South America before South America separated from the ancient supercontinent some 140 million years ago. Australia had broken away from Antarctica by about 30 million years ago, which allowed the continent’s life to evolve on its own afterward. Some of the largest marsupial species included Diprotodon—a genus of giant wombats that included the world’s largest known marsupial, D. opatum, which likely weighed more than 2,700 kg (about 3 tons) and measured as much as 4 metres (13 feet) long—and the marsupial lion (Thylacoleo carnifex), which weighed about 90 kg (200 pounds) and measured 1.5 metres (4.9 feet) long. Other large animals included the Megalania (Megalania priscus or Varanus priscus), the largest known lizard, whose length ranged from 3.5 to 5 metres (about 11.5 to 16.4 feet). All species on Sahul weighing more than 40–44 kg (88.1–97 pounds), along with several other species weighing less than 40 kg, went extinct about 42,000 years ago. While the specific circumstances of this die-off remain elusive, many researchers note that it likely resulted from a series of environmental factors, including climate change and desertification, rather than from human hunting pressure.