January 21, 2010, 10:55 Science Text size A A A

Madagascar settled stream

Animals settled Madagascar by swimming across the Mozambique Channel

Alexandra Borisova Small mammals populated Madagascar by crossing 422 km of the Mozambique Channel on natural rafts, and not by crossing the now-vanished land bridge, as previously thought. Computer modeling of ocean currents from 65 million years ago showed that they were capable of transporting trees and their small inhabitants from Africa to the island.

Islands remote from the mainland - Easter Island in the Pacific Ocean (3703 km from Chile ), Saint Helena Island (2800 km from Angola ) and the Tristan da Cunha archipelago (2816 km from South Africa ) in the Atlantic - have always been a mystery and a subject of debate among scientists . How and when did people get there using only primitive means of transportation? How did isolated civilizations develop and why was ancient colonization not repeated? Many of these questions will never be answered; extinct cultures keep their secrets.

Against the backdrop of such a scale, the island of Madagascar seems almost part of the mainland: the minimum width of the Mozambique Strait (by the way, which is the longest on Earth - 1760 km), separating the island from Africa, is “only” 422 km.

But Madagascar keeps its own mystery. If the flora and fauna of Easter Island, for example, was completely isolated and became extinct with the advent of “imported” species, then Madagascar was colonized by African animals 65 million years ago. Little sailors - lemurs, flying foxes and narrow-striped mungos - were able to cross the strait. But how?

answers this question A study published in today's issue of Nature . Scientists believe that the island's biodiversity was determined by the direction of ocean currents.

At a certain period in history, the waters of the ocean moved exactly from the mainland to the island, transporting furry sailors there on natural rafts.

Now the Mozambique Strait is characterized by a stable (albeit rather slow - 1-1.5 knots) current from north to south. In this situation, passive sailors will be carried towards the Southern Ocean, and they will not be able to reach Madagascar.

However, professors Matthew Guber from Indiana and Jason Ali from Hong Kong found that millions of years ago, ocean currents in this region looked very different. Traveling from the mainland to the island was not only possible, but also very fast - without this, the “colonizers” would not have reached the “desired” shores alive.

Interest in studying the flora and fauna of Madagascar has not dried up for many years. Its isolation from the continents made it a living laboratory for evolution. The number of endemic (found only in one territory) animal species in Madagascar is truly enormous - only Australia has a larger number of such species . For example, the island is home to 70 species of endemic lemurs, and 90% of the mammals inhabiting this piece of land are endemic.

It was initially believed that the animals came to Madagascar by land back in the days when it was part of the mainland. This hypothesis was put forward in 1915. It seemed logical: it is unlikely that mammals could make such a long journey across the sea without dying of hunger or being washed away from trees or pieces of grass by storms.

However, further research showed that Madagascar became an island at least 120 million years ago, and the first animals appeared on it much later - about 65 million years ago. So the “bridge” hypothesis became untenable.

In 1940, paleontologist and evolutionary theorist George Gaylord Simpson first hypothesized that animals could have arrived in Madagascar as a result of a “lottery” change in ocean currents. This happened only once, after which the species that found themselves on the island evolved independently.

The authors of the article claim that they were able to verify Simson's guess.

For three years, scientists conducted computer simulations of the ocean currents between Madagascar and Africa as they were millions of years ago.

During this time, Madagascar and Africa continued to drift (like all other continents), as a result they shifted significantly to the north, which could not but affect ocean currents.

The parameters that characterized the environment of that time were taken as the initial conditions for the computer model of the ancient ocean. The planet was much warmer - so much so that crocodiles lived in the Arctic regions not covered with ice. Modeling showed that in the period 60–20 million years ago (it was at this time, according to biologists, colonizing animals arrived in Madagascar) ocean currents carried the waters of the Mozambique Strait to the east, just towards the island. The current was fast enough to allow smaller, hardier mammals to reach the island. Large animals could not withstand the road. At the same time, the weather in the region then (as now) was unstable. Frequent tropical cyclones and storms tore trees from the ground and carried them into the ocean along with their small inhabitants.

These data allow us to consider the “maritime” theory of the colonization of Madagascar to be completely justified and correct. Indirect evidence - the dating of the separation of Madagascar from the mainland, the appearance of animals native to Africa on it, as well as the absence of large African predators on the island - are in full accordance with it.