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David Attenborough
More books on Animals and Plants
About 250mya, when fish were already eastablished in the sea, some of the cold-blooded animals that had by then developed four legsand colonised the land, began to return. Dinosaurs such as plesiosaurs and mosasaurs which became extinct, but also turtles and penguins.
Then about 50mya the ancestors of whales, and a few million years after that, bear family beasts gave rise to sea-lions and walruses. These latter creatures have not become as totally adapted to marine life as the whales. They still retain their hind legs and they still have to come to land to mate and give birth.
There are many species of mangrove, from different plant families, but the rquirements for living in brackish swamps has led them all to develop very similar characteristics. They cannot send down deep roots, bc the mud just below the surface is corrosively acid. Instead they send out broad platform of horizontal roots.
Seaweed is basically marine alae. Plants in sea lot less complex bc don't need support, don't need to transport water, and don't need to organize seed dispersal. Don't have sap, so the saltiness of sea not a problem.
Town dwelling pigeons are descended from wild rock doves. Afew still live in the wild but they are vastly outnumbered by urban descendants.
DNA testing shows that wolf-dog ancestor was not like today's wolves. The ancestor has died out, leaving the two canine cousin lines.
Reindeer herds are followed bu Sami nomads. Although they do not control the wandering of the herds, they have altered them. Young males usually driven off by dominant stags to wander off and establish own groups. To prevent theselosses, the Sami castrate most young males. The males selected to survive entire are most docile ones. Now the reindeerare happy to stay in huge herds of a thosand or so, which is something their N Am cousins, the caribou wll not do.
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