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CHAPTERS ELEVEN AND TWELVE Geographical Distribution In which Darwin demonstrates the importunce a/geographical barriers and climate change to exploin the distribution of life as we see ittodoy Penguins are charming birds with 1500kilometres. Already the ancestral between 17 and 20 species, depending penguins had almost lost their wings. on which classification is used. They Fossils and DNA each showthatthe take avarietyofforms, ranging from penguins' spread matches the advance . the statuesque emperor found inthe and retreat of the ice. Starting around Antarctic, to the fairy penguin of 35 million years ago, a series of ice ages Australia, just t/20th its weight. Other made the Antarcticuninhabitable, and penguins llve In Newzealand, South the birds retreated northwards as the Africa, SouthAmerica and the Galapagos. glacier spread. In addition,Icy currents Theycannot lIy (although the DNA swept some westwards, eastwards and suggests that albatrosses are among closer to the equator. theirclosestrelatives), so how did they Afterto million chillyyears, the world reach such scatteredplaces? warmed, cooled and warmed again, and Theoldest penguin fossils appear the birdsfollowed the retreatingedge of shortly after the demise of the dinosaurs the ice sheet into the far south. Theyieft around 65 million years ago. This behind colonies scattered on cold-water ancestor of all living specieslived in shores across the globe. In the years southern New Zealand and Marie since then, isolation and the challenges Byrd Land, Antarctica, which were at faced by eachseparate group have led that time separated by less than to the diversity of penguins seen today. CHAPTER NINE On the Imperfection of the Geological Record In which Darwin considers the absence of intermediate varieties and explains whyourpalaeontolagical callemans arefull afgaps CHAPTER TEN On the Geological Succession of Organic Beings In which he describes how his theorycan acrountforthe pattern afsuccessian fromfossils to livingforms The geological record Is llke having just others retained the sharp teeth found In a few lines ofa few pages of the history earlierwhales and In today's kiliers. of the world. Much afit is incomplete, More recent deposits reveal the and because soft-bodied creatures are splits betweendolphins and whales. rarely preserved in the rocks some parts Arecord that was once little more may be fragmentary at best. Since than an enormous gap has, with infinite Darwin's day, however, vast numbers labour and some luck, provided a offosslls have been found across the complete history of the evolution of the world, and his concern that the largest animals that everlived. geological record falls to support his It has also given whales their rightful theory now seems unduly pessimistic. place-untilnotlong ago quiteobscure- Darwincould only guess at the age within the family of mammals. Their of each stratum by estimating the rate at earliest ancestors were close to those which rock was worn away.Todaywe can that gave rise to the hippopotamus. date fossils directly by examining how Whales, unique as they may seem, are their chemicalelements breakdown with hence members of a larger group that time. Thefirst life has been traced back contains hippos, pigs, giraffes and cattle. more than3 billionyears and the death DNA analysis backs up the record ofthe of the dinosaurs to 65 millionyears ago. rocks. The whale's whole storyhas been Some of the records of that immense revealed within less than haifa century. period are impressivelycomplete. The Himalayas are full offossils-not of mountain creatures but of those of the sea, for long ago their peaks made up the lloor of the Tethys OCean. The fossils include the antecedents of great whales. The bones of the earliest ancestor of all cetaceans are found in beds some 50 million years old.They belong to a creature that had four legs and a tall, lived on the shore, and looked alittle like a seal. Its ears, though, had a unique structure, now found only in whales. The next prominent player, a mIlIlon or so years later, "the swimmlng-wallclng whale" in Latin, looked like a 3-metre- long otter. Another millionyears on and the animal's nostrils had migrated up the snout and the pelvis moved away from the backbone. Afurther 5million years saw the oceans inhabited by a long mammal with tiny limbs. Thencameagreat split. The ancestors of the blue whale and its relatives- those that filter tiny creatures from the water- began to develop gigantic sieves within their mouths, while Page six 1 NewScientist 114 November 2009
