There are a lot of books and web sites that can give you details of
this, but here are the basics from something I recently wrote. This is
written for adults, but I"m sure you're smart enough to figure it out!
EVOLUTION OF CETACEANS (WHALES, DOLPHINS AND PORPOISES)
All marine mammals are believed to have evolved at various times from
land-dwelling ancestors. We can only speculate on the reasons behind the
movement of terrestrial animals into aquatic environments and their
eventual evolution into species that spent some or all of their lives in
the water. They were almost certainly taking advantage of new food
sources, and perhaps also seeking escape from terrestrial predators. The
major groups of marine mammals are united much more by their shared use
of a similar environment than by a common evolutionary descent. While
cetaceans, seals, sirenians, and otters have different evolutionary
origins, they have often developed similar adaptations to life in the
aquatic realm. Among the most important of these adaptations are the
modification of limbs into flippers (or, in the case of the otters,
flipper-like hind paws), the development of highly efficient insulation
in the form of blubber or fur, and a range of complex diving abilities.
In addition, the cetaceans have evolved powerful tails for propulsion.
Among marine mammals, the cetaceans are the most completely adapted to
an aquatic existence. This transformation began 55 to 60 million years
ago, and the cetaceans were already well diversified by 53 million years
before the present. The two modern major cetacean groups (suborders)
are the baleen whales (mysticetes) and the toothed whales
(odontocetes). Most scientists accept that these share a common origin
in a third, extinct, suborder, the Archaeocetes. The closest living
relatives of the cetaceans are the artiodactyls (even-toed ungulates
such as the cow and camel), and a recent DNA study has suggested that
cetaceans are more closely related to hippos than to any other
terrestrial mammal. Whether cetaceans evolved from ancient
artiodactyls, or (with the hippo) diverged from another group of ancient
animals, is still the subject of much debate.
> gregory wrote:
> Hi Phil, my name is Nicholle and I'm researching the evolution of
> whales. I just happened to come across you're site, and was hoping
> you could send me some information regarding my study. Thank you.
-- The Society for Marine Mammalogy will be holding its 14th Biennial Conference from 28 November to 3 December 2001, in Vancouver, BC. Visit the conference Web site at www.smmconference.org for full details of this important meeting.
Phillip J. Clapham, Ph.D. Large Whale Biology Program Protected Species Branch Northeast Fisheries Science Center 166 Water Street Woods Hole, MA 02543, U.S.A.
tel. 508 495-2316 fax 508 495-2066 email: firstname.lastname@example.org
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