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Embargoed until 2 P.M. EDT
NSF PR 02-35
- May 8, 2002
Researchers Discover Clues to Whale Evolution
A team of international scientists, including Hans
Thewissen, an anatomist and paleontologist at the
Northeastern Ohio Universities College of Medicine
(NEOUCOM), has discovered that the inner ear of whales
evolved much more quickly than expected, allowing
the animals to become fully aquatic early in their
evolution. The team's research, funded by the National
Science Foundation (NSF), shows that the semicircular
canals, the organ responsible for balance and located
in the inner ear, was adapted to aquatic life approximately
45 million years ago. The discovery was published
in the May 9 issue of the journal Nature.
Cetaceans (whales, dolphins and porpoises) have unique
semicircular canals that allow them to be highly acrobatic
swimmers without becoming dizzy. By investigating
this organ in ancient fossils, the researchers found
that early whales acquired this special trait quickly
and early on in their evolution. This was a defining
event that likely resulted in their total independence
of life on land.
"The early evolutionary development of small semicircular
canals by cetaceans opened an entirely new mammalian
niche for habitation and contributed to the broad
diversity of marine living habits that we see in whales
today," said Rich Lane, director of NSF's paleontology
program, which funded the research. "The evolutionary
acquisition of such specialized organs or abilities
(like the brain and upright walking habit of man)
provide mechanisms by which highly evolved organisms
dominate in certain environments."
The semicircular canals sense head movements and this
vital information is used to coordinate the body during
locomotion. This happens subconsciously, and humans
only become aware of an organ of balance when things
go wrong, such as during sea sickness, drunkenness
and wild roller coaster rides.
The researchers found that in living cetaceans the
semicircular canals are much smaller than in any other
mammal of the same body size. In fact, the semicircular
canals of the huge blue whale are smaller than those
of humans. In general, cetaceans are more acrobatic
than similarly sized land animals (imagine an elephant
making the jumps of a similar-sized whale). This could
be the result of the small canals, because the small
size makes the canals less sensitive, preventing the
animal from becoming dizzy (i.e. experiencing vertigo).
Between 40 and 50 million years ago, early cetaceans
evolved from land mammals into swimmers. Over the
last decade many new whale fossils have been found
which show how this dramatic change happened. Skeletons
of the transitional species ("whales with limbs")
demonstrate that they were adept, otter-like swimmers.
Just last year, Thewissen's discovery of two early
whale ancestors showed that the earliest whales were
mainly land animals, and resolved a controversy over
the relationships of whales, showing that they are
most closely related to modern even-toed ungulates
(such as pigs, hippos, camels, deer, and sheep) than
to an extinct group of meat-eating mammals.
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