By Will Dunham
WASHINGTON, Sept 23 (Reuters) - The origins of the enamel
that gives our teeth their bite is no ordinary fish tale.
Scientists said on Wednesday fossil and genetic evidence
indicates enamel did not originate in the teeth but in the
scales of ancient fish that lived more than 400 million years
ago, and only later became a key component in teeth.
Enamel is the hardest tissue produced in the bodies of
people and other vertebrates but scientists have been uncertain
about its beginnings.
The researchers examined fossils of two primitive bony fish
from the Silurian Period, a time of evolutionary advances in
marine life, and found an enamel coating on their scales but no
enamel on their teeth. Only millions of years later through
evolutionary processes did fish exploit the enamel to make teeth
harder and stronger, they said.
"This is important because it is unexpected. In us, enamel
is only found on teeth, and it is very important for their
function, so it is natural to assume that it evolved there,"
said paleontologist Per Erik Ahlberg of Sweden's University of
Uppsala, whose research appears in the journal Nature.
"As the wolf in 'Little Red Riding Hood' said: 'All the
better to eat you up with!' They are hugely important as
food-processing structures."
Enamel, shiny and white, is one of the main tissues in teeth
in most vertebrates, composed almost entirely of calcium
phosphate.
Fish are the ancestors of terrestrial vertebrates including
amphibians, reptiles, birds and mammals, including humans.
"Although this tissue on our teeth is used for biting
or shearing, it was originally used as a protective tissue such
as in living primitive fishes including gars and bichirs," added
paleontologist Qingming Qu of Uppsala University and the
University of Ottawa.
Fossils showed a fish called Andreolepis that lived 425
million years ago in Sweden had a thin enamel layer on its
scales. Another called Psarolepis, from 418 million years ago in
China, had enamel on its scales and also the bones of the face.
Neither had tooth enamel.
The genome of the spotted gar, a freshwater fish from the
central and southern United States largely unchanged since
the age of dinosaurs, provided more clues.
Gar scales, like those of Andreolepis and Psarolepis, are
covered by a shiny enamel-like substance. The researchers
pinpointed genes relating to enamel formation that were active
in the gar's skin, showing that this substance really is a kind
of enamel.
(Editing by Eric Walsh)