>lo—Lancaster Farming, Saturday, July 21,1984
LONG BEACH, Calif. - To
begin with, the fossils are
beautiful. Scientists who have seen
some of the fossiled fish,
crustaceans, snails, and other
specimens from a quarry at Tepexi
de Rodriguez, 130 miles east of
Mexico City, call them “exquisite”
and “elegant.” They are startling
in their completeness, vivid in
their details.
But that is just the beginning.
For the Tepexi fossils are yielding
huge amounts of information about
water-dwelling animals of a little
known time, about 115 million
years ago. In two years, the quarry
has produced more than a
thousand specimens. About 425 are
fish, including representatives of
45 species, most of them new to
science.
A Lizard, Too
And it has produced one land
animal, a little lizard related to
contemporary skinks, complete to
the last detail, including its
toenails.
“It is a world-class specimen,”
says Dr. George Callison, a
biologist at California State
University at Long Beach.
Callison, an expert on
prehistoric lizards, is leading the
scientific study of the Tepexi
fossils, along with a Virginia-born
colleague, Shelton P. Applegate of
the Geological Institute of the
National University of Mexico.
Their work is supported by the
National Geographic Society.
To Callison, the most important
thing about the quarry is that it
provides the opportunity to study a
total community of prehistoric
creatures. He can examine their
relationships to each other and to
previously known sites, older and
younger.
The fossils began to turn up in
the early 19605, when the family of
Miguel Aranguthy, frustrated by
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Mexican quarry workers find prehistoric treasure trove
their inability to grow crops in the
rocky soil and semiarid climate of
Tepexi, decided to dig out some of
the area’s colorful stone and sell it
to builders.
The rocks pried out by
Aranguthy and his five sons
seemed to be laminated, and came
out in layered slabs with red and
yellow patterns. The family
thought they could be used to
decorate houses, and sold them to
truckers passing on a nearby road.
It was not until the early 1980 s
that the fossils first came to the
attention of the scientists. A
technical assistant at the
Geological Institute, Pompeyo
Lopez Neri, took some fossils by
bus from Tepexi to Mexico City,
where he showed them to Ap
plegate.
“Let’s go to Tepexi tomorrow,”
Applegate said immediately.
Family Cooperates
Applegate won the cooperation
of the Aranguthy family, and the
support of a Mexican government
agency that helps Indians. The
agency is now building a museum
for the fossils. Most of them will be
cared for at the Geological In
stitute.
Though Tepexi today is far from
any ocean, it apparently was
located near the edge of what is
now the Pacific during the time the
fossils began forming. The actual
fossil site was a lagoon separated
from the ocean by a reef.
“A lagoon environment is much
quieter than the ocean itself, less
subject to currents or wave ac
tion,” Callison explains. “But
because it is isolated from the
main part of the ocean, it can
occasionally become inhospitable
to life. That’s what happened
here.”
Callison is not sure precisely
what happened, but periodically
something would kill everything
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that lived in the lagoon.
It might be an enormous bloom
in microorganisms that would
exhaust available oxygen, or an
increase in the salinity of lime
content of the water. Whatever it
was, the skeletons would sink to
the bottom and eventually be
covered by a layer of limestone.
Then ocean water would burst in
over the reef barrier, bringing in
new life, and the process would
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start all over again. Callison does
not know how often the life-and
death cycle took place; it may
have been seasonal, annual, or
every few years. But the evidence
for the cycle is in the fossil record.
The predominance of fish is
important because they are nearly
evenly divided between two
groups: Holosteans, with thick,
rhomboid-shaped scales and
lacking a true backbone, and
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Teleosts, with circular thin scales
and a well-formed backbone.
An Unusual Site
Few similar marine sites from
the Cretaceous period, the time of
the Tepexi deposits, have produced
fish fossils. The best-known site is
at Solnhofen in southern Bavaria,
which has produced fossils for 500
years, dated at about 140 million
years ago. A site in Lebanon has
fossils about 75 million years old.
(Turn to Page B 12)