January 2025 - 36

Seven species of perch-like fish have also been
documented at Fossil Butte. A species of troutperch
also was found at the location. While no
trout-perch are found in Wyoming today, there
are two species of trout-perch still found in eastern
North America.
Two species of freshwater stingrays are found
in Fossil Lake. Because sting rays have skeletons
mostly comprised of cartilage, it's uncommon to
find a fully-preserved fossil.
" Fossil Lake is the only place where fossil freshwater
stingrays are found complete, " Aase said. " All
other places with these fossils preserve only teeth. "
All ages of these rays have been found from
embryos all the way to adults. This allows the full life
cycle of the ancient rays to be studied. Freshwater
stingrays are alive today in tropical river systems of
South America, Asia, Australia and Africa.
Several fish with no living relatives are found in
Fossil Lake. These include two species of " mystery
fish " with no identifiable traits to be placed in an
existing family. These fish are assigned their own
family: Asineopidae. It's believed these fish went
extinct during the middle Eocene Epoch.
MORE THAN FISH
Heliobatis radians had small teeth for crushing snails and other mollusks and barbed spines on the tail for defense.
The stingray is approximately 30 centimeters long.
waters. Only one specimen of this pike is known
from Fossil Lake. This suggests they primarily lived
in tributaries of the lake, so they are not commonly
found in the lake sediments.
There are several fossilized fish with relatives still
found in the world today. Of four species of gar,
three are similar to modern gar. While no gar live in
Wyoming today, seven species are still alive in freshwater
in southeastern North America and Central
America. Two species of bowfin, another primitive
fish, have been found in the lake as well. Bowfin are
no longer found in Wyoming, but one genus is native
to the eastern U.S.
One species of paddlefish is also known from Fossil
Lake, but that could become two if newly discovered
short-billed specimens prove to be a new species
rather than variation in the recognized species. Currently
there is one living species of paddlefish still
swimming in North America's Mississippi River basin.
Unlike modern paddlefish that feed on plankton, the
paddlefish found at Fossil Lake were predatory and
have been preserved with fish in the belly.
36 | January 2025
Although most fossils found in Fossil Lake are
those of fish, other creatures have been preserved
there, too.
More than 10 mammal species have been documented
there. Although Wyoming is now known
for some large mammals, the mammals found at
Fossil Butte are generally small and different from
those we see today.
" People like to come to Wyoming to see deer,
elk and other wildlife, but they hadn't yet evolved
back then, " Aase said.
Three species of odd-toed ungulates are known
from Fossil Lake - the dawn horse (Protorohippus
venticolus), the wave beast (Lambdotherium popoagicum)
and a yet unidentified tapiroid - a family
that includes modern tapirs. The most complete
specimen of a dawn horse ever discovered was
found in the middle of Fossil Lake, although it's
unclear how the land mammal ended up there. The
species had longer back legs than front, suggesting
it was a good jumper.
" This was an ancestral horse about the size of
a border collie, " Aase noted. " They used the long
hind legs to hop through the dense vegetation that
was around at that time. "
Three species of bats have been found at the site,
none of which have been documented elsewhere.
The most primitive bat found there, the Onychonycteris
finneyi, was most likely active during the
day, unlike modern bats that are most active at
night. Other mammals found at the monument

January 2025

Table of Contents for the Digital Edition of January 2025