Dinosaur Mountain - Cretaceous Arizona
Sediments from the late Cretaceous Period have
been found in scattered localities across
southeastern Arizona, and deposits of similar age
occur in Utah, New Mexico, and Sonora, Mexico. These
areas yield information about the plants and animals
of Arizona at this time.
Tryannosaurus rex
Tyrannosaurus rex was obviously a very
large meat eater, but that’s only the beginning of
the story. Was T. rex a fierce predator, or
did he scavenge the kills of other animals? Most of
today’s large carnivores will happily do both.
Scientists’ differing interpretations depend on how
they reconstruct the anatomy of Tyrannosaurus rex.
In the southwestern United States,
Tyrannosaurus is known from New Mexico, Texas,
and Colorado. In Arizona, we have found fragments of
bone from animals belonging to the tyrannosaur
family, but we do not have enough to be sure of
their specific identity.
The specimen shown is a juvenile; an adult would be
about twice as big.
Pentaceratops
Only fragmentary remains of the horned dinosaurs
have been recovered in Arizona, but Pentaceratops
is the most abundant form in the nearby San Juan
Basin of New Mexico. Fully adult Pentaceratops
have the largest skull of any vertebrate animal.
“Five Horned Face,” as the name means, refers to the
nasal horn in the middle of the face, the two brow
horns, and the horns in the cheek region known as
“jugal horns.”
Paleosaniwa
This large lizard is a relative of today’s
monitor lizards and Australian goannas. Like the
monitors, Paleosaniwa was likely an
opportunistic predator who would welcome the chance
to raid nests of many creatures in the hope of
getting an easy meal.
Alphadon
The first mammals in North America are found in
the early Jurassic Kayenta Formation of Arizona. By
the late Cretaceous, mammals with more modern
characteristics appeared, including Alphadon,
a common opossum-like marsupial. Alphadon
likely had an appearance and habits like the modern
opossum. This little Alphadon bides his time
in a recess near the great Tyrannosaurus.
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