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.
Tyrannosaurus rex was obviously a very large meat eater, but
thatâ€™s only the beginning of the story. Was T. rex a fierce predator,
or did he scavenge the kills of other animals? Most of todayâ€™s large
carnivores will happily do both. Scientistsâ€™ 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.
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. â€œFive Horned Face,â€ 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 â€œjugal horns.â€
This large lizard is a relative of todayâ€™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.
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.