Geoscience Reference
In-Depth Information
gaea began to split apart, which lasted from 206 million years ago to
144 million years ago. This period saw the evolution of most of the
largest dinosaurs that ever lived. We have already introduced some of
them, including the sauropods, a group of enormous herbivores such
as
Apatosaurus
(formerly called
Brontosaurus), Diplodocus,
and
Bra-
chiosaurus,
which thrived in the tropical and subtropical climates that
predominantly characterized this interval. But this period also wit-
nessed the evolution of such terrifying carnivorous forms as the
twenty-foot-long
Allosaurus
with its three-foot-long skull and four-
inch-long, serrated teeth. In addition to these large dinosaurs, the ear-
liest-known flying descendants of dinosaurs—birds—began to
compete for dominance in the skies. Their primary rivals were ptero-
dactyls and other flying reptiles, whose bodies were not covered with
feathers and whose wings were constructed very differently from
those of birds.
But the dinosaurs at Auca Mahuevo lived during the last period of
the Mesozoic era, the Cretaceous period, which lasted from 144 mil-
lion years ago until 65 million years ago. During the Cretaceous,
rifting between the subcontinents of ancient Pangaea gave rise to the
modern continents that we recognize today. This period also wit-
nessed the origin of our modern biota, for many groups of living
vertebrates arose then, as well as the flowering plants and their ubiq-
uitous insect pollinators. In North America, this period saw the evo-
lution of the duck-billed dinosaurs such as
Anatotitan,
the horned
dinosaurs, such as
Triceratops,
and the fearsome carnivore
Tyran-
nosaurus rex. Tyrannosaurus
was long recognized to be the "king" of
dinosaurs, as denoted by its species name. At almost thirty-five feet
long, its slender but powerful hind legs probably made it a relatively
swift and agile predator for its impressive size, although some pale-
ontologists have recently argued that it primarily filled the ecological
role of scavenger. Regardless of the feeding niche it filled,
Tyran-
nosaurus's
four-foot-long skull, studded with eight-inch-long teeth
shaped like steak knives, made it the most imposing carnivore on the
North American continent. In Argentina, as mentioned earlier, the
Cretaceous saw the evolution of the largest dinosaur yet discovered,
the herbivorous
Argentinosaurus,
and a ferocious carnivore that may
well have been larger than
'Tyrannosaurus, Giganotosaurus.
Even as we
write this topic, fossils are being excavated near Plaza Huincul in
