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per away from danger the way modern crocodile young do. However, a fossil
discovery of Maiasaura,which literally means “good mother lizard,” suggests
that dinosaur adults were tender, nurturing parents whose young remained in
their nest for feeding and protection.
The blood vessel density of dinosaur bones was higher than living mam-
mals, another warm-blooded hallmark. Some dinosaur skulls display signs of
sinus membranes, which exist only in warm-blooded animals. Respiratory
turbinates, which act as thermal exchangers common in the nostrils of warm-
blooded species, appear to have been present in dinosaurs as well. Bones of
carnivorous dinosaurs found in Antarctica suggests that they either adapted to
the cold and dark by being warm-blooded or migrated to nearby South
America across a land bridge.
Dinosaur tracks (Fig. 138) are the most impressive of all fossil footprints
because the great weight of many species produced deep indentations in the
ground. Their footprints exist in relative abundance in terrestrial sediments of
Mesozoic age throughout the world.The study of dinosaur tracks suggests that
some species were highly gregarious and gathered in herds. Large carnivores
such as Tyrannosaurus rex(Fig. 139), whose name means “terrible lizard,” were
swift, agile predators that could sprint as fast as a horse according to their tracks.
Females of some dinosaur species might have had live births like mam-
mals. Many nurtured and fiercely protected their offspring until they could
fend for themselves, allowing larger numbers to mature into adulthood, thus
Figure 138Dinosaur
trackways in the
Chacarilla Formation,
Tarapaca Province, Chile.
(Photo by R. J. Dingman,
courtesy USGS)187TRIASSIC DINOSAURS