Geoscience Reference
In-Depth Information
bones of the same ceratopsian species tell us these dinosaurs were likely group-ori-
ented also.
Knowingthatmanymammalianherbivorestodaytravelinsizeablegroups,the
preceding insights on the social lives of sauropods and ornithopods are probably
not big surprises. But what about theropods? Do their tracks ever show that they
hung out with one another, shared time in the same place, and hunted together like
wolves or other social predators? Oh yes, and in some instances these trackways
paint nightmarish scenarios for their intended prey.
At one site in Middle Jurassic (about 165
mya
) rocks of Zimbabwe, trackways
of at least five large theropods, with calculated hip heights of more than 2 m (6.6
ft),indicatetheyweretravelingtogether.Atthissite,someofthetheropodsstepped
on each others' tracks, further suggesting they had some sort of pack arrangement
with one or more theropods taking the lead in a loose formation. An Early Creta-
ceous (about 125
mya
) site in China also shows six theropod trackways, equally
spaced and pointing in the same direction, all of their tracks about the same size,
24 to 28 cm (9-11 in) long, and with only two toes on each foot. Yes, that's right,
these are dromaeosaurid tracks. The track sizes further indicate hipheights ofabout
1 to 1.1 m (about 3.5 ft), or slightly smaller than the fictional “
Velociraptors
” of
the
Jurassic Park
movies. Yet these tracks reflect a chilling reality, one in which
smallorlargepreywouldhavebeenstalkedandterrorizedbysickle-clawed predat-
ors. Running dromaeosaur trackways—which I've seen at a spectacular tracksite in
Utah—amplify this empathy, whether for the hunter or hunted.
Dinosaurs Who Stalk and Feed
Based on what you just learned about dinosaur pack-hunting behavior from
tracks, along with other evidence, paleontologists have no doubt that some dino-
saurs hunted other dinosaurs, birds, mammals, lizards, and additional animals. For
example, gut contents in a few rare specimens tell us directly about a dinosaur's
last meal (which will be detailed in a later chapter). But what happened just before
that meal was acquired? How did predatory dinosaurs hunt their prey? And how do
