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pigs, and deer. Reptiles with their continuous growth achieve a measure of
eternal youth, whereas mammals grow rapidly to adulthood and then slowly
degenerate and die.
A large body allows a cold-blooded reptile to retain its body tempera-
ture for long periods. A large body retards heat loss better than a small one
because it has a better surface area to volume ratio.Thus, the animal is less sus-
ceptible to short-term temperature variations such as cool nights or cloudy
days. Conversely, a large reptile takes much longer to warm up from an
extended cold period than a small one. Muscles also generate body heat,
although for reptiles they only produce about a quarter of that of mammals
during exertion. High steady body temperatures maintain an efficient metab-
olism and enhance the output of muscles.Therefore, the performance of some
large dinosaurs probably could match that of large mammals.
The generally warm climate of the Mesozoic produced excellent grow-
ing conditions for lush vegetation, including ferns and cycads, to satisfy the
diets of the plant-eating dinosaurs. Much information can be obtained about
dinosaur diets by studying coprolites (Fig. 152), which are masses of fecal mat-
ter preserved as fossils and are usually modular, tubular, or pellet shaped.
Dinosaur coprolites can be quite massive, even larger than a loaf of bread.
Coprolites are often used to determine the feeding habits of extinct ani-
mals. For example, coprolites of herbivorous dinosaurs are black and blocky
shaped and usually filled with plant material. Those of carnivorous dinosaurs
are spindle shaped and contain broken bits of bone from dining on other ani-
mals. Some dinosaur species swallowed cobbles called gizzard stones, similar to
the grit used by modern birds in order to grind the vegetation in their stom-
achs into pulp. The rounded, polished stones called gastroliths were left in a
heap where the dinosaur died. Sometimes deposits of these stones are found
atop exposed Mesozoic sediments.
Figure 152Coprolites
are fossilized dinosaur
droppings.207JURASSIC BIRDS