Geology Reference
In-Depth Information
TABLE 22.1
Summary Chart for the Orders and Suborders of Dinosaurs (lengths and weights approximate, from several sources)
Order
Suborder
Familiar Genera
Comments
Theropoda
Allosaurus, Coelophysis,
Compsognathus, Deinonychus,
Tyrannosaurus,
*
Velociraptor
Bipedal carnivores. Late Triassic to end of
Cretaceous. Size from 0.6 to 15 m long, 2 or 3 kg
to 7.3 metric tons. Some smaller genera may have
hunted in packs.
Saurischia
Sauropoda
Apatosaurus, Brachiosaurus,
Camarasaurus, Diplodocus,
Titanosaurus
Giant quadrupedal herbivores. Late Triassic to
Cretaceous, but most common during Jurassic.
Size up to 27 m long, 75 metric tons.** Trackways
indicate sauropods lived in herds. Preceded in fossil
record by the smaller prosauropods.
Ornithopoda
Anatosaurus, Camptosaurus,
Hypsilophodon, Iguanodon,
Parasaurolophus
Some ornithopods, such as
Anatosaurus
, had a
fl attened bill-like mouth and are called duck-billed
dinosaurs. Size from a few meters up to 13 m long
and 3.6 metric tons. Especially diverse and common
during the Cretaceous. Primarily bipedal herbivores
but could also walk on all fours.
Pachycephalosauria
Stegoceras
Stegoceras
only 2 m long and 55 kg, but larger
species known. Thick bones of skullcap might have
aided in butting contests for dominance and mates.
Bipedal herbivores of Cretaceous.
Ornithischia
Ankylosauria
Ankylosaurus
Ankylosaurus
more than 7 m long and about
2.5 metric tons. Heavily armored with bony plates on
top of head, back, and sides. Quadrupedal herbivore.
Stegosauria
Stegosaurus
A variety of stegosaurs are known, but
Stegosaurus
with bony plates on its back and a spiked tail, is
best known. Plates probably were for absorbing and
dissipating heat. Quadrupedal herbivores that were
most common during the Jurassic.
Stegosaurus
up to
9 m long, 1.8 metric tons.
Ceratopsia
Triceratops
Numerous genera known. Some early ones bipedal,
but later large animals were quadrupedal herbivores.
Much variation in size;
Triceratops
up to 7.6 m long
and 5.4 metric tons, with large bony frill over top
of neck, three horns on skull, and beak-like mouth.
Especially common during the Cretaceous.
*
Until recently,
Tyrannosaurus
at 4.5 metric tons was the largest known theropod, but now similar, larger animals are known from Argentina and Africa.
**
Partial remains indicate even larger brachiosaurs existed, perhaps measuring 30 m long and weighing 100 metric tons.
paleontologists note that the thick skull bones are found in
juveniles, but not in adults. In any case, pachycephalosaurs
were bipedal herbivores that varied from 1 to 4.5 m long.
Their fossils are known only from Late Cretaceous-age rocks.
The fossil record of ceratopsians (horned dinosaurs)
shows that small Early Cretaceous animals were the ances-
tors of large Late Cretaceous genera such as
Triceratops
.
Tric-
eratops
and related genera with huge heads, a large bony frill
over the neck, and a horn or horns on the skull were very
common in North America. Fossil trackways show that these
large, quadrupedal herbivores moved in herds. Furthermore,
bone beds with fossils from a single species indicate that
large numbers of ceratopsians perished quickly, probably
during river crossings.
The most distinctive features of
Stegosaurus
, a medium-
sized, herbivorous quadruped from the Jurassic Period, are a
spiked tail, almost certainly used for defense, and plates on
its back (Table 22.1). The exact arrangement of these plates
is uncertain, although they are usually depicted in two rows
with the plates on one side offset from those on the other.
Most paleontologists think that the plates functioned to ab-
sorb and dissipate heat.
All ankylosaurs were quadrupedal herbivores and more
heavily armored than any other dinosaur (Table 22.1). Bony
armor protected the animal's back, flanks, and top of the
head. The tail of some species, such as
Ankylosaurus
, ended
in a bony club that undoubtedly could deliver a crippling
blow to an attacking predator.
Various media depict dinosaurs as aggressive, dangerous
beasts, but we have every reason to think that they behaved
much as land animals do today. Certainly, some lived in herds
and no doubt interacted by bellowing, snorting, grunting,
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