| Ranging from the
size of a sparrow to the size of an airplane, the
pterosaurs (Greek for "wing lizards") ruled the
skies in the Jurassic and Cretaceous, and included
the largest vertebrate ever known to fly: the late
Cretaceous Quetzalcoatlus. Pterosaurs are not
closely related to either birds or bats.
It was once thought
that pterosaurs were not well adapted for active
flight and relied largely on gliding and on the wind
to stay in the air. However, based on analyses of
pterosaur skeletal features (including work done by
Berkeley's own Kevin Padian), it is now thought that
all but the largest pterosaurs could sustain powered
flight. Pterosaurs had hollow bones, large brains
with well-developed optic lobes, and several crests
on their bones to which flight muscles attached. All
of this is consistent with powered flapping flight.
The largest
pterosaur (Quetzalcoatlus, wonderfully named
for the Aztec winged serpent god) had a wing span
from eleven to twelve meters long (about forty
feet). The wing's main support was an amazingly
elongated fourth digit in the hand. Fibers in the
wing membrane added structural support and
stiffness. At least some pterosaurs may have had
some sort of hair-like body covering, which could
very well mean that they were endothermic.
Pterosaurs had a diverse range of head types, as you
can tell from the pictures below. Their ability to
fly probably allowed them to evolve into many
niches, taking advantage of many different food
sources, which would explain the range of skull
morphology seen.
Pterosaurs consist
of two main types (they do form a single (monophyletic)
group, though): the "rhamphorhynchoids," more
properly termed the basal Pterosauria, which
had long tails, and their descendants the "pterodactyloids,"
which had shorter tails. Why is the term "rhamphorhynchoid"
an invalid one? Since the later Pterosauria (the"pterodactyloids")
are the descendants of the basal Pterosauria, "rhamphorhynchoid"
is a paraphyletic term, which phylogenetic
researchers shy away from using.
What was Pteranodon like?
The genus
Pteranodon includes several species of large
pterosaurs from the Cretaceous period in North
America. As you can tell from this photo, it had a
large crested head, a huge wingspan (some 20-25
feet; the UCMP specimen is about 22 feet), and a
comparatively small body. This is deceiving; it
looks like the head and wing bones were too bulky,
and the hindlimbs appear small and weak. Not so; the
bones of Pteranodon are actually completely
hollow (about 1 millimeter thick!), and were quite
light. The whole animal probably weighed about 25
pounds, only slightly heavier than the largest
flying birds. The hindlimbs are actually perfectly
sized for the body; Pteranodon would have
been capable of bipedal terrestrial movement (but
was no rapid runner, unlike its ancestors, some of
whom seem to have been fast bipedal runners). The
wing bones look thick because a large bone diameter
is more vital for resisting the bending stresses
involved in flight (as opposed to large bone
thickness, which is important for resisting
compressive forces, such as those imposed by the
weight of a large body), so actually the wings of
Pteranodon were more than adequate for flight.
Pteranodon
was almost certainly a soaring animal; it
used rising warm air to maintain altitude; a common
strategy among large winged animals (among birds,
albatrosses and vultures are adept at soaring). Its
scooplike beak was used for snapping up fish as it
soared over the oceans that it nested by. A good
modern analog for Pteranodon would be the
pelican.
The UCMP's mounted
specimen of Pteranodon ingens is actually a
composite specimen, pieced together from a few
different specimens to form a complete one.i (Return to
FOSSILS index) |
