Geology Reference
In-Depth Information
◗
Figure 22.23
The Angiosperms or Flowering Plants
Pistil
contains ovule
Stamen
produces pollen
Flower
Mature
plant
Fertilization
b
Archaefructus sinensis
from Lower Cretaceous
rocks in China is among the oldest known
angiosperms.
Developing
embryo
Seedling
Mature
seed
a
The reproductive cycle in angiosperms.
Archosaurs and the Origin of Dinosaurs
Reptiles known
as
archosaurs
(
archo
meaning “ruling,” and
sauros
meaning
“lizard”) include crocodiles, pterosaurs (fl ying reptiles), di-
nosaurs, and birds. Including such diverse animals in a sin-
gle group implies that they share a common ancestor, and
indeed they possess several characteristics that unite them.
For instance, all have teeth set in individual sockets, except
today's birds, but even the earliest birds had this feature.
All dinosaurs share a number of characteristics yet differ
enough for us to recognize two distinct orders: the
Saurischia
and
Ornithischia.
Each order has a distinctive pelvic structure:
saurischian dinosaurs have a lizard-like pelvis and are thus called
lizard-hipped dinosaurs; ornithischians have a birdlike pelvis
and are called bird-hipped dinosaurs (Figure 22.25). For de-
cades, paleontologists thought that each order evolved indepen-
dently during the Late Triassic, but it is now clear that they had
a common ancestor much like archosaurs known from Middle
Triassic rocks in Argentina (see Geo-inSight on pages 618 and
619). These dinosaur ancestors were small (less than 1 m long),
long-legged carnivores that walked and ran on their hind limbs,
so they were
bipedal
, as opposed to
quadrupedal
, animals that
move on all four limbs.
Dinosaurs
Sir Richard Owen proposed the term
dinosaur
in
1842 to mean “fearfully great lizard,” although now “fearfully”
has come to mean “terrible,” thus the characterization of di-
nosaurs as “terrible lizards.” Of course, they were not terrible,
or at least no more terrible than animals living today, and they
c
Restoration of
Archaefructus sinensis.
Search WWH ::
Custom Search