Saurischian dinosaurs

Saurischians include two major groups. Sauropodomorpha are
mainly large-bodied creatures with pillar-like legs, extraordinarily
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Unravelling the genealogy of dinosaurs
long tails, long necks ending in small heads, and jaws lined with
simple, peg-shaped teeth, indicating a mainly herbivorous diet.
These include such giants as members of the diplodocoid,
brachiosauroid (Figure 31), and titanosaurian groups. Theropoda
are markedly different to their sauropodomorph relatives. They are
almost entirely agile, bipedal, and predominantly meat-eating
dinosaurs (Figures 30, 31). A long, muscular tail counterbalances the
front of the body at the hip, leaving the arms and hands free to be
used to grab their prey; their heads also tend to be rather large, and
their jaws lined with sharp, knife-like teeth. These types of dinosaur
range from small and rather delicate creatures similar to
Compsognathus, which are commonly referred to as coelurosaurs,
through to such enormous creatures such as the legendary
Tyrannosaurus, while other equally large and fearsome-looking
theropods include Giganotosaurus, Allosaurus, Baryonyx, and
Spinosaurus. Although some of these dinosaurs may be well known,
the group as a whole is proving to be extraordinarily diverse, and in
some cases quite bizarre. Newly discovered therizinosaurs, for
example, appear to have been huge, lumbering creatures with long,
scythe-like claws on their hands, enormous bellies, and ridiculously
small heads whose jaws were lined with teeth that are far more
reminiscent of plant-eaters than conventional meat-eaters. Yet
other theropods known as ornithomimians and oviraptorians were
lightly built, rather ostrich-like creatures that were entirely
toothless (and therefore beaked just like living birds). However, the
source of greatest interest among this entire group of dinosaurs is
the subgroup known as dromaeosaurians.
Dromaeosaurians include such renowned creatures as Velociraptor
and Deinonychus, and a host of similar but less famous creatures
that have been discovered recently. Their particular interest lies in
the fact that their skeletal anatomy is closely similar to that of living
birds; indeed, the similarities are so great that they are thought to
be direct bird ancestors. Dramatic new discoveries, at sites in
Liaoning Province, China, that exhibit truly exceptional
preservational conditions, of dromaeosaurian theropods reveal a body covering made of either keratinous filaments (like a coarse
form of hair) or in some cases genuinely bird-like feathers, which
emphasizes their similarity to modern birds.