Sauropodomorpha
Ornithischia
Sauropodomorpha includes the sauropods and their
ancestral relatives. Sauropoda comes from the Greek,
meaning ‘lizard-footed’. They were long-necked,
long-tailed herbivores that eventually evolved into
quadrupeds (walked on four legs) that became the
largest animals that ever walked the Earth. They were
the dominant terrestrial herbivores throughout the
Mesozoic Era, from the mid-Triassic until their decline
and extinction at the end of the Cretaceous Period.
Ornithischians are ‘bird-hipped’ dinosaurs. The
name ornithischia comes from the Greek ornitheos
meaning ‘of a bird’ and ischion meaning ‘hip joint’.
All ornithischians have a pubis pointing backwards,
running parallel with the ischium and birds also have
pelvises in which the pubis points backwards.Their hip
structure is bird-like even though birds actually belong
to the ‘lizard-hipped’ dinosaurs (the saurischians).
Similar to giraffes, sauropods developed extremely long
necks to reach the high foliage and fauna available on
the high up trees. They had light, tiny skulls on the end
of a very long neck, with long tails to counterbalance
this, as well as provide defence from any predatory
dinosaurs.
Their teeth were weak, shaped like leaves or spoons,
and instead of grinding teeth, they had stomach stones
to help digest any tough plant fibre.
They were initially bipedal (walking on two legs), but as
they increased in size they became graviportal (weight
bearing) quadrupeds, like elephants, physically adapted
for moving slowly across land. Their hind legs were
straight and powerful, with club like feet with five toes,
although only the inner three or four had claws, and
their forelimbs were more slender ending with pillarlike hands built for supporting weight, with only the
thumb having a claw.
There are several major sauropod families, including:
Cetiosaurids – ‘Whale lizards’ with almost solid
vertebrate and a shorter tail; Brachiosaurids – ‘Arm
lizards’, with a giraffe like stance, front legs longer than
the rear legs, nostrils above their eyes a short, thick tail
and chisel like teeth; Titanosaurids – ‘Titanic lizards’ with
armoured skin, peg-like teeth and a wide head, with
vertebrate not hollowed out; Diplodocids – ‘Double
beams’ with a whip like tail, small head, nostrils above
their eyes, hollows in their vertebrate, a very long neck
and pencil like teeth in the front of their mouth; and
Camarasaurids – ‘Chambered lizards’ with a shorter neck
and tail, hollowed out chambers in their vertebrate,
chisel-like teeth, a relatively big box-like head and
nostrils above and ahead of their eyes.
The ornithischians can be divided into two distinct
subgroups: Cerapoda and Thyreophora. The cerapods
are further subdivided into the Ornithopoda,
Pachycephalosauria, and Ceratopsia, though some
scientists link the Pachycephalosauria and Ceratopsia
together in a group called Marginocephalia. The
Thyreophora consisted of the Stegosauria and
Ankylosauria and their relatives.
Ornithischian skulls also had small, reduced openings
(known as antorbital fenestrae) between the eye socket
and the nostrils, unlike saurischians.
ilium
Ornithischians outnumbered the Saurischians (the
lizard-hipped dinosaurs, theropods and sauropods) and
were all herbivores.
ischium
pubis
FRONT
Plateosaurus
Pentaceratops
Brachiosaurus
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