Page 84 - Ultimate Visual Dictionary (DK)

PREHISTORIC EAR TH
The dinosaurs STRUCTURE OF

SAURISCHIAN PELVIS
Hook of preacetabular
THE DINOSAURS WERE A LARGE GROUP of reptiles that Ilium process
were the dominant land vertebrates (animals with Postacetabular Ilio-pubic joint
backbones) for most of the Mesozoic era (245–65 process
Acetabulum
million years ago). They appeared some 230 million
years ago and were distinguished from other scaly, Pubis
Ilio-ischial joint
egg-laying reptiles by an important feature: dinosaurs Pubic foot
had an erect limb stance. This enabled them to keep their Ischium
bodies well above the ground, unlike the sprawling and
semisprawling stance of other reptiles. The head of the
dinosaur’s femur (thighbone) fit into a socket in its
pelvis (hip-bone), producing efficient and mobile GALLIMIMUS
A saurischian dinosaur
locomotion. Dinosaurs are categorized into two groups
according to the structure of their pelvis: saurischian
(lizard-hipped) and ornithischian (bird-hipped) dinosaurs.
In the case of most saurischians, the pubis (part of the pelvis)
POSITION OF PELVIS IN A
jutted forward, while in ornithischians it slanted SAURISCHIAN DINOSAUR
back, parallel to the ischium (another part of STRUCTURE OF Ilium
the pelvis). Dinosaurs ranged in size ORNTHISCHIAN PELVIS Preacetabular process
from smaller than a domestic cat Postacetabular
to the biggest land animals ever process Ilio-pubic joint
known. The Dinosauria Ilio-ischial joint Prepubis
were the most successful land Acetabulum
vertebrates ever, and survived
Pubis
for 165 million years, until
Ischium
most became extinct
65 million years ago.
HYPSILOPHODON
An ornithischian dinosaur

POSITION OF PELVIS IN AN
COMPARISON OF ORNITHISCHIAN DINOSAUR
ANIMAL STANCES

SPRAWLING STANCE
BAROSAURUS The thighs and upper arms
A saurischian dinosaur project straight out from the
body so that the knees and
elbows are bent at right angles. COMMON IGUANA
(Iguana iguana)
A present-day reptile

ERECT STANCE SEMISPRAWLING STANCE
The thighs and upper arms The thighs and upper arms
project straight down from project downwards and DWARF CROCODILE
the body so that the knees outwards so that the knees (Osteolaemus tetraspis)
and elbows are straight. and elbows are slightly bent. A present-day reptile

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