Palaeos Vertebrates: Dinosauria
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Dinosauria
Taxa on This Page
- Dinosauria
- Saurischia
One of the most successful lifeforms to inhabit the surface of the Earth, the dinosaurs dominated all medium to large terrestrial herbivore, omnivore, and carnivore
niches
and
guilds
for some
150 million years
, were an important component of small terrestrial vertebrate fauna for the same period, as well as including the largest land animals ever to live, as well as being by far the most successful of the three clades of vertebrates that achieved powered flight and by far the most diverse and important aerial vertebrates for 130 odd million years. (yes,
birds
are
dinosaurs
,
cladistically
speaking!) MAK120206
Dinosaur Groups
Traditionally,
the dinosaurs were divided into two orders,
depending on the structure of the hip bones. Those that had a
reptilian-like pelvic bone were put in the Order
Saurischia
or
"lizard-hips"; while the ones with a bird-like pelvic bone made up the
Order
Ornithischia
or "bird-hips". (Paradoxically, it was
from "lizard-hipped" and not the "bird-hipped" forms that
birds evolved). This classification is still adhered to in some (especially
older) popular and academic books, but has pretty much been rejected in favour
of the cladistic
interpretation.
The
earliest proto-dinosaurs
[1]
(basal
Ornithodira
)
were a group of
small early dinosaur-like
archosaurs
,
known only from a few scrappy Argentinian fossils of
Mid-Triassic
age. These are neither saurischian nor ornithischian. These creatures, previously considered
ornithosuchid
thecodonts,
are not even formally considered dinosaurs (although they are
dinosauromorphs
, which means dinosaurs and a few related
forms more closely related to dinosaurs then to pterosaurs.). They are the stem forms from
among which which the dinosaurs evolved. It
has also for some years been felt that they are closely related to the
Pterosaurs
(flying reptiles). There is however a
rival theory which derives the pterosaurs from
prolacertiform
"lizards,"
or perhaps even more distantly related stock.
The
Saurischia or "lizard hipped" dinosaurs are those more closely related
to birds than to
Triceratops
. Conventionally, they are divided in
turn into two groups, one largely carnivorous, the other herbivorous. The
first of these are the
Theropoda
,
the bipedal carnivorous dinosaurs, with their bird-like legs and necks.
Theropoda means "beast-feet", a rather inappropriate name;
"bird(-like) feet" would have been better. Included in this huge
and diverse group are both small forms (including the
birds
themselves) and
large predators such as
Allosaurus
and
Tyrannosaurus
.
The
other group of Saurischia, the
Sauropodomorpha
,
were herbivores. There are two main subgroups, the
Sauropoda
(the inappropriately named "lizard-feet"), and their ancestors or
uncles, the
Prosauropoda
("before the sauropods"). Although the prosauropods
were relatively small, the more advanced types, and all of the sauropods, were elephantine giants with tiny heads, very long necks and tails,
massive bodies, and pillar-like legs. This group includes the famous
"
Brontosaurus
" (or
Apatosaurus
) and its relatives. Like modern-day
elephants, they relied on their great size as a defense against carnivores.
The
Ornithischia
("bird hipped" dinosaurs), or
Predentata
(so called beacuse they posses a unique extra predentary bone in front of the jaw, which
served as a sort of beak) were a more diverse group of herbivores. Being
much smaller than the sauropods, they survived because they evolved various other means to
avoid becoming fast food for their meat-eating theropod contemporaries. The
ornithopods
, for example, depended on fleetness of foot and acute sight and
hearing. The
Ceratopsian
dinosaurs (
Triceratops
, etc) were the rhinoceroses of the dinosaur world,
their formidable horns at least appear to be ample protection against even the largest and fiercest
carnivores. There is a substantial body of opinion that these horns were
more decorative than functional -- although we have probably not heard the end
of this issue. The
Stegosaurs
and
Ankylosaurs
evolved armour plates, spikes, and tail-clubs as defensive and offensive
weapons.
The Ornithischia -- unlike saurischian dinosaurs,
reptiles
and birds
--
possessed mammal-like cheek muscles and cheek pouches to aid in chewing. In
this respect they paralleled the mammalian form. Certainly, many
Ornithischia filled ecological roles similar to those of the mammalian
ungulates
.
So we see among the dinosaurs the tendency towards both an
avimorphisation
or bird-form-tendency in the Theropods, and a
theromorphisation
or
mammal-form-tendency) in the Ornithischia. The dinosaurs of the
Mesozoic
era
in a sense presaged the
birds
and mammals of the
Cenozoic
era
.
A word now about birds. Most palaeontologists and dino-enthusiasts
today also consider the
Birds
to be a subgroup of dinosaurs. Cladistically (phylogenetically) speaking this is correct: birds evolved from dinosaurs, so if
dinosaurs are to retain their monophyletic status they must include birds.
MAK010930. Revised ATW050609.
[1]
The discussion here assumes a more or less conventional view of
archosaur evolution. We are aware of unpublished work which might
drastically alter this view. For both scientific and historical reasons,
the data sets used to produce the present consensus tree of the archosaurs are
weak. Some of those factors are discussed
elsewhere
.
A complete restructuring of archosaur evolution, based on new data, is not at
all out of the question.
Descriptions
Dinosauria
:
Eoraptor
. LCA
birds
&
Triceratops
.
Range:
fr mT.
Phylogeny:
Dinosauriformes
:
Lagosuchidae
+ (
Silesauridae
+ *:
Ornithischia
+
Saurischia
.
)
Characters:
Ectopterygoid lateral to
transverse flange of pterygoid;
$
postfrontal absent;
$
temporal muscles extend anteriorly onto skull roof; quadrate head laterally
exposed; S-shaped neck; dorsal vertebrae shorter;
$
at least 3
fully incorporated sacral vertebrae (with 3rd incorporated from dorsal
vertebrae); forelimb < 50% length of rear (reversals in several groups);
deltopectoral crest extends further down humerus;
$
humerus
with elongate deltopectoral crest; manus 4 with <4 phalanges; claws on 1-3
only; semi-perforate (usually fully perforated) acetabulum with buttress; brevis
shelf on ilium; ischium with obturator process restricted to anterior 1/3rd;
$
femur with ball-like head; medial tuberosity of femur reduced; shaft of femur
straight or bowed anteriorly; femur vertical; femur has greater, lesser & 4
th
trochanters;
$
tibia with cnemial crest;
$
well-developed ascending process of astragalus on anterior face of tibia;
$
calcaneum with concave surface for articulation of fibula; metatarsals elongate
and function as
part of pes.
Links:
DINODATA
;
The
Dinosauria
;
Dinosaur
Links
(links to many significant sites);
Dinosaur
Paleontology
(more);
The Dinosauricon
;
Dinosauria On-Line
;
Dinosauria
;
National Museum of Natural History
- Dinosaur Exhibits
;
Dino
Russ's Lair
;
Paul Sereno's Dinosaur
Web Site
;
Dinosaur
evolution title page
;
Dinorama
@ nationalgeographic.com
;
The
Unnatural Museum - Dinosaur Safari
(a good, often overlooked, site);
Discovery
Channel: Walking With Dinosaurs
;
New
Scientist | The Rex Files | Everything you wanted to know about dinosaurs
;
Zoom
Dinosaurs - EnchantedLearning.com
;
Dann's
Dinosaur Reconstructions
;
Dinosauri
- by MediaSoft
;
Royal
Tyrrell Museum Tour: The Origin of Dinosaurs
;
Archives
of the DINOSAUR Mailing List
.
Discussion:
The limiting factor is that muscles contract only about
30% of their length. Increasing muscle length therefore increases motion of the
bone.
Tetrapod
Model:
Simple,
tri-radiate structure. Pubis, ileum & ischium meet at Y-shaped junction.
Acetabulum located at the junction, and head of femur extends outward at 90
?
along its long axis.
Protraction
: Pubis extends antero-ventrally.
Muscles insert on femur (pubofemoral) and protract (forward) it .
Retraction
:
Tail (and/or ischium?) extends posteriorly and retract femur (caudofemoral).
Abduction
:
Ileum extends posteriorly and muscles inserting on femur abduct it towards
mid-line. Basic
Tetrapod
pelvis is plate-like. Extensions of pelvic bones
are relatively small, and ileum articulates with only 1-2 vertebr
ae in sacrum.
Muscles to pubis and ischium extend ventrally, countered to some extend by
iliofemoral muscles.
The
Problem
: As the femur rotated downwards to become more vertical, the length
of the muscle running from the pubis and ischium shortened relative to the
length of the femur.
The Solutions
: Open acetabulum with bracing dorsally.
Saurischians
:
extended pubis & ischium and rotated pubis antero-dorsally. Early
ornithischians
retroverted pubis (parallel to ischium) and protracted femur by attachment to
anterior extension of ileum (see image). Later ornithischians secondarily
developed an anterior projection of the pubis, as well as retaining the
retroverted shaft.
References:
Benton
(1997)
;
Hutchinson &
Gatesy (2000)
;
Novas (1996)
;
White
(2001)
. 010324.
Saurischia
:
All
dinosaurs
closer to
birds
than to
Triceratops
.
Range:
from
Middle Triassic
.
Phylogeny:
Dinosauria
:
Ornithischia
+ *:
Sauropodomorpha
+
Theropoda
.
Introduction:
The Saurischia or
"lizard hipped" dinosaurs are conventionally divided in turn into two
groups, one carnivorous, the other herbivorous. The first
of
these are the Theropoda, the bipedal carnivorous dinosaurs, with their bird-like
legs and necks. Theropoda means "beast-feet", a rather
inappropriate name; "bird(-like) feet" would have been better.
Included in this huge and diverse group are both small forms (among them the
ancestors of
birds
) and large predators such as
Allosaurus
and
Tyrannosaurus
.
The
other group of Saurischia, the Sauropodomorpha, are the herbivores. There
are two main subgroups, the
Sauropoda
(the inappropriately named "lizard-feet"), and their ancestors, the
Prosauropoda
("before the sauropods". Although the primitive prosauropods
were relatively small, the more advanced types, and especially all of the
sauropods, were elephantine giants with tiny heads, very long necks and tails,
massive bodies, and pillar-like legs. This group includes the famous
Apatosaurus
and its relatives. Like modern-day elephants, they relied on their great
size as a defense against carnivores.
Characters:
No contact between maxillary
process of premaxilla and nares;
$
subnarial foramen;
antorbital fenestrae;
$
forked post process of jugal;
$
jugal overlaps laterally onto lacrimal; temporal musculature extends
into frontals; neck elongated & S-shaped; posterior cervical vertebrae
elongated;
$
axial postzygapophyses lateral to prezygapophyses;
trunk vertebrae have accessory articulations; enlarged manus I; metacarpal I
short, robust, & has 2 asymmetrical distal condyles so that digit is set off
at an angle (the "grasping hand"); manus III longest (hand characters
would exclude
Herrerasauridae
);
$
ischium with rod-like shaft; pubis points forward (propubic);
wedge-shaped ascending process of astragalus.
Links:
anatomy
;
The
Saurischia
;
Saurischian
Dinosaurs - Enchanted Learning Software
.
010708.
checked ATW031023, page last modified MAK120301