Dinosaurs
What shared novelties unite the dinosaurs?
• Dinosaur means "Terrible lizards"
• Dinosaurs were mostly large, bipedal or quadrupedal diapsid
reptiles with an upright posture.
• Most of the traits that characterize dinosaurs are related to their
upright posture and locomotion.
Features inherited from near relatives
• 90° angle between shaft and head of the upper leg bone (femur).
• The ball-shaped femur head fits into a socket in the hip.
• A crest on the hip bone holds the leg in place.
• The knee is in a
straight line between
hip and foot.
• Advanced ankle
structure: the ankle
bones are welded to
the lower leg.
• When these animals
walked, only their
toes touched the
ground, not their
heels.
Dinosaur Hip Bones
New features
• The middle toe in the foot supports most of the animal's weight,
other toes are reduced.
• Open hip socket.
• Opposable digits
Comparing Dinosaur Hip Bones
Ornithischia: The
bone on the bottom
of the pelvis has a
large projection
that points toward
the back of the
animal.
Saurischia: The
bone on the bottom
of the pelvis has a
large process
pointing toward the
front of the animal.
Scientists divide dinosaurs into two groups--ornithischians
and saurischians--according to the structure of the hips.
Ornithischians, such as Corythosaurus, had a birdlike hip
structure. Saurischians, such as Allosaurus, had hips like
those of lizards. The two groups differed in the three bones
that made up the hipbone--the ilium, ischium, and pubis.
What did the first dinosaurs look like?
• The earliest dinosaurs are known from the mid-to-late Triassic,
~230 Mya.
• To date, the best fossils from this time period have come from
Argentina, though recent reports suggest that very early dinosaurs
were present in Madagascar as well.
• Three early dinosaurs from Argentina: Herrerasaurus, Eoraptor,
and Pisanosaurus
Herrerasaurus
Herrerasaurus was large, over 4 m long.
• Herrerasaurus had all but a few of the characters which define the
dinosaurs, lacking only certain features of the hip and leg bones.
• Slashing teeth and three finger on their hands with slashing nails.
• The pelvic structure is similar to saurichian dinosaurs, which had
previously led to Herrerasuarus being classified in that group.
• This arrangement of hip bones, however, is ancestral in the
archosaurs and not uniquely derived.
• Systematic relationships of Herrerasaurus and its relatives are far
from certain.
• While some analyses suggest they are sister to the dinosaurs, others
consider them Saurischian or even theropods.
• The importance of this group is that they give us some idea of the
time at which dinosaurs evolved (towards the end of the Triassic) and
what the earliest dinosaurs would have looked like.
Eoraptor
Eoraptor was tiny, only ~1 m long.
• It also had slashing teeth and three finger on their hands with
slashing nails.
• One of the earliest known dinosaurs and a contemporary of
Herrerasaurus, its already bipedal stance and short, specialized
forelimbs suggest an affinity with theropod dinosaurs.
• Eoraptor lends support to the hypothesis that dinosaurs diverged
rapidly and at small body sizes from a common ancestor, and that the
main herbivorous and carnivorous lineages were already present by
the Middle Carnian.
• The general picture: Active, bipedal carnivores.
• They were both lizard-hipped dinosaurs that were closely related to
the theropods.
Pisanosaurus was a small (>1 m), bipedal dinosaur with serrated,
shearing teeth.
• It was an herbivorous bird-hipped dinosaur.
Saurischian dinosaurs: "Lizard-hipped" dinosaurs
• The saurischian, like all other tetrapods, had pelves (hips) composed
of three elements: the ilium, ischium, and pubis.
• What distinguishes saurischians (among other major characteristics;
including a grasping hand, asymmetrical fingers, and a long, mobile
neck) is the pubis that points downward and forward at an angle to the
ischium
• In addition, the pinkie toe in the foot is small, and the index finger
(the one next to the thumb that you use for pointing) in the hand is
longest.
• The oldest known dinosaurs, from the middle Triassic of South
America, were saurischians.
• The saurischians are often divided into three major groups:
Sauropoda, Therapoda, and Prosauropoda
Sauropoda "Lizard foot"
Jurassic-Cretaceous: quadrupedal herbivores, largest land animals,
up to 35 m long, 12 m tall, 80,000 kg (or more), small heads, broad
snout with peg-like teeth (and gastroliths in gut), very long necks
and tails, massive pillar-like limbs, short broad hands and feet with
claws, large lightweight vertebrae.
e.g., Diplodocus.
The Sauropoda were large herbivores such as Apatosaurus and
Diplodocus
Diplodocus
• A Late Jurassic SAUROPOD with a long, snaky neck, a long, whiplike tail, and front legs shorter than the hind legs. .
• It is the longest dinosaur skeleton ever found; 90 feet (27 m) long,
and has a 26-foot (8-m) neck and a 45-foot (13.7-m) tail; stood 13 feet
(4 m) tall at the hips and probably weighed 25 tons (22.7 metric tons).
• The elephant-like feet and legs of this four-legged plant eater indicate
that it was a land or swamp dweller.
• Because its nostrils were on top of its head, scientists once thought
that it lived on the bottom of lakes with only the top of its head above
the water, because the pressure of the water would have been too great.
Diplodocus cont.
• Diplodocus may have used its tail as a weapon.
• The Y-shaped SPINES on the tail vertebrae could have
provided extra places of attachment for muscles that made it
possible to move the tail from side to side.
• Its long neck enabled the animal to lift its head to see and
approaching enemy from a long distance.
• Diplodocus may have lived into Early Cretaceous times.
Sauropod Saurichians
Diplodocus
Theropoda
Bird-like, bipedal carnivores. The hand has three or four fingers with
claws. They had a long bony tail. They reduced their toes until just 3
touch the ground.
The Theropoda were bipedal carnivores (meat eaters), ranging from
the chicken-sized Compsognathus and the fearsome Deinonychus
and……….
Therapod Saurichians
• 30 very sharp,
curved teeth in a
long, flat snout, an
s-shaped neck; long
thin legs; arms with
three-fingered
clawed hands and
four-toed clawed
feet
Velociraptor
Therapod Saurichians cont.
The most unusual
feature of this
theropod is the pair of
ridges along the top
of the skull
Dilophosaurus did
not have a neck frill
(it had standard neck
ribs) nor did it spit
venom (it lacks
hollow fangs through
which snakes expel
venom).
Dilophosaurus
Therapod Saurichians cont.
A group of large carnivorous dinosaurs that roamed North America
and Asia during the last part of the Cretaceous, 85 to 65 million
years ago.
The most famous tyrannosaur, of course, is Tyrannosaurus rex, one
of the last non-avian dinosaurs to walk the earth before the great
extinction.
It stood approximately 15
feet high and was about
40 feet in length, roughly
six tons in weight.
In its large mouth were
six-inch long, sharp,
serrated teeth.
Tyrannosaurus rex
T. rex: Scavenger or Predator?
• Paleontologist Jack Horner has proposed that T. rex could not have
been a predator.
• His arguments against predation include its small eyes (needed to
see prey), small arms (needed to hold prey), huge legs (meaning
slow speed) and that there is no evidence for predation — bones
have been found with tyrannosaur teeth embedded in them or
scratched by them, but so far no study has shown that tyrannosaurs
killed other dinosaurs for food (a bone showing tyrannosaur tooth
marks that had healed would be strong evidence for predation).
• His evidence supporting scavenging include its large olfactory
lobes (part of the brain used for smell), and that its legs were built
for walking long distances (the thigh was about the size of the calf,
as in humans).
• There are arguments against scavenging: most large living
predators do scavenge meat happily when it is available, but most do
prefer fresh meat.
Note:
• Living birds had common ancestors on the theropod lineage.
• Oddly, birds are derived from the "lizard-hipped" dinosaurs and
not from the "bird-hipped" ornithischian dinosaurs.
• The "bird-hipped" condition of a pubis pointing toward the back of
the animal occurred twice independently, once in the ornithischians
and once in the lineage leading to birds, an example of convergent
evolution.
• Thus "ornithischia," taken literally, is a misnomer, since the
ornithischians have ornithischian-like pelves, not bird-like. Only
birds (and their immediate ancestors) have bird-like pelves.
Prosauropoda "Before lizard foot":
• Triassic-Jurassic: Bipedal to quadrupedal, small to large herbivores,
up to 10 m long, small head, long neck, bulky body, long tail, 5 toes
and 5 fingers, thumb claw for grasping veggies, massive hind limbs,
slimmer front limbs.
• Ridged spoon-shaped teeth. Gastroliths.
Prosauropod Saurichians
• Unearthed all over western Europe.
• Like most of its kind, the Plateosaur was heavy, sturdy limbed,
and its tail made up half its length.
• Its head was stronger
and deeper than most
prosauropods. It walked
on all four legs, rearing
up on its hind legs to
search at higher levels or
gain access to higher
foilage.
Plateosaurus
Ornithischia: Bird-hipped dinosaurs
Have an extra lip bone and the middle finger on hand is longest.
Eurypoda: have plates on their backs
Stegosaurs "Roof lizards":
• Jurassic-Cretaceous: 3 to 9 m long, 300 to 6500 kg. Quadrupedal
with two rows of plates along spine, shoulder and tail spikes, small
head, pointy snout, short neck, bulk body, hind limbs longer than
front limbs. No evidence of gastroliths. Plates for protection and
perhaps thermoregulation.
Stegosaurs
Ornithischia cont.
Ankylosaurs: "Fused lizards":
Jur-Cret: 5 to 9 m long. Quadrupedal with heavy flexible armor of
fused plates, studs, and spikes. Broad shielded skull, short massive
limbs, sturdy tail with club.
Ornithischia cont.
Ceratopsians: "Horned faces":
Cret: bipedal and
quadrupedal, small to
large (1 to 9 m long),
triangular skull often
with bony frill, tall
narrow snout with
parrot-like beak,
battery of shearing
teeth, horns.
Evidence for
herding.
Triceratops
Ornithischia cont.
Pachycephalosaurs:"Thick-headed lizards":
Jur-Cret: bipedal, small to large (0.5 to
5 m long), thick domed or flattened
heads (Head butting) with bumbs, strong
hips and legs, short arms, stiffened tail,
spine horizontal.
Ornithischia cont.
Ornithopods: "Bird-foot":
Tri-Cret: diverse and abundant herbivorous group, bipedal
quadrupedal, small to very large (1 to 15 m long), legs longer than
arms, fingers with claws or hooves (5th one reduced), toes with hooflike nails (5th toe reduced), long stiff tail held off ground for balance,
large head with cropping beak and battery of self- sharpening cheek
teeth, cheek pouches.