first animals and plants to invade land required water
to complete their live cycles. Spore producing plants such
as lycopsids, horsetails, and ferns need wet environments
so that sperm can swim to and fertilize eggs. Amphibian
eggs must be laid in moist conditions that allow the tadpole,
fish-like, larval stage to live and develop in an aquatic
innovations that appear in the Carboniferous
period would free plants and animals from a life cycle
tied to water. As we have already discussed, seed plants
sperm to eggs via wind carried pollen. Seeds provided
plant embryos with an independent life support unit,
provided nourishment and protection from dry conditions.
Among tetrapods the reptile-like amphibians would give
rise to the amniotes that reproduced on dry land delivering
evolved an independent
life support unit for their embryos in the
of the amniotic
or cleidoic egg.
Amniotes include reptiles, birds,
protomammals, and mammals. Specialized membranes support
amniote embryos carried in eggs or inside the female. Amniotes
can be identified by specific skull and skeletal
The amniotic egg would allow early amniotes to lay their
eggs on land due to two key features. First, the amniotic
egg possesses a semipermeable shell that is either calcareous
or leathery. The shell allows for gas exchange, but is
watertight. Second, the amniotic egg possesses three
extraembryonic membranes that lie outside the embryo, the
chorion, amnion, and allantois. The amnion surrounds the
embryo with water and functions in gas exchange and protection.
The chorion surrounds the embryo and yolk sac and also
functions in gas exchange and protection. The allantois
forms a sac that functions in respiration and waste collection.
As the embryo develops the yolk sac is depleted while
the allantois fills up.
The amniotic egg allows the embryo
to fully develop into a terrestrial hatchling and skip
the aquatic larval stage. The materials needed to make
these eggs are resource intensive, so amniotes generally
lay fewer eggs than fish or amphibians (Benton, 2005, p.
111). The first fossil eggs are from the Triassic, so it
that identify the first amniotes. We will briefly discuss
amniote skull structures.
amniote evolutionary lines are documented by temporal fenestrae,
openings in the skull behind the eye. These holes function
to reduce use of bone and provide additional edges for
jaw muscle attachment. Anapsid amniotes (subclass Anapsida)
have no temporal fenestrae and include turtles and most
of the earliest reptiles. Diapsid amniotes (subclass Diapsida)
have two temporal fenestrae and include
lizards, snakes, crocodiles, dinosaurs, pterosaurs, sphenodonts
and the extinct marine reptiles (formerly grouped as the
Euryapsid). Euryapsids have one upper temporal fenestra.
Synapsid amniotes (class Synapsida and class Mammalia)
have one lower temporal fenestra and include protomammals
(formerly referred to as mammal-like reptiles) and mammals.
Reptiles were the first amniotes and appear in the Carboniferous.
The subclass Anapsida and Diapsida are in the reptilian
first reptiles (class Sauropsida) were small lizard-sized
tetrapods living in damp forests of the mid-Carboniferous
feeding on insects and worms. In Nova Scotia there
are sedimentary deposits that contain upright lycopod
tree stumps. Since
1852 thirty Sigillaria tree stumps have
produced abundant tetrapod remains. These tetrapods
were living in the rotted out Sigillaria trunks.
Hylonomus and Paleothyris are two
tetrapods that were preserved in the hollow tree
stumps and represent the oldest known amniotes (Benton,
2005, pp 110-111). Reptiles remained relatively small
during the Carboniferous and into the Permian. Multiple
new families of anapsid type reptiles appear in the
Early Permian. We will mention just a few.
& Continental Drift
Members of the family Mesosauridae represent the
first reptiles to adapt to an aquatic existence,
their ancestors were terrestrial. This family of
reptiles appears and goes extinct during the Permian. Mesosaurus was
a freshwater species in this group, which acted
as a key piece of biological evidence in favor
Wegener’s theory of Continental Drift and the
existence of Pangea. Mesosaurus fossils
are found in both South America and South Africa.
This animal could not have crossed the Atlantic
Ocean thus the continents must have been joined
when Mesosaurs was
alive (Dixon, 1988, p.65). Mesosaurus was up
to 1 meter long with a long jaw, neck, and flat-sided
The tail was used for swimming. The jaw was lined with
needle-like teeth suited for catching arthropods and
fish and then straining water before swallowing (Benton,
of the family Bolosauridae are rather rare. However,
the bolosaurid Eudibamus, from the Early
Permian, has the distinction of being the first known
reptile had a long tail, long hindlimbs, and short
forelimbs. The teeth of Eudibamus suggest
a diet of tough plant material.
of the family Pareiasauridae were large, heavily
built herbivores. Pareiasaurs had their legs placed
underneath their body, so they could walk
more upright. Pareiasaurus and Scutosaurus were
typical members of the family reaching
lengths of 8ft.
remained at low diversity during the Early Permian,
but underwent an adaptive radiation in the Late Permian.
Coelurosauravus (Family Weigeltisauridae)
was a small lizard-like diapsid with a very interesting
adaptation. The ribs of this weigeltisaurid could
fold out forming
structures. This organism could have glided from
tree to tree like the living lizard Draco does.
important diapsid group, which makes its first appearance
in the late Permian, is the archosaurs (Infraclass
Archosauromorpha). While some archosaurs had the
standard reptilian sprawling gate (limbs directed
sideways) others evolved a more erect posture. Archosaurs
had legs that were placed more directly under
the body, an important terrestrial
A more erect posture increases stride length. Legs
tucked beneath the body can support the organisms
with less stress.
Archosaurs would undergo a great
adaptive radiation during the
Triassic. One group of archosaurs would give rise
to two evolutionary lines one, leading to the
crocodilians the other, to pterosaurs, dinosaurs,
and birds (Benton, 2005, pp. 138-143). Diapsid reptiles
would come to rule the land, sea, and air during
Richard Owen (1804-1892), a British comparative anatomist
and paleontologist, created the taxon Dinosauria
large terrestrial reptiles that walked upright, clearly
different from other fossil or living reptiles. He
based Dinosauria on the grouping of three taxa including
Megalosaurus, Iguanodon, and Hylaeosaurus.
The Dinosauria were inaugurated in an 1842 published
version of an 1841 lecture given to the British
Association for the Advancement of Science in Plymouth
(Padian, 1997, p. 175).
Dinosaurs (Superorder Dinosauria "terrible
or fearfully great lizards")
range from the Triassic to the Cretaceous (to the
present if you include birds). The oldest dinosaurs,
Coelophysis, were small bipedal, carnivorous
organisms. Dinosaurs diversified into many forms
and came to dominate terrestrial faunas during the
Jurassic and Cretaceous.
In 1887 Harry Seeley (1839-1904),
a British paleontologist, proposed that Dinosauria
could be divided into two groups based on their hip structure,
braincase, and vertebrae (Padian, 1997, p. 494). Seeley's
scheme has persisted to this day.
The order Saurischia includes dinosaurs with a lizard-like
hip structure. The order Ornithischia includes dinosaurs with hip
structures reminiscent of birds. Representatives
from both groups appear in
the Triassic period, although Ornithischians remained relatively rare
until the Jurassic.
Saurischian dinosaurs have a "primitive" pelvic
girdle with the pubis pointing forwards and the ischium
Saurischians also share an elongate, S-shaped neck,
and asymmetrical hands with a distinct thumb (Prothero,
1998, p. 372). Saurischian dinosaurs can be placed into
two major groups, the theropods (Suborder Theropoda) and the
Sauropodomorphs (Suborder Sauropodomorpha).
Theropoda ("beast feet")
carnivrous dinosaurs, which range from chicken size to the 6-tonne
giants of the Cretaceous. Theropods have
hollow, thin-walled bones. In general, the forth and fifth
digits on the hand and foot are reduced. Only three toes
on each foot are weight bearing. Most theropods have sharp
recurved teeth and claws at the end of each finger and
toe (Wagonner, 1995, Theropod Page). Let's take a look
at three major theropod groups.
Coelophysoids (Infraorder Coelophysoidea)
were the first theropods. Coelophysoids
were small, slender, bipedal, dinosaurs with
a long tail and long narrow-snouted skull. These
small carnivorous dinosaurs range from the
Triassic to the Jurassic and were widespread geographically. Coelophysis bauri is
New Mexico's state fossil. Ghost Ranch in New
Mexico represents a
bone bed dominated by specimens
of Coelophysis. The victims of
this bone bed may have died as a result of drought and were subsequently
and deposited into a bone bed by flooding.
Ceratosauria) were closely related to the coelophysoids. Many
ceratosaurs had crests on their skulls (Benton, 2005, p. 191). Dilophosaurus ("two
crests"), from the Early Jurassic, had two flat-sided
crests oriented vertically on either side of its skull. The
crests may have
been used in sexual
displays. Dilophosaurus was
up to 6 meters long and is the creature that kills Dennis Nedry
in the film Jurassic Park. There
is no scientific evidence to support the poisonous nature of
these dinosaurs as depicted in the film. Eubrontes giganteus are
believed to be the tracks of Dilophosaurus and are
the state fossil for Connecticut. Dinosaur tracks in general
are the state fossil for Massachusetts.
from the Late Jurassic, was the same size as Dilophosaurus. Ceratosaurus had
a pair of horns, possibly used for mating displays, on the
nasal bones. Ceratosaurus had small bony plates running
down its neck, back, and tail, giving it a serrated crest.
to be that of Ceratosaurus found in the Morrison Formation
of the western USA suggest these dinosaurs moved in groups.
theropods and birds belong to the infraorder Tetanurae. Tetanurans
first appear in the Jurassic and can be grouped into two
major divisions the Carnosauria and the Coelurosauria
are the first well-known tetanurans and were large predators. Megalosaurus ("great
lizard") was a 9 meter long carnosaur that ranges from Early
to Late Jurassic.
Megalosaurus was the first dinosaur to be scientifically
named and described in the 1820's. It was one of the creatures
that prompted Sir Richard
Owen to coin the term Dinosauria
At 12 meters long, 4.6 meters tall, and up to 2 tonnes, Allosaurus ("different
lizard") was the
largest carnosaur of the Late Jurassic. Joints in the upper and
lower jaws allowed Allosaurus to wolf down large chunks
Allosaurus was equipped with more than seventy teeth
up to 7 cm long and three sharp claws up to 25 cm long on each
forelimb. Horn-like structures
were located above and in front of each eye (Lessem & Glut,
1993, pp. 19-20). Allosaurus is the state fossil for Utah.
Saurophaganax maximus is an Allosaur-like theropod that
is the state fossil for Oklahoma.
are a diverse clade of theropods that are more closely
related to birds than to the carnosaurs. Coelurosaurs
include the tyrannosaursids (formerly grouped with
carnosaurs) of the Late Cretaceous, ornithomimids,
first coelurosaurs appear in the Jurassic and include
such dinosaurs as Coelurus ("hollow tail") and
jaw"). Tyrannosaurids of the Late Cretaceous,
like Tryrannosaurus ("tyrant lizard") are
among the largest known terrestrial carnivores. Tyrannosaurus measured
up to 12 meters long and weighed up to 6 tonnes. Tyrannosaurus had
a large skull, over 1.35 meters in length. It's jaw was lined
with serrated teeth up to 16 cm long and 2.5 cm wide. It is estimated
that Tyrannosaurus had a bite force of up to 13,400
Newtons. Tyrannosaur coprolites contain bones of Triceratops and
pachycephalosaurids (Benton, 2005, p. 193). Tyrannosaurs had
small, but powerful forelimbs equipped with two clawed fingers.
The large powerful hind limbs possessed three large claws. It
estimated that T. rex could achieve speeds of up to
Ornithomimids of the Early Cretaceous were slender theropods
with ostrich-like bodies, small heads, relatively long
necks, limbs and fingers. Ornithomimids would reach their
greatest diversity during the Late Cretaceous period. Struthiomimus ("Ostrich
mimic") from the Late Cretaceous possessed a toothless
jaw covered with a keratinous beak. Struthiomimus's anatomy
suggests that it was a fast organism, reaching speeds of up
to 60 km/h.
of small lizards and mammals.
Maniraptorans are the most
derived theropods and include such familiar organisms as troodontids,
dromaeosaurids, and birds. Eshanosaurus from the Early
Jurassic of China may represent the first known maniraptoran.
theropods from the Early Cretaceous of China, such as Sinosauropteryx,
Beipiaosaurus, Protarchaeopteryx, Microraptor,
provide evidence that feathers evolved in the earliest
and functioned as insulation and possibly for display. Maniraptoran
fossils exhibit an evolutionary progression through different
types of feathers from simple bristles to advanced contour feathers.
Although contour feathers do appear on some maniraptorans they
have played a role in flight until the first known bird Archaeopteryx (Benton,
2005, pp 199-201).
The suborder Sauropodomorpha
includes both the prosauropods and the sauropods.
In general, they are herbivorous quadrupeds
with a small head, long neck, large body with legs tucked
beneath, and a long counterbalancing tail. The small
head contained jaws with lanceolate or spatulate
for stripping vegetation from branches. Food was ground
by gastroliths. Their pillar-like legs supported a deep
body to accommodate an enormous digestive system. Sauropodomorphs
had five-toed, spreading feet. They possessed a large
thumb claw that
used for digging and no claws on fingers 4 and 5. Sauropodomorphs
had large nostrils set higher on the skull than most
Although basal sauropodomorphs were bipedal omnivores
trend in this group was towards quadrupeds of increasing
size. To accommodate ever larger sizes the vertebrae
evolved with increasing bone pneumaticity (hollow spaces).
developed only along the lines of stress. The massive
pelvic girdle became firmly fused to the backbone by
4 and later
5 sacral vertebrae. The spaces in these bones may have
been filled with air sacs connected to the lungs as in
modern birds. These hollowed out bones with air sacs
would have reduced weight and enhanced respiratory efficiency
(Benton, 2005, p. 202).
Plateosaurus ("flat lizard"),
of the Late Triassic, is the best known and largest prosauropod.
Plateosaurus was 8 meters long and could adopt
either a bipedal or quadrupedal posture. Gizzard stones
have been found in the upper rib cage of specimens. The
abundance of reamins suggest a herding behavior for this
Several Late Jurassic sauropods are familiar
people. Camarasaurus ("chamber lizard")
is the best- known sauropod from North America. This
18 meter long
browser had a relatively short neck and tail. The forelimbs
were only slightly shorter than the hindlimbs. Camarasaurus
had a box-like skull with large nasal openings. Camarasaurus had
heavy, spoon-shaped teeth that could handle tough plant
Adults and juveniles have been found in the Morrison
formation indicating they traveled in herds. Within these
are found isolated piles of polished stones, which may
represent regurgitated gizzard stones. The eggs of Camarasurus may
have been laid in lines instead of nests.
lizard") was once known as Brontosaurus ("thunder
lizard"). Othniel Charles Marsh (1831-1899), an
American paleontologist, described two specimens as separate
animals; Apatosaurus in
1877 and Brontosaurus in
1879 (McIntosh, 1990, p. 349). Later, it was realized
that the two specimens represented separate
genus. Apatosaurus was the first genus given,
so by taxanomic convention it is the name used. Apatasaurus
was 21 meters
long and up to 30 tonnes. For almost one hundred years
the skull of Camarasaurus was used as a model
The relatively small head of Apatosaurus was
found in 1975. The teeth of Apatosaurus were
all at the front of the mouth and served to rake foliage
most sauropods Apatosaurus had five toes on
each foot. The front foot had a large claw on the thumb,
back foot had 3 claws. Each ankle joint had thick wedges
of weight-bearing cartilage. The long whip-like tail
in many sauropods like, Apatosaurus, may have
been used for defense as well as a counter balance to
Brachiosaurus ("arm lizard")
was one of the tallest and largest sauropods, designed
high in the trees. Brachiosaurus was
up to 25 meters long, 16 meters tall, and weighed in
tonnes. Unlike other sauropod families Brachiosaursids
had front legs that were longer than the hind legs. The
neck of Brachiosaurus accounted for half of
its height. The humerous was enormous accounting for
of the animal's height and giving it the name "arm
Brachiosaurus had a relatively short tail and
the whole body sloped down from its highest point at
not unlike the modern giraffe. The vertebrae were marvals
of engineering with large hollowed
on the sides
making a lightweight framework that provided maximum
strength along the lines of stress with a minimum amount
(Dixon, 1998, p. 129). Pleurocoelus is a brachiosaurid
and the state dinosaur for Texas. The Cretaceous-aged
sauropod, related to Brachiosaurus, Astrodon
the state dinosaur for Maryland.
dinosaurs have a pelvic girdle in which the pubis
runs back parallel to the ischium. There is also
process pointing forwards. Ornithischians were all
herbivorous dinosaurs and possessed a
predentary bone, which is a beak-like bone in front
of the lower jaw. The predentary bone is matched
with the premaxilla or the rostral (in ceratopsians)
in the upper jaw.
These bones helped Ornithischians clip
vegetation. Ornithischians possessed cheek teeth
that are inset into the jaw, suggesting they had
fleshy cheeks for holding food (Prothero, 1998, p.
Ornithischian dinosaurs can be divided into
ornithopods (Infraorder Ornithopoda), pachycephalosaurs
(Infraorder Pachycephalosauria), and ceratopsians
(Infraorder Ceratopsia). The suborder Thyreophora
includes the ankylosaurs
(Infraorder Ankylosauria) and stegosaurs (Infraorder
("bird feet") were the most diverse and
successful group of ornithischians and included the
Ornithopods evolved complex chewing
mechanisms making them unique among reptiles. Two
different solutions to chewing can be seen in the
jaw structures of Ornithopods. Heterodontosaurids
possessed a ball and socket joint that allowed the
jaw to rotate, creating a shearing action between
the cheek teeth. All later ornithopods possessed
pleurokinetic hinges in the upper jaw, which allowed
sides of the upper jaw to flap in and out, creating a
lateral shearing action between the cheek teeth.
Ornithopods were the most successful herbivores during
the Cretaceous because of their ability to chew (Benton,
2005, p. 207).
Iguanodon ("lizard tooth") was
the second dinosaur ever described. Dr. Gideon Mantell,
amateur geologist, described
Iguanodon from some teeth in 1822 and credited
their discover to his wife Mary Ann Mantell. Iguanodon's hand
is unusual, digit 1 is reduced to a thumb spike,
and digits 2 and 3 have small hooves. Iguanodon could
walk both bipedally and on all fours. The thumb spike
of Iguanodon was first believed to be a horn positioned
on the snout.
and Hylaeosaurus were
the first dinosaurs to be represented as three-dimensional
restorations. They were part of London's Sydenham
Park built to showcase the glass and iron structure
named Crystal Palace, which had been featured at
the 1851 Great Exhibition held in London. Twelve
inside the incomplete mould of Iguanodon at
a New Year's dinner party on December 31, 1853. Richard
Owen supervised the restorations, which suffered
from misinterpretations and incomplete information
(Sarjeant, 1997, pp, 161-164).
lizard") or duck-billed dinosaurs were the most
successful ornithopod clade. Hadrosaurs had long
rows of grinding
cheek teeth arranged in closely packed batteries.
Plant material was ground with a sideways shearing
movement as the pleurokinetic hinge pushed the cheeks
in and out with each bite. The jaws also moved forward
and backward providing additional grinding action
(Benton, 2005, p. 209).
Hadrosaurs all have similar
skeletons and skulls; however, many possessed various
shaped crests. Parasaurolophus ("by
lizard crest") was a highly derived hadrosaur
of the Late Cretaceous. Parasaurolophus could
walk on all fours as well as on two legs. The 9 meter
two tonne hadrosaur had a head equipped with
a curved horn-like
crest up to 1.8 meters long. The crest had two hollow
from the nostrils back to the tip of the crest and
curved back down to the throat region. It is believed
that hadrosaur crests may have acted as resonating
chambers. It is common to find several species of
hadrosaurs in the same formation, so they probably
roamed in mixed groups. Hadrosaurs were the dominant
herbivores towards the end of the Mesozoic and one
can imagine the reverberating sounds of dinosaurs
the air in ancient North American and Mongolian forests
of the Late Cretaceous.
The hadrosaur Maiasaura peeblesorum is
the state fossil for Montana. Maiasaura nests
on Egg Moutain provide evidence that this dinosaur
was nest bound as a hatchling and required parental
care. The ends of the hatchling leg bones are not
fully formed and the egg shells are found in pieces. Jack
Horner and Robert Makela, American paleontologists,
found Maiasaura. Horner named the dinosaur Maiasaura ("good
of the evidence that it took care of its hatchlings. Hadrosaurus
the state fossil for New Jersey.
("thick head lizard") are the dome-headed
dinosaurs. These bipedal herbivores range in size from
1 to 5 meters
long. Fossils of thickheaded dinosaurs are restricted
to the Cretaceous. In one specimen of Pachycephalosaurus
wyomingensis the skull was 22 cm thick. The thickened
skull bones of Pachycephalosaurs suggest to many that
they engaged in a head-butting behavior not unlike moder
bighorn sheep (Sues, 1997, p. 512).
("horned faces") are a diverse group of ornithischians
from the Late Cretaceous. Ceratopsians have a triangular
shaped skull when viewed from above and a beak-like rostral
bone on the upper jaw that meets with the predentary
bone on the lower jaw. Ceratopsians evolved neck frills
horns. Later forms also had skeletons adapted for galloping.
Triceratops ("three horn face")
is the best-known horned dinosaur. Triceratops was
8 meters long and weighed in at 4.5 tonnes. The
brow horns of Triceratops reached
lengths of 1 meter and the neck frill up to 2.5 meters
wide. The teeth of Triceratops were elongated
blades designed for shearing. This herbivore did not
chew, it may have
browsed on fibrous plant material like cycad or palm
Triceratops is the state dinosaur for Wyoming
and the state fossil for South Dakota.
are known mainly from the Late Jurassic. Stegosaurs
have small heads, massive bodies, and rows of alternating
bony plates that extend down either side of the backbone.
Their heavy tail is equipped with pairs of long,
sharp spikes. Stegosaurs hindlimbs are much longer
than their forelimbs, which hint at a bipedal ancestry.
Stegosaurus (roof lizard) is the state fossil
for Colorado and is the largest and most well known
the stegosaurs. Stegosaurus was up to 9
meters long and weighed in at over 2 tonnes. Stegosaurus was
not equipped to chew food, so it probably utilized
a gizzard to help grind food, as did many other herbivorous
dinosaurs. The Stegosaurus brain was the
size of a walnut. A cavity in the hip vertebrae of Stegosaurus housed
a nerve ganglia to help control the hindquarter movements.
In some big-hipped dinosaurs this nerve
ganglia or sacral "brain" was larger than the brain
(Dixon, 1988, p. 156). The back plates of Stegosaurus show
evidence of extensive vascularization and probably
functioned to thermoregulate body temperature. They
been used for
sexual and deterrent displays (Benton, 2005, p. 217).
arose in the Mid-Jurassic and diversified during
the Early Cretaceous. Hylaeosaurus ("belonging
to the forest lizard") is
the earliest known primitive ankylosaur (nodosaur)
by Gideon Mantell in 1832. It was the third kind
of dinosaur to be named and one of the specimens
by Richard Owen when erecting the term Dinosauria.
Nodosaurs are primitive ankylosaurs without tail
clubs. Ankylosaurus ("curved lizard")
is the largest known ankylosaur and survived to the
the Cretacous. Ankylosaurus was up to 10
meters long and weighed in at 3.6 tonnes. The body
(up to 5 meters wide) and squat supported by powerful
legs. Ankylosaurs had a massive bony club at the
end of their tail, which would have made a formidable
continue to examine evidence concerning the physiology
of dinosaurs. Debate continues as to whether
or not dinosaurs were endothermic (“warm-blooded”)
organisms, maintaining a constant body temperature from
a high metabolism or ectothermic (“cold-blooded”),
relying on external, environmental sources of heat. Robert
Bakker provided multiple lines of evidence in favor of
viewing dinosaurs as endotherms. Benton (2005, pp. 219-223)
outlines the evidence.
Paleoclimate & Dinosaur
remains are found in both northern and southern Polar
Regions. Dinosaurs above latitudes of 60 degrees
would need to migrate if they were ectotherms. The dinosaur
fossils found in Alaska and Southern Australia are ambiguous
concerning physiology because they could have been migrating
organisms consume 10 times as many calories as cold-blooded
organisms. Thus, there is a metabolic
cost for being an endotherm, one must consume greater
amounts of food. The need to consume more food affects
predator-prey ratios. One hundred antelope could be used
to sustain one warm-blooded lion or ten cold-blooded
crocodiles (Benton, 1984, p. 151). Robert Bakker found
that present day spiders and the Permian carnivore Dimetrodon had
predator-prey ratios of 25% or more. Fossil mammals and
dinosaurs have predator-prey ratios of between 1 and
5%. Benton (2005) points out that these ratios seem to
vary with the size as well as thermoregulatory state
Gait & High
The erect stance, like that found in dinosaurs, is today
found only in living endotherms (birds and mammals).
Fossil trackways suggest that dinosaurs could achieve
high speeds, especially small bipedal forms.
is the study of blood flow or circulation. Long-necked
dinosaurs, like Brachiosaurus, would need
an efficient, strong heart to push well-oxygenated blood
to the brain. Many argue you would need a four-chambered
heart like a mammal for this kind of a job and that the
three-chambered heart of most reptiles would not
suffice. Other scientists
point out that possessing a four-chambered heart is not
necessarily evidence of endothermy; crocodilians
are ectothermic and possess a four-chambered heart.
Dinosaur bones are highly vascular, unlike modern reptiles.
Many dinosaurs have haversian canals like that found
in mammals. However, some small birds and mammals with
high metabolic rates lack haversian canals. Fibrolamellar
bone found in many dinosaurs is a compact, fast-growing
bone formed without growth rings. This bone is also found
in large, fast growing mammals and some birds. However,
lamellar-zone bone that grows slowly, forming growth
rings is also found in some dinosaurs and modern reptiles.
like large mammals, were fast growers achieving adult
size in only a few years; even large sauropods reached
in 10 to 15 years. Modern reptiles grow slowly.
Benton (2005) points out that Bakker was ridiculed when
he suggested that some dinosaurs might have feathers
(p. 221). It is now known that feathers evolved in theropods.
The insulation provided by feathers is an indication
& Peripheral Temperatures
isotope ratios of O-18/O-16 in peripheral versus
core bones can be correlated to body temperature.
of dinosaur bones seems to be consistent with endotherms,
while crocodilians from the same time period are consistent
with present day ectotherms.
Modern birds and mammals have thin nasal bones called
turbinates that function to recapture water from exhaled
air. Modern ectotherms and dinosaurs lack turbinates.
Size & Body
Some scientists argue that large sauropods were homeotherms,
they maintained constant body temperatures by virtue
of being large.
of these arguments taken alone can be regarded as
concerning the possibility of endothermy
in dinosaurs. As a young person interested in science,
what impressed me most about Robert Bakker’s case
for warm-blooded dinosaurs was the fact that he employed
multiple lines of evidence. For example, dinosaurs with
low predator to prey ratios are also the ones with fast
growing bone and high average walking speeds (Bakker,
1986, p. 392). I am sure that paleontologist will find
new ways to test ideas about dinosaur metabolism in the
(Order Pterosauria "winged reptile") were
the first vertebrate fliers and range from the Late
to the Late Cretaceous. Pterosaurs are
not dinosaurs, but they are close relatives. These
flying reptiles had wings of skin connecting the
entire length of the body and thigh to the forelimbs,
which extended out some distance due to a greatly
elongated fourth finger. Pterosaurs occupied many
of the same habitats dominated
by living birds
and ranged from sparrow size to giants with 12-meter
wingspans. Pterosaurs are divided into two groups.
Rhamphorhynchs (suborder Rhampho-rhynchoidea) range
from the Late Triassic to the Late Jurassic. Pterodactyles
(suborder Pterodactyloidea) range from the Late Jurassic
to Late Cretaceous (Padian, 1997, p. 614). This classification will most likely change as the Rhamphorhynchoidea is a paraphyletic group.
("beak snouts") were the first group of pterosaurs
to evolve. Eudimorphodon ("true dimorphic
tooth") appears in the late Triassic and exhibits
many of the characteristics
of the group. Eudimorphodon’s wings,
like all pterosaurs, were made of membranous skin
attached along the length of the elongated fourth
finger and connecting back along the body to the
level of the thigh. Wing-like skin also attached
the wrist bones and neck. In addition to the elongated
fourth finger the hand was equipped with three short
grasping fingers. The foot had five long toes. A
vertical, diamond-shaped flap of skin adorned the
tip of the
tail and was
probably used as a rudder in flight. Eudimorphodon had
two types of specialized teeth for capturing and
recently discovered pterosaur, Darwinopterus
the Middle Jurassic of China represents a transitional
fossil linking primitive long-tailed pterosaurs and more
advanced short-tailed pterodactyls (Lu, Unwin, Jen, Liu, & Ji,
2009, p. 1). The genus Darwinopterus (“Darwin’s
Wing”) is for Charles Darwin, honoring the 2009
anniversaries of his birth (200 years) and the publication
of On the Origin of Species (150 years). The species
name modularis is Latin for “composed of interchangeable
species name focuses on a key aspect of this transitional
fossil. Darwinopterus does not exhibit
characteristics intermediate between basal pterosaurs
and derived pterodactyloids; rather, it possesses the
body and limbs of a primitive pterosaur and the head
and neck of a pterodactyloid. This mosaic of primitive
and derived characteristics provides evidence for modular
evolution. Natural selection may have acted on modules
instead of individual characteristics. In the first
phase of pterosaur evolution the head elongated,
reduced, the braincase enlarged, and the neck became
more flexible. In the second phase, body and limbs
modifications improved locomotion on the ground (Lu
et al., 2009, p.
genetic basis for modular selection may ultimately
be found in the study of regulatory genes or homeotic
genes. Regulatory genes such as Hox genes are found
in all multicellular organisms and control the
development of body plans and organ systems. A small
genes can produce a significant change in body plan
(Prothero, 2007, p. 102).
("winged finger") are the best-known flying
reptiles. Pterodactyls had the same general structure
however, the tail was shorter, the neck longer and
the skull more elongate. Pteranodon ("wing
toothless") is one of the largest and best-known
pteranosaurs. Pteranodon had
a wing span of up to 8 meters and was probably a
glider. A crest on the back of the head doubled the
skull length. The crest may have acted as stabilizer
during flight, although it was sexually
dimorphic. The jaws of Pteranodon were toothless,
which is unusual for a pterosaur. Pteranodon may
have fed on fish like the modern Pelican. The cervical
vertebrae had pneumatic foramen that served
and increase respiratory efficiency.
were 1 mm thick and made of several layers including
striated muscles, collagenous fibers,
dermis, and epidermis. The membranes of several species
were reinforced with parallel stiff fibers, termed
actinofibrils. The actinofibrils embedded in the
wing helped to ensure a stable aerodynamic shape
and proper folding when not in use. The fact that
Pterosaurs could fly and were covered with
(hair) is strong evidence that they were endothermic
or warm blooded (Wellnhofer, 1991, p. 40).
pterosaurs used all four limbs with legs
in the middle
and hands a short distance in front and to the side,
wing tips (formed from the elongated fourth finger)
slanted upwards on either side of the head. The
largest known flying vertebrate of all time is Quetzalcoatlus from
the upper Cretaceous of Texas. Quetzalcoatlus is
known from a single wing that measures 12 meters
2005, pp. 224-229).
variety of marine predators hunted fish and cephalopods
in the Mesozoic seas. Pterosaurs and crocodilians
fed on fish near the surface. The main reptilian
predators were the ichthyosaurs, sauropterygians
and finally the mosasaurs.
(Infraclass Ichthyosauria) range from the Triassic
to the Cretaceous. Ichthyosaurs and sauropterygians
have a euryapsid type skull. Euryapsids have a single
upper temporal opening and use to be placed in their
own subclass. It is now believed that
the euryapsid skull pattern arose from diapsids that
lost the lower
temporal opening (Benton, 1997, p.641).
streamline bodies not unlike tuna, had long snouts
and large eyes. Ichthyosaurs filled a niche similar
to modern day dolphins and ranged in lengths from
1 to 16 meters. Ichthyosaurs were air-breathing reptiles
that propelled themselves quickly through the water
with a powerful tail. These reptiles were
so specialized for aquatic life that they gave birth to live young
in their marine habitat. The stomach contents of ichthyosaurs include
fish scales, hooklets from the arms of cephalopods
and in one specimen, from the late Cretacous, a primitive
turtle hatchling and bird.
Ichthyosaurs had the
largest known eyeballs of any animal. The 9 meter
long Temnodontosaurus had a 300 mm diameter
eyeball. These eyes must have been used for detecting
in low light conditions (Benton, 2005, pp. 246-247).
Ichthyosaurs may have been ectotherms that maintained
a body temperature higher than their surroundings
by high levels of exercise, such as modern tuna do
today. The cruising speed of Ichthyosaurs is estimated
to have been around 5.4 km/h (Benton, 2005, p. 247).
The ichthyosaur Shonisaurus popularis is
the state fossil for Nevada. This 50 foot long ichthyosaur
preyed on cephalopods while cruising in the Triassic
seas. The remains of 37 specimens were uncovered
from what is now Berlin-Ichthyosaur State Park in
(Superorder Sauropterygia) range from the Triassic
to the Cretacous and include the placodonts and nothosaurs
the plesiosaurs and pliosaurs of the Jurassic and
were the least specialized reptilian swimmers; some
evolved turtle-like shells. The evolution of these
turtle-like shells is a good example of convergent
evolution as placodonts and turtles evolved from
different reptilian lines. Many placodonts specialized
in eating shellfish. Nothosaurs had streamlined bodies
with long necks and tails. Most nothosaurs had webbed
feet, while others had flippers. Nothosaurs ate fish.
(order Plesiosauria) make their first appearance
during the Triassic, but do not become well established
until the Jurassic. Plesiosaurs can be divided into
two major groups. Plesiosaurs (suborder Plesiosauroidea)
have long necks, short heads and paddle-like flippers.
Plesiosaurs fed on fish and cephalopods. Pliosaurs
(suborder Pliosauroidea) had short necks, long heads,
and paddle-like flippers. Pliosaurs fed on fish,
cephalopods, sharks, ichthyosaurs, and even plesiosaurs.
Jurassic) used its flippers to quickly maneuver and
its long neck to snatch swimming fish. Muraenosaurus (late
Jurassic) had a neck and flippers that were longer
than Plesiosuarus. The elongation of the neck and
flippers along with an increase in the rigidity of
the body was the evolutionary trend in plesiosaurs.
Interestingly, pliosaurs exhibit an almost opposite evolutionary trend, an
increase in head size, a shortening of the neck, and lengthening of the paddle-like
flippers. Plesiosaurs forelimbs were always longer than their hindlimbs, while
pliosuars evolved to have hindlimbs longer than the forelimbs. Pliosuars were
built for speed and maneuverability.
Macroplata (early Jurassic) was an early pliosaur that
still had a fairly long neck, making it look like a plesiosaur. Liopleurodon (late
Jurassic) exhibits the classic pliosaur look, large streamlined
body with a heavy head and short neck. It almost has a whale-like
appearance (Dixon, 1988, pp 76-77).
(Order Squamata) became important shallow marine
predators in the Late Cretaceous. Mosasaurs ("Meuse
river lizard") were air-breathing
lizards adapted for a marine life that looked somewhat
like a crocodile with flippers. Mosasaurs have an
elongate body, deep
paddle-like fins, and large skulls lined with sharp
conical teeth. Mosasaurs ranged in length from 2
to 10 meters and ate fish and other marine animals.
Mosasaurs were so fully adapted to a aquatic life
gave birth to live young in their marine habitat. Platecarpus and Plotosaurus are
two mosasaurs found in the Late Cretaceous chalk
deposits of Kansas.
Ammonite shells have been found with mosasaur tooth
Mosasaurus hoffmani was one of the
largest and most derived mosasaur marine reptiles.
A 1-meter long mosasaur jaw found in 1786
was known as the "Beast of Maastricht" named
Holland where it was found. Napoleon's troops occupied
Holland and brought the jaw to Paris in 1795, where
it was studied by the great French anatomist George
Cuvier (1769-1832). The jaw is still housed in the
Natural History Museum
Beast of Maastricht was important because it encouraged
scientists to consider and debate the possibility
of extinction, which was a very controversial idea
at the time (Palmer, 1999, pp. 120-121).
largest mass extinction at the end of the Permian
period provided reptiles with the opportunity to
become the dominant vertebrate life forms on Earth.
Roughly, one hundred and eighty-six million years
later the second largest mass extinction would take
away Mesozoic reptilian dominance and usher in the
Cenozoic, an age for mammals.
Diapsid reptiles underwent
great adaptive radiations during
the Triassic and Jurassic. Reptiles dominated the
land in the form of dinosaurs, crocodilians, and
air in the form of pterosaurs, and the marine environment
in the form of ichthyosaurs, plesiosaurs, and mosasaurs.
Modern forms of diapsid and anapsid reptiles (lizards,
snakes, turtles, and birds) would diversify from the Late
Cretaceous to the present. Although successful to
the present day the mass extinction event at the
end of the Cretaceous would mark an evolutionary
in tetrapod evolution from diapsid dominated faunas
to mammals (Benton, 2005, p. 247).
At the end of
the Cretaceous, 65 million years ago, 85% of all
species would go extinct, making this event second
only to the
Permian mass extinction (Hooper Museum, 1996). Sixteen
percent of marine families and 18% of terrestrial
would go extinct (Siegel, 2000). Dinosaurs, pterosaurs,
marine reptiles, ammonoids, and belemnoids
Many organisms were already on the decline during
the Late Cretaceous.
at the University of California at Berkeley including
Luis and Walter Alvarez, Frank Asaro, and Helen Michel
discovered an iridium anomaly in a fine-grained clay
layer in several K-T (Cretaceous/Tertiary) boundary
sites around the world (now the Cretacous/Paleogene
boundary). The group recognized that iridium is abundant
stony meteorites and proposed that the fallout from
on the order of 10 kilometers could explain the anomaly
and possibly the extinction event. Subsequently,
a crater was found beneath
the Gulf of Mexico off the Yucatan Peninsula during
exploration for oil. The Chicxulub crater is of the
right size and age. Volcanic activity may also act
as a source of iridium. The Deccan Traps in India
a large terrestrial flood basalt. Ironically, the
Deccan Traps would have been positioned on the opposite
side of the Earth at the time of the Chicxulub impact.
There is also evidence for climatic changes as well
as floral and fauna changes leading up to these events
(Stanley, 1987, pp. 133-171).
Olympiad Fossil Event
2016 Science Olympiad Fossil List includes ichthyosaurs (order Ichthyosauria), plesiosaurs (order Plesiosauria), mosasaurs (family Mosasauridae), and pterosaus (order Pterosauria) under the class Reptile.
The Science Olympiad Fossil List places dinosaurs in the clade Dinosauria. Dinosauria is broken down into the order Saurischia (Lizard hipped) and Ornithischia (Bird
hipped). Within the Saurischian category the following
genera are listed: Allosaurus, Apatosaurus, Coelophysis,
Deinonychus, Plateosaurus, Velociraptor,
and Tyrannosaurus. Within the category Ornithischians
the following genera are listed: Iguanodon, Stegosaurus,
Triceratops, and Parasaurolophus.