Diapsids
First Diapsids
Originally defined by the presence of two temporal openings. They also have
a suborbital fenestra in the palate below the eye. They have long slender
feet with overlap in the bases of the wrist and toe bones. Some of the earliest
representatives of the group have the characteristics of the wrist bones
without the temporal fenestrae, and have formerly been included as "anapsids"
(captorhinids, Hylonomus, Plaeothyris, Protorothyris)
A
site showing some dinosaur basics
Euryapsids
The euryapsids returned to the water and formed two groups: Ichthyosaurs
and Plesiosaurs.
Ichthyosaurs
and breathing
Lepidosaurs (Lizards and Snakes)
Lepidosaurs include two groups, the sphenodontids and the squamates.
The sphenodontids are represented by one living group, the tuatara
(sphenodon), and the squamates include the modern lizards and snakes.
Unique characteristics: The lepidosaurs are characterized by the
presence of scales made out of two types of protein, skin shed all at
once, cloaca is a slit across the body, hemipenes, forked tongue (this
is not a dinosaur characteristic).
Sphenodontids have a hooked beak with teeth fused to the edge
of the jaw. They were abundant from the Triassic to the Cretaceous, but
fossils are not found after the Cretaceous. Currently they are restricted
to Islands around New Zealand.
you
too can own this beautiful sculpture
About
the tuatara
LSD
and the Third Eye!!!
More on the mystical side of
the third eye
Squamates include the modern lizards and snakes. Lack bony strut
across base of temporal openings, which makes the jaw much more flexible
for swallowing prey. They are also pleurodont, having teeth attached
to the inside of the jaw, not in sockets.
Oldest squamate fossil is Upper Jurassic, but they probably started
a while before that. Groups include geckos, iguanids and chameleons,
skinks and lacertids, and the varanids (komodo dragon, monitor
lizards), Oldest snake-like fossil is an elongate varanid from the
middle Cretaceous. Monitor lizards also were the largest marine
reptiles, the mososaurs.
oldest
fossil snake
Komodo
Dragon
More
komodo Dragon
mososaurs from
Kansas
Archosaurs
The archosaurs include the Crocodiles, pterosaurs, and dinosaurs.
Characteristics of the Archosaurs
Archosaurs are characterized an antiorbital fenestra, mandibular fenestra,
eye opening is upside down triangle, teeth set in sockets (thecodont),
specialized ankle bones, new trocanter on femur, limbs partly or completely
under the body, stiffened spine so they don't wiggle back and forth while
walking. well developed diaphragm for breathing, heart ventricals are completely
separated and other features of the heart, muscular gizzard filled with
stones.
Earliest Archosaurs
- The earliest archosaurs were mostly about the size of chickens, and
included bipedal and quadrapedal forms.
- Protorosaurs Upper Permian of Europe to Triassic An odd bunch
of critters
- Rhyncosaurs fat bodies, short limbs, were herbivorous--the
most common animals in the triassic.
Pseudosuchians
- phytosaurs (Triassic) looked like crocodiles, but had a nostril
on the top of their heads
- erythrosuchids (bloody crocodiles) (Triassic) up to 5 meters
in length.
- aetosaurs (Triassic) plant eating types, long spikes in the
edge of their back armor, larger near the shoulders.
- crocodilians (modern crocodiles and alligators) Started out
with long slender legs, and did not become aquatic until the phytosaurs
went extinct at the end of the Triassic. They ranged from marine to
fresh water and in the Mesozoic, reached up to 15 meters in length (skull
2 meters long). Crocodiles are restricted to the tropics, which have
been getting smaller since the Eocene, when they ranged to the arctic
circle.
Want to dig up these things?
here is your chance through earthwatch
A web Page
about the Triassic Newark Group and the Chinle that mentions Pseudosuchians
a wordy web page
on phytosaurs
Ornithosuchians
Ornithosuchians include the pterosaurs and the dinosaurs. The early
ornithosuchians were bipedal and walked upright. They started in the Early
Triassic, one example is Euparkeria, which looked like a small dinosaur.
Another example is Lagosuchus (rabbit crocodile) which looked like
it could hop. The dinosaurs and pterosaurs apparently began in the late
Triassic. These are united by possessing the mesotarsal joint--the ankle
joint is between the bones of the ankle, not between the shin bone and the
ankle bones like the human (primitive) ankle joint. Birds still retain this
feature (note this next time you eat chicken-the thick cartilege at the
small end of the drumstick is all that is left of these ankle bones).
Introduction
to Euparkeria
also
called ornithodires
Pterosaurs
- Pterosaurs support the wind with the fourth (ring) finger of the
hand. (the fifth finger was lost). Their bones were hollow. Their hip
vertebrae were fused to form a synsacrum.
- Eudimorphodon Late Triassic, first with fully developed wing.
In the Jurassic the pterosaurs were diverse, and about the size of birds,
like Ramphorynchus and Pterodactylus.
- The greatest diversity is in the Cretaceous, which includes odd types
with straining teeth (Pterodaustro), Pteranodon with it's
head crest (toto, you're in Kansas now) and Quetzalcoatlus that
reached wingspans of 15 m.
- Pterosaurs went extinct at the end of the Cretaceous.
an analysis
of pterosaur flight
Pterosaur sitings in Texas
Pronunciation
Guide
The pterosaur
page
Dinosaurs
Dinosaurs are now thought to be a monophyletic group with numerous characteristics
in common, so they probably all descended from common bipedal ancestor,
similar to Euparkeria. Characteristics include front legs short,
back legs long, legs completely under the body (head of Femur has right-angle
bend). The hip socket is perforated, the walk was digitigrade (on the toes,
not the sole).
Classification of the Dinosaurs
- Divided into saurischians and ornithischians.
- Saurischians include the long necked sauropods (Apatosaurus,
Brachiosaurus, Diplodocus), and the predatory theropods
(Ornithomimus, Allosaurus, Velociraptor, Deinonychus,
and Tyrannosaurus etc.)
- Ornithischians are divided into the thyrophora and
the cerapoda. The thyrophora include the stegosaurs
(Stegosaurus) and the ankylosaurids (Ankylosaurus).
The cerapoda include the marginocephalia and the ornithopods.
The marginocephalia include the pachycephalosaurs (Pachycephalosaurus),
and the ceratopsids (Triceratops). The ornithopods
include heterodontosaurs, iguanodonts (Iguanodon),
hadrosaurs (Hadrosaurus, Anatosaurus), and ,
- Sauropods were once thought to be so heavy that they could
no possibly hold their own weight on the land. Footprints demonstrate
otherwise. There is also a question about how they fed such a large
bulk with such a small mouth and long neck.
Hadrosaur for
sale
UCMP
hadrosaur
UCMP Dinosaurs
Characteristics of Saurischians (Lizard hips)
Saurischians retain the primitive arangement of the hips, specifically
the pubic bones point forward. This is the reason they are called saurischians,
but it is a primitive feature that does not unite them. However, it is not
the only feature: an S-shaped neck, an assymetrical hand with a thumb, etc.
are unique to this group, so it is currently thought to be monophyletic
Characteristics of the Ornithischians
The ornithischians are named for the fact that the pubic bone is turned
backward (a true synapomorphy), like a bird, but this is superficial, because
birds are saurischian dinosaurs. They also have an extra bone in front of
the jaw called a predentary, cheek teeth set into the jaw (suggesting cheeks
for more efficient chewing),
Timing of the Dinosaur Events.
- Upper Triassic - first theropods found. Saurischians became
very abundant in the upper Triassic
- Latest Triassic - First Ornithischians
- Jurassic - lots of sauropods and theropods, Ornithischians
less diverse or common. They consisted of ornithopods and stegosaurs.
- End of Jurassic, Stegosaurs extinct
- Cretaceous sauropods dwindled. The Theropods got gigantic,
like Tyrannosaurus. Duck billed dinosaurs were abundant and diverse,
Ankylosaurs replaced stegosaurs, and the ceratopsians originated.
- End of the Cretaceous = end of non-avian dinosaurs. Ceratops
bones are found in the latest sediments.
Were Dinosaurs Warm Blooded?
- Originally proposed by Robert Bakker. Smaller dinosaurs were probably
warm blooded, but larger dinosaurs would have had a difficult time dissapating
the heat. They probably had constant temperature just because it would
be impossible to heat them up or cool them down in the course of a day.
- Stegosaurus scutes were well supplied with blood.
- Predator prey ratio is similar to warm blooded creatures
- Bony structure is similar to mammals
Fossil
Dinosaur Bone microstructure
How Social were Dinosaurs?
- Jack Horner digging in Montana has found lots of evidence of the
sociality of Dinos.
- Dinosaur nests with eggs and young in various stages of growth (different
nests)
- nests filled with vegetable material.
- Same tracks found over very large regions.
- Tracks grouped as if moving in large heards.
Dinosaur tracks
How big were the dinosaurs?
- skeletons are frequently imcomplete, and must be surmised from related
animals.
- leg length can be measured from foot prints.
- you can make plastic models and dip them in water and get a size
estimate from that.
- You can use the size of the leg bones to estimate the weight that
they carry.
- Track strides can be used to estimate speed once weight is known.
- Tones can be measured from the nasal passages of the duckbills.
How did the Dinosaurs go Extinct?
- Mammals ate their eggs
- they were irradiated by cosmic rays
- changes in climate and mountains, land and sea caused their extinction
- Asteroid impact
The Birds
Where do birds come from?
Archeopterix is the earliest known bird fossil from the Jurassic. It has
some avian characteristics and a lot of theropod characteristics. Birds
in general show 120 shared characteristics with the dinosaurs. There are
few differences at all between Archeopterix and the theropods so that the
Archeopterix specimens that lack feathers were originally identified as
the dinosaur Campsognathus. It is thought that even feathers were sported
by dinosaurs originally.
Reconstruction
of dinos with feathers
Fossil dinosaur
with evidence of feathers
Problems with
the origin and evolution of birds
Unique Characteristics of Birds
In a nut shell: They can fly. To support flight, later birds developed
a large sternum, a wishbone, and a massively fused synsacrum. The tail was
reduced to a stubby pygostyle for better control. Teeth were eventually
lost in the modern surviving groups. the three fingers that are elongated
in Archeopterix are fused together in later birds. The motion in the wrist
was modified to aid in folding the wings.
Origin of Flight SWAGs
- Climbed trees and started as gliders
- started flying as fast running ground predators.
Bird history.
- Birds as early as jurassic. The fossil record of birds is rather
poor.
- Birds became abundant in the cretaceous, but the large majority of
them died out at the end of the cretaceous.
- The surviving birds did not resemlbe the most abundant cretaceous
groups, and gave rise to the modern birds. Bird relationships are still
highly debated.
- One interesting side is the development of the large flightless birds
in the eocene of South America exemplified by Diatrema, which
stood 2 meters tall, and was the principle predator until mammal predators
moved from north america when the Isthmus of Panama joined the two continents.
Earliest
Beaked Bird
More on Confuciusornis
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