Basal Archosaurs

• Archosaurs are diapsid reptiles. They can be divided into two groups: – Lepidosaurs (lizards, snakes, and their ancestors) – Archosaurs (dinosaurs, pterosaurs or flying reptiles,

crocodilians, and birds)

Dinosaurs • The name "dinosaur" comes from the Greek deinos =

"terrifying" and sauros = "lizard." • Dinosaurs appeared during Late Triassic, about 225

m.y. ago.• The earliest dinosaurs were small. Many were less

than 3 ft long.• By the end of Triassic, dinosaurs were up to 20 feet

long.• They became much larger later during Jurassic and

Cretaceous.

Dinosaurs

Two Orders of dinosaurs are distinguished on basis of hip or pelvic structure:

• Saurischian dinosaurs - lizard-hipped

• Ornithischian dinosaurs - bird-hipped

Saurischian Dinosaurs • "Lizard-hipped." Pelvic structure like lizards. • Both two-legged and four-legged types. • Both herbivores and carnivores. • Teeth extended around entire margin of jaws, or were

limited to the front.• Teeth adapted to cutting and tearing, but not chewing.• Food was ground up in the gizzard, probably aided by

stones the dinosaurs swallowed, called gastroliths. • The earliest dinosaurs and their basal archosaur

ancestors were saurischians.

Saurischian Dinosaurs

Two groups:

1. Theropods - bipedal carnivorous dinosaurs

2. Sauropods - large quadrupedal herbivorous dinosaurs

SauropodsLarge 4-legged herbivorous dinosaurs - "long necks"

• Seismosaurus • Argentinosaurus • Nuoerosaurus • Diplodocus

•Apatosaurus•Brachiosaurus •Supersaurus •Ultrasaurus

Supersaurus (right two)

Seismosaurus

Ornithischian Dinosaurs • Evolved near the end of Triassic • "Bird-hipped" - Pelvic structure resembles that of

modern birds. • Includes both two-legged and four-legged types. • All herbivores. • Lacked teeth in the front of the upper and lower jaws.

Beak for cropping vegetation. Teeth were limited to the sides of the jaws, and were well adapted for crushing and grinding vegetation.

• Front legs shorter, indicating descent from two-legged forms.

Ceratopsians• Triceratops • Styracosaurus• Protoceratops• Monoclonius

Stegosaurs The plates on the backs of stegosaurs may have served as body temperature-regulating devices. They may have been used as "radiators" to dissipate body heat, or as "solar panels" to catch the sun's rays.

Interesting Facts about Dinosaurs Fossil dinosaur eggs with embryos inside have

been found in Upper Cretaceous rocks of the Gobi Desert, Mongolia.

Interesting Facts about Dinosaurs

• The jaws of Tyrannosaurus could exert more than 3000 pounds of biting force (compared with the lion, at "only" 937 pounds of biting force).

• Its tail was held out horizontally to the back, serving as a counterbalance to the forward part of the body.

Interesting Facts about Dinosaurs

• Sauropods, with their long necks, apparently fed on vegetation high in the treetops. Their heads were relatively small, which avoided a heavy burden on the long necks.

• The large size of the sauropods provided an advantage in dealing with predators, and served to prevent body heat loss. (Large animals lose body heat slower than small animals.) Animals which preserve body heat as a result of their large size are called homeotherms.

Interesting Facts about Dinosaurs • Some duck-billed dinosaurs

(hadrosaurs) had bony skull crests with hollow tubes which may have served as vocal resonating chambers for producing sounds.

• Nests of dinosaur eggs suggest that some groups of dinosaurs cared for their young. The Maiasaura were apparently one group of dinosaurs which nurtured their young, as their babies stayed in the nests and grew after hatching.

Interesting Facts about Dinosaurs

• Were dinosaurs warm blooded? Paleontologist Robert Bakker has argued since 1968 that dinosaurs were warm blooded like birds. If so, they would no longer be classified as reptiles.

• Lines of evidence for warm bloodedness include: – The stance and gait of dinosaurs (as judged from

trackways), – The microscopic structure of the bones, – Isotopic analyses of bones, and – Proportions of predators to prey.

Flying Archosaurs or Pterosaurs

• The word pterosaur means "winged lizard." • The earliest flying reptiles were probably gliders. • Later forms were active fliers, with flapping wings,

rather than gliders. • There were two groups of pterosaurs:

– Rhamphorhyncoids, which had long tails with a diamond-shaped tip.

– Pterodactyls, which were more advanced and tail-less. Pteranodon.

Pterosaurs• Pterosaurs dominated the skies for more than 100

million years. They existed from Late Triassic to Late Cretaceous.

• Jurassic and Cretaceous pterosaurs had large heads and eyes, and long jaws with thin slanted teeth.

• The bones of the fourth finger were elongated to support the wing membrane.

Pterosaurs

Eudimorphodon (right front), a 60-cm pterosaur with sharp teeth for catching fish, and Peteinosaurus (left)

Pterosaurs• The largest pterosaur was Quetzalcoatlus which had a

50 foot wingspan. Late Cretaceous of western Texas. It was the largest known flying vertebrate that ever lived on the Earth.

• Some Mesozoic flying reptiles were covered with hair or fur, indicating that they were warm blooded. An example is Sordes pilosus, whose name means "hairy devil."

Pterosaurs

Quetzalcoatlus

Birds • Birds are warm-blooded (endothermic), have wings

and feathers, have a toothless beak, and lay eggs. Most can fly, but some are flightless.

• Bird bones are hollow, and not easily preserved.• Birds may have evolved from basal archosaurs, or

from small Triassic theropod dinosaurs. Both groups were bipedal and birdlike in the structure of their limbs, shoulder girdles, and skulls.

• Several theropod dinosaurs had feathers, hollow bones, and keeled breastbones.

Birds• Feathers evolved from reptilian scales. The earliest

feathers may have been used for insulation, camouflage, or display, rather than flight.

• It has been proposed that birds are closely related to dinosaurs, and that the two should be reclassified into Class Dinosauria. This would eliminate Class Aves (where birds are currently classified). This has not yet been generally accepted.

Archaeopteryx • The best known bird fossil is Archaeopteryx, which

was the first to be discovered, although perhaps not the oldest.

• It was found in the roughly 150 million year old Jurassic Solnhofen limestone in Bavaria, Germany in 1861.

• Fewer than a dozen specimens have been found. • The word Archaeopteryx means "ancient wing."

Archaeopteryx

• Archaeopteryx has some bird-like features and some reptile-like features.

• Bird-like features of Archaeopteryx: – Feathers – Wings

Archaeopteryx

• Reptile-like features of Archaeopteryx: – Dinosaur-like (theropod-like) skeleton – Teeth – Long lizard-like tail – Forelimbs with claws – The sternum or breastbone lacks a keel, meaning

that there were no strong muscles for sustained flight. It would have been a weak flier.

Archaeopteryx

Origin of Birds• Bird-like features are found in some dinosaurs,

including feathers or protofeathers, in Sinosauropteryx prima, more than 120 million years old, and Caudipteryx zoui, a dinosaur with a feathered tail.

• The line between dinosaurs and birds has blurred with the new discoveries, so it is difficult to say when the first bird appeared.

• Birds probably appeared near the end of Jurassic. • Many different types of birds lived during Cretaceous.

Therapsids• Mammals are synapsids, a group that includes Late

Paleozoic sail-backed pelycosaurs. • Therapsids probably arose from the pelycosaurs.• Mammals evolved from therapsids that survived the

Permian extinction. • Therapsids were small to moderate sized vertebrates,

with several mammalian skeletal traits. – Differentiated teeth – Legs beneath body

Cynodonts

• One group of therapsids became common during Triassic. These were the cynodonts (meaning "dog toothed").

• The cynodonts had several mammal-like traits including a bony palate which permitted breathing while chewing, an important trait for an animal evolving toward the mammals.

The Rise of Mammals• Therapsids became extinct during Early

Jurassic, after giving rise to the mammals. • Mammals evolved during Late Triassic. • Early mammals were rodent-like, and

remained small throughout Mesozoic.

Morganucodon, an early mammal from Late Triassic

Mammals• Mammals are warm-blooded (endotherms), and are

distinctive because they: – Have hair or fur – Females have mammary glands that secrete milk to

feed their young • Fossils of early mammals, show evidence of "whisker

pits" on the snout region of the skull, indicating that they were covered with hair or fur.

MammalsLiving mammals can be divided into three groups:

1. Monotremes - primitive mammals that lay eggs, including the duck-billed platypus and the echidna or spiny anteater.

2. Marsupials - carry their young in pouches (opossums and many Australian animals such as the kangaroo)

3. Placentals - the young are retained longer within the mother's body and a highly developed placenta is present.

Mammal Teeth

• Mammals have differentiated teeth including incisors, canines, premolars, and molars.

• Several groups of Mesozoic mammals can be identified on the basis of tooth morphology.

Mammal Teeth

7. Therians - "true mammals." Appeared during Late Cretaceous, but probably arose somewhat earlier during Early Cretaceous.

As the reptiles declined near the end of Mesozoic, mammals quickly expanded into habitats that the reptiles had vacated. The mammals experienced an adaptive radiation during Cenozoic.

Land Plants

Why are Plants Important?• They are primary producers and form the base of the

food chain, providing food for land-dwelling animals • Variations in the abundance of plants over time

probably caused changes in the amounts of oxygen and carbon dioxide in the atmosphere, affecting global climate.

• Decaying vegetation leads to soil formation. • Plant roots hold the soil in place to prevent erosion. • Plant remains form coal deposits.

Three major advances in the evolution of land plants:

• Seedless spore-bearing plants, like ferns, appearing during Ordovician

• Non-flowering plants that pollinate and produce seeds, the gymnosperms: cycads, seed ferns, conifers, and ginkgoes, appearing during Late Devonian.

• Flowering plants or angiosperms, appearing during Early Cretaceous.

Geologic ranges, relative abundances and evolutionary relationships of vascular land plants

1. Ferns - spore-bearing plants, dominant during Triassic.

2. Seed ferns - less abundant than during Paleozoic, but survived into the middle part of Mesozoic. Extinct.

3. Lycopods (scale trees) and sphenopsids survived into Mesozoic. Most were small. The decline of lycopods, sphenopsids and cordaites trees began before end of Permian.

Early Mesozoic was dominated by plants which did not bear flowers. These included:

4. Gymnosperms - dominant trees during Triassic and Jurassic. Pollinated by wind. Their seeds are exposed, rather than being enclosed within fruits. "Gymnosperm" means "naked seed." Types of gymnosperms include:

a. Cycadsb. Ginkgoesc. Conifers

Cycads• Seed plants without true flowers. • Mesozoic could be called

"Age of Cycads." • Cycads appeared during

Triassic, and grew to be tall trees during Jurassic.

• They experienced a marked decline during Late Cretaceous, and only a few species survive to the present, including the sago palm, a common house plant.

Ginkgoes• Ginkgoes have naked fleshy seeds.

• Appeared during Late Paleozoic.

• The oldest genus of tree that is still living.

• Fossil ginkgoes more than 200 million years old are nearly identical to living ginkgoes.

Conifers• Conifers appeared during Late Paleozoic, declined

during Permian, and expanded again during Mesozoic.

• Conifers became the dominant gymnosperms during Mesozoic.

• Six groups of conifers were present during Jurassic and Cretaceous, including large numbers of pines.

Angiosperms

• The angiosperms or flowering plants made their first appearance during Cretaceous.

• Angiosperms diversified while the gymnosperms declined during Late Cretaceous.

• Angiosperms provide many examples of coevolution with Mesozoic insects, dinosaurs, mammals, and birds.

• Coevolution occurs when two or more different organisms become dependent on one another.

• An example involves the coevolution of insects and flowering plants.

• Insects depended on the plants for food, and the plants depended on the insects for pollination.

• Plant differences evolved due to competition for pollinators.

• Different insects were attracted by different varieties of flowers.

Mass Extinction at the end of Mesozoic: the end-Cretaceous catastrophe

A mass extinction occurred at the end of Cretaceous, which caused the disappearance of about 1000 genera of marine animals, and about 25% of all known families of animals.

• Many groups died out gradually, and others disappeared suddenly.

• The extinctions did not all happen simultaneously.• On land, only small (less than 50 lb) animals survived. • Of the reptiles, only turtles, snakes, lizards, crocodiles,

and the tuatara (a reptile from New Zealand) survived the extinction.

• More than 75% of the marine plankton species disappeared at the end of Cretaceous.

Animals both on land and in the sea were affected. The extinction at the end of Cretaceous totally wiped out these groups: – Dinosaurs – Pterosaurs (flying reptiles) – Ammonoids (cephalopod molluscs) – Large marine reptiles (ichthyosaurs, plesiosaurs

& mosasaurs) – Rudists (bivalve molluscs) – and many other invertebrate taxa

There were drastic reductions of these groups, wiping out entire families. Some of these groups had very few survivors:

– Coccolithophores (calcareous phytoplankton) – Planktonic foraminifera – Radiolarians – Belemnoids (cephalopod molluscs) – Echinoids – Bryozoans

Evidence for extraterrestrial causes of end-Cretaceous

• A thin layer of clay with a concentration of iridium is found at the boundary at the end of Cretaceous (the boundary clay).

• Because iridium is more abundant in meteorites than in normal Earth's surface rocks, it was proposed that a large impact of an extra terrestrial object with the Earth at the end of Cretaceous might have spread iridium around the globe.

• Other things may also have been responsible for the presence of the iridium, and all possibilities must be considered.

• Shocked quartz (from an impact)• Tiny glass spherules or tektites (cooled droplets of

molten rock from an impact) • Carbon soot (remnants of forests burned in a firestorm

caused by an impact)

Other evidence for extraterrestrial causes

Location of giant meteorite impact: Chicxulub, Mexico

Chicxulub structure, a buried circular crater-like structure on the Yucatan Peninsula of Mexico.