GEO3 Exam 4

Mesozoic Era

Follows the end-Permian mass extinction.

Consists of the Triassic, Jurassic, and Cretaceous periods (in order of oldest to youngest).

Marks the transition into modern fauna.

Dinosaurs

Evolved from tetrapods.

Sauropsida

A clade that includes lizards, snakes, crocodiles, dinosaurs, and birds.

Dominated the Mesozoic.

What happened to therapsids?

3 out of 20 families survived the end-Permian extinction.

Sauropsida occupied the niches of the extinct families.

Cynodonts

A therapsid family that gave rise to mammals.

Archosauria

A clade that dominated the Triassic period.

Were the most recent ancestors of crocodiles, dinosaurs, and birds.

Characteristics:

Small and lizard-like

Very diverse

Bipeds, quadrapeds, gliders

Had a semi-erect gait

Triassic dinosaurs were...

Diapsids

Evolved from small bipedal Archosaurs

Had an erect gait

Small carnivores

Why were dinosaurs in the Triassic period small?

Therapsids still filled many niches, so dinosaurs weren't given many opportunities to dominate the terrestrial realm.

End-Triassic Extinction

Extinction where therapsids go extinct, and dinosaurs inherit the earth.

What happened after the end-Triassic extinction?

Jurassic period begins.

We begin seeing bigger dinosaurs in the Jurassic because they get to occupy the empty niches that therapsids used to occupy.

Mammals are mostly nocturnal, small, and burrowers or tree climbers.

Cretaceous period

Dinosaurs diversify more and new forms arise.

Examples: T-rex, triceratops, velociraptors

Ornithischia

"bird-hipped" dinosaurs

Herbivores

Pubis bone points backwards

Had massive specialized grinding teeth, similar to modern elephants

Examples: Stegosaurus, triceratops

Saurischians

"lizard-hipped" dinosaurs

Pubis bone points forwards

Herrerasauridae

Smaller, carnivorous dinosaurs

Have some features of Sauropods and features of other dinosaurs

Believed to be one of the earliest dinosaur to evolve

Sauropoda

Sister taxa of Herrerasauridae

Long necks

Quadrupedal

Herbivores

Have simple, weak teeth

Swallow stones to digest plant material (gizzards and gastroliths)

Largest land animal ever!

Theropoda

Bipedal carnivores

Have conical teeth, some with serrated edges to tear meat apart (similar to sharks and sabertooth cats)

Fast, agile

Big claws

Big eyes, good vision

Includes birds!

How can dinosaur postures be interpreted from the fossil record?

Functional morphology: putting bones together and interpreting what they were used for by comparing them to extant animals

How can dinosaur behaviors be interpreted from the fossil record?

Trace fossils like dinosaur tracks and nests, and body fossils like eggs

Encephalization Quotient (EQ)

Compares brain size vs. body size.

Rates intelligence of animals

Dinosaurs have a wide range of EQ, but not within a range that is unfamiliar to us.

Endothermic

"warm-blooded"

Body temperature is regulated internally (thermoregulation) at a constant temperature (homeothermic)

Animals have a fast metabolism and require more food, more respiration

Ectothermic

"cold-blooded"

Animals rely on an external source of heat to regulate body temperature

Body temperature varies depending on environment (heterothermic)

Slow metabolism

Are dinosaurs likely endothermic or ectothermic? Why?

Likely endothermic.

Reasons:

Some have feathers

Egg brooding

Passive thermoregulation (too big to cool down)

There were dinosaurs at high latitudes (cold environments)

Bone growth rates similar to mammals

Oxygen isotopes are constant throughout dinosaur bones (homeothermic transport of oxygen)

Specialized teeth/feeding (endothermy requires efficient food processing)

Erect gait (better posture for breathing)

Running speed

Brain size (large brain size likely correlates with endothermy)

Predator-prey relationships (ratio consistent with that of endotherms)

The Mesozoic Marine Radiation is characterized by...

Animals with more fleshy biomass and are larger than Paleozoic fauna

Expanded modes of living (deep burrowing, predation)

High diversity driven by "arms race"

Co-evolution of predators and prey

Convergent evolution of marine animals that originated from terrestrial animals despite having been evolved separately

Why did flight evolve in animals?

To escape predators

Catch prey

Move from place to place

Access to new food sources

What are the 4 modes of air travel?

Passive flight

Parachuting

Soaring

Active flight

What characteristics do animals need in order to actively fly?

Strong, but light skeleton

Streamlined, aerodynamic body

A modified pectoral girdle for power strokes

Cursorial Hypothesis

"Ground Up Flight"

Wing assisted running that led to flying, evolved by the power stroke

Arboreal Hypothesis

"Trees Down Flight"

Jumping from tree to tree, or gliding/parachuting from tree to ground

Pterosaurs

Not dinosaurs!

Evolved from small bipedal Archosaur

First vertebrates capable of active flight

Scientists unclear whether they were cursorial or arboreal

Birds

Evolved by Late Jurassic from therapod dinosaurs

Low diversity until late-Cretaceous

Very successful groups with >9000 species

Archaeopteryx was the "first true bird"

Bats

2nd most diverse group of mammals

Only mammals to have active flight

Scientists hypothesized they may have evolved from a nocturnal, arboreal glider that ate insects

Did pterosaurs, birds, and bats evolve convergently or together?

They evolved convergently.

Convergent evolution

Evolution toward similar characteristics in unrelated species