BIOL010 - Midterm #4

When did the oldest known fossils appear, and what do they represent?

Around 3.5 billion years ago (Ga). These are prokaryotic microorganisms, indicating the earliest life on Earth.

When did eukaryotic life first appear, and why is this significant?

Around 1.9 Ga. Eukaryotes have complex cells with nuclei, marking a major evolutionary step toward multicellular organisms.

What major evolutionary event happened approximately 600 million years ago (Ma)?

The first appearance of multicellular animals in the fossil record.

What is the Cambrian Explosion, and why is it important?

A rapid diversification of animal life during the Cambrian Period (~540 Ma), where most major animal phyla appeared.

During which period did vertebrates first move onto land, and what was its significance?

The Devonian Period. This marks the transition of vertebrates from aquatic to terrestrial environments.

When did dinosaurs first appear?

In the Triassic Period, around 230 Ma. They evolved from small bipedal Archosaurs.

When did the dinosaurs go extinct, and what era began afterward?

Around 65 Ma, during the Cretaceous–Paleogene extinction. The Cenozoic Era (Age of Mammals) followed.

What is the largest mass extinction event in Earth’s history, and what caused it?

The End-Permian Mass Extinction (~252 Ma). Likely caused by massive Siberian volcanism, high CO₂, sulfur emissions, ocean acidification, and marine hypoxia.

How severe was the End-Permian extinction in terms of biodiversity loss?

Wiped out 90–96% of marine species and about 70% of terrestrial tetrapod families, including many insects.

What was the major continental configuration at the time of the End-Permian extinction?

Pangaea (supercontinent) and Panthalassa (global ocean).

What are tetrapods, and when did they first appear?

Tetrapods are four-limbed vertebrates, including amphibians, reptiles, birds, and mammals. They first appeared in the Late Devonian.

What adaptation allowed amniotes to reproduce away from water?

The amniotic egg, which contains membranes that protect the embryo and facilitate gas exchange.

What are the two main branches of amniotes?

• Sauropsida: Gave rise to reptiles, birds, and dinosaurs.

• Synapsida: Gave rise to mammal-like reptiles and modern mammals.

Who were the dominant terrestrial vertebrates in the Permian period?

Synapsids, especially a subgroup called Therapsids, which showed early mammal-like traits.

What are some features of Therapsids?

• Carnivorous and herbivorous species

• Possibly endothermic (warm-blooded)

• Lived in mid to high latitudes

• Had semi-erect gaits

• Dominant in the Late Permian

What group of amniotes ruled the Mesozoic era?

Sauropsids, particularly the Archosaurs, which include crocodiles, pterosaurs, and dinosaurs.

What anatomical trait allowed Archosaurs to move more efficiently than earlier reptiles?

A semi-erect posture, reducing side-to-side (medial-lateral) spine undulation and allowing faster movement.

How did dinosaurs differ from other reptiles?

• Evolved from small bipedal archosaurs

• Had a fully erect gait

• Were entirely terrestrial

• Showed great diversity in size and form

The largest mass extinction was.......

The end-Permian

The Triassic was.....

Short (51 million years)

What group did dinosaurs evolve from and what traits did they inherit?

Dinosaurs evolved from small bipedal archosaurs. They inherited a fully erect gait, were terrestrial, and developed a wide range of body sizes.

What are the three major dinosaur groups and their key features?

1. Sauropods (Saurischians): Long-necked, quadrupedal herbivores with weak teeth. Largest land animals ever.

2. Theropods (Saurischians): Bipedal carnivores (e.g., T. rex, raptors). Sharp teeth, large eyes, fast/agile. Includes birds.

3. Ornithischians: "Bird-hipped" herbivores with a backward-pointing pubis. Includes armored, horned, and duck-billed dinosaurs.

How do paleontologists study dinosaur behavior and environment?

Through a combination of:

• Modern analogs

• Functional morphology

• Sedimentary records

• Trace fossils (tracks, nests)

• Phylogenetics

How did sauropods process plant material with their weak teeth?

They used gastroliths in their gizzards to grind up tough cellulose from plants — a trait also seen in modern birds.

What dental adaptations did Ornithischians have for herbivory?

They evolved massive, specialized grinding teeth to chew and break down plant material efficiently.

What features supported carnivory in Theropods?

• Sharp, often serrated teeth

• Large claws (forelimbs or hind limbs)

• Forward-facing large eyes for good depth perception

• Agile bipedal locomotion

What kinds of dinosaur behavior can trace fossils reveal?

Trace fossils (like tracks and nests) can indicate:

• Movement and speed

• Preferred environments

• Social structure (herds vs. solitary)

• Predator-prey interactions

• Nesting and parental care

What evidence supports head-butting behavior in some dinosaurs?

Pachycephalosaurus had fused, thick cranial bones and strong cervical vertebrae — like modern rams that head-butt.

What functions did Hadrosaur head crests possibly serve?

• Social display through color changes (vascular tissue)

• Sound resonance (e.g., Parasaurolophus could make low-frequency calls for communication)

What fossil evidence suggests parental care in dinosaurs?

• Eggs arranged in clutches

• Nests found in colonies

• Fossils of adults with juveniles

• Brooding postures (similar to birds)

What does the Encephalization Quotient (EQ) measure?

The EQ compares brain size to body size. Higher EQ suggests more advanced cognition. Dinosaurs varied widely, but were generally below mammals.

What's the difference between endothermy and ectothermy?

• Endothermic animals produce internal heat, have fast metabolism, and maintain constant temperature.

• Ectothermic animals rely on environmental heat and have variable body temperature.

What are five current hypotheses about dinosaur metabolism?

• Fully endothermic like birds.

• Intermediate physiology between endo- and ectothermy.

• Too little evidence to conclude.

• Inertial homeotherms (ectothermic but large enough to retain heat).

• Simple ectotherms, but active due to warm climate.

What evidence supports the idea that some dinosaurs were endothermic?

• Feathers (thermoregulation in Theropods)

• Brooding behavior like birds

• Gigantothermy — being large helps maintain stable body temperatures

• High activity levels inferred from bone structure and fossil evidence

What are the metabolic demands of endothermy in dinosaurs?

• Need to eat up to 20× more food

• Need to breathe up to 10× more often than ectothermic animals

Non-avian dinosaurs lived aside Humans

True or False

False

Birds are direct decendents of dinosaurs and so are considered dinosaurs

True or False

True

Dinosaurs had amniotic eggs

True or False

True

Dinosaurs include the largest animal ever to live on land

True or False

True

What skeletal special feature (an evolutionary advantage) did dinosaurs have that is still present today in non-extinct dinsours?

Air sacs (pockets of soft tissue)

What is a plausible use for Tyrannosaurus rex's (T. Rex) tiny arms?

Stability

What are Sepkoski’s Three Great Evolutionary Faunas and their dominant organisms?

• Cambrian Fauna: Trilobites, inarticulate brachiopods, primitive mollusks and echinoderms.

• Paleozoic Fauna: Articulate brachiopods, crinoids, cephalopods, corals.

• Modern Fauna: Gastropods, bivalves, bony fish, crustaceans, echinoids.

What caused the major shift from Paleozoic to Modern marine faunas?

The Permian Mass Extinction, which selectively eliminated many Paleozoic taxa, allowed modern faunal groups with higher biomass and more fleshy bodies to dominate.

What are some differences between Paleozoic and Modern marine faunas?

• Paleozoic: Smaller body size, low biomass, few fleshy animals.

• Modern: Larger, more fleshy, diverse in lifestyle and body types. Greater biomass per individual.

What is the Mesozoic Marine Revolution?

A major ecological shift in which all major modes of marine life were occupied. There was a big expansion in deep burrowing and predation, making the ecosystem more complex and competitive.

What are marine sauropsids, and why did reptiles return to the sea?

Marine sauropsids are reptiles that evolved back into aquatic life due to:

• Abundant food

• Stable ocean temperatures

• Efficient migration opportunities
  Examples include ichthyosaurs, plesiosaurs, mosasaurs, and marine turtles.

What are key challenges for reptiles adapting to marine life?

1. Breathing: Must remain air-breathers.

2. Feeding: Range from fish to shellfish eaters.

3. Locomotion: Use flippers or tail propulsion.

4. Reproduction: Either lay eggs on land or evolve live birth.

Who were the first aquatic reptiles and what were their traits?

Mesosaurs (Early Permian, Gondwana):

• Long needle-like teeth for fish

• Webbed hands/feet, deep tail for swimming

• Possibly retained eggs internally

• Poor land locomotion

What are ichthyosaurs and what were their adaptations?

• Evolved from land reptiles

• Streamlined bodies with flippers and tail fins

• Large eyes for deep-sea hunting

• Fast swimmers, likely could not live on land

• Ate fish and squid; some suction feeders

How long did ichthyosaurs exist, and what was their size range?

from Early Triassic to early Late Cretaceous

ranged from 0.4 m to 15 m long.

What are the two major body plans in plesiosaurs?

1. Elasmosaurs (long neck, small head): Ate small fish and squid

2. Pliosaurs (short neck, large head): Ate larger fish and marine reptiles
   Note: Some large-headed forms evolved multiple times from long-necked ancestors.

What are some unique features of plesiosaurs?

• Used four large flippers to swim

• Possibly gave live birth to a single large baby

• May have provided extended parental care

What were mosasaurs, and what did they eat?

• Late Cretaceous marine lizards

• Had large cone-shaped teeth

• Ate fish, squid, ammonoids, and other marine reptiles

• Some had crushing teeth for shellfish

What anatomical features helped mosasaurs adapt to marine life?

• Forelimbs became strong, webbed flippers

• Reduced hind limbs

• Powerful, deep tail for swimming

• Retained young inside the body (live birth)

How did Mesozoic marine turtles differ from land turtles?

• Limbs became flippers

• Forelimbs did most of the swimming

• Thinner shells for mobility

• Came ashore only to lay eggs

What is Archelon, and why is it significant?

Archelon was a giant Cretaceous marine turtle — among the largest turtles ever. It exemplifies how big marine reptiles got during the Mesozoic.

What recent evidence suggests about marine reptile metabolism?

Some marine reptiles (e.g., ichthyosaurs, plesiosaurs, possibly mosasaurs) may have had elevated metabolisms, closer to endothermy than traditional cold-blooded ectothermy.

Mosasaurs are dinosaurs

True or False

False

Ichthyosaurs, although reptiles, gave live birth

True or False

True

The Marine Mesozoic Revolution was characterized by

ecological replacement of brachiopods by bivalves (clams)

What are the main evolutionary advantages that led to the development of flight in animals?

• Escape from predators

• Catch prey

• Migrate long distances

• Access unoccupied niches

• Reach new food sources

What are the four basic modes of air travel in animals?

1. Passive flight (e.g., spores)

2. Parachuting (simple, slow descent)

3. Soaring (gliding long distances with little effort)

4. Powered/active flight (requires muscle-driven wing strokes)

Who were the first animals to evolve true flight?

Arthropods – specifically hexapods (insects) during the Carboniferous period.

How did insect wings evolve according to current hypotheses?

From gills or swimming legs, allowing insects to retain all their walking limbs.
Hox genes controlled limb and segment development.

When did gliding and parachuting first appear in vertebrates, and what are examples?

• Parachuting: Originated in the Permian (e.g., Coelurosauravus)

• Gliding: Expanded in the Triassic (e.g., Kuehneosaurus, Sharovipteryx)
  These forms used extended membranes or ribs to control descent.

Which three vertebrate groups evolved powered flight independently?

• Pterosaurs (Late Triassic – extinct)

• Birds (Aves) (Jurassic – present)

• Bats (Chiroptera) (Early Cenozoic – present)
  This is an example of convergent evolution.

What key skeletal adaptations did pterosaurs evolve for flight?

• Light, pneumatic bones

• Keeled sternum

• Short robust humerus

• Pteroid bone (supports wing membrane)

• Wing supported by a single elongated digit

What are the two main hypotheses for how pterosaurs developed powered flight?

• Cursorial hypothesis (ground-up): Running + wing flapping

• Arboreal hypothesis (trees-down): Gliding and leaping

What are defining features of birds (Aves)?

• Feathers

• Warm-blooded (endothermic)

• Air sacs/lungs

• Hollow bones

• Toothless beaks

• Large brains

• Furculum (wishbone)

Where did feathers originate, and what were their likely original functions?

Found in non-avian theropods, likely evolved for:

• Insulation

• Brooding eggs

• Display

• Possibly later adapted for flight

What is Archaeopteryx and why is it important?

• Late Jurassic fossil, considered the first "true bird"

• Had feathers and furculum, but also teeth, fingers on wings, and small sternum

• Shows mix of bird and reptile features (transitional fossil)

What hypotheses explain the evolution of wings in birds?

1. Escaping predators

2. Catching prey

3. Aiding leaping or gliding

4. Freeing hindlimbs as weapons

5. Accessing new niches

Name examples of flightless birds and their adaptations.

• Penguins: Use wings for underwater swimming

• Ratites: (e.g., ostriches, emus, kiwis) ancient flightless birds from the Southern Hemisphere

• Some use feet to dive rather than fly.

What is unique about bat wings compared to birds and pterosaurs?

• Wings are formed by elongated fingers with skin membrane

• Supported by arm and uropatagium (membrane between hind limbs)

• Greater maneuverability and echolocation in many species

What traits likely characterized the bat ancestor?

• Nocturnal

• Insectivorous

• Arboreal glider

• Had good senses (echolocation or keen vision)