Lecture Three

Question 1

Multicellular organisms emerge toward the end of which period?

Answer 1

The Precambrian; after 88% of the Earth’s history had passed.

Question 2

What did the end of the Precambrian (540 MYA) and start of the Paleozoic historically define?

Answer 2

The first appearance of multicellular life in the fossil record - we now know this actually occurred as early as 800 MYA.

Question 3

What is the earliest known occurrence of multicellular animals?

Answer 3

Ediacaran fauna of South Australia (about 640 MYA) - some of these Ediacaran animals resemble modern jellyfish and segmented worms.

Question 4

What are fossils preserved in?

Answer 4

Sedimentary rock that is formed from sediments that pile up over geologic time and become rock. Organisms that are buried quickly and have hard parts have a reasonable chance of being preserved - the Law of Superposition helps with relative aging.

Question 5

What periods of life are within the Paleozoic?

Answer 5

The Devonian, Ordovician, and Cambrian.

Question 6

What is the Devonian?

Answer 6

The Age of Fishes; first insect fossils, fish were dominant, first land plants; 400-350 MYA.

Question 7

What is the Ordovician?

Answer 7

The Age of Invertebrates (490-443 MYA), first fish, trilobites dominant, first organisms with shells.

Question 8

What is the Cambrian?

Answer 8

The Age of Invertebrates (540-490 MYA), first fish, trilobites dominant, first organisms with shells.

Question 9

What isotope is used for young fossils?

Answer 9

Carbon 14 (100,000-30,000 YA).

Question 10

What isotopes are used for older fossils?

Answer 10

Potassium-40(Argon-40), Rubidium-87(Strontium-87), Uranium-235(Lead-207), Uranium-238(Lead-206).

Question 11

What was the Cambrian Explosion?

Answer 11

The beginning of the Cambrian (first period within the Paleozoic); saw a major increase in the diversity of animal species. Includes all the major invertebrate types found today, there were approximately 100 animal groups by the early Cambrian (30 remain today).

Question 12

What is the significance of the Burgess Shale?

Answer 12

Simmilar to the Ediacaran fauna, the Burgess Shale in the mountains of BC has a highly unusual preservation of soft bodied organisms.

Question 13

What is important about the biota of the Burgess Shale?

Answer 13

It is typical of Cambrian deposits in many ways. The biota consists of a range of organisms including rare free-swimming organisms, and common bottom dwelling organisms and scavengers.

Question 14

What are the two hypotheses to the Cambrian Explosion?

Answer 14

1. Advances just before the explosion allowed subsequent groups to exploit new environments and rapidly adapt to them (diversity breeds diversity).
2. Diversity may be related to rising oxygen levels (Cambrian is as high as today)

Question 15

What occurred during the Ordovician period that changed biodiversity?

Answer 15

Life on land - early to mid Ordovician was warm and humid. Marine invertebrates were very diverse (ancestral jawless fish were present). The invasion of land by ancestral plants and likely arthropods took place-this invasion represents another set of new environments to be exploited (resulting in new species/biodiversity). The last new niche for life.

Question 16

When did land plants evolve?

Answer 16

Approximately 472 MYA (liverworts - lack stems or roots).

Question 17

What is the common ancestor of land plants?

Answer 17

Coleochaetales (an algae). Evidence is found in morphology and genetics.

Question 18

What were the first land plants called?

Answer 18

Bryophytes (liverworts, hornworts, mosses). They lack vascular tissue. They are the simplest land plants.

Question 19

What is the Pneumodesmus newmani?

Answer 19

A species of millipede that lived 428 MYA in the Late Silurian that is the first myriapod and the oldest known creature to have lived on land. Had a hard body, which is why there are records of it.

Question 20

What challenges did life on land present?

Answer 20

Gravity, lack of water, need to develop a way for obtaining energy, temperature regulation.

Question 21

How did gravity present a challenge to organisms?

Answer 21

Gravity requires some form of rigidity. Animals developed the ability for locomotion on land (muscles and skeletons), plants developed roots for anchoring and rigid cells to maintain vertical stance.

Question 22

How did the lack of water present a challenge to organisms?

Answer 22

Water was no longer everywhere. Animals developed an outer layer that prevented inner tissues from drying out. Plants developed waxy cuticle to retain water and use roots to obtain ground water.

Question 23

How was obtaining energy challenged by life on land?

Answer 23

Animals were heterotrophs and developed new means of eating plants and other organisms.
Plants grew upright to obtain sufficient sunlight for photosynthesis, this requires support tissue.

Question 24

How did temperature challenge life on land?

Answer 24

Temperature on land is highly variable relative to water. Plants use evaporative cooling through pores (stomata) and develop spores that can persist through cold periods.
Animals burrow or rest in shade, become nocturnal, develop sweat glands, fur, feathers, migrate, hibernate.

Question 25

Are more organisms invertebrates or vertebrates?

Answer 25

Invertebrates.