Lecture 9

Question 1

Ediacaran

Answer 1

• very limited, not divers, very 2D
• radiation of basal animals of cnidarians grade and perhaps the first bilaterian (leaves feeding pattern that looks like it has a mouth and a trail that shows it moves)

Question 2

Multicellularity

Answer 2

• very big step in animal life
• single cell divides and the cells don’t separate but stick together
• cell to cell differentiation arises to result in different structures
• probably no body axes
• first Ediacarans were made up of a single sheet of cells

Question 3

Ediacaran body plan innovations

Answer 3

• based on evolving genetic controls over development
• single cell ancestor–>simple multi cell organism: cell-cell adhesion, cell-cell communication, limited differentiation, no body axes, likely single cell gametes–>single cell sheet Ediacaran: 2 body axes, some cell differentiation, single-cell gametes

Question 4

Pre-Cambrian body plan innovations

Answer 4

• animals with body cavity surrounded by a cellularized layer
• diploblasts

Question 5

Diploblasts

Answer 5

• specilization of cellular layers
• mouth
• tissues
• three body axes
• simple nerve net

Question 6

Bilaterians

Answer 6

• triploblasty, pass through gut, organs, central nervous system
• may appear in Edicaran Kimberella?
• rapidly evolve in the cambrian
• body cavity isn’t just a gut
• capable of body movement, have muscle cells
• all takes place in sea

Question 7

Segmentation

Answer 7

• segments form then they become different from each other
• shown well in annelids, arthropods, and chordates
• trilobites (major Paleozoic arthropods) show early evolution of segmentation

Question 8

Indiana

Answer 8

-used to be on equator which is why we have lots of fossils of tropical things here

Question 9

Cambrian Radiation and fossil sites

Answer 9

• important sites are Chengjiang and Burgess Shale
• give us important picture of Cambrian Radiation
• all of the basic animal niches were filled by Cambrian radiation and now new phyla have evolved since

Question 10

Cambrian geography

Answer 10

-all animals were marine but lived at continental edges so geographically distinct

Question 11

Cambrian innovations

Answer 11

• bilaterians
• triploblasty
• rapid body plan evolution
• eyes (compound eyes present)
• advanced central nervous system and behavior
• coelomic cavities
• segmentation
• skeletons
• appendages
• bright body colors
• allow rapid evolution of differentiated and sophisticated structural innovations and ecosystem complexity

Question 12

Cambrian innovations led to

Answer 12

• ability to burrow
• ability to swim
• carnivory and arms race
• social interactions among individuals

Question 13

Trace fossils

Answer 13

-not seen in Pre-cambrian because animals didn’t have the ability to burrow yet

Question 14

Vertebrates in Cambrian

Answer 14

• not that impressive

- only a few at first and then later on the most important ones were insects

Question 15

Disparity

Answer 15

• how many phyla are there?

- basic body plans and diversity goes up

Question 16

Echinoderms

Answer 16

-cambrian vs. today do not look the same at all really

Question 17

Annelids vs. Mollusks

Answer 17

• have common ancestor
• don’t work the same way
• annelids work hydraulically like echinoderms
• coelom is filled with fluid and then the body wall muscles contract and the segments beomce long and thin and the worm becomes narrow and if they relax they become widere and this is how they burrow
• only mollusks have radula

Question 18

Acoelomates

Answer 18

-no body cavity but got goes through mesoglea cells

Question 19

Pseudocoelomates

Answer 19

-organs loose in body cavity

Question 20

Eucocelomates

Answer 20

• make possible large body size
• this is the important kind
• complicated
• gut goes through and so do body organs
• all aspects firmly anchored in place by structures that are a part of the body wall=mesentery
• forms form mesoderm in developent

Question 21

Primitive Vertebrates and Chordates

Answer 21

• appear in Chengjiang and Burgess
• show chordate dorso-ventral layout, and basal features like gill slits, paired body muscles, a notochord, and a dorsal fin
• primitive vertebrates appear in the earlier Chengjiang making them about as old as other bilaterian phyla

Question 22

Cambrian radiation vs world today

Answer 22

• declies in the fates of once prominent groups of animals, and rise of others that were not very important in cambrian faunas
• i.e. lobopods were once major players and are now nearly extinct
• vertebrates were minor and unimportant and are now very important
• arthropods were strong and remain dominant but new clades have replaced those of the cambrian

Question 23

Summary of Cambrian Radiation (graph/chart)

Answer 23

(1) the time of onset is constrained by
 evolution of the environment
(2) duration controlled primarily by rates
of developmental innovation
(3) uniqueness of the event is either
due to ensuing developmental limitation
or to ecological saturation

Question 24

The meaning of phyla

Answer 24

**look at this slide

Question 25

Echinodermata

Answer 25

• living members have characteristic pentameral symmetry but they are bilaterian and related to chordates
• basal echinoderms had non-radial and non-pentamerous symmetry
• genes tell us about the close link but only fossils can tell us about the history of extreme body plan transformation

Question 26

Annelids

Answer 26

• provide hydrostatic skeleton
• vital for locomotion and particularly for burrowing
• body wall muscles contract and relax

Question 27

Arthropods

Answer 27

• exploited segmentation in remarkable adaptations
• rigid exoskeleton
• modification and specialization of appendages
• tagmosis-segment fusion to functional units

Question 28

Remarkable genetic controls of development-mutations as tools

Answer 28

-as insects develop genes control overall polarity, segment number and position, and segmental identity

Question 29

Burgess Shale of Canada

Answer 29

• extrodinary preservation here
• reveals animals of Cambrian radiation
• include mostly soft-bodied animals representing primitive members of living phyla and a few representatives of possible ancestors to more than one later phylum
• cambrian ecology revealed was already complex and included predation and advanced sense organs coupled to central nervous systems and locomotory organs

Question 30

Cambrian soft-bodied faunas

Answer 30

• Burgess Shale-Canadian Rockies Charles Walcot
• Sirius Passet, Greenland
• Chengjiang, China
• even with invention of skeletons, most animals in sea were and are soft-bodied
• skeletons only preserve small part of entire living animal