Lecture 9 Flashcards
Ediacaran
- 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)
Multicellularity
- 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
Ediacaran body plan innovations
- 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
Pre-Cambrian body plan innovations
- animals with body cavity surrounded by a cellularized layer
- diploblasts
Diploblasts
- specilization of cellular layers
- mouth
- tissues
- three body axes
- simple nerve net
Bilaterians
- 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
Segmentation
- 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
Indiana
-used to be on equator which is why we have lots of fossils of tropical things here
Cambrian Radiation and fossil sites
- 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
Cambrian geography
-all animals were marine but lived at continental edges so geographically distinct
Cambrian innovations
- 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
Cambrian innovations led to
- ability to burrow
- ability to swim
- carnivory and arms race
- social interactions among individuals
Trace fossils
-not seen in Pre-cambrian because animals didn’t have the ability to burrow yet
Vertebrates in Cambrian
- not that impressive
- only a few at first and then later on the most important ones were insects
Disparity
- how many phyla are there?
- basic body plans and diversity goes up
Echinoderms
-cambrian vs. today do not look the same at all really
Annelids vs. Mollusks
- 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
Acoelomates
-no body cavity but got goes through mesoglea cells
Pseudocoelomates
-organs loose in body cavity
Eucocelomates
- 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
Primitive Vertebrates and Chordates
- 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
Cambrian radiation vs world today
- 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
Summary of Cambrian Radiation (graph/chart)
(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
The meaning of phyla
**look at this slide
Echinodermata
- 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
Annelids
- provide hydrostatic skeleton
- vital for locomotion and particularly for burrowing
- body wall muscles contract and relax
Arthropods
- exploited segmentation in remarkable adaptations
- rigid exoskeleton
- modification and specialization of appendages
- tagmosis-segment fusion to functional units
Remarkable genetic controls of development-mutations as tools
-as insects develop genes control overall polarity, segment number and position, and segmental identity
Burgess Shale of Canada
- 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
Cambrian soft-bodied faunas
- 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
