Paleozoic Invertebrate Evolution (midterm 2) Flashcards
Describe the significance of the Ediacaran Environment
- during the precambrian until the cambrian
- fossils of soft bodied organisms
- but hard parts were also first found in Ediacaran fauna
- The Ediacaran environment marks the first evidence of simple ecological interactions > organisms sort of just existing side by side
What is the significance of the Cambrian Environment compared to the Precambrian (Ediacaran environment)?
- more complex in terms of ecological interaction (ex. more predator - prey)
- many new body parts evolved
- animals moving into new ecological niches
- highest percentage of these kinds of experiments than any other period of geologic history
What was the Cambrian Explosion?
- most of today’s animal phyla first appear in the fossil record during the Early Cambrian
- most animals found from this time period can be attributed to modern groups (even if they look weird) > contain morphological and genetic information
- there was a huge apparent burst in diversity > or does it just appear that way because of the fossils record
*animals with skeletons appeared rather abruptly in the fossil record
What were the potential causes of the Cambrian explosion?
Global warming > snowball earth just ended - warming earth favours more biodiversity
Change in ocean chemistry > increased volcanic activity raised calcium content
Predators > the need to escape predators and to catch prey are strong drivers of natural selection
Oxygen levels (increasing)
Explain the stages of oxygen increasing in the atmosphere (and relating to the cambrian explosion)
Stage 1 (3.85-2.45 Ga): Practically no oxygen in the atmosphere so not much life happening
Stage 2 (2.45-1.85 Ga): Oxygen produced (great oxidation event) but absorbed in oceans and seabed rock
Stage 3 (1.85-0.85 Ga): Oxygen starts to gas out of the oceans but is absorbed by land surfaces (remains at a steady level for a while) - formation of ozone layer
Stages 4 and 5: (0.85 Ga-present): Huge increase in oxygen *during Cambrian explosion! - major bump happens during the Carboniferous (coal deposits with lots of plant material and oxygen happening) > then it goes down and levels out to modern levels (about 0.2)
Explain the emergence of a Shelly Fauna (first hard parts of organisms)
- the earliest known organisms with hard parts were small and calcareous tubes found in the Neoproterozoic Ediacaran faunas
*just before the Cambrian - the first microscopic skeletonized fossils appeared in the early Cambrian > *first evidence of an organism producing an exoskeleton
- first endoskeletons (internal) and exoskeletons (external shells)
What are the benefits of an exoskeleton?
- provides UV protection = can move into shallower waters
- prevents drying out in intertidal environments
- allows body size to increase
- provides attachment points for muscles
- offers protection against predators
Define organisms that are…
Pelagic
Plankton
Phytoplankton
Zooplankton
Nekton
Pelagic = organisms that live in the water column
Plankton = floaters, go where the current takes them (passive)
Phytoplankton = planktonic plants (passive)
Zooplankton = planktonic animals (passive)
Nekton = active swimmers > vertebrates (fish) and invertebrates (squids)
Define organisms that are…
Benthic
Epifauna
Epiflora
Infauna
Sessile
Mobile
Benthic = organisms that live ON the seafloor
Epifauna = animals on the seafloor
Epiflora = plants on the seafloor
Infauna = animals that live IN the seafloor
Sessile = live in one place
Mobile (motile) = move around on seafloor
What are the 4 different animal feeding strategies?
Suspension feeders (filter feeders): remove microscopic plants, animals and dissolved nutrients from seawater
Herbivores: feed on plants
Carnivores: feed on animals
Sediment-deposit feeders: extract nutrients from sediments
What are trophic levels in the marine food web?
They are the tiers of food production and consumption
List the different trophic levels of the food web
- Primary producers (autotrophs): produce their own food from energy and the sun (plants)
- Primary consumers: mostly suspension-feeders
- Tertiary consumers …
- Apex predators (ex. orca)
Also
Transformers and Decomposers: breakdown dead organisms that have not been eaten
Explain the developments/characteristics of the Cambrian Marine Community & list the dominating organisms of the time
- global transgression (rising sea level) created new shallow sea habitats > lots of new space for organisms to move into > huge range of new body parts and types to adapt to surroundings
- dominated by trilobites, inarticulate brachiopods, and archaeocyathids
Describe the characteristics of the Trilobites
- they are about 50% of all Cambrian fauna
- benthic (on the seafloor), mobile, sediment-deposit feeders
- Appeared early cambrian, rapidly diversified > Max diversity in late Cambrian
What were some of the Trilobite adaptations during the Cambrian?
- sun shields on their eyes providing blinders from the sun
- trident - maybe a kind of horn for protection
- spikes - for protection
Describe the characteristics of Brachiopods (& 2 adaptations?)
- Benthic, sessile, suspension feeders
- still alive today
Adaptations of 2 different shells depending on environment:
- inarticulate: chitinophosphate shells (softer)
- articulate: calcium carbonate shells > tooth and socket arrangement of hinge
Describe the characteristics of Archaeocyathids
- sponges > major reef builders during the Cambrian
- benthic, sessile (live in one place on the seafloor), suspension feeders
- went extinct at the end of the Cambrian
Explain the discovery of Burgess Shale and how they were preserved
1909 > Charles D. Walcott discovered soft-bodied fossils in the Burgess Shale of British Columbia, Canada
The Burgess Shale was deposited at the base of a steep submarine escarpment
> mud banks became unstable
> organisms buried and preserved in the deep-water anaerobic environment
> carbonized impressions of soft-bodied organisms
> provides more information than just the shelly fossil record
What is the interesting characteristic associated with the Velvet worm (Hallucigenia)
They have some spikes that were originally thought to poke out the back but later found that they have feet at the end of them
(found in the Burgess Shale Biota)
What is the significance of the continued discovery of the Anomalocaris arthropod
- Weird mouth appendages
- First fossils found of Anomalocaris → originally thought to be separate organisms - thought to be some kind of shrimp
- But then they found the more fully completed fossil realized it was its own creature
*One of the first fossils that show evidence of predation - predator prey evolutionary battle helped it survive through the Cambrian explosion
