Lecture 28 Flashcards
What were the pre-cambrian animals (580-545 Million years ago)? -Ediacaran fauna=580 mya
-pre-cambrian complex metazoans may have been cnidarians (they resemble jellyfish, corals and anemones) -there are many specimens that defy categorisatioj
How is geological time divided?
-divisions based on differences in rocks
Why is the Ediacaran fauna remarkable?
-preservation of soft-bodied animals in sandstone -earliest known complex animals -previously thought that such animals arose in cambrian explosion
When did the Cambrian explosion take place and what was it?
545-510 Mya -Most major animal phyla appeared within a relatively short time period -in cambrian time platyhelmines= don’t have fossils but probably evolved then too
Where does most our knowledge of the Cambrian explosion come from?
-one site in the Canadian Rocky Mountains= Mount Burgess -enormous number of fossilised animals found in the Burgess shale (510 Million years old) -fossil bed was once the base of a cliff where anoxic mud (and dead animals) collected -shows most modern phyla and also some that we can’t classify
Why did the Cambrian explosion occur? 4 reasons!
1.Body plans: appearance of the triploblastic body allowed more diversity 2. Genetics: the origin of Homeobox (Hox) genes(Hox genes= set of genes, control body plan, up and bottom etc.= then can get adaptations) 3. Environment: oxygen levels reached optimum (known to increase at the end of the pre-Cambrian -break up of land masses (more shallow seas) more movement 4. Ecological communities: greater interactions between organisms led to evolution of many forms including more advanced sensory structures
What were trilobites ancestors of?
-arthropods (they were early ones) -sub phylum: Trilobita -more than 17 000 species known -marine -exoskeleton, segmentation, one pair of antennae, biarmous appendages -diversity of forms -existed from early Cambrian (530Mya) to the end of Permian (250 Mya) but declined after the end of Devonian (360Mya) -sexual dimorphism emerging mechanism for protection= curling up
What is extinction what causes it etc?
–species (class/subphylum) can either go extinct or evolve -average life span for a species is surprisingly short- mammals= avg 1 million years no mammals currently older than 10 million -on average, the fossil record indicates that between 10 to 100 species go extinct each year -there is enormous variation in extinction rates
How many mass extinctions were there in history?
5 -sudden mass declines in biodiversity = extinction events or mass extinctions
When did the Permian-Triassic extinction occur?
-250 Mya -the largest extinction event in Earth’s history -about 90% of species were lost- 95% marine, 70% terrestrial -happened within 1 million, maybe as little as 10 000 years
Why did the Permian-Triassic extinction occur?
-more volcanic activity (geological evidence form Siberia) created nuclear winter followed by -global warmin- more than 5C rise from rise in CO2 levels led to= -more global warming caused by release of methane hydrate locked in the sea beds-led to another 5-10 C rise in temp
Who were some of the losers of the Permian-Triassic extinction event?
trilobites, blastoids=sea buds,eurypterids(seas scorpions)
What happened after the Permian-Triasic mass extinction?
-radiation -reptiles saw an enormous explosion in diversity in the Triassic -there had been large reptiles in the Permian which also fell in the mass extinction -terrestrial lizards= dinosaurs -predominant land vertebrates for 165 million yrs from triassic (230Mya) until the end of Cretaceous (65Mya) -over 1000 species known
Why were dinosaurs so successful?
-niche availability- from previous large reptiles dying out at the end of Permian -appearance of flowering plants enriched the terrestrial ecosystem (130Mya) -warm blooded? -upright posture?(would regulate temp better= less sun exposure) -or just luck?
When did the Cretaceous-Tertiary extinction occur and who were the losers?
-65Mya -end of the dinosaurs -70% of species lost(only 10% of fish died, even fewer amphibians, almost all mammal lineages survived -most of the ammonites (cephalopod molluscs= lived from 400-65mya, similar to nautilus but 1000s of species) -organisms that relied on photosynthesis (land plant lost 50%) phytoplankton and corals (98%) -herbivores(molluscs,echinoderms, dinosaurs) -top carnivores- dinosaurs, mossaurs, pterosaurs etc. =detritivores, insectivores and omnivores more likely to survive!
