Ordovician Flashcards
When was the Ordovician?
495 MYA - 440 MYA.
What is the Ordovician Radiation?
A major event of the Ordovician where the organisms from the Cambrian increase in types/species. More burrowing animals, so the sediment starts to stir up more.
Where is Laurentia in the Ordovician?
Along the Equator - it has started to tip. Other continents are moving towards Laurentia to collide and form the Appalachian Mountains.
What life appeared in the Ordovician?
Finer level groups - great radiation and diversification of graptolites and nautiloids. Burrowers expanded, and life in the sediment exploded. This pumped oxygen-bearing water into sediment. There was also the diversification of worms and other soft-burrowers.
What was Ordovician Life on the Seafloor like?
Diversity of benthic organisms increased - more jawless fish, grazing snails, rynchonelliform brachiopods, and crinoids. Reefs appear for the first time - Coral-strome Reefs. (Rugose corals, tabulate corals, Stromatoporoids).
What are Stromatoporoids?
Important reef building sponges that were around from the Ordovician to Oligocene. There were a group of early sponges that were important for reef building during the Silurian and Devonian, and were superficially similar to stromatolites.
What are Receptaculita?
“Sunflower Corals” from the Ordovician-Devonian, they are an extinct group with an uncertain relationship. They have been placed in the porifera and in the algae; they are moderately common in lower and middle Paleozoic carbonate rock. They might be another type of heavily calcified sponge or algae, or they are their own group. Always have radiating honeycomb or sunflower looking structures.
What are Rugose Corals?
From the Ordovician to the Permian, one of the two types of coral common in the Palaeozoic, both are extinct. They can be either solitary or colonial and have distinctive four fold symmetry of the septa. Septa is important in determining what they are from fossils. Can have tabulae that are hard to see.
What are Tabulate Corals?
From the Cambrian-Permian, more obvious in the Ordovician. The second common type of Palaeozoic corals; always colonial, usually lack septa. Have well developed, distinctive, tabulae.
What are Nautiloids?
From the Ordovician-Recent, they are a group of cephalopods with straight or coiled shells. Primitive (earlier) members have straight cells, while later members have coiled shells. They are mostly free-swimming predators.
What are Nautiloid Shells structured like?
The shells are divided into chambers that are separated by septa. As the animal grows, it lays down new shell and then pulls forward and lays down a new septa. The chambers are connected by a siphuncle that is used to pump gases and liquids into the chambers to control buoyancy (don’t twist when they rise or sink).
Explain late Ordovician Extinction.
Occurred in 2 phases; both phases seem to have been caused by global cooling, caused by glaciation in Gondwana. Tropical species were the hardest hit. 1st phase had a drop in sea level, while the 2nd phase had a rise in sea level due to ice melting.
