Flashcards in Graptolites Deck (17):
Phylum and class
Describe the morphology of a graptolite
Colonial organisms, sclereoprotein skeleton, zooids lives in built thecae, first zooid lives in sicula, adjoining zooids make up stipe, entire skeleton is rhabdosome
Mode of life?
Lived within water column, pelagic, sicula aperture faced downwards, colony presumed to have floated, may have been attached to floating object by nema. Filter feeders, most planktonic
How are graptolites simmilar to pterobranches?
Simmilar structure of rhabdosome, filter feeders, attach to sea floor, live in colonies of zooids, however made from collagen, filter water with cilia and tentacles may be related to Echinoderms
Why do Graptoloidea make such good zone fossils.
Ordivician to end Silurian, rapid evolution, abundant and widespread as planktonic, protein based so preserved below CDC. However delicate and liable to scavenging so not preserved as well in shallow water, mostly in anoxic muddy conditions
How did number of stiles change throughout evolution?
In general, multiple stipes in Ordovician, to one in Silurian
How did attitude of the stipes change?
Always compared to sicula which has attitude pointing downwards, thecae may grow pendent, horizontal or scandent. Rough trend from pendent to scandent with time
Thecae are added on two sides of the stipe
The aye are added outwards from the sicula
Thecae are added downwards from the sicula
Thecae grow upwards or horizontal
Thecae are growing vertically upwards from sicula
Thecae are added on one side of the stipe
What are the changes to shape if thecae with evolution?
Evolved from simple tubes to more elaborate shapes, may have benefit more efficient filter feeding
How was the arrangement of thecae on the stipe changes with evolution?
Uniserial if on one side, biserial if on both, some have intermediate stage, general is that early forms were Uniserial, then biserial, but back to mostly Uniserial in Silurian
What are typical features of graptolite found in the Ordivician?
Uniserial, pendant, simple thecae, probably had two stipes