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Geology F795 > Graptolites > Flashcards

Flashcards in Graptolites Deck (17):
1

Phylum and class

Hemichordata
Graptolithinia

2

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

3

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

4

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

5

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

6

How did number of stiles change throughout evolution?

In general, multiple stipes in Ordovician, to one in Silurian

7

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

8

Define biserial

Thecae are added on two sides of the stipe

9

Define horizontal

The aye are added outwards from the sicula

10

Define pendent

Thecae are added downwards from the sicula

11

Define reclined

Thecae grow upwards or horizontal

12

Scandent

Thecae are growing vertically upwards from sicula

13

Uniserial

Thecae are added on one side of the stipe

14

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

15

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

16

What are typical features of graptolite found in the Ordivician?

Uniserial, pendant, simple thecae, probably had two stipes

17

What are typical features of graptolite found in the Silurian?

Uniserial or biserial, scandent, one stipe