Graptolites

Question 1

Phylum and class

Answer 1

Hemichordata

Graptolithinia

Question 2

Describe the morphology of a graptolite

Answer 2

Colonial organisms, sclereoprotein skeleton, zooids lives in built thecae, first zooid lives in sicula, adjoining zooids make up stipe, entire skeleton is rhabdosome

Question 3

Mode of life?

Answer 3

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

Question 4

How are graptolites simmilar to pterobranches?

Answer 4

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

Question 5

Why do Graptoloidea make such good zone fossils.

Answer 5

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

Question 6

How did number of stiles change throughout evolution?

Answer 6

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

Question 7

How did attitude of the stipes change?

Answer 7

Always compared to sicula which has attitude pointing downwards, thecae may grow pendent, horizontal or scandent. Rough trend from pendent to scandent with time

Question 8

Define biserial

Answer 8

Thecae are added on two sides of the stipe

Question 9

Define horizontal

Answer 9

The aye are added outwards from the sicula

Question 10

Define pendent

Answer 10

Thecae are added downwards from the sicula

Question 11

Define reclined

Answer 11

Thecae grow upwards or horizontal

Question 12

Scandent

Answer 12

Thecae are growing vertically upwards from sicula

Question 13

Uniserial

Answer 13

Thecae are added on one side of the stipe

Question 14

What are the changes to shape if thecae with evolution?

Answer 14

Evolved from simple tubes to more elaborate shapes, may have benefit more efficient filter feeding

Question 15

How was the arrangement of thecae on the stipe changes with evolution?

Answer 15

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

Question 16

What are typical features of graptolite found in the Ordivician?

Answer 16

Uniserial, pendant, simple thecae, probably had two stipes

Question 17

What are typical features of graptolite found in the Silurian?

Answer 17

Uniserial or biserial, scandent, one stipe