Graptolites

Graptolites is an important index fossil for Paleozoic rocks and common throughout the world. As in Pakistan the sequences from the Ordovician to carboniferous age missing but these strata are exist in Noshehra and Chitral, so thats why its more valuable as regional fossil of sub-continent.

1. Graptolites ISHTIAQ AHMAD Department of Earth & Environmental S ciences Bahria university Islamabad

2. General Characteristics Graptolites belong to the phylum Hemichordata Graptolites are the marine-colonial animals which growing three dimensionally . Some of them were attached to the sea bed (benthic) and many of them were floated freely(pelagic) in the sea. Bilaterally symmetrical and tentacled .

3. Cont… Graptolie derived from Greek word that means writing on rock( Grapto =writing &litho= rock). They lived from Cambrian to Carboniferous times and flourished in sea environment. Size is 6 inches & some of them were up to 30 inches. Scientifically they known as Graptolithina .

4. Cont… The early Graptolietes are use as fossil guide for Paleozoic rocks. Due to its flattened 3-D structure very hard to identify as fossil. Preserved in the form black carbon film on surface of rocks and in tectonically disturbed sequence as light gray film.

5. Classes There are two main classes of Graptolites on the basis of their branches. Graptolithina Dendritic Graptolites Dendritic Graptolites: Dendritic mean many branched Graptolites of order Dendroidea . These were the benthonic marine animals i -e lives or attached to the sea floor and lived till the Carboniferous period .

6. Cont… Graptolithina : The few branched Graptolites that belong to the order Graptoloidea were good swimmer i -e pelagic. Graptolithina were survived up to the Devonian period.

7. M orphology Graptolites Consist of numbers of branches that is called stipes . stipes originated from s icula . Sicula : Individual organism of graptolites join to make the tube like structure . It is initial growth point of colony of the Graptolites Rhabdosome : A single colony of Graptolite

8. Cont… Theca: Each succeeding micro-organism is hosted in tree or tube like structure. Arrangement of theca and braches are very useful criteria to recognize the fossils of Graptolites. Nema : This is a thin tube at larva stage of Graptolite that originated from the apex of sicula .

9. Cont… Aperture: In graptolites the point/end at which the theca opened is called aperture. Vergulla : The spine at the siculum end. Dissepiment : The bar which connects adjacent stipes into the rhabdosomes of dendroid graptolites.

10. Occurrences in Pakistan Found all over the world in the rock of Ordovician to Carboniferous with their divers verity and shape. In Pakistan the sequences from the Ordovician to carboniferous age missing but these strata are exist in Noshehra and Chitral . In Chitral , Graptolites fossils are present in Broghil Formation, Lun shale of Chitral Shogram Formation