Sticklike or serrated colonial marine organisms
of the class Graptolithina (phylum Hemichordata) that lived
from the Cambrian to Pennsylvanian. Most are less than an
inch in length, but they range from 0.2 inch to 3.3 feet (5
mm–1 m) in length. They typically appear as faint sticklike
serrated carbon films on bedding surfaces. Since graptolites
are relatively common and abundant in Paleozoic shales and
show rapid morphological changes, they form useful index
fossils for biostratigraphic correlation. They are most common
in rocks deposited on the outer continental shelves, and
most probably lived in the planktonic near-surface environment,
with fewer deepwater varieties preserved.
Reconstruction of some of the best preserved graptolites
has revealed details of the structure of the colonies. Graptolites
apparently reproduced by asexual budding, with new individuals
producing new overlapping sawblade-like arms known as
thecae, with overlapping branches known as stipes. The stipes
formed the frontal parts of a feeding apparatus attached to a
zooid, which was probably part of a larger animal.
There are several different orders of graptolites, classified
on the basis of their mode of life. Bush-like forms that
were originally attached to the seafloor are known as Dendroidea
and were common from Cambrian through Pennsylvanian,
whereas Graptoloidean were planktonic forms,
abundant from the Ordovician through Early Devonian. Several
other orders were much less common, with most exhibiting
encrusting types of morphologies.
See also PALEONTOLOGY.
Tidak ada komentar:
Posting Komentar
Catatan: Hanya anggota dari blog ini yang dapat mengirim komentar.