Fossil Record
Undisputed fossils of tunicates are rare. The best known (and earliest) is Shankouclava shankouense from the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming (South China). There is also a common bioimmuration of a tunicate (Catellocaula vallata) found in Upper Ordovician bryozoan skeletons of the upper midwestern United States.
There are also two enigmatic species from the Ediacaran period - Ausia fenestrata from the Nama Group of Namibia and a second new Ausia-like genus from the Onega Peninsula, White Sea of northern Russia. Results of new study have shown possible affinity of these Ediacaran organisms to the ascidians. These two organisms lived in the shallow waters of a sea, slightly more than 555-548 million years ago and are likely the oldest evidence of the chordate lineage of metazoans.
A Precambrian fossil known as Yarnemia has been referred to the Urochordata, however this assignment is doubtful. Complete body fossils of tunicates are rare, but in some tunicate families, microscopic spicules are generated which may be preserved as microfossils. Such spicules have occasionally been described from Jurassic and later rocks. Few paleontologists are familiar with them; tunicate spicules may be mistaken for sponge spicules.
Read more about this topic: Tunicate
Famous quotes containing the words fossil and/or record:
“The earth is not a mere fragment of dead history, stratum upon stratum like the leaves of a book, to be studied by geologists and antiquaries chiefly, but living poetry like the leaves of a tree, which precede flowers and fruit,—not a fossil earth, but a living earth; compared with whose great central life all animal and vegetable life is merely parasitic.”
—Henry David Thoreau (1817–1862)
“The case of Andrews is really a very bad one, as appears by the record already before me. Yet before receiving this I had ordered his punishment commuted to imprisonment ... and had so telegraphed. I did this, not on any merit in the case, but because I am trying to evade the butchering business lately.”
—Abraham Lincoln (1809–1865)