SILURIAN MARINE ALGAE
Well-preserved fossils of fleshy algae occur
occasionally in Silurian dolostones of America. Several examples are
shown below.
Medusaegraptus mirabilis Ruedemann, 1925 (left: 4.9 cm tall; right:
8.7 cm tall) preserved as carbonized compressions in argillaceous dolostones of
the Upper Silurian Goat Island Formation from western New York State,
USA. Rudolf Ruedemann originally identified these fossils as dendroid
graptolites. Modern workers have assigned this material to the dasyclad
green algae (Plantae, Chlorophyta, Ulvophyceae, Dasycladales, Seletonellaceae,
Dasyporelleae, Medusaeporinae).
Locality:
Lafarge Gasport Quarry, Gasport, eastern Niagara County, western New York
State, USA.
Stratigraphy: Medusaegraptus Epibole (part of the “Gasport Channel” or
“Gasport Lens”), mid-Niagara Falls Member, lower Goat Island Formation,
Lockport Group, ~lower Ludlovian Series, lower Upper Silurian.
Manitobia sp. (left) preserved as a carbonized compression in Silurian
argillaceous dolostone from Ontario, Canada (FMNH PP46685, Field Museum of
Natural History, Chicago, Illinois, USA).
Manitobia newlinii (White, 1902) (right) preserved as a carbonized
compression in dolostone from the Kokomo Member of the Wabash Formation (Upper
Silurian) from Kokomo, north-central Indiana, USA (UC 875, University of Chicago,
Chicago, Illinois, USA).
Both of these algae have been previously assigned to Buthotrephis,
a nominal genus that is a junior synonym of the branching trace fossil Chondrites.
These algae have been reassigned to Manitobia, a possible fossil red
alga (see Fry, 1983, An algal flora from the Upper Ordovician of the Lake
Winnipeg region, Manitoba, Canada. Review of Palaeobotany and
Palynology 39: 313-341).
cf. Rhizomorphia from the Silurian of Herkimer
County, east-central New York State, USA (FMNH PP 46694, Field Museum of
Natural History, Chicago, Illinois, USA).