Minnesota PaleoWeb: Cephalopods
Minnesota PaleoWeb > Ordovician Gallery > Cephalopods
Fossil cephalopods are extinct ancestors of today's squid, octopus, and chambered nautilus.
A good web resource on living cephalopods is Dr. James Wood's
Cephalopod Page. The large channel running
the length of the animal is the siphuncle, through which a liquid was pumped to aid in buoyancy.
The mechanism of the modern Nautilus involves pumping blood through a strand of tissue
running the length, changing an osmotic gradient against the surrounding salt water,
and releasing gases into the emptying chamber. The animal can achieve
neutral buoyancy in relation to the surrounding water. The separate chambers
are septum. It may be that Ordovician cephalopods had no predators early on, except possibly
other cephalopods, and were among the largest invertebrates during the
Ordovician. With the arrival of large fish in the Devonian,
they must have faced new competition in their position at or near the
top of the food chain.
Following is a series of pictures involving my reconstruction of a highly fragmentary
cephalopod, probably an Endoceras. I did this strictly for personal reward -- certainly
not for profit. I realize this is somewhat eccentric today,
but people did this sort of thing before succumbing passively to radio, television and the internet.
A friend of mine and I discovered it in abandoned quarry in Goodhue County in October 1998.
It wasn't an accident -- we were looking for fossils in this region. The quarry sat at the
edge of a farm field, and was excavated to a level a few meters below the surface soil and
glacial till.
The fossil was found on the "shelf" near the center of the photograph below, the top of a
Platteville limestone formation. The hill sloping to the right is glacial till
and topsoil, currently being farmed. The picture to the right is the surface of this
exposure, cephalopod parts of several other individuals were present in the vicinity. This
served as the cephalopod's graveyard for approximately 450 million years:
What struck me as interesting was the number (and size diversity) of cephalopods present
at the site, all seemingly located in the same layer. It's not possible
to say with certainty whether they died simultaneously from an event,
or whether they died separated by months, decades, or centuries.
The specimen was highly fragmentary, requiring reconstruction. The fragmentary preservation
provided for an excellent cross-section view of various parts of the animal -- a sort of
fossilized dissection. It was a geometric and biological learning experience to
reassemble. In packing the fossil for transport, I divided the length into about four or five sections
and bagged each of them separately. This meant solving several small puzzles rather than a
single very difficult one.
The length of the restored section is nearly a meter. I estimate the overall length of
the living animal to be closer to two meters, since much was missing. This photograph shows
the specimen cleaned and glued with ordinary white wood glue, about two months later.
I deliberately left a few sections unglued, so that the fossil could be disassembled for
transport and examination. During this process, I fortunately had my wife's patience
(not many people in Little Canada, MN, regularly piece cephalopods
together across their apartment living room floor).
