straight horned fusillade,
storm of black and white bullets
shot through ancient seas
racing head and foot into
Orthoceras are ancient mollusks. They first emerged nearly 500 million years ago and went extinct nearly 200 million years ago. (They existed from the Ordovician through the Triassic. They had a 200 million year overlap with their younger cephalopod cousins, the ammonites.)
Their name is descriptive, it means straight horn. They were soft bodied creatures that lived in the newest segment of the shell. Periodically they would grow a separating wall called a septa and close off the too small part of the shell. The different composition of septa and the external shell allowed them to fossilize differently, so we can still see their shapes today. (The curved lines running perpendicular to the outline of the fossil.)
The long channel you can see running along the center of the fossil-two parallel thin dark lines-was a hole that housed a strand of tissue called the siphuncle. It was (and is in nautiluses today) a way for them to filter water in and out of closed chambers, controlling buoyancy.
They probably worked in a similar fashion to those of creatures living today. It’s a pretty interesting method of control. It isn’t a muscular thing like you’d imagine. Instead it works by osmosis. Basically the change was controlled by blood salinity. Water would move from areas of lower salinity to higher in an attempt to achieve an equilibrium. Gases dissolved in the blood would slowly fill the chambers as the water moved elsewhere.
Despite the likelihood of this passive method of control, some propose that this might also have aided in propulsion.
Since all of orthoceras relatives were/are predators, it is fair to guess that they were as well.
Their fossils are often found in assemblages-like sheets of them mostly parallel-the only species present. It looks like an Edward Gorey inspired repeating wallpaper pattern! You see beautiful displays of them in museums or at fossil shows. (I’ve also seen really cool things made out of them, including the best bathroom sink ever!) Interestingly these groupings are found mostly amongst the older of the fossils.
Scientists aren’t sure why this is. Some believe it is evidence of post mating mass deaths, others that they simply traveled in schools. It’s been suggested that they are aligned so nicely because they shifted after death due to currents over the ocean floor.
I’m fascinated by the elegant simplicity of orthoceras fossils. They’re often black and gray and the smooth bullet like shape is a lot of fun to work with. It suits a lot of different styles. In my most recent turn with them I used three different colors of wire to try to mimic the tones and striped effect of the chambers in a simple woven frame.