Cameroceras
As Cameroceras you would live inside a long, straight, cone-shaped shell, steering with tentacles through Ordovician seas as one of the biggest animals around.
A shell like a lance
Cameroceras was an endocerid, a type of nautiloid cephalopod – a distant relative of squid, octopus and the living nautilus. Your body occupied the front of a long, straight shell divided into chambers. A tube called the siphuncle ran through the chambers, and by adjusting gas and fluid inside them you could control your buoyancy.
In front, you had tentacles and probably a beak, like other cephalopods. The soft parts are not preserved, so details of your head are reconstructed from living relatives. To keep the long shell from tilting, endocerids deposited mineral weights inside the siphuncle near the tip. These counterweights helped hold the body horizontal in the water, like a balanced torpedo.
How big, really?
Popular accounts often claim Cameroceras reached 9–11 m. That figure is based on an old report of a very large endocerid shell that has not been confirmed. Most well-documented endocerid shells are much smaller; the largest reliably measured specimens are a few metres long. A cautious answer is that some endocerids probably reached several metres, which still made them among the largest animals of their time. Even at a few metres, though, you would have been a giant.
A day in the Ordovician
You lived about 470–440 million years ago, in warm, shallow seas covering parts of North America and Europe. You were probably a predator or scavenger of trilobites, eurypterids and other cephalopods, though some researchers suggest large endocerids moved slowly near the seafloor rather than chasing prey in open water.
Endocerids declined towards the end of the Ordovician, when a major glaciation triggered one of the five great mass extinctions.
