Some Cephalopods: Inking About Squid Pens
by Trish Weaver
As an invertebrate paleontologist and someone who frequently sticks her foot in her mouth, it’s only natural that my research focuses on fossil cephalopods. Yes, cephalopods! Those head-footed critters such as squid, cuttlefish, octopuses, nautiloids, and etc…
Before I get started on squid pens, there are some important things to know about cephalopods. First, some cephalopods have external shells (nautiloids & ammonites), some have internal shells (cuttlefish & belemnites), some have vestigial shells (squid), some have no shells (most octopuses), all have their heads at their “feet” and all are mollusks.
Second, all cephalopods have arms, but only squid and cuttlefish have actual tentacles. Who knew? Walt Kelly had it right when he wrote “”He who is forewarned is forearmed, and he who is four armed is half an octopus, and who wants to be that?”
Lastly, just because squid have ink it doesn’t mean they write with their pens. The philosopher Descartes was not a squid and never actually said “I ink therefore I am”.
So squid pens… I’ve been thinking a lot about squid pens lately. Probably because I’ve spent that past month or so sitting in the Nature Research Center Paleontology Lab slowly removing the sediment from around a fossil squid pen. The pen I’m working on belongs to Tusoteuthis a big Cretaceous squid. In life this particular squid specimen was probably about nine feet long, though its pen is only about two and a half feet and at the moment it is in two pieces. My colleagues, Dan Lawver, Mike Everhart and I collected this pen during last summer’s big squid hunt in western Kansas.
So just what are squid pens? Squid pens, or gladii, are the vestigial internal shell of squid. They’re used primarily to support squids’ muscular tissues and organs. The flexible pen allows for jet propulsive swimming. Pens in extant squid are made of chitin. This allows the squid to live in deep water without the danger of crushing a mineralized pen.
As far as I know all fossil squid pens are mineralized.
Wondering why? Me too! That’s the question my colleagues and I are trying to answer with our research. If you’re interested please come watch the continued preparation of the fossil squid pen in the Paleontology Lab of The Nature Research Center and follow this blog as we head out for our next big squid hunt in early July.