Cephalopod Awareness Days: Nifty Nautiloids
Greetings Blogophiles! It’s October 9th, day two of Cephalopod Awareness Days. Today is nautiloids and other lesser known cephalopods. Most of you are probably already aware of nautiloids, they show up as jewelry, as table decorations and for all you math enthusiasts, the shell of the chambered nautilus is frequently used as an example of Euclid’s golden ratio. It is good to be aware of nautiloids.
Nautiloids are a group of cephalopods belonging to the subclass Nautilidea. They have been around since the Late Cambrian, over 500 million years. The shape of their shells has varied greatly between the nautiloid orders and over geologic time. Some were slightly curved, known as cyrtocones, some had straight shells, known as orthocones. Some orthocone cephalopods even had shells that start off tightly coiled but then straighten out, making them look almost like a shepherd’s crook. Orthocone cephalopods went extinct it the Late Triassic.
The extant genus Nautilus, a tightly coiled form, is a distant relative of a nautiloid order which evolved sometime in the Early Devonian, about 400 million years ago. Nautilus is considered to be a living fossil. Please note: there was no clear transition from straight to curved shells as many of these forms co-existed with each other.
Here are some fast facts:
- Nautiloids flourished in the Paleozoic but only a few species are alive today.
- Extant Nautiloids live in deep water, usually 100-500 meters deep.
- Nautilus has ~90 arms or tentacles, which have ridged surfaces instead of sucker discs.
- Nautiluses can live over 20 years
- Extant nautiluses do not have ink sacs
- The paper nautilus is not a nautiloid. It is technically and taxonomically an octopus. Its “shell” is really a brood chamber.
- The beaks or jaws of nautiloids are preserved as fossils called rhyncholites (the upper jaw) and conchorhynchs (the lower jaw). I recently co-authored a paper on them: Weaver, P.G., Ciampaglio, C.N., Sadorf, E.M., 2012. Rhyncholites and conchorhynch (calcified nautiloid beaks) from the Eocene (Lutetian/Priabonian) Castle Hayne Formation, southeastern North Carolina. Neues Jahrbuch fur Geologie und Paläontologie. Abhandlung. 264 (1):61-75.
So please wave a many armed salute to our friends the nautiloids and tune in tomorrow for day three of Cephalopod Awareness Days.