LAST SUPPERS: CALAMARI DAL MESOZOICO

Squid is an acquired taste – one that many people cheerfully never acquire (check out the Odori-do video clip at  <http://www.youtube.com/watch?v=dxQmOR_QLfQ>  for a good reason why).  But many marine organisms relish them. Most living squid species lack any internal hard parts, making them poor candidates for fossilization.  However, extinct, primitive squid (known as belemnoids), have substantial hard parts that can sometimes provide us a remarkable look into ancient ocean food chains.

As if raw squid wasn't bad enough, this Japanese dish Odori-don really brings a meal to life.  

If you were scuba diving in the seas of the Mesozoic and had the opportunity to see a living belemnoid you would instantly recognize it as a squid. They had a long, tubular, fleshy body, paired fins at the back end, large eyes, and ten arms surrounding the mouth.  Most grew to a length of about 1 foot, although some (Megateuthis gigantea) reached nearly 10 feet.

A well preserved belemnoid with fossilized soft tissues.

As with many living squid, belemnoids traveled and fed in groups.  These were carnivores and at least one remarkable belemnoid fossil is preserved with its fish prey still held captive in its arms. 

A well preserved belemnoid with its fishy prey still entangled in its arms.

Another 160,000,000 million-year-old belemnoid preserves an ink-sac, showing that, like their modern descendent, belemnoids used ink to confuse and escape predators.

A Jurassic belemnoid ink sac preserved in 3-D

The fleshy arms of belemnoids seem to not have suckers but instead bore rows of sharp, mineralized hooks.  The hooks can be easily fossilized, sometimes revealing the shape and arrangement of the arms, even though the flesh of the arms is not preserved. 

A beautiful fossil of Phragmoteuthis conocauda exhibiting rows of arm hooks.

Belemnoids had a heavily mineralized, bullet shaped internal "shell".  This hard part is durable and is the most common kind of belemnoid fossil.  They can occur in remarkable abundance.   

The fossilized internal shell of a belemnoid (above) and a drawing of how it fit (shown in white) in the living animal (below).

In the middle Jurassic marine beds in and around Dinosaur National Monument known as the Curtis Formation, those belemnoid fossils are common enough to earn their own tourist sign along the Drive Through The Ages on US 191 running north from Vernal, Utah.

While belemnoids were common carnivores, they were by no means at the top of the food chain, and their remains have been found in the fossilized stomachs of several groups of predatory Mesozoic marine reptiles. 

The porpoise/whale like ichthyosaurs (above) and the unearthly plesiosaurs (below) were two groups of Mesozoic marine reptiles that regularly fed on belemnoids.

Pollard (1966) described masses of belemnoid hooks preserved in the stomachs of ichthyosaurs. Boucot and Poinar (2010) reported similar occurrences in plesiosaur stomachs. 

  

The magnificent fossil of the shark Hybodus hauffianus.  The original is on exhibit at the Staatliches Museum fur Naturkunde, Stuttgart.

However, the most spectacular occurrence of belemnites as prey comes from a skeleton of male Jurassic shark Hybodus hauffianus from the 180,000,000 year-old Posidonia Shale, a rock formation deposited on the floor of a Jurassic sea.  We know it is male because of the presence of pelvic claspers which are used during copulation. It is one of those rare shark fossils that preserves not just the teeth, but the entire cartilaginous skeleton as well as the skin, thus giving a detailed outline of the shark’s shape.  

To top this off, it has preserved stomach contents consisting of a mass of over 200 closely packed belemnoid internal shells.  Sharks have strong stomach acids yet these ancient squid fossils are very well preserved, indicating that the shark died soon after dining on a shoal of belemnoids.

Detail of the Hybodus huffianus specimen, showing a stomach filled with the internal shells of belemnoids.

But this Hybodus fossil provides even more insight into ancient feeding behavior. The shark fossil has preserved internal shells but the numerous ichthyosaur and plesiosaur specimens with belemnoids in their stomach contain only the hooks from the arms.  A likely explanation for this pattern is that Hybodus ate the squid whole, while the marine reptiles ate the arms and head but not the body containing the thick internal shell. 

Finally, a fantastical exhibit in the Urwelt-Museum Hauff in Germany really brings this magnificent shark fossil to life.  Hanging from the ceiling is a life size flesh restoration of Hybodus swimming through and feeding on a shoal of belemnoids, with one partially sticking out of its mouth.   

Cleverly, this exhibit is near the entrance to the museum’s cafeteria, although it is unclear what calamari dishes are on the menu.

Thanks to Ben Creisler for directing me to a pdf of Schmidt’s 1921 paper on the Hybodus specimen.

SOURCES

Boucot, A.J. and Poinar, G.O. 2010. Fossil Behavior Compendium. CRC Press: 424 pages.

Glass, K., Ito, S., Wilby, P.R., Sota, T., Nakamura, A., Bowers, C.R., Vinther, J., Dutta, S., Summons, R., Briggs, D.E.G., Wakamatsu, K., and Simon, J.D.  2012. Direct chemical evidence for eumelanin pigment from the Jurassic Period.  Proceedings of the National Academy of Sciences 109(26): 10218-10233. Freely available at http://www.pnas.org/content/109/26/10218.full.pdf+html

Percival, L. 2009. Coeleoids from the Christian Malford Lagerstatte. Set in Stone: the Natural History Museum  Palaeontology Newsletter 6(4): 14-15 (Freely available at http://www.nhm.ac.uk/resources-rx/files/sis-64-69344.pdf

Pollard, J.E.  1968. The gastric contents of an ichthyosaur from the Lower Lias of Lyme Regis, Dorset.  Palaeontology 11(3): 376-388. Freely available at: http://palaeontology.palass-pubs.org/pdf/Vol%2011/Pages%20376-388.pdf

Schmidt, 1921. Hybodus hauffianus und die Belemnitenschlachtfelder. Jh.

Vaterl. Ver. Naturk. Wurttemberg. 77: 203-106. Ffreely available at: http://www.biodiversitylibrary.org/page/37081360#page/135/mode/1up

IMAGES

Dancing squid: http://www.youtube.com/watch?v=dxQmOR_QLfQ

Belemnoid fossil showing soft tissues and belemoid with fish: squid with fish

Percival, L. 2009 http://www.nhm.ac.uk/resources-rx/files/sis-64-69344.pdf

Belemnoid diorama: http://www.britannica.com/EBchecked/media/91400/Reconstruction-of-squidlike-belemnoid-cephalopods-from-the-Cretaceous-Period

Belemnoid fossil ink sac: Glass et al 2012 http://www.pnas.org/content/109/26/10218.full.pdf+html

Phragmoteuthis_conocauda:

licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license

http://en.wikipedia.org/wiki/File:Phragmoteuthis_conocauda.JPG

Belemnoid internal shell in hand: http://www.discoveringfossils.co.uk/charmouth_fossils.htm

Home of fossil squid:  http://library.byways.org/assets/74941

Ichthyosaurs: http://www.adinoszauruszokkiralya.eoldal.hu/fenykepek/dinok/ichthyosaurus.html

Plesiosaurs: http://www.dl-library.net.cn/uploads/111019/_122FBY.jpg

Hybodus huffianus, fossil and restoration: http://dinosaurpalaeo.wordpress.com/2012/12/24/paleontology-of-sw-germany-3-1-5-hauff-finally/