A few weeks ago Ferrebeekeeper featured a post about belemnites, extinct cephalopods from the Mesozoic which teemed in immense schools through the reptile-haunted oceans of that bygone era. Yet belemnites were certainly not the only cephalopods which swam in the Mesozoic seas. Numerous shelled cephalopods—the ammonites—were widespread in every sort of marine habitat. Ammonites are personal favorites of mine so I am not going to write a comprehensive explanation/description of the subclass. Instead I wish to provide you with an idea of how big ammonites could get by providing a few pictures of large ammonite fossils which have been discovered. Imagine these monsters jetting through the water with huge tentacles and big intelligent eyes scanning for giant predatory reptiles and you will have a better idea of the Mesozoic Oceans!
This one is only .7 meters (two feet) in Diameter but it sure is pretty.
ferrebeekeeper 
18 comments
Comments feed for this article
March 29, 2012 at 8:52 PM
Val
This is my first comment here, so I must begin by telling you how much I enjoy your blog. I’ve been following it since your post on the flamboyant cuttlefish (a favourite creature of mine).
Re ammonites, you may be interested in Simon Winchester’s book The Map That Changed the World. Or perhaps you’re already familiar with it. If not, it recounts how William “Strata” Smith developed the first geological map of Britain, using fossils such as the ammonite to identify geologic ages in the rock strata. The locals knew them as”Chedworth buns” or “pound stones” and used them as weights as they were very plentiful in Oxfordshire of the late 1700s and early 1800s.
I certainly had no idea that they ever got as big as the examples above. Wouldn’t it have been a treat to be able to gaze upon the Mezozoic sea — from the safety of a well-armoured submersible of course!
April 1, 2012 at 8:43 PM
Wayne
Thanks so much for the kind comment! I really like flamboyant cuttlefish as well. It’s a shame they are not more famous.
I know that ammonites are major index fossils and that substantial effort has gone into understanding when certain species lived and where (so that geologists could better get a handle on the age of various rock layers) but I don’t know the specific story. I appreciate the book suggestion and the folk history that ammonites were used as weights!
I sometimes also dream of the Mesozoic ocean but maybe it is best that I can’t go to those violent depths!
March 30, 2012 at 1:53 AM
dianaarterian
Holy crap!
May 3, 2012 at 8:09 PM
A'GAPE
OMG. BIGGEST FOSSILS I’VE EVER SEEN.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
October 10, 2012 at 7:55 AM
Amy Bullard
I work at a lime stone guarry in Maple Hill NC and come a cross a lot of the smaller mullusk and then found a large ammonite in a sump hole we dug , it is about 12 to 14 inches in diameter.In no way as large as the ones on here but never the less exciting for us here.
October 10, 2012 at 9:52 AM
Wayne
That’s an exciting find (the best I ever discovered was a fern leaf from the Carboniferous): you must see all sorts of amazing fossils!
October 12, 2012 at 12:50 PM
Amy Bullard
I would love to find some plant fossils all shell here and the shark teeth i have found 4 large Rickulitus teeth best one is about 3 in but our fossil hunts have found a whale that had legs think about 40 mil yr old from what they say If only they would let me wander around looking instead of driving a truck! Lol
October 14, 2012 at 12:01 AM
Wayne
At least you have a quarry! I’m stuck looking for fossils from a cubicle.
October 18, 2012 at 10:58 PM
Amy Bullard
Sorry does make it kind of hard to find them from there!:(
December 22, 2012 at 7:09 AM
steven
Since I have a snail phobia… this just made my head turn hehe. I did dug out some smaller ones in France. But they were like 2-3 inch in diameter.
Cool photo’s tho!
December 25, 2012 at 9:03 PM
Wayne
Yeah, snails are surprisingly alien, but there is no need to be afraid–unless you are dealing with cone snails.
October 21, 2013 at 7:32 PM
Martha Sherwood
I’ve been looking at pictures of knights fighting giant snails in the margins of Medieval manuscripts (they are surprisingly common) and wonder if large ammonite fossils suggested the idea.
October 22, 2013 at 12:34 AM
Wayne
I don’t know. Do you think they might be allegories of the battle against sloth (which monks, knights, and I all must fight again and again)? Or perhaps the images are caricatures of grasping noblemen. Do you have some examples–they sound amazing. Maybe I can do a post about mollusk marginalia!
February 6, 2014 at 2:09 PM
Malka Ostchega
Sorry, I was wondering where these pictures were taken?
February 13, 2014 at 9:49 PM
Wayne
I wish I knew…I found them around the internet and had trouble attributing them properly.
March 3, 2014 at 10:27 PM
Steve D
Stroll the streets of Verona, Italy and in the limestone paving blocks there are lots of cephalopods up to two feet in diameter. Not as big as these, but a very classy place to find fossils.
March 4, 2014 at 1:04 AM
Wayne
I would LOVE to do that! I’ll put it on my long list of fantasy destinations. [sadly shaking a mostly empty piggybank and dreaming of Verona]
December 1, 2014 at 7:37 PM
Stuart Beard
Hi there, I’m sorry to say that the big ammos you have pictured are fake, the first one is made of fiber glass and was made as an in-joke at Lyme Regis, Titanites Gigantia are often found up to 30inchs across but rarely more and never in the dimensions shown in the picture, Likewise the girl stood between the dino fossil and ammo if you look closely you can see the dino is a model! The biggest ammo ever found is in the Museum of New Zealand the Lytoceras taharoaense, is 1.42 metres in diameter and weighs 1,200 kilograms. It was discovered in February 1977 by Jean Gyles of Wellington at Taharoa, 10 kilometres south of Kāwhia Harbour on the Waikato Coast, in a small roadside slip. Excavation took several attempts, with the final chunk recovered in April 1978. It is late Jurassic in age (around 140 million years ago). I curate a small museum and have a fairly large collection of ammos the biggest is a Paracoroniceras Charlsi and is a whopping 24inchs across and takes two strong men to move!