... well it got me thinking ... comparing the squidcam versions. Has anyone a photo of a Nautilus egg that they could post online? Has anyone described/reported anything like this in the fossil record? Surely if cephalopod soft parts can (albeit rarely) fossilize, surely an egg with an outer, hardened egg capsule could fossilize also.
Anyone want to hazard a guess whether ammonites and nautiloids deposited few large eggs to the seabed, brooded their young, or did as most squid do, that is release eggs freely into the water column, singly or in large gelatinous structures, or attach them to the seabed, singly or in gelatinous strings.
Remains of cirrate (finned octopods) eggs litter the deep sea in places around New Zealand, depths > 2500m, as do squid beaks.
Phil obviously used the new Binford 9000 nuclear incubator, with the 32.3 gigawatt flux capacitor to incubate fossil ammonoid and nautiloid eggs. So he should have some left over to photograph.
From what I can gather, Nautilus eggs are very large, about 1" (25mm) and ammonoid eggs were small, about 1/32" (1mm). See a newly hatched nautilus here. Some rocks are full of ammonitellas, the initial chamber of the ammonoid shell, (you can see an ammonitella in the center of my avatar), these are possibly either egg masses or deposits of alot of newly hatched ammonoids.
I done a little poking around for you and it seems that unfortunately fossil nautiloid eggs are unknown. That said, estimates of the size of hatchling nautiloids have been made based on the size of the protoconch, the shell that develops inside the egg before hatching. As eggs are unknown I suppose it is impossible to guess whether these eggs were deposited individually or in strings; that’s simply something we will never know for certain unless an exceptionally unlikely fossil turns up. Given this, I very much doubt that any ammonoid eggs are known given that they are believed to be a magnitude smaller.
According to Prof. Theo Engeser’s Nautiloidea Homepage the Recent Nautilus has an embryonic conch of just over 3cm which makes it the largest of all the nautiloids with seven completed septa by the time it hatches. Fossil forms were probably smaller but still much larger than the ammonoids, which as Kevin has pointed out, were planktonic in size. It is believed that ancient nautiloids never hatched with under three septa completed in the embryonic form, and most hatched with more. Engeser also states that the average nautiloid diameter (or length) of the embryonic conch is about 2 cm or less. I suppose with fewer complete septa development time must have been less. It would be certainly nice to find out at what stage in development orthoconic nautiloids hatched and how large they would have been.
Diminishing size of hatchlings, and an increasingly faster growth rate (?) seems to something that the ammonoids developed . This might help explain why the ammonites varied and speciated so quickly, whereas the nautiloids and Nautilida seemed to be so consistant and resistant to alteration. One took the sluggish, slow, cold and stable path, whereas the other evolved for a fast short lived shallow water lifestyle, breeding fast and dying young and fell victim.