Orthocone Pathology

[Architeuthoceras]

While enlarging this picture to put on my web site I noticed an anomaly in the very fine transverse lirae. Upon closer inspection I found that the shell had been damaged and repaired a few times. I don't think the mantle was ever harmed but the front edge of the shell obviously was. Could this be the result of environmental factors or the product of failed predation? Or both?

The following pics were taken through the lens of my microscope. The diameter of the shell near the injury is approx. 6mm.

 

[Jean]

Hi Kevin,

I dunno about ancient forms but modern molliscs can definitely repair their shells, often from quite dramatic damage.

Also I have a nautilus shell that has evidence of repaired damage. In modern molluscs the mantle can retract pretty darn fast so the shell can be damaged without harming anything else, I s'poseit culd be the same for these ancient forms?

J

 

[Phil]

Hi Kevin

I'm afraid I really don't have any idea what caused this.

One thought is that it may have been some form of parasitic infection causing blistering on the shell. According to Neale Monk's Ammonites blisters have been observed on the shell of the heteromorph ammonite Baculites (p.105). I would imagine clear deformation would be a result. Maybe this is similar, and you have a particularly sick orthocone with multiple infections?

Just guessing...

Phil

 

[Phil]

You may find this link of some interest:

http://taylorandfrancis.metapress.c...al,6,16;linkingpublicationresults,id:105669,1

Cheers,

Phil

 

[Architeuthoceras]

Thanks for that Phil

Growth line interruption in the form of repair of minor shell damage at the aperture, commonplace in contemporary Nautilus, is essentially absent in Baculites, suggesting that its members fed on small prey in the water column.

I don't understand why the size of prey would determine the amount of shell damage and repair, when this nautiloid is much smaller than mature baculites? Unless these small orthocones were savage beasts attacking animals many times their own size

Or is that referring to position in the water column?

 

[Phil]

Yes, I quite agree. That statement does not make any sense does it?

As an aside, I have read that the straight-shelled ammonite Baculites had no counterweight at the apex of its shell and, unlike orthocones, would have hung vertically in the water. If they could swim at all, and did not simply bounce along the bottom sediment looking for crustaceans to eat, then they could only have swum vertically. Orthocones probably had a horizontal posture, maybe the difference in lifestyle is what is being driven at. On the other hand, maybe these baculites undertook vertical migrations during the day and night like many modern squid?

Not sure....it's certainly a weird statement. Perhaps orthocones were just bullies!

 

[Architeuthoceras]

I suppose that a Baculite filter feeding in the water column would have less chance of shell damage than a small nautiloid down on the floor bouncing off corals, brachiopods and other things. Or maybe the prey items were just taking one last nip on their tormenter? Like that mouse pointing it's middle finger at that owl. :|