Heteromorphs

[Terri]

Wow, thanks for posting that article Hajar. Of course I had to skim over a lot of the technical stuff, but fascinating images. I now see how they came up with the reconstruction. Seeing the different life stages of the fossil, really cool!

 

[DWhatley]

Hajar,
Greg is looking for papers on cephalopod evolution (to write a paper) and I have cross posted these and some of the news bits I remembered but nothing overly helpful. If you know of good reference material he may find useful please add to his post:

http://www.tonmo.com/forums/showthread.php?27797

 

[Hajar]

Thanks D, Greg's off on the right track I think.

Allright, looking at the Dissimilites movie, how are the animals supposed to be driving themselves? They cruise regally forwards with hyponomes static and also pointing forwards. They seem to be pulling themselves through the water with their arms, which looks very odd to me (especially after watching Ramses and Neville).

 

[DWhatley]

Is the movie on-line somewhere or did you go to the exhibit?

 

[Hajar]

"Movie 1" here D: http://www.sciencedirect.com/science/article/pii/S0098300412001264?v=s5

 

[Terri]

They seem to be pulling themselves through the water with their arms, which looks very odd to me

It does look odd, awkward even...I can't imagine how they could pull themselves forward.

 

[DWhatley]

IMO the forward motion is someone's imagination. I don't see any way the arm movement shown could produce the movement they show. I don't know why they even suggest it since we have nautilus as an example.

 

[Architeuthoceras]

Looks to me like the ammonites are stationary and the camera is moving. The arm movement may just be feeding action. Remember, this movie was made by scientists, not the folks at PIXAR.

 

[DWhatley]

If it was a PIXAR production, they would be talking and then the movement would not appear to be backwards from the arm/tentacle action

 

[Hajar]

I think you're right Kevin. I wrote to ask what was intended.

 

[DWhatley]

I've rerun that movie 4 times and still see it as the camera following the front animal from left to right. I suppose it should not bother me except the paper states that they determined how they moved and the forward movement makes no sense.

 

[Hajar]

Forgot to post this. I had a very nice reply from Alex Lukenender a week and a bit ago:
"„Swimming direction“ is more a result of gradually changes in camera position, but animal could have been swimming forward and backwards, in my opinion. But that is a big question in the whole fossil cephalopod (ammonoids, belemnoids), are they passive drifters or active swimmers? I think there were both styles, and connective ones. The orientation was ascertained with experiments with replicas in tanks and from literature data concerning balance points and buoyancy."

 

[Hajar]

Since the old page of heteromorphs linked to above no longer exists, here's a new link: Heteromorph ammonoids by Hajar