Life reconstruction of the Ammonoid Koenenites

[Bringing Fossils to Life]

Here's the reconstruction of Koenenites I promised. Koenenites was a Devonian ammonoid with a very compressed shell and sharp keel. It was designed for fast swimming and thanks to the shape of its suture, it could accelerate very quickly compared to the ammonoids around it without its cameral fluid sloshing around and shifting its center of gravity. Because of its evolute shell, it likely had a large hyponome, which goes with the shape of its shell. After looking at some pictures of Koenenites fossils from Michigan that may have preserved the Supercephalic Attachment Area, I arrived at the proto-hood size in the picture. The eye size was inspired by the "ammonite preserved out of its shell", which preserved what is likely the ammonite's eye-cups, though eye size varies greatly. I based the hooks off of those of the much later ammonites, so Koenenites may have had ones different form those shown here. These preserved hooks were in positions similar to those on today's squid's tentacles, so ammonoids likely had elongated tentacles. The 8 thin, retractable arms were inspired by fossils of Baculites ammonites, though Koenenites was an active pursuit predator and Baculites a planktivore. Koenenites could afford smaller arms, though, because it likely had two muscular tentacles. I reconstructed this ammonoid's shell with a monochromatic color pattern, because nektobenthic ammonites have been found with this. Shell orientation based on preserved Supercephalic Attachment Areas.

The second picture shows how Koenenites' (3A, 3B) suture shape helped it accelerate faster without its cameral fluid sloshing than other ammonoids like Agoniatites (1A, 1B) and Tornoceras (2A, 2B). bottom shows what would happen when the ammonoids started cruising at a slow to moderate pace, top shows what would happen when they tried to accelerate quickly. The lobe of the next suture would break the wave of cameral fluid so that its entire weight would not all hit the venter, but only a little bit. This shows that while Koenenites and Tornoceras were comfortable accelerating quickly, Agoniatites was more stable at cruising at an even speed.  

Any suggestions would be helpful! If there are any papers about ammonoid (or more specifically ammonite) soft tissue, that would be helpful too.     

Edited January 21, 2022 by Bringing Fossils to Life

[ftlcgi]

Cool reconstruction, i am planing to make an ammonite to and the details you shared here will be help me, i saw some good nautiloids drawings on your website, like the shell pattern, that helped me with my project

Edited January 21, 2022 by ftlcgi

[Al Dente]

14 hours ago, Bringing Fossils to Life said:

The second picture shows how Koenenites' (3A, 3B) suture shape helped it accelerate faster without its cameral fluid sloshing than other ammonoids like Agoniatites (1A, 1B) and Tornoceras (2A, 2B). bottom shows what would happen when the ammonoids started cruising at a slow to moderate pace, top shows what would happen when they tried to accelerate quickly. The lobe of the next suture would break the wave of cameral fluid so that its entire weight would not all hit the venter, but only a little bit. This shows that while Koenenites and Tornoceras were comfortable accelerating quickly, Agoniatites was more stable at cruising at an even speed.

 

Nice illustrations. Is there a paper you read about cameral fluid affecting ammonoid acceleration? If ammonoids were anything like modern nautilus, then there wouldn't be much fluid in the chambers except the one directly behind the living chamber. At least that is what I have read.

[Bringing Fossils to Life]

Yes, there is a paper! I don't have access to the full paper, but I read the abstract and that was almost enough ( I still want to read the entire paper). It is also good to remember that modern nautiluses have very short body chambers, while ammonoids had much longer ones (the highest septa on each picture is the first). The paper was dealing with much more advanced ammonoids, but it can still be applied to the earlier ammonoids.

https://www.sciencedirect.com/science/article/abs/pii/S0195667117300319

Glad my reconstructions were helpful! I can't wait to see 3D models of nautiloids and ammonites!