Allocrioceras reconstruction

[Jared C]

Recently, while exploring the upper unit of the lower eagle ford formation (late cenomanian), I found a sandstone slab riddled with impressions of the charismatic Allocrioceras, potentially A. hazzardi or A. annulatum (I'm trending to the latter). 

 

Despite their usefulness as index fossils (A. hazzardi in west Texas indicates the lower Boquillas fm), sought after status, and amazing specimens like a Cenomanian A. annulatum found with gut contents, no life reconstructions exist of this genus online. So, I thought I'd give it an effort and reconstruct it myself. This is my first time attempting paleoart since elementary school so despite the many errors I notice now, I'm actually pretty pleased with it. 

 

 

 

 

 

 

 

I have several finds that no paleoart exists for that I'm keen to try reconstructions on now too. Next in queue is probably the enigmatic fish Hadrodus, and I'd love to do a cretaceous sea floor scene with Stereocidaris in it, particularly the Austin Chalk specimens I found - matching the background ammonite, fish, and reptile fauna. I'd also love to reconstruct the new mosasaur my brother and I found, but for the description paper an actual artist will be called in. 

Edited January 2 by Jared C

[Mikrogeophagus]

So cool! Now I'm gonna need you to do every Cretaceous shark...

[Tidgy's Dad]

Nice work.

But it seems to have eaten all the comatulids, the greedy ammonite.

[Jared C]

11 hours ago, Mikrogeophagus said:

So cool! Now I'm gonna need you to do every Cretaceous shark...

Especially the little guys. Most of the larger sharks have good art that exists, Cretoxyrhina and Leptostyrax especially, plus Ptychodus and Pseudomegachasma have gotten some beautiful illustrations recently made by good artists too. Cretolamna and Squalicorax not so much. Cretodus has two accurate depictions that one can find online, Scapanorhyncus a couple as well. Nothing for Carcharias and kin...hmmmm

[Bringing Fossils to Life]

Nice reconstruction! Which program did you use? Why are the aptychi on top of the head, instead of having a dual purpose within the mouth?

[Jared C]

5 hours ago, Bringing Fossils to Life said:

Nice reconstruction! Which program did you use? Why are the aptychi on top of the head, instead of having a dual purpose within the mouth?

Thanks! I used Procreate. That’s how I’ve seen them reconstructed in other ammonite illustrations. If that’s not where they belong then I’ve learned something new!

[Bringing Fossils to Life]

Numerous more recent studies have suggested that the aptychi acted as jaws, but could be used to close off the body chamber and thus protect the ammonoid's soft tissues from danger. This has also been the leading theory concerning Aptychopsis, a "genus" of calcified plates located in the cephalic region in Orthocerid "Nautiloids". Below is a reconstruction of a Devonian ammonoid (Agoniatites, an Agoniatitid) in cross section, showing the aptychi as jaws that can be used for protection when the head is pulled into the body chamber. The ammonoid thrusts its lower jaw outward, while collapsing its mouth and arm crown into the resulting cavity. This behavior has not been suggested for Devonian ammonoids, but is much more well documented in Cretaceous Ammonites (Ammonitida, hence the capitalization), where the aptychus is oriented in the way discussed above and pictured below. This interpretation fits with what we know about the jaws of other cephalopods and also makes sense from a morphological standpoint - why have sharp structures on top of the head, where they could be harmful?. Not all ammonoids used their aptychi as opercula, as some had other jaw structures that were more designed for a specialized diet, while sacrificing the defense mechanism. Ammonoids, however, did have fleshy pads on top of their heads, sometimes referred to as protohoods, which helped anchor the ammonoid's head to the dorsum of its body chamber to support the internal organs so that they would "hang" instead of collapsing on themselves from their own weight. These were likely not used in defense, but are visible in many recent reconstructions (although unfortunately many still put the aptychi on top of the head as opercula).

I'm sorry to criticize your work; it's really good for just starting out with paleoart. Keep at it!

From my website, http://bringingfossilstolife.infinityfreeapp.com/2023/04/09/cephalopods/

[Jared C]

On 1/4/2024 at 5:36 PM, Bringing Fossils to Life said:

Numerous more recent studies have suggested that the aptychi acted as jaws, but could be used to close off the body chamber and thus protect the ammonoid's soft tissues from danger. This has also been the leading theory concerning Aptychopsis, a "genus" of calcified plates located in the cephalic region in Orthocerid "Nautiloids". Below is a reconstruction of a Devonian ammonoid (Agoniatites, an Agoniatitid) in cross section, showing the aptychi as jaws that can be used for protection when the head is pulled into the body chamber. The ammonoid thrusts its lower jaw outward, while collapsing its mouth and arm crown into the resulting cavity. This behavior has not been suggested for Devonian ammonoids, but is much more well documented in Cretaceous Ammonites (Ammonitida, hence the capitalization), where the aptychus is oriented in the way discussed above and pictured below. This interpretation fits with what we know about the jaws of other cephalopods and also makes sense from a morphological standpoint - why have sharp structures on top of the head, where they could be harmful?. Not all ammonoids used their aptychi as opercula, as some had other jaw structures that were more designed for a specialized diet, while sacrificing the defense mechanism. Ammonoids, however, did have fleshy pads on top of their heads, sometimes referred to as protohoods, which helped anchor the ammonoid's head to the dorsum of its body chamber to support the internal organs so that they would "hang" instead of collapsing on themselves from their own weight. These were likely not used in defense, but are visible in many recent reconstructions (although unfortunately many still put the aptychi on top of the head as opercula).

I'm sorry to criticize your work; it's really good for just starting out with paleoart. Keep at it!

From my website, http://bringingfossilstolife.infinityfreeapp.com/2023/04/09/cephalopods/

I learned a lot here! Please, don't be afraid to give constructive criticism like this, this is great. The construction of invertebrates is fascinating and sometimes too alien to comprehend for vertebrate oriented simpletons like myself . I'll definitively consider this for in future reconstructions