More frequent preservation of shark skeletal elements than teeth in the Astoria formation of Oregon and Washington?

[Necropedia]

Edit* Title changed to say shark skeletal elements ( previously said bones). 

 

This is an interesting topic  that was brought up by my mentor and vertebrate paleontology professor during a lecture about a year ago. He mentioned that for some reason there seems to be a higher occurrence of shark bones and relative scarcity of teeth in the Astoria formation. That is the verbage he used. 

 

I am willing to bet this is some kind of collection bias where people just aren't recognizing the teeth as often as skeletal elements for some reason. I haven't been able to find information on Google scholar or really anywhere else that has provided information on depositional environments that would favor the preservation of shark skeletal elements over teeth, especially where there are plentiful well preserved invertebrate shells. 

 

Most of the fossils are locked in concretions or embedded in concrete-hard sandstone. There is intermittent softer sandstone and siltstone, but seems like most of the vertebrate and invertebrate fossils occur in the harder layers. 

 

This is something that has interested me as a research topic, but I haven't been able to make it out in awhile to do any collecting of my own. 

 

It would be interesting to set up a transect say from Newport to Lincoln City, take a group out and just collect fossils  over a period of time across the transect to get an idea of fossil type, frequency, etc. And see if there really is something lending itself to a higher frequency of shark skeletal elements. 

 

On a side note  it does seem like there is an usually high occurrence of young vertebrates such as pinnipeds and whales in the sections of the formation I've collected. 

 

It would be interesting to hear your thoughts on the matter as well as any additional insights you may be able to provide. 

 

What do you think?

 

 

 

 

 

Edited March 20 by Necropedia
Conciseness

[DPS Ammonite]

Consider rephrasing the question and ask what conditions are favorable for preservation of cartilage since sharks do not have bones; they have cartilage. A guess would be that rapid burial, anoxic conditions and mineralizing microbes might help with preservation of cartilage. Look for papers describing the formation of phosphatic steinkerns, or internal molds, especially in young gastropods and the earliest formed part of coiled gastropods.

The composition of the fossilized cartilage might also give clues.

 

See:

https://www.thefossilforum.com/topic/63387-ordovician-micromorph-fauna-near-cincinnati/

 

https://www.nature.com/articles/s42003-021-02627-8

 

https://onlinelibrary.wiley.com/doi/full/10.1002/bies.201700167

 

Edited March 20 by DPS Ammonite

[Fossildude19]

@Boesse

[Necropedia]

5 hours ago, DPS Ammonite said:

Consider rephrasing the question and ask what conditions are favorable for preservation of cartilage since sharks do not have bones; they have cartilage. A guess would be that rapid burial, anoxic conditions and mineralizing microbes might help with preservation of cartilage. Look for papers describing the formation of phosphatic steinkerns, or internal molds, especially in young gastropods and the earliest formed part of coiled gastropods.

The composition of the fossilized cartilage might also give clues.

 

See:

https://www.thefossilforum.com/topic/63387-ordovician-micromorph-fauna-near-cincinnati/

 

https://www.nature.com/articles/s42003-021-02627-8

 

https://onlinelibrary.wiley.com/doi/full/10.1002/bies.201700167

 

I could rephrase this to say skeletal elements. I just said bones because that's the verbage my professor used. Some might consider it a stretch, but you could argue that sharks have bones since they are "bony fish" that reverted back to the ancestral cartilaginous state. For some reason mineralized bones aren't advantageous to being a shark it seems. 

[Necropedia]

6 hours ago, DPS Ammonite said:

Consider rephrasing the question and ask what conditions are favorable for preservation of cartilage since sharks do not have bones; they have cartilage. A guess would be that rapid burial, anoxic conditions and mineralizing microbes might help with preservation of cartilage. Look for papers describing the formation of phosphatic steinkerns, or internal molds, especially in young gastropods and the earliest formed part of coiled gastropods.

The composition of the fossilized cartilage might also give clues.

 

See:

https://www.thefossilforum.com/topic/63387-ordovician-micromorph-fauna-near-cincinnati/

 

https://www.nature.com/articles/s42003-021-02627-8

 

https://onlinelibrary.wiley.com/doi/full/10.1002/bies.201700167

 

When I was doing my initial search I looked up things similar to what you suggested (what environments would favor preservation of cartilage or poorly mineralized skeletal elements over teeth). 

 

I didn't find much, but what I did find suggested acidic environments where dissolution of biominerals dominates, but in these conditions things like bivalve and mollusc shells probably wouldn't be present or would be uncommon and/or feature some kind of dissolution features when found.  This isn't the case. It would be interesting if teeth really are a rarity here relative to skeletal elements. 

 

I tend to agree that rapid burial and anoxic conditions would be ideal for preservation of soft tissue like cartilage, but this would also favor the preservation of mineralized elements like teeth. 

 

Thank you for the papers. 

Edited March 20 by Necropedia

[Necropedia]

1 hour ago, Fossildude19 said:

@Boesse

Thank you. 

[Coco]

22 hours ago, Necropedia said:

...but you could argue that sharks have bones since they are "bony fish" that reverted back to the ancestral cartilaginous state.

No. Sharks, rays and chimeras are chondrichtyans, in other words cartilaginous fishes, unlike all other fish that are bony (ostechthyans).

 

Coco

[bockryan]

On 3/21/2024 at 11:25 AM, Coco said:

No. Sharks, rays and chimeras are chondrichtyans, in other words cartilaginous fishes, unlike all other fish that are bony (ostechthyans).

 

Coco

 

There is debate on this, with some favoring an initial bony ancestor for sharks, with all-cartilage skeletons being a derived trait, rather than an ancestral one. Here is an article that summarizes this a bit: https://phys.org/news/2015-05-fossil-ancestor-sharks-bony.html

 

[shark57]

I think you are debating a moot point. For instance, mammals are descended from reptiles, but they are no longer reptiles - they have evolved and are now mammals. Just because early sharks may have had bone doesn't change their current condition as cartilaginous fishes.

[siteseer]

When you say "bones" or "skeletal elements," are you referring to shark vertebrae?  It would be unusual to find a lot of shark vertebrae but not many teeth.  It's possible that other people are finding all the teeth and not recognizing the vertebrae as anything.

[FranzBernhard]

8 hours ago, siteseer said:

It's possible that other people are finding all the teeth and not recognizing the vertebrae as anything.

Very good point!

Before I saw your thought, I had the idea that this could be grave assemblages? Could this be?

[siteseer]

It would interesting to see what specimens are being called "shark bones."  The vertebral centra (plural of centrum) are the most commonly-found skeletal elements of sharks outside of teeth and dermal denticles.