Mammal Bone from the surf of Asbury Park

[Bear_Pigs]

Hi all,

 

Back again with a new ID request. Found a mammal bone in the surf of Asbury Park, NJ (USA); this area overlies and regularly exposes fossils from the Kirkwood formation which is known to have been a near-shore marine environment laid down during the early Miocene. The surf also occasionally reveals Pleistocene mammal bones as well as those of modern animals (have found bone bits and crab parts at various stages of fossilization for reference which makes it difficult to decide what's Neogene and what's Quaternary).

 

My initial hunch was that this was a worn marine mammal rib and posted it to a local Facebook group with that in mind. It's very dense with minimal porosity (it was at the tide-line closest to the wave action where dense bone collects and was basically getting pulled back in by the coming high tide) which said dolphin or manatee bone to me. The responses I got were varied though. Some believed it to be a tooth due to an dark, enamel-like layer at the top of the 'top' of the specimen (it's 10cm or nearly 4 inches tall so that's a pretty big tooth). My assumption at that point was it might be Squalodon or some other odontocete from the Miocene. Another person believe it be specifically a incisor from the giant beaver Castoroides (based on the vertical striations) which would place it roughly Pleistocene in age.

 

The final opinion, and the one that is prompting me to message here, confirmed my initial hunch that this is a rib fragment from a Miocene delphinid. I know that marine mammal fossils are relatively common on this forum and there are several experts that lurk around here... anyone have a clue?

 

I've attached images of the specimen in question. It's ~10cm/~4in 'tall' and ~1.5cm/~0.6in 'wide' for reference. Sorry about the sand in the bone, it's basically impossible to get that out at this point.

Will also take more pictures if needed. 
 

Edited February 21, 2023 by Bear_Pigs

[Fossildude19]

@Boesse  @Harry Pristis  @Shellseeker

[Brandy Cole]

This looks like rib bone to me.  I'd say your first picture indicates very dense trabecular bone.

[Shellseeker]

I guess I just have to say... I do not know..... If , at the 40mm mark,  that is not a junction between enamel and dentine (like a cetacean tooth), I would like to hear an alternate explanation...

That 1st photo had me thinking Walrus... 

I have seen lots of dolphin ribs...and the outside does not look like this... so let me repeat.  I just do not know.

[Bear_Pigs]

Oh great, it seems I've posted another headscratcher 

 

I'll wait for a few more opinions on this (thanks for the tags @Fossildude19); but here's a few photos of identified material known from fauna represented in New Jersey's fossil record if that helps anyone (image credit goes to their respective owners):

 

Castoroides sp. (online fossil retailer.com)

 

Squalodon sp. (@BellamyBlake on the forum!)

 

Whale rib from the Kirkwood Formation of NJ (Fossil and Artifact Group from NJ)

 

Cetacean rib from the same location as my find (Fossil and Artifact Group from NJ)

 

Walrus Ivory (https://activeartist.net/)

 

[Boesse]

Dolphin rib. Not a tooth, as it has cancellous bone on the inside. Kirkwood is a reasonable guess as to the stratigraphic origin.

[Bear_Pigs]

Thank you all for your input @Boesse@Shellseeker@Brandy Cole. I'll label this in my collection under Odontoceti indet. with Kirkwood as the origin then. Really appreciate the insight everyone!