"Embedded" bone from San Diego formation

[Quiescence]

Found this recently when grubbing around my San Diego Formation (Pliocene) riverbed that is full of marine fossils. 

 

Most bones I have found are from baleen whales, or 'other' marine mammals. 

 

This bone fossil seems somewhat different than other whale (or other cetacean?) bones I have found. It is smaller.. which doesn't mean much, but the ratio of inner to outer cortex maybe also seems different. I do not know exactly what distinguishing qualities are that would allow one to differentiate from something like a bird, or dolphin. I previously found a manatee rib, but was only sure of this because a curator at the Nat helped ID that. 

 

Two images are of the embedded bone, the next two are of a presumably baleen whale bone that was also found that day. 

 

[Fossildude19]

@Boesse

[Rockwood]

The contrast between cancellous and cortical bone does tend to be more pronounced in terrestrial animals. I think there is a good chance this bone is an example. Birds, on the other hand, do not have cancellous bone. So, they can be eliminated.

[Quiescence]

13 hours ago, Rockwood said:

The contrast between cancellous and cortical bone does tend to be more pronounced in terrestrial animals. I think there is a good chance this bone is an example. Birds, on the other hand, do not have cancellous bone. So, they can be eliminated.

 

Thanks Rockwood. Based on the assemblage of terrestrial mammals listed in Wagner et al. attached below, I speculate that it could be a horse (Plessipus simplicidens), or cat/lynx (Felis rexroadensis) fossil. But I am well aware of the reach I am making here!!! Fun to entertain ideas though. Just based on the size of the fossil, I can rule out most of the rodents/lagomorphs they describe here. And that is if it is a non-marine species. I am not sure if Pinnipeds have comparable bone structure. 

 

The locations described in this publication are very close to where I found this, so I feel comfortable entertaining some of these ideas. They also describe horse footprints in mudstone - which correlates to an extent with the occurrence of this fossil embedded in mudstone (is this mudstone? eek). But I know this probably also a big reach! 

Wagner_2001.pdf

[Rockwood]

Sory. Your reach exceeds my grasp. 

[Quiescence]

That's fair. The train departed from speculation station some time ago 

[Boesse]

The most common mammals from the San Diego Fm are marine mammals, and cetaceans in particular - the land mammal fauna from Wagner et al. 2001 is just one small unusual locality in the San Diego Fm. I'd wager these are whale bones, and the histology supports this.