Miocene whale jaw or rib?

[HemiHunter]

I posted in a trip report a few weeks ago that one of my boys found two big fragments--including the joint--of whale jaw in a cliff fall from Calvert cliffs.  The assumption of jaw was based on what seemed like a good comparison to a jaw on fossilguy.com plus overall shape.  But a commenter suggests that the joint is maybe not flat enough to be from a mandible and that this could really be a rib.  So I'm looking for any second opinions.  We would really like to get a proper ID, especially as my son wants to fill in the missing segment and make a single piece out of the two pieces for display. Because of the way they came out of the fall, although they were with each other, we aren't 100% sure of what the orientation of the two pieces ought to be with respect to one another.  I have put the two pieces in a few different configurations just to show what each might look like. Having a proper ID would really help.  Any whale experts, please have a look and let me know what you think.

 

 

[HemiHunter]

[HemiHunter]

A few possible configurations

[Brett Breakin' Rocks]

17 minutes ago, HemiHunter said:

and that this could really be a rib

Hi There,

 

I would agree .. this looks like a rib. In my experience (and I'm not a whale expert) you are missing any visible foramen (the nutrient grooves/pores) that you should see on the surface of the mandible.

 

Here is a good example of a partial find in California. Note the pores and surface shapes that erupt from those locations.

 

Cheers,

Brett

 

PS. Here is a partial of my own .. again, no expert but I'm pretty sure this is what you would see in a jaw partial.

 

[Miocene_Mason]

Definite rib, very nice!

[MarcoSr]

Rib.

 

Marco Sr.

[Harry_]

100% rib. Nice find

[HemiHunter]

Thanks, guys!  I totally see that, now.  Good to have the right ID on it.  Can anybody say which end of the long piece would be closer to the backbone--the more oval end or the flatter end?

[Harry_]

1 minute ago, HemiHunter said:

Thanks, guys!  I totally see that, now.  Good to have the right ID on it.  Can anybody say which end of the long piece would be closer to the backbone--the more oval end or the flatter end?

I think it would be the oval end as the rib then tapers down towards the end of the rib and middle of the belly. But I am no expert on whale bones

[HemiHunter]

@Harry_, @MarcoSr, @WhodamanHD Any thoughts as to which end of the long rib fragment would be closer to the spine--the flatter end or the oval end?  I have looked at various Miocene and other whale rib examples and I think the flatter end would be up, but there are a lot configurations and few cross-sections to compare directly.  Plus I don't know exactly which position this rib is.

[Miocene_Mason]

Not my area of expertise, but my guess would be flatter end ventral and thicker end dorsal, but I’d leave it to those who know more than myself

[Mahnmut]

Ahoi!

 

to me the middle of your configurations looks most plausible.

I would also say that the distal/ventral/bottom ends tend to be more flattened.

Although rib shape is somewhat diverse in cetacea (see Caperea for example!)

In my little Orca-skeleton (3d printed from scan data) the distal ends are flatter.

It seems to be the same in Bowhead whales ( https://www.researchgate.net/figure/Images-of-cross-sectioned-ribs-of-bowhead-whales-CT-slices-of-second-rib-of-bowhead_fig2_304332021 ) so there are at least examples from toothed and baleen whales.

 

Aloha!

J

[Boesse]

This is a rib - mandible fragments will have a clear mandibular canal in cross section. This is such a common question I see here and elsewhere that I made a comic to help explain it:

 

[HemiHunter]

Thanks, @Boesse.  Yes it's clearly a rib.  Didn't realize others often had the same confusion.  I LOVE your comic!  Only here would you find that kind of thing.

 

Any thoughts on which end of the longer piece is "up" ?

[Boesse]

The flatter end of the rib is the distal end, and the end that is more 'square' or rectangular in cross section is the proximal part of the shaft. So, this is the configuration that is most accurate, though possibly still missing some bone:

 

[HemiHunter]

Thanks, again.  I really appreciate it!