Any ideas what this might be? Found in Capitola CA

[Ornithurae]

I found this on the beach in capitola ca right under the cliffs, any ideas what it could be? its approximately 7 inches and it is still covered in a pretty thin layer of stone but the shape is still mostly clear.

[Rockwood]

Sirenian rib.

[Fossildude19]

@Boesse

[Boesse]

@RockwoodIn ~15 years of collecting at Capitola, neither I nor anyone else has found a sirenian element - they only occur in a single bonebed at the base of this unit a few miles away. Now, if you look closely, the bone is quite porous, and it also only curves in one plane - indicating it's from a baleen whale, and not a rib. I think this is a partial baleen whale radius or possibly most of an ulna, but missing the proximal part with the olecranon process.

[Rockwood]

Then would red blood cell production be primarily in the, vertebrae ?

[Boesse]

@rockwood Good question - I have no idea regarding marrow distribution in different groups of mammals/vertebrates! I've often wondered the same.

[Rockwood]

Perhaps our perception of the scale of one cell has been distorted. There could be more than ample volume available without requiring what we would call marrow.

[ChristineR]

On 11/15/2021 at 6:44 AM, Rockwood said:

Then would red blood cell production be primarily in the, vertebrae ?

Forgive my ignorance. I need help following this conversation. What was said that prompted your question. Was it the porosity of the bone?

[Rockwood]

2 hours ago, ChristineR said:

Was it the porosity of the bone?

Yes. The long bones of most mammals, including the faster swimming cetaceans, I think, is much more porous. It often has almost a honeycomb look, and is referred to as marrow. 

[ChristineR]

11 minutes ago, Rockwood said:

Yes. The long bones of most mammals, including the faster swimming cetaceans, I think, is much more porous. It often has almost a honeycomb look, and is referred to as marrow. 

My apologies, I didn’t understand you were referring to sirenian blood cell production.  I was wondering why a whale’s prolific marrow would not produce blood cells? 

 

I found a study on extant sea cows informative. Thanks for your great patience. 

The West Indian manatee, Trichechus manatus, has amedullary, pachyostotic long bones. Since marrow cavities of the long bones typically are the locations of hemopoiesis in adult mammals, the manatee has evolved an alternative primary site of hemopoiesis. Histological examinations of spleens, livers, kidneys, and vertebral bodies indicate that the last-named location is the main site of erythropoiesis and granulopoiesis in T. manatus. This conclusion is based on the presence in the vertebrae of bone-marrow-containing diagnostic cell types including erythroblasts, megakaryocytes, and myelocytes, which are the precursor cells of erythrocytes, platelets, and granular leukocytes, respectively. No developing lymphocytes were found, so that the location of lymphopoiesis remains unknown.

 

Bazzini, M. D., Reynolds, J. E., 3rd, & Essman, R. A. (1986). Erythropoiesis and granulopoiesis in the West Indian manatee, Trichechus manatus (Mammalia: Sirenia). Acta anatomica, 126(3), 150–152. https://doi.org/10.1159/000146205