Swordfish Rostrum?

[uscedisto]

I found this yesterday in a Lowcountry SC creek where I have found fossils from the Oligocene, Miocene & Pleistocene epochs. At first glance I thought it was a bone fragment, but it is tapered widthwise and has striations along the top half.

[Auspex]

Huh...maybe the edge of a turtle shell?

[tmaier]

Seems too dense to be turtle shell.

Here a cross section of turtle shell I did. Sorry about the low resolution. It was fairly good resolution for a digital photo a few decades ago...

It would be more dense than the above if it was the edge of the shell, or an ornamentation of the shell, or an odd species with high density, but with turtle sheel I expect to see more cavities than this.

[uscedisto]

Doesn't look like turtle to me.

[Auspex]

The surface texture reminds me of bones/scutes that were thinly covered with vascular tissue in life.

[tmaier]

Notice the bizarre swirl patterns on the bottom of the specimen. And then at the top it is all straight grooves. That is saying something important, but I can't hear it.

As long as the swirls aren't tool marks from cleaning...

[uscedisto]

Not from cleaning, I used a soft-bristled toothbrush & Dawn detergent. Gently scrubbed parallel to the striations instead of a circular motion.

[Harry Pristis]

Looks mighty fishy to me, but don't know what fish-part it represents. Don't think it's a billfish rostrum. http://www.thefossilforum.com/index.php?/gallery/image/16947-billfish-rostrum/

[Boesse]

I agree with Harry - this is certainly fish (bony or cartilaginous). No turtle bone looks like this. That "flaky" pattern is characteristic of fish bone.

While it's not from a billfish bill (wrong cross-sectional shape), the possibility remains that it's another bone in the skull. I just flipped through a couple papers by Harry Fierstine but couldn't make a match. If not billfish, there are all sorts of other large bony fish that this could have belonged to - and unfortunately most other Oligocene bony fish are not osteologically well known.

The other possibility, perhaps more unlikely, is that this is some sort of ossified chondrichthyan element - I've seen that texture and histology, if I recall correctly, on large hybodont spines and large batoid tail spine fragments. Obviously it's not hybodont, but I'm just saying that a small possibility exists that it's chondrichthyan.