Unidentified fossil (triangular section)

[Mick Zealand]

Hi again all,
this is another fossil from the same area in Egypt that I would greatly appreciate having ID'ed. It located about half a mile from the previous 'black-rock-bone' fossil I posted previously.
It feels heavier than bone, but I would call it a 'light' rock. I tried burning it with a plasma lighter and a corner became red-hot under the flame but it didn't emit any smoke or smell.

The colour is black, as in image nr.9 - in the other images the piece looks lighter in colour than it actually is due the wacky lighting I used to get the details out. I stuck all the images into one big image to keep it all managable.

The shape is unusual: Nearly completely flat on the 'underside' with a kind of spine with very round slopes on each side. First I thought it was piece of plastic, then I thought it looked like that squishy cartiligenous thing in a chicken. Now I don't know what to think. Maybe you have an idea?

Any feedback is very welcome.

Have a great day, Mick

[Paleoworld-101]

Age and geological formation will be important in identification. I am getting a slight turtle shell vibe but could be completely wrong. Where is it from in Egypt more specifically?