Bitten edges definitely are mint errors, but they are comparatively common. Nevertheless, I have only found two or three in pocket change in my life. Easy enough to obtain from a coin dealer.
It's called an incomplete planchet, or more commonly, a clip. Yours looks to be genuine, even without evidence of the Blakesley effect -- an area of weakness 180 degrees from the clip formed during the upsetting process. I believe your error is genuine because of the weakness in the beads around the clip and the pinch off of the rims approaching it.
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