Schoolyard Safari
Bootleg recording of the only episode to have resurfaced thus far.
Schoolyard Safari is a series of 1 minute animated shorts that aired on Nickelodeon (and later Nicktoons TV) hosted by a kid who treated a regular school day as though it was a big safari.
Only one short has been uploaded to the internet to this day from an off air recording (see video to the right), but it's known that at least three were produced. A particularly memorable sequence from one lost short about the seating arrangements in a classroom came when a tough kid (sitting in the back of the classroom) shot a spitball at a nerd (sitting at the front of the class).
The reason that this particular short series hasn't been uploaded to the internet in full is likely because Nicktoons TV was not in the basic cable package at the time these shorts were aired. Therefore, it is unlikely anyone that wanted to could have recorded them. It is also likely that Nickelodeon has forgotten about the series (a similar hypothesis has been brought forward with another series of lost Nickelodeon shorts, Astrology with Squidward).