A cheeky animal
Gluteus minimus is an extinct animal from the upper devonian period. Most people have hear of the muscle in humans Gluteus maximus and are familiar with its location on a humans rear end. The lesser known muscle Gluteus minimus is a similarly located muscle. The authors Davies and Semken noted that the fossil resembles a human backside and rather cheekily (excuse the pun) used the muscle's name as the generic name and specific epithet.
Fossils of Gluteus minimus were first uncovered in 1902, but were not described until 1975. This was because no one can figure out what they are. Specialists of various kinds will not take responsibility for them, there has been speculation that they are various different body parts of various different animals, but nothing can be confirmed with any reasonable certainty. They have not been assigned to any Phylum, but due to their chemical composition we are fairly sure they are animals, and they look to me like we need not look outside the bilateria.
Gluteus minimus is extinct, whatever it was.
Phylum: incertae sedis
Class: incertae sedis
Order: incertae sedis
Family: incertae sedis
Species: Gluteus minimus