I think it is. I've seen this happen with rats before. I used to work for the schools in NC during the summer moving furniture (back when the county I was living in was still using the old 1940's school buildings). If you went into the schools' attic areas or basement areas, you could find rats that had fallen into the AC air shafts and died that looked about like this. It mainly just depends on the environmental conditions at the time. If there is something (freezing temps, constant wind, etc...) that dries them out before they rot, you have a natural mummy.
I personally wouldn't purchase it though. It wouldn't be treated and preserved (like taxidermy) and could still draw in bugs or cause other health issues.
When I got my house 27 years ago I found a large, dead, mummified cat in the crawlspace, he died with his head reared back, mouth open, scary! He is still in that crawlspace, somewhere?
The old furnaces that had a round tin jacket and a conical top full of sand (For fire protection and keeping heat in) would see numerous dead rodents in that sand with a cat sometimes, a nice heated litter box!
I was once given a cow skull for a house decoration. After I had it awhile and the Summer arrived .. I began smelling this mildly terrible odor . Not ALL of it's brain cells were removed! The skull came from some mountain area in California, I believe , high and dry there .
Outdoors when victims walk through the tomb, they begin walking on steel grating and under the grating are real cow/horse bones, they don't stink, they were brought to town from some digging at a farm when this City needed some black dirt. These bones I believe, are Very Old and they were buried. They must not be too "Yummy" since the skunk and raccoons left them alone.
and which of the house human skeletons are real? Just two of them, mine and my Wife's! we are still using them, we depend upon them for "support"!