Before we conclude that here was some unheard of creature from some other dimension, let us try to imagine this carefully and see if it corresponds to anything familiar.
I think it was a Gray Kangaroo. The tail of the kangaroo would have been the third leg. It would have looked particularly like a leg if the kangaroo had been leaning back on it. But what would a kangaroo have been doing in Wabash Valley?
Strange as it may seem, there have been a number of reports of "phantom kangaroos" in the United States over the years. They have not been congregating in large numbers, but they have certainly been reported. An early specimen surfaced at New Richmond (Wisconsin) in 1899. In 1900 a "kangaroo man" was seen in the Sixes River area of Oregon. The description sounds like that of a fairly ordinary kangaroo. There have been many more.
It is fairly unthinkable that the United States boasts its own species of kangaroo. However, it is not absolutely impossible, as the Americas harbor other species of marsupial. But, owing to the fact that such sightings seem isolated, one wonders if a breeding pair was once let loose in the wilderness and they produced offspring.
Perhaps this is where they came from.
A kangaroo reported from Oklahoma in 2013 may have a simple explanation. A pet kangaroo had escaped about a year before.