[Texas Songwriter]

I suspect this is a thanatoscenose assemblage of Pleistocene megafauna. They probably died due to a large rain (flood) and their bodies washed down into a common chokepoint on the river, the bodies decayed and ended up on some riverbottom. With time the channel of the river changed and the bones became the property of an oxbow lake which finally filled in through eutrophication. They laid there until they were found.

[ForGod'sSake]

They probably died due to a large rain (flood) and their bodies washed down into a common chokepoint on the river, the bodies decayed and ended up on some riverbottom.

A possibility to be sure. Would 40 day and 40 nights do it? Could it be they succumbed to the same nastiness as THESE GUYS?