Wavefront .obj format.
Yes, it is plain ASCII.
It's not perfect. For one thing, there doesn't seem to be any way of recording the scale (except as a comment in the file). 1 unit in Poser is around 8 feet (it's changed between versions for no apparent reason), while in other systems it might be a metre or a foot or a half-fathom.
There's usually three sub-sections to the file. First, the set of vertices. These can be referenced by the modified line-number. Then the UV coordinates of each point (Mapping the 3D point onto a 2D texture--limited use here). Finally the polygons, made up of edges defined by pairs of vertex numbers.
Poser uses 6 digits after the decimal place, which for a scale of 100 inches per unit means you can define a shape to 1/10000 of an inch. Is that excessive detail?
There are elements of the format, such as defining the material of a polygon, which have little obvious use. In the example of the dinosaur footprint one might want to distiguish the footprint from the surrounding surface. And the UV map data might be useful for rendering software, allowing 2D images to be mapped onto a 3D model.
It's maybe easier to translate to some future format than some file formats are. Does it record enough the right data for this use? I've noticed quite a few resolutely proprietary formats in the world of 3D models. They can be a pain in the butt.