Lyonothamnus parvifolius (Ironwood), is a type of evergreen tree.
The really interesting thing about these specimens is that they are both a fossil and a trace fossil. Firstly they are fossilized ironwood. Secondly they are trace fossils. Trace fossils are evidence that an animal or plant left to show that it was there, but left no actual remains. Examples of trace fossils are footprints, leaf prints, or bite marks, etc.
In the case of these fossils the trace fossil is gnaw marks, most likely from a giant beaver (possibly Castoroides ohioensis). These giant beavers would have been over eight feet long, weighing up to 220 pounds. Their teeth would have been larger broader and longer than those of current day beavers (up to 6 inches long). If you have ever noticed the tree stumps around a beaver pond, they look very much like the pointed end of the specimen on the right. The original specimen was a single piece which was cut in half to make a set of bookends as you see them presented here.
Specimens are from a private collection and are not available for sale!
Lyonothamnus parvifolius - Ironwood 
Quantity in Basket: None
Code: OFC-600
Price: $0.00
Shipping Weight: 9.88 pounds
Time: Miocene, approximately 16 million years ago.
Location: Northwestern, Arizona, USA.
Dimensions: Both sections are: 6-1/2" x 3-1/2" x 3-1/4" each.