This photo was sent to us from Linda Morse at the College of William and Mary. The specimen was found by William and Mary student Jason Lunze on the James River, in either the Cobham Bay Member of the Eastover Formation or the Sunken Meadow Member of the Yorktown Formation.
This is the left humerus (upper arm bone) from the flipper of a large whale. It is almost certainly from a member of the family Balaenopteridae, the group that includes the living blue and humpback whales.
The large knob on the left is the ball part of the ball-and-socket shoulder joint, and attached to the shoulder blade (the scapula). The two flat surfaces at the other end are the elbow joint, where the humerus attached to the forearm bones, the radius and the ulna. Whales can move their flippers quite a bit at the shoulder, but have almost no ability to bend at the elbow.
The photo below, of the flipper of VMNH’s skeleton of the baleen whale Eobalaenoptera harrisoni, shows how the humerus fits in with the rest of the flipper bones.