This is a Fossil of a Manatee Neck Vertebra. This specimen was found in Bone Valley, Florida and dates to an Ice Age. .  This piece measures approx. 105 x 61 mm: thickness is 29 mm: weight is 135 grams. 
 
Manatee’s fossils form the last Ice Age have been found in coastal waters of Texas, indicating that Manatees have existed for at least the last 50 million year or at least their ancestors were around 50 million years ago.