The 78-million-year-old, 15.4-foot-long (4.7-meter-long) adult specimen is a Polycotylus latippinus, one of the giant, carnivorous, four-flippered reptiles that lived during the Mesozoic Era.
Dr. Robin O'Keefe of Marshall University in West Virginia and Dr. Luis Chiappe, Dinosaur Institute director of the Natural History Museum in Los Angeles County, have determined that it is the fossil of an embryonic marine reptile contained within the fossil of its mother.