The Snapping Turtles shell was about 16 inches long. I looked up the following information up on the internet.

"Snapping turtles, as we know them today evolved already about 40 million years ago, and they are the ancestors of about 80% of all the turtles today. Today’s snapping turtles have hardly changed from 215 million years ago when Proganochelys, the most primitive turtle known, lived. In comparison the age of the dinosaurs was approximately 150 million years ago, 100 million years more recent than the first turtle. Turtles were one of the few reptile groups, which survived the impact of a six mile wide meteorite on earth and the following nuclear winter about 65 million years ago. To put things into proportion: humans evolved a mere short 3.5 million years ago.
A 10-year-old individual measures about 7 inches (18 cm) and a 25-year-old individual about 11 inches (27 cm). Growth rates in northern populations are slower and body sizes larger than in southern populations.The largest snapping turtle ever recorded was 18.5 in (47 cm) (carapace length). Weights of 35 to 45 pounds are reached (8 to 14 inch individuals). The heaviest snapping turtle ever caught in the wild weighed 68 lbs." source - tortoisetrust.org