Lissodus selachos

That's a great tooth for the species - for any hybodont really. As you noted, the root is almost always gone. Maybe one in 50 or more has about as much root as your specimen. I know the "dinosaur guys" tend to ignore them and even some shark collectors are underwhelmed, but this species turned out to be the last of a successful lineage of sharks - a lineage that dwindled during the Cretaceous to just a few species before dying out completely with the dinosaurs.