My family and I just spent a 3 day weekend on Casey key. My wife's favorite pastime on this beach is treasure hunting! She is a collector of Shark's teeth and this is the shark tooth capital of the world. She has jars full of these teeth that are fossilized relics from years gone by. Florida was under the ocean thousands of years ago and at this time scientists theorize that the area of Manasota Key, Casey Key and Venice beach were baby shark breeding grounds. Sharks loose hundreds of teeth throughout their lives. There are millions of these teeth washing around in the beach sand. Bring a bucket because you'll need one for all of the sharks teeth you will find.
I hope you find a Megladon tooth. They are rare but can fetch hundreds and even thousands of dollars if they are the right size and condition.