So just what is a fossil, anyway?

Fossils are the preserved remains – or traces of remains, in the case of nests, burrows, dung (coprolite), or footprints – of once living organisms. There are several types of fossils, but here we’ll focus on the most common: permineralized. For this kind of fossilization to occur, an organism needs to be buried in sediment soon after its demise. Either the plant or animal has to die in (or close to) a body of water or its remains have to be transported there, by floods or scavengers. Once buried, it must remain undisturbed for millenia (though the time it takes to fully fossilize varies, it’s typically at least 10,000 years). Slowly, minerals in the water and sediment begin to seep into the porous areas of plants or the bones, teeth, and occasionally even soft tissues of animals, depositing a mineral matrix where cells once existed. A permineralized fossil is, in essence, a mineral copy of the original organism.

Why are there so many fossils in Florida?

Florida inherited an immense quantity of mineral-rich sands and clays from the erosion of the Appalachian Mountains, is surrounded by shallow seas and intersected by extensive river systems, has had very little geological volatility (things like earthquakes or volcanic eruptions, which could disturb the fossilization process), and served as an ideal habitat for a wide variety of ancient plant and animal species. These conditions, spanning tens of millions of years, led to Florida having some of the richest and most varied Cenozoic era fossil deposits in the world. It’s worth noting, however, that fossilization was and still is an incredibly rare occurrence, and that the vast majority of organisms to have ever lived have been lost to the [almost] unstoppable biological forces of nature. Every fossil is the result of a series of highly unlikely events, and that’s part of what makes them so special.

How old are these fossils?

Florida began its rise out of the sea during the Oligocene epoch, as a landmass called Orange Island, 30 some odd million years ago (mya). So while you won’t find any dinosaur fossils here (we missed them by around 30 million years), you’ll find an abundance of mammal, bird, fish, reptile, amphibian, and invertebrate material, predominantly dating from the Miocene onward through the Pliocene and Pleistocene and into our modern epoch, the Holocene (~23 million to 10,000 years old), with some rare finds dating as far back as the Eocene, over 50 mya.

Why do you sometimes find marine fossils on land and terrestrial fossils at sea?

Florida, being so low in elevation, is uniquely prone to the effects of shifts in global climate. During cooler (glacial) periods, much of the earth’s water gets locked up in vast ice sheets and glaciers, which results in drastic drops in global sea levels (called sea level lowstands). Inversely, during warmer (interglacial) periods, all that ice melts and sea levels rise (sea level highstands). These swings can be several hundred feet, and during extremes (glacial maxima and minima, respectively), Florida has been over twice as wide as it is today (as recently as ~18,000 years ago) or almost completely inundated by water (during multiple stretches of the Miocene, 23 to 5.3 mya). This means that 14 foot tall mammoths grazed where there is now over 400 feet of water and megalodon sharks bigger than school buses terrorized seas that covered almost the entire state.

Why do you find older fossils mixed in with younger ones?

In geology, there is something called “the law of superposition.” It states that each rock or sediment layer (strata) is younger than the one it sits on top of. Older rock must form first, then younger rock forms on top of that, and so on. Fossils are the same way. The older a fossil is, the deeper it should be in relation to younger fossils. But in Florida it’s not uncommon to find 20 million year old shark teeth in the same layer as 20,000 year old horse bones, for example. Why is that? Well, when sea levels fall extensive river systems often form, eroding through layers of long undisturbed strata and exposing, transporting, and consolidating previously formed fossils, potentially from many different time periods. As sea levels once again rise, or river systems inevitably change course, these fossils, now all jumbled together, become reburied in sediment, occasionally with recently deceased friends in tow who are just starting their fossil journeys. As Florida is on the front line for changes in sea level, this scenario has played out countless times throughout its history. The resulting mish mash of fossils can be frustrating for paleontologists who have to try to work their way back through history but exhilarating for us hobbyists!

How do you find all this stuff?

Perhaps the easiest and most accessible way to find fossils in Florida is to buy a scoop and sifter and head to the Venice area beaches, where a fossil-rich deposit called the Peace River Formation is exposed just offshore. Fossils, especially shark teeth, are constantly eroded out of this layer and washed ashore through tidal action, currents, and storms. Sometimes you don’t even need to sift, they’ll be washed right up on the shoreline! Digging and sifting in the creeks and rivers that crisscross the state is another fantastic option (pro-tip: look for areas with lots of gravel). If you’re comfortable underwater, snorkeling or SCUBA/hookah diving is my favorite way to hunt, either off the Venice coast or in creeks and rivers (just watch out for sharks, gators, and snakes!). Last but not least are land sites. As construction or mining crews dig, they occasionally expose rich fossil deposits. Some of the best finds in the state have been in phosphate mines, where numerous fully articulated skeletons have been found. As tempting as it can be to go waltzing through an active construction site, however, be forewarned that trespassing on a construction site or mine is a potential felony! Best to seek permission first or find a site that is open to the public. No fossil is worth landing in jail.

*A fossil hunting permit is required if you plan on collecting anything other than fossilized shark teeth or invertebrates (shells, echinoids, etc) on public land in Florida. They’re only $5 per year and available to residents and visitors alike. I highly recommend obtaining one if you plan on doing any fossil hunting in the state. Google “Florida fossil permit” to learn how.

What other kinds of animals lived in Florida?

Ground-dwelling sloths up to 20’ long; 7’ tall carnivorous “terror birds;” 30’ long crocodiles; 5’ tall beavers; 6’ long tortoises; mammoths, mastodons, gomphotheres, and other, even more bizarre, shovel-tusked elephant relatives; short faced bears; dire wolves; saber toothed cats; giant armadillos and their relatives, the glyptodonts, the latter of which grew to the size of a VW Beetle; basilosauruses; jaguars; American lions; hornless rhinos; miniature three-toed horses and a multitude of other proto-horses; walruses; seals; tapirs; capybara; bison; humpless, long-necked “giraffe” camels; llamas; and much, much more.