Friday Fossil Feature – It would be Folly to pass this site up

By Robert Boessenecker (@CoastalPaleo) and Sarah Boessenecker (@tetrameryx)

 

Photo by R. Boessenecker

Folly Beach is a popular destination near us here in Charleston, and thousands of swimmers, sun tanners, and surfers flock to the beach during the summer and relatively warm spring and fall months; the water is a few degrees warmer than Hawaii, and we will on occasion leave work early every couple of weeks to go swimming. Folly started out as a bit of an artist’s village, and is where George Gershwin wrote the opera “Porgy and Bess” about life in Charleston. Folly Beach is a barrier island, separated from Charleston Harbor to the northeast only by the relatively small Morris Island – the location of Battery Wagner. Battery Wagner was a Confederate artillery battery guarding Charleston Harbor, assaulted in 1863 by Union troops including the 54th Massachusetts Volunteer Infantry – one of the first African American units in the Union Army – and depicted in the 1989 film “Glory”. Hurricanes occasionally uncover Civil War era artifacts, and after Hurricane Matthew last fall, beach walkers found an uncovered store of cannon balls – unclear if solid “round shot” or mortar shells filled with black powder – which, regardless, were detonated by a bomb squad.

Tropical Storm Hermine and Hurricane Matthew uncovered quite a bit of older material this last fall, chiefly fossils and limestone blocks dating to the last 30 million years. A variety of fossils can be found on the beach at Folly, and while not as plentiful as at Edisto Beach, Folly is much closer to us. We’ve gone several times recently, and collected many pounds of fossils. One major scientific issue with collecting fossils from Folly is that the source of the specimens is inconclusively known – and any consideration of the stratigraphic (i.e. geologic) source of the fossils is speculative. Fossils occur isolated on the beach, and except in rare cases, vertebrate fossils do not have any adhering rock. No fossiliferous exposures crop out at Folly, and fossils come from two different sources: 1) natural submarine exposures just offshore and within rivers, washed back onto the beach and 2) sediment delivered by beach renourishment. Folly Beach has been eroding away, and within living memory the width of beach and dunes has decreased noticeably, with hurricanes like Hugo (1989) contributing; other factors include the construction of the Charleston harbor jetties, which prevent sediment from Sullivan’s Island being transported south to Morris and Folly. Sediment for renourishment is either dredged or piped up from “borrow” areas – some of which are in river mouths, but most is from about 3 miles offshore. Renourishment in 2015 from the offshore borrow area introduced a large number of limestone nodules, which have been the source of much ire and complaining from Folly residents, but possibly a boon for geologists.

We still don’t have a great idea of what strata are exposed in these areas, and several problems plague stratigraphy in the Charleston embayment: 1) Exposures are rare and many deposits are known only in the subsurface, either from well cores or seismic data; 2) many deposits, according to seismic data, are not laterally extensive and taper out over a few miles – making mapping and correlation a bit of a nightmare. We’ll be using the stratigraphic framework from the geologic map of the area published recently by USGS stratigrapher and paleontologist Rob Weems and others (2014). But before we get there, what fossils can you find?

Photo by R. Boessenecker

Hemipristis serra, the snaggle tooth shark. Photo by R. Boessenecker

Photo by R. Boessenecker

Most visitors come for the shark teeth – and shark teeth can be found. They are perhaps not as common at Folly as at other beaches in the southeastern USA, but I’ve walked away with a dozen after only a couple hours of searching. Common shark teeth include Sand tigers (Odontaspis, Carcharias; Oligocene-Recent), and reef and lemon sharks (Carcharhinus, Negaprion; Eocene-Recent). These all have long stratigraphic ranges, and are notoriously difficult to identify – and could come from any of the Oligocene through Pleistocene strata in the Charleston area. Some of the rarer, larger, and more highly sought after teeth including great white sharks (Carcharodon carcharias, Pliocene-Recent), “bigtooth makos” (Carcharodon hastalis, early-late Miocene), and the megatoothed sharks (Carcharocles megalodon, early middle Miocene to early Pliocene; Carcharocles angustidens, Oligocene), tiger sharks (Galeocerdo, Physogaleus spp.), and snaggletooth sharks (Hemipristis serra, Eocene-Pleistocene) are somewhat better age indicators. Confusingly, all of these occur at Folly Beach – indicating that Oligocene, Miocene, and Pliocene rocks all occur nearby or in the borrow areas. Other sharks including bat rays also occur, and shark/ray vertebrae are also known.

Photo by R. Boessenecker

Fossils of bony fish are common, but typically left behind. Common examples include beaks of the pufferfish Chilomycterus schoepfi (early Miocene to Recent), partial skulls of sea robins (Prionotus sp., Pliocene-Recent), partial skulls of bonitos (Sarda sp.; Eocene-Recent), and osteoderms of a sturgeon (Acipenser sp., Cretaceous to Recent). Fish bones are a bit of a nightmare for paleontologists, since fish have such a high number of bones that typically disarticulate, and comparable parts are rarely found. At Folly, mostly well-preserved, dense elements resistant to destruction are found, meaning that it is relatively easy to find consistently occurring specimens of the same morphology. Unfortunately, we have no record of the more delicately built fishes.

Photo by R. Boessenecker

Reptile fossils are in abundance, unlike equivalent deposits on the west coast. Turtle shell elements are actually quite common, and readily identifiable – for someone who knows about turtles. Shell identification of turtles has always seemed like a black art, but we’ve got quite a few now. Specimens obvious enough for chelonian novices like us include large tortoises (Geochelone, Eocene-Recent, or Hesperotestudo, Miocene-Recent), some sort of a large softshell turtle (Trionychidae indet., Cretaceous-Recent), and pond turtles (Emydidae, Cretaceous-Recent). Our collection includes a large, somewhat flat leg spur of a large tortoise. Sea turtles should be encountered, but it’s unclear if our preliminary searches have uncovered any; a single possible osteoderm of a leatherback sea turtle (Dermochelyidae indet., Eocene-Recent) was collected just a few days ago. Crocodilian remains are comparably rare, and we recently collected a partial osteoderm (scute) of extant Alligator (Eocene-Recent).

Photo by R. Boessenecker

Mammalian bones are the most commonly encountered fossils, and these are almost always left behind. These are fragments of much larger bones – by volume, most I assume are from whales (ribs, mandibles). On occasion highly dense bone fragments likely represent pieces of sea cow (Sirenian) ribs. It is worth picking up each one and checking it over to make sure it’s not an identifiable specimen before chucking it back into the sand.

Photo by R. Boessenecker

Land mammal remains are quite common, and include shards of thin-walled bones with a large marrow cavity (clearly not marine mammals), teeth, and tooth fragments. Horse teeth and fragments thereof are perhaps the most common (Equus sp., Pliocene-Recent), and fragments of teeth and tusks of American mastodon (Mammut americanum, Pliocene-Recent) and woolly mammoths (Mammuthus spp., Pleistoecne-Recent). Tusk fragments of the latter can be identified based on distinctive cross-hatching in cross-section. Teeth of artiodactyls are less common (e.g. Bison, Pleistocene-Recent). Our growing collection also includes remains of edentates – including osteoderms of the giant armadillo Holmesina.

Photo by R. Boessenecker

Occasionally identifiable specimens of whales and dolphins (Cetacea) are found. Marine mammals are more difficult to identify than terrestrial mammals, as teeth are either completely absent (baleen whales) or the teeth are similar between species (toothed whales). Earbones are quite important instead, and two different types of earbones may be found – the periotic and the tympanic bulla. Each look quite strange, but if complete enough, are identifiable to the family, genus, and occasionally species level. One recent find by us includes a partial periotic of baleen whale similar to Parietobalaena from the early-middle Miocene Calvert Formation of Maryland. Another specimen, recently donated by Edisto State Beach Ranger Ashby Gale, is a periotic of a pygmy sperm whale (Kogiidae indet.), an unnamed species that is so far known only from periotics from the Pliocene of North Carolina and Florida. The specimen is not photographed here because it is currently being molded and casted.

Photo by R. Boessenecker

For every genuine vertebrate tooth or bone on the beach, there are about a thousand shells and a handful of black phosphate pebbles. Phosphate is a type of sedimentary “nodule” or concretion formed during periods of low sea level with slowed deposition. Slow deposition also favors the formation of vertebrate rich bonebeds – when phosphate pebbles are present in an area, they are usually concentrated and formed under the same conditions that characterize the concentration of vertebrate fossils into bonebeds. Simply put, if black phosphate pebbles are common, look for bones and teeth! Also keep your eyes peeled for coprolites – fossilized poop. Phosphate pebbles which look like poop are very likely to be just that. Coprolites, bones, and teeth are all phosphatic, and share the same chemistry with phosphate pebbles.

So, we know that there are fossils from the Oligocene, sometime in the early-middle Miocene, the Pliocene, and the Pleistocene from Folly Beach – all mixed together, naturally and by beach renourishment. The geologic map of Charleston published by Rob Weems includes deposits of the lower Oligocene Ashley Formation, the lower Miocene Marks Head Formation, the Pliocene Goose Creek Formation, and the upper Pleistocene Wando Formation. We think that these strata are the likely sources of the fossils from Folly Beach, with the terrestrial reptiles and land mammals all originating from the Pleistocene Wando Formation.

We need your help! The vertebrate fossils of Folly Beach have never been published before in a scientific paper. We are currently seeking donations of vertebrate fossils from Folly Beach to help “fill out” the fossil assemblage in our collection in order to permit scientific study of the locality. If you have found some of the more uncommon fossils – in particular, whale or dolphin earbones or mammal teeth – we encourage you to consider donating the specimens to CCNHM for scientific study and display in our museum!

 

Sources Cited:

Weems, R.E., Lewis, W.C., and Lemon, E.M., Jr., 2014, Surficial geologic map of the Charleston region, Berkeley, Charleston, Colleton, Dorchester, and Georgetown Counties, South Carolina: U.S. Geological Survey Open-File Report 2013–1030, 1 sheet, scale 1:100,000, http://dx.doi.org/10.3133/ofr20131030.

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3 comments on “Friday Fossil Feature – It would be Folly to pass this site up
  1. craig says:

    Great photos. We have found a few similar black clasts or ‘bones’ found on the west coast of southern africa thought to be whale bones.
    Thank you.

  2. Kathryn Kissam says:

    Great article and helpful for Folly fossil finders like me. I have a super cool tooth I found and can’t identify. Lots of other pieces. Can I

  3. Barbara Hill says:

    Who should we address the mammal fossils to at CCNHM?

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