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    Inner Workings: Fossil farmAmber DanceScience Writer

    Eighteen million years ago, a sinkhole openedup in what is now Gilchrist County, Florida.Thousands of unlucky animals fell infrogsand snakes, ground doves and turkeys, evennow-extinct camels and rhinoceroses thatonce roamed North America. Some likelysurvived for a time before starving or fallingprey to predators that also took the plunge.Today, that sinkhole provides paleontolo-

    gists with a rich understanding of Early

    Miocene life. The Thomas Farm site, nowmanaged by the Florida Museum of NaturalHistory, was named for original ownerRaeford Thomas. When he dug a well in1931, he didnt find water but he did uncoverfossils. Since then, researchers have dug downabout 10 m and they estimate that the sink-hole goes down another 10 m based on coresamples of the earth, says vertebrate paleon-tology collections manager Richard Hulbert.

    Thomas Farm is valuable due to the numberof speciesmore than 100andwide range ofanimal sizes represented, Hulbert says. Nearly50,000 quality specimens have been identified,and there are tens of thousands still awaitingcurators attention. Because the sinkhole wasonly open for a couple thousand years, it offersa snapshot of the animals that wandered an-cient Florida. Limestone lining the sinkholehas helped preserve the fossils by preventingacidic groundwater from seeping in. The find-ings include thousands of horse fossils from atleast three different species; Hulbert is cur-rently working to prove that one of thosegroups is really two distinct species.Other finds have included remnants of

    novel species, such as two skulls of a kind ofmustelid, a family that includes wolverinesand weasels. Proof of Zodiolestes freundi,christened in honor of the fossils discoverer,volunteer John Freund of Gainesville, Florida,extended the animals known range (1).The layered clay and sand yield easily to

    scientists screwdrivers and picks; it takes justminutes to uncover a piece of tortoise shellor a small horse hoof. Excavators bag allof the soil, literally tons of sediment, saysHulbert. Then they run that silt througha sieve to catch every last tiny fossil, suchas rodent teeth or snake vertebrae. Forexample, researchers identified an extinctspecies of bat, Primonatalus prattae, fromthese siftings (2). The bats probably livedin caves in the sinkhole walls.Researchers, students, and volunteers

    uncover so many fossils that they toss thelower-quality specimens on a scrap heapfor visiting schoolchildren to excavate.However, there are plenty of good ones left.Hulbert still gets a rush when he or a volun-teer unearths a fossil he knows is new.

    1 Hochstein JL (2007) A new species of Zodiolestes (Mammalia,

    Mustelidae) from the early Miocene of Florida. J Vert Paleo 27(2):

    532534.2 Morgan GS, Czaplewski NJ (2003) A new bat (Chiroptera: Natalidae)

    from the early Miocene of Florida, with comments on Natalid

    phylogeny. J Mammol 84(2):729752.

    Paleontologists Richard Hulbert Jr. (Left) and Jonathan Bloch (Right) dig for fossils at theFlorida Museum of Natural Historys Thomas Farm site, an ancient sinkhole chock full ofbones from a variety of animals. PNAS | January 6, 2015 | vol. 112 | no. 1 | 3