. ▁Pi pe ▁Creek ▁S ink hole , ▁however , ▁was ▁buried ▁by ▁the ▁gla ci ers ▁and ▁the ▁de br is ▁they ▁left , ▁making ▁it ▁the ▁only ▁known ▁P li oc ene ▁example ▁in ▁the ▁central ▁part ▁of ▁the ▁eastern ▁half ▁of ▁the ▁continent . ▁ ▁The ▁sink hole ' s ▁e col ogy ▁The ▁ancient ▁wet land ▁was ▁home ▁to ▁a ▁large ▁and ▁dense ▁plant ▁and ▁animal ▁population ▁that ▁includes ▁both ▁ext inct ▁and ▁ext ant ▁forms . ▁ ▁The ▁climate ▁was ▁warm ▁and ▁temper ate , ▁but ▁somewhat ▁dry , ▁possibly ▁supporting ▁a ▁grass land - for est ▁trans itional ▁zone . ▁The ▁preserved ▁verte br ate ▁fa una ▁are ▁domin ated ▁by ▁aqu atic ▁species , ▁particularly ▁le op ard ▁fro gs , ▁which ▁are ▁still ▁common ▁throughout ▁the ▁United ▁States . ▁M amm al ian ▁finds ▁include ▁an ▁early ▁r hin oc eros ▁( T ele oc eras , ▁possibly ▁from ▁the ▁Mi oc ene ▁epo ch ), ▁can ids , ▁pe cc aries ▁and ▁short - fac ed ▁bear . ▁ ▁Back ed ▁by ▁a ▁grant ▁from ▁the ▁National ▁Science ▁Foundation , ▁research ers ▁from ▁the ▁Indiana ▁State ▁Museum ▁and ▁several ▁univers ities ▁substantial ly ▁completed ▁field ▁work ▁at ▁the ▁sink hole ▁in ▁the ▁summer ▁of ▁ 2 0 0 4 , ▁but ▁there ▁was ▁about ▁one ▁week long ▁dig ▁a ▁year ▁from ▁ 2 0 0 5 ▁to ▁ 2 0 1 1 . ▁What ▁probably ▁was ▁the ▁last ▁work ▁at ▁the ▁site ▁took ▁place