natural history museum specimen enigmatic fossil tooth million years ago peru fossil site uncertain age possibly late tooth poorly preserved degraded acidic water passed predator digestive tract largest dimension triangular shape bears surround middle tooth basins connects separate microscopic structure poorly preserved described colleagues tentatively interpreted tooth left upper saw similarities south american early believed tooth likely small poorly known group known cretaceous southern continents thought cretaceous similar discovery context discovered santa fossil site peru fauna contains fossils unique species possible bat fauna published volume science series included paper colleagues described discussed age fauna remains highly uncertain fossils found easily placed known unit fossils distinct known fossil provide precise estimate summary volume tentatively referred land age placed near boundary million years ago colleagues suggested fauna substantially later young late million years ago according campbell mammals likely lived habitat contained rivers description poorly preserved like tooth largely lacks recognizable surface shows small grooves holes crown surface suggests tooth degraded acidic water passed digestive tract predator roots broken remaining pulp suggest presence main roots partially joined pairs smaller pulp cavity roots suggests likely presence fifth root slight depression tooth represent root crown tooth triangular contains connected low surround prominent low lying basins smaller complexity crown colleagues interpreted number roots arrangement shape tooth upper end longest flat low compared suggesting outer face imply tooth left jaw interpretation length tooth width height height convenience colleagues designated corner tooth face corner inner face corner face large located smaller intermediate smaller nearly round largest triangular shape separated smaller rounded deep valley low crest connects separating valley connects long crest reaches small groove valley separates crest shaped forms wall intermediate described odd fact consist fused triangular crest issuing separates intermediate larger crest separates nearly reaches triangular separated valleys bordered internally connecting rounded tooth clearly recognizable evidently tooth degraded structures resembling hunter bands recognizable identity complexity crown colleagues identified tooth non groups like complex teeth approach level complexity seen find resemblance including including related groups general upper early south american arrangement different early asia north_america central groove lacks prominent shelf edges tooth lacks tooth resembles large group extinct mammals teeth shapes valleys lack usually teeth longitudinal rows separated central valley features resembles small enigmatic group mammals cretaceous southern continents related particular late cretaceous argentina similarly formed connect center tooth upper unknown low crowned teeth lack deep members higher crowned family colleagues conclude likely represents member family youngest known
LACM 149371