Geochemical analyses suggest stratigraphic origin and late Miocene age of reworked vertebrate remains from Penanjong Beach in Brunei Darussalam (Borneo)

We report on sporadic fossil vertebrates from Brunei Darussalam (Borneo). Most of these isolated remains are reworked  and  derive  from  Penanjong  Beach  known  for  former  coastal  cliffs  used  to  be  rich  in  marine molluscs.  Previously,  the  only  vertebrate  remains  reported  were  shark  teeth.  With  new  material,  the  fish fauna  is  now  represented  by  six  shark  and  a  single  ray  taxa,  while  remains  of  three  turtle  families  were discovered  (Trionychidae,  Cheloniidae,  Geoemydidae).  This  fauna  is  compared  to  nearby  upper  Miocene fossiliferous  beds  from  where  remains  of  cheloniid  and  trionychid  turtles  were  unearthed.  To  assess  the origin  of  the  reworked  remains,  rare  earth  element  (REE)  concentrations  of  the  fossil  bioapatite  were compared  between  the  reworked  and  the  geographically  closest  in-situ  Ambug  Hill  fauna.  The  obtained trend in REE variations are identical, revealing similar REE uptake mechanism and early diagenetic condi-tions. With the additional fact that the succession outcropping at Ambug Hill cuts the coastline imply that the majority of the reworked fossils derive from the local Miocene beds. This is supported by Sr-isotope ages from reworked calcite bivalve shells ranging from 9.74 to 6.62 Ma. These turtle remains thus represent the hitherto known first Neogene fossil tetrapods from Borneo.