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

ABSTRACT

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 conditions. 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.

KEYWORDS:

• Testudines
• Selachii
• rare earth elements
• bioapatite
• taphonomy
• strontium isotope

Acknowledgments

Fieldwork and analyses was funded by the Universiti Brunei Darussalam research grants UBD/RSCH/1.4/FICBF(b)/2019/023, and earlier seed grants UBD/PNC2/2/RG/1(325) awarded to K.L. and the Volkswagen Foundation “Research in Museums” grant (Grant no. Az. 90 978) awarded to M.R. G.B. received funding from the ÚNKP-20-5 New National Excellence Program of the Ministry for Innovation and Technology, Hungary (Grant no. ÚNKP-20-5-ELTE-129), János Bolyai Research Scholarship of the Hungarian Academy of Sciences (Grant no. BO/00024/19/10), and the National Research, Development and Innovation Office of Hungary (Grant no. NKFIH, PD 131557).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the ÚNKP-20-5 New National Excellence Program of the Ministry for Innovation and Technology [ÚNKP-20-5-ELTE-129]; Volkswagen Foundation ‘Research in Museums’ [Az. 90 978]; János Bolyai Research Scholarship of Hungarian Academy of Sciences [BO/00024/19/10]; Universiti Brunei Darussalam Research Grant [UBD/RSCH/1.4/FICBF(b)/2019/023 & UBD/PNC2/2/RG/1(3]; National Research, Development and Innovation Office [NKFIH, PD 131557].