Discovery and Analysis of Subfossil Hippopotamus in Ranomafana National Park, Madagascar

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Participants

  • Vola Hortense Raherisoa; Director, Ranomafana National Park, Madagascar
  • Patricia C. Wright; Distinguished Service Professor, Stony Brook University, USA
  • Dominic Stratford; Research Professor, Stony Brook University, USA
  • James Hansford; Lecturer at Queen Mary University of London, UK
  • Voajanahary Ranaivosoa; Professor, University of Antananarivo, Madagascar
  • Jean Freddy Ranaivoarisoa; Professor, University of Antananarivo, Madagascar
  • Michael Bliss; PhD Student, Texas A&M University, USA
  • MJ Ingmanson; PhD Student, University of Massachusetts Amherst, USA
  • Alicia del Prado-Rebordinos; Master’s Student, Maastricht University, Netherlands
  • Rakotonirainy Kanto Sarobidy Tsiory; Master’s student, University of Antananarivo, Madagascar
  • Mahazomila Andriamahery; Master’s Student, University of Antananarivo, Madagascar
  • Dina Andrianoely; Biodiversity Field Manager, Centre ValBio, Madagascar
  • Manjaka Rasolonjatovo; Laboratory and Collection Manager, Centre ValBio, Madagascar
  • Rakotovao Remi; Senior Research Technician, Centre ValBio, Madagascar
  • Randrianirina Georges Renee; Senior Research Technician, Centre ValBio, Madagascar
  • Randrianasolo Laurent Ralisoa; Senior Research Technician, Centre ValBio, Madagascar
  • Zakamanana François; Senior Research Technician, Centre ValBio, Madagascar
  • Raherinirina Toussaint Georges; Research Technician, Centre ValBio, Madagascar
  • Tanjononizaka Kathy Williams; Research Technician, Centre ValBio, Madagascar
  • Laurie Godfrey; Emeritus Professor, University of Massachusetts Amherst, USA

Summary

During our November and December 2024 expeditions, supported by first-year emergency grant funding from The Leakey Foundation, our team explored an extensive cave system within Ranomafana National Park (RNP), Madagascar. We documented and extracted subfossil remains for paleontological analyses, including two specimens of Hippopotamus spp., marking the first discovery of subfossils in a high-elevation rainforest (Humid Forest ecoregion) in Madagascar. This discovery provides direct evidence of previously undocumented megafauna in this region and offers critical insight into past ecosystem structures. Our goals are to map the cave system, identify additional subfossils, and preserve and analyze Hippopotamus spp. specimens.

Background

Madagascar’s Holocene megafauna included crocodiles, tortoises, dwarf hippopotami, giant lemurs, and giant ratites, many of which went extinct within the last 2,000 years. Extensive prior subfossil research has focused primarily on drier regions, leaving the wet Humid Forest ecoregion largely unexplored due to acidic soils and rapid nutrient cycling. Our discovery within RNP, spanning elevations of 600–1,500 m and receiving approximately 3,600 mm of annual rainfall, addresses this gap in the fossil record. Florence’s Cave (21°13'36.49"S, 47°27'18.11"E) and Toussaint’s Cave (21°13'32.21"S, 47°27'18.15"E) present unique taphonomic environments capable of preserving both near-complete individuals and fragmentary deposits, providing a rare opportunity to investigate faunal assemblages in Madagascar’s wettest forests and in the same ecosystem in which the animals lived. These caves may reveal the ecological roles and extinction chronology of previously undocumented megafauna in high-elevation rainforest habitats.

Methods

We conducted reconnaissance surveys and excavations across multiple cave chambers, recording GPS coordinates, chamber dimensions, sediment characteristics, and faunal material. Subfossils were photographed, catalogued, individually numbered, wrapped, and transported to the Centre ValBio Research Station. We mapped cave entrances across 180m stretch of valley, and identified undiscovered chambers for future exploration. Expeditions included careful taphonomic assessment to prioritize specimens at risk of seasonal water damage.

Techniques

Cave mapping, systematic subfossil excavation, photographic documentation, sedimentary and taphonomic analyses, specimen cataloguing, DNA extraction and sequencing, isotopic analyses, and morphometric comparisons.

Aim

Our objective is to document and analyze subfossil remains of megafauna from RNP, clarify their taxonomic identities, and reconstruct ecological and taphonomic histories. These data will advance understanding of Madagascar’s past ecosystems, extinction dynamics, and potential human-megafauna interactions.

Findings

A total of 63 subfossil specimens were recovered from Florence’s and Toussaint’s Caves, including partially intact crania, teeth, and long bones of Hippopotamus spp. Preliminary morphological comparisons suggest these specimens may represent a previously undescribed species. Taphonomic patterns indicate pitfall trap-like scenarios, in which individuals fell into the caves. Initial mapping identified over 15 cave entrances along a 180m valley stretch, suggesting the system may extend further and contain additional faunal deposits.

Next Steps

We will continue systematic exploration and mapping of the cave system to identify additional subfossil deposits. Excavations will prioritize specimens at risk from seasonal flooding. Extracted specimens will undergo detailed DNA, isotopic, and morphometric analyses to clarify taxonomic status and ecological history. RNP staff will be trained in cave monitoring, subfossil excavation, and preservation techniques to ensure sustainable management. Finally, we plan to establish a small museum near the RNP entrance to support research, foster education, and provide sustainable community benefits through ecotourism.

Appendix

Figure 1. Location of the Ranomafana Cave system.

Figure 2. Hippopotamus maxilla, canine and other dentition, found in Florence’s cave.

Figure 3. Hippopotamus humerus (left) and femur (right) in Florence’s cave.

Figure 4. Canine from Hippopotamus sp. and bone fragments found in Touissant’s cave.

Figure 5. The entrance to Florence’s Cave, typical of entrances to this system.

Figure 6. Cave interior where the subfossil remains were discovered in Florence’s cave.

Poster


Poster designed by Manjaka Rasolonjatovo