Résumé
Aquatic environments are critical components of past ecosystems that shaped species distribution and survival. Yet in hominin-bearing fossil sites, they are often treated as uniform or poorly detailed elements of “mosaic” landscapes, failing to capture their ecological complexity. In the northern Chad Basin, the late Miocene Toros-Menalla area records vast perilacustrine systems where aquatic and terrestrial ecosystems were deeply interconnected. While terrestrial vertebrate assemblages have been well characterised as reflecting a heterogeneous landscape, the aquatic component remains poorly resolved. Variations in depositional settings, aquatic vertebrate diversity, stable isotope data, and field observations point to a more complex and dynamic network of freshwater habitats. An integrative study of aquatic and semi-aquatic vertebrate assemblages from five Toros-Menalla sites reveals distinct faunal structures reflecting different ecological preferences and depositional conditions, ranging from perilacustrine floodplains to swampy, vegetated, or marginal waters and large open waterbodies with current. These environments, distributed across several hundreds of meters up to 30 km, represent lateral habitat diversity rather than temporal succession, as most assemblages formed geologically instantaneously (except for TM266, where vertical mixing could be hypothesised). Comparison with the present-day Bol Archipelago on the northeastern shores of Lake Chad provides a suitable analogue for the Toros-Menalla paleoenvironment. There, interdunal water bodies of varying depth and connectivity create a dynamic network of aquatic habitats at a similar spatial scale. This study underscores the need for systematic, grid-based collection and sieving of fossils to capture representative aquatic biodiversity and structure, and to reconstruct freshwater paleoenvironments with greater ecological precision.