Preferential preservation of low-elevation biotas in the nonmarine fossil record

Modern coastal sedimentary basins typically lie at low elevations (<600 m), whereas inland basins commonly occupy elevations as high as 4000–5000 m. Individual basins of all types typically preserve a narrower span of elevations, generally <1000 m, and typically near 200–300 m in coastal basins. As a result, the nonmarine fossil record is expected to preserve mainly low-elevation habitats and a relatively narrow range of elevations. Because many of the basins that preserve high elevations are likely to undergo subsequent destruction via erosion or continental collision, the dominance of low-elevation habitats is likely to become stronger into deep time. This selective preservation of nonmarine communities from sedimentary basins, and specifically from low elevations, suggests that much or even most of ancient nonmarine biodiversity is not preserved. Given the occurrence of many modern biodiversity hotspots in regions of high elevation, long ghost lineages are likely common in the nonmarine fossil record, and divergence times estimated from the nonmarine fossil record may be systematically far too short. The spans of elevations that are preserved in sedimentary basins suggest that the fossil record may preserve gradients in community composition that are correlated with elevation, yet they have been largely undetected.