Earliest oceanic tetrapod ecosystem reveals rapid complexification of Triassic marine communities
Aubrey J. Roberts, Maciej Ruciński, Benjamin P. Kear, Øyvind Hammer, Victoria S. Engelschiøn, Thomas Holm Scharling, Ronald Larsen, Jørn H. Hurum
Abstract
Tetrapods invaded oceanic environments after the cataclysmic end-Permian mass extinction (EPME), with temnospondyl amphibian to reptile-dominated assemblages succeeding across the Early Triassic [~251.9 to 247.2 million years ago (Ma)]. However, conflicting fossil occurrences, divergence estimates, and stratigraphic time averaging make the tempo of this landmark evolutionary transition uncertain. In this work, we describe an oceanic tetrapod ecosystem from a condensed mid-Early Triassic (early Spathian, ~249 Ma) bone bed on the arctic island of Spitsbergen. Apex predator ichthyosaurians, small-bodied ichthyopterygians, durophagous ichthyosauriforms, semiaquatic archosauromorphs, euryhaline temnospondyls, coelacanths, lungfish, ray-finned fish, and sharks formed an unexpectedly complex trophic network. Comparative diversity analyses further show that heterogeneous marine vertebrate communities were well established by the late-earliest Triassic (Dienerian-Smithian, ~251 Ma) and integrated fully variegate tetrapod niches by ~3 million years after the EPME.