THE EARLY TRIASSIC MARINE BIOTIC RECOVERY: A PREDATOR’S PERSPECTIVE

Several times in the geological past, life on Earth was severely affected by global catastrophic events, known as mass extinctions. Furthermore, the recovery dynamics of large predators provide a key for evaluation of the pattern and tempo of ecosystem recovery because predators are interpreted to react most sensitively to environmental turbulences. Following the end-Permian event 252 million years ago, the most severe mass extinction ever, the paradigm persists that the recovery of oceanic ecosystems was prolonged, lasting up to 8 or 9 million years into the Middle Triassic (Anisian). The ecological or trophic ‘pyramid’ was thus assumed to recover step by step bottom upwards, with producers recovering before consumers and at last the apex predators.

We conducted a survey of the global distribution and body size spectra of Early Triassic and Middle Triassic marine predatory vertebrates (cartilaginous and bony fishes, amphibians and reptiles) to elucidate diversity and trophic structure in marine ecosystems after the end-Permian event. The body size survey was done by compiling maximum standard lengths for bony fishes and some cartilaginous fishes (n=218 taxa), and total size (estimates) for the tetrapods (n=41 taxa). The data revealed that many species were globally distributed and that the taxonomic composition of the faunas was well balanced whereas, on the other hand, there was no indication for species dominance as would be indicative for disaster taxa.

Furthermore, the data indicated that there was no truncation of food chains to the lower levels in the marine realm, but the food chains were already topped by large predators very early in the aftermath of the end-Permian mass extinction (from the Griesbachian onwards). Furthermore, no significant size increase in predators is observable from the Early to the Middle Triassic. Two major faunal community changes occurred around the end-Permian mass extinction however: the first one from fish-dominated to fish/amphibian-dominated communities across the mass extinction event and a second one from fish/amphibian-dominated to fish/reptile-dominated systems about two million years later in conjunction with another extinction event (the end-Smithian crisis). Both extinctions can be linked to massive volcanic eruptions and ensuing global climatic changes.