Though paleontologists have understood mass extinctions for a long time now, much of what we know and understand about the end-Devonian extinction is very recent. For decades, the “Late Devonian mass extinction” was recognized as one of the five largest mass extinctions in Earth history, but considered to be an instance of low species origination instead of high species die-off. Crucial work by Lauren Sallan [Sallan and Coates 2010] was key in clarifying the story. The “Late Devonian” extinction was actually two separate events: an invertebrate extinction coincident with the Kellwasser event at the end of the Frasnian stage (c.372 million years ago) and a vertebrate extinction coincident with the Hagenberg event at the end of the Devonian (358 million years ago.) The end-Frasnian extinction was not a mass extinction for vertebrates, but it had catastrophic effects on invertebrates. During the Devonian, reef systems were more extensive than at any other point in Earth history; these were wiped out in the end-Frasnian extinction, and reef-building organisms did not fully recover for over 40 million years. The end-Devonian extinction eliminated the last of the ‘ostracoderm’ jawless fishes, placoderms (eg. Dunkleosteus), and many sarcopterygian (“lobe-finned”) fishes. Tetrapods, actinopterygian (“ray-finned”) and chondrichthyan fishes were the principal survivors, and their post-extinction radiations include the origins of numerous modern lineages. In this way, our modern vertebrate biota has its roots in the end-Devonian extinction.
The Hagenberg event is named after the global layer of black shale laid down at the end of the Devonian. At the end of the Devonian, the supercontinent Gondwana moved over the South Pole. This provided an easier place for ice to form, eventually reducing sea level [and blah blah something something anoxia] leading to the deposition of the Hagenberg shale.
Much fruitful work has been done on the end-Devonian extinction recently, particularly in clarifying the timing and mechanisms of the Hagenberg event. However, the full impact of this extinction has yet to be understood. It is not yet clear whether the extinction had the same effect in different environments, and on different groups of organisms. Also, while there has been some ecological work on the extinction aftermath, many areas and organisms have not been looked at yet, and the reef collapse at the end of the Frasnian has yet to be factored in.
Our research on the end-Devonian extinction focuses on understanding the post-Devonian world. Our morphological and phylogenetic work on chondrichthyans, actinopterygians, and tetrapods seeks to understand how the evolution of these groups was or was not impacted by the extinction. We are also becoming more interested in ecology, both in the origin of new morphologies and niches and changes at the ecosystem level. Through this week we aim to add to the ever-growing body of work on this crucial and under-studied interval in Earth history.