u/Palaeocast

Website: https://www.palaeocast.com/cambrian-fecal-revolution/

The Cambrian Explosion is one of the most significant events in evolutionary history. Classically, it describes the sudden appearance of complex fossils (including all major animal groups) at the beginning of the Cambrian Period. Before then it was thought that only relatively simple single-celled or multicellular life existed. We now understand this event to be a lot more nuanced, recognising many of the geological biases at play and having discovered complex fossils in the earlier Ediacaran Period. Many researchers therefore consider the term 'Cambrian Radiation' to be a better representation of the event.

Whether an explosion or a radiation, determining the events of the Ediacaran and Early Cambrian and their causes is a constant area of palaeontological research. Numerous drivers behind the event have been hypothesised ranging from oxygen availability and nutrient cycling to an arms race between predators and prey. It is likely that no single factor will be identified as an underlying cause, but the relative extent to which each contributed to the event will be debated for many years to come.

In this interview, we are joined by Dr Julien Kimmig, Staatliches Museum für Naturkunde Karlsruhe, Germany, who recently co-authored a study on the coprolites of the Early Cambrian, the evolution of guts, and the influence the 'Cambrain Fecal Revolution' may have had on the wider Cambrian Radiation.

Image: Phosphatized microscopic fecal pellets from the Gaotai Formation (Miaolingian, Wuliuan) Guizhou, China.

https://www.palaeocast.com/insect-gigantism/

The Carboniferous period is host to some of the largest arthropods to have ever lived. Giant taxa such as the griffenfly Meganuera and the millipede Arthropleura are almost talismanic and are often depicted in reconstructions of the period. Since many other groups also have giant representatives in the Carboniferous, what is it about this time that allows for arthropods to grow to such large sizes?

Arthropods breathe very differently to how we do with many using a series of branching hollow tubes called trachea for gas exchange throughout the body. This tracheal system relies upon the process of diffusion where oxygen and carbon dioxide will be exchanged from areas of higher concentration to lower concentrations. In 1995, a study in the journal Nature suggested that elevated oxygen concentrations in the Carboniferous (approximately 30%, as opposed to 21% today) allowed for gigantism in arthropods since oxygen could diffuse deeper/further into their larger bodies.

A recently published study in the same journal is now casting doubt on that interpretation and in this interview, we are joined by one of the authors, insect physiologist Prof. Jon Harrison from Arizona State University. He introduces us to the tracheal system and its link to the size of insects during the Carboniferous.