Host Dr. Ben Garrod interviews Dr. Julien Kimmig about the 'Cambrian Fecal Revolution' and how the evolution of guts shaped early animal life.
13 May 2026TRANSCRIPT
Episode 176: Insect Gigantism Pt2
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 uses diffusion and advection to exchange oxygen and carbon dioxide 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 (https://www.nature.com/articles/s41586-026-10291-3) 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 in the Carboniferous.
2 May 2026TRANSCRIPT
Episode 175: Insect Gigantism Pt1
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 (https://www.nature.com/articles/s41586-026-10291-3) 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 in the Carboniferous.
Inside a recent episode
Episode 177: Cambrian Fecal Revolution
Published 17 Aug 2026 · Transcript excerpt
[…] And then the more we get towards the modern, the more advanced the whole system gets. OK, so you've described this change as the Cambrian fecal revolution. To what extent is that a driver for the Cambrian radiation, for the evolution of life through the Cambrian up until today? How important is it relative to any of the other drivers of the Cambrian radiation? I would say it definitely plays on a level with the oxygenation at the end, from what we can see. how important fecal matter is in modern marine ecosystems. Because we don't only get nutrients being made easier available, but we also get nutrients into deeper water systems, into substrate. […]
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