From ScienceDaily:
The researchers conclude that already the least common ancestor of caseids and mammals had a diaphragm more than 300 million years ago — that is about 50 million years earlier than previously assumed. An efficient respiratory system is intertwined with the evolution of warmbloodedness, which in turn molded our entire behavior. This assumed early origin of the diaphragm now demands a reevaluation of these developments.A fossil diaphragm probably will never be found, simply due to its bad chances to become preserved. Science, according to Prof. Perry, therefore depends on functional approximations to trace the origin of this important evolutionary novelty. Dr. Lambertz: “We still don’t know that much about these animals. It has been a long way towards mammals, but the origin of the diaphragm marked a turning point on it.” Paper. (paywall) – Markus Lambertz, Christen D. Shelton, Frederik Spindler, Steven F. Perry. A caseian point for the evolution of a diaphragm homologue among the earliest synapsids. Annals of the New York Academy of Sciences, 2016; DOI: 10.1111/nyas.13264 More.
So there was that much less time for the diaphragm to evolve, Darwinian style.
See also: Soil micro-organisms older than thought Researcher: “With cell densities of over 1,000 per square millimeter and a diversity of producers and consumers, these microfossils represent a functioning terrestrial ecosystem, not just a few stray cells.
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