Katagenesis
Katagenesis is a term used in evolutionary biology and paleontology to describe a process where a lineage or group of organisms becomes progressively simpler or less complex over time. This contrasts with anagenesis, which typically involves increasing complexity. Katagenesis is often associated with a reduction in the number of specialized features or a loss of complex structures. It can occur when organisms adapt to stable or simplified environments, or as a consequence of specialization where certain functions are no longer necessary for survival.
Examples of katagenesis are sometimes debated and can be difficult to definitively identify. Some proposed instances