microxelia
Microxelia is a term used in evolutionary biology and paleontology to describe the phenomenon of a lineage exhibiting a reduction in size over evolutionary time. This contrasts with the more commonly observed trend of an increase in body size, known as Cope's Rule. Microxelia can occur for a variety of reasons, often related to environmental pressures or selective advantages associated with smaller body size.
One significant factor contributing to microxelia is resource availability. In environments with limited food or space,
Another driver of microxelia can be predation pressure. Smaller prey animals may be able to escape predators
Microxelia has been documented in various taxa throughout the fossil record, including mammals, reptiles, and invertebrates.