What about oldest mammal species still living today?

Determining the "oldest" living mammal species is complex because evolution is a continuous process rather than a series of abrupt changes. Because all living species share a common ancestor, every living mammal has an evolutionary history that stretches back millions of years [3].

However, when researchers discuss "ancient" or "primitive" mammal species still alive today, they often refer to groups that diverged very early from the rest of the mammal family tree:

• Solenodons: Recent genetic research indicates that the solenodon belongs to an evolutionary branch that diverged from other lineages (such as hedgehogs, shrews, and moles) approximately 73.6 million years ago [1]. Because of this early divergence, they are often highlighted as a lineage that has remained relatively distinct for an exceptionally long time.
• Defining "Species": Scientists often point out that identifying the "oldest" living species is difficult because species boundaries are often "fuzzy" [2]. If you define a species by the ability to interbreed, it becomes challenging to pinpoint exactly when an ancestral population transitioned into what we identify as a modern species today [2].

In short, while we can identify groups like the solenodon that split off from other mammals tens of millions of years ago, there is no single "oldest" species because every modern mammal represents the current endpoint of a continuous, multi-million-year evolutionary journey [3].