Tara Collins and Jelle Hoogenboom have already attempted to explain this concept in the previous conversation, but it may be better understood with the help of relationship diagrams.

Using a simplified family tree, let’s address the following question:

Is your brother or sister more closely related to your cousin?

After careful consideration, the fact is that both your brother and sister are equally related to your cousin. Swapping the positions of brother and sister in the family tree would not change this relationship.

The same principle applies when comparing mammals with their closest relatives:

Are birds or lizards more closely related to mammals?

Once again, it is not possible to determine whether birds or lizards are more closely related to mammals. Swapping their positions in the relationship diagram would not alter the nature of this relationship.

This also implies that no specific species of birds is more closely related to mammals than other bird species. The same principle applies to lizards, turtles, and other related animals. All these groups are equally related to mammals, just like your siblings are equally related to your cousin.

It is worth mentioning that if any other synapsid, such as an edaphosaurid, had somehow survived and existed today, the answer would have been more specific than the broader categories of “reptiles and birds”. However, if multiple species of edaphosaurids existed, they would all be equally related to mammals.

In summary, all birds, lizards, turtles, and other related species are equally related to mammals for the same reasons illustrated in the previous examples.