The evolutionary lineage beyond the non-mammal members of the Synapsid family, commonly referred to as “mammal-like reptiles,” remains a subject of debate. These Synapsids are now extinct, and their classification as reptile ancestors is not without controversy.

Moving up the taxonomic hierarchy, the category of Amniotes encompasses all reptiles. However, recent genetic research has challenged our understanding of reptile evolution. It has become apparent that certain features, such as fenestrae (holes in the upper skull), have appeared and disappeared throughout evolutionary history, making classification attempts frustrating. While genetics provides valuable insights, the lack of genetic information from extinct species from this distant past hampers a complete reconciliation with the fossil record, which itself is already complex and perplexing.

If pressed to speculate, one possibility could be the Tuatara, a group of primitive lizards that still exist in New Zealand. However, in terms of genetic relatedness, they remain quite distant from other reptiles.

Image credit: Tuatara lizard male

A thorough examination of the challenges in establishing relationships can be found in discussions surrounding Amniota, shedding light on the complexities involved in this field of study.