What is the affinities of sphenodon?

The Sphenodon, also known as the Tuatara, is a genus of reptile native to New Zealand. Despite its lizard-like appearance, it is not a true lizard and belongs to the order Rhynchocephalia, which is distinct from the order Squamata (lizards and snakes).

The affinities (or evolutionary relationships) of Sphenodon are as follows:

1. Rhynchocephalia:
   • Sphenodon is the sole surviving member of this order, which was once much more diverse during the Mesozoic era. The Rhynchocephalians are characterized by their unique dentition, where the upper jaw has two rows of teeth that fit over the lower jaw.
2. Sauria and Lepidosauria:
   • Rhynchocephalians, including Sphenodon, are closely related to the Lepidosauria group, which includes modern lizards and snakes. However, they form a separate lineage within the Lepidosauria.
   • Sphenodon is considered an evolutionary “living fossil” because it retains many primitive features that were present in early lepidosaurs, which evolved during the Triassic period (approximately 250 million years ago).
3. Archosaur and Lepidosaur Split:
   • The lepidosaurs (which includes Sphenodon) split from the archosaurs (which include crocodiles, birds, and dinosaurs) in the late Permian or early Triassic period. This division marks an early evolutionary divergence in reptiles.