Datarama Tuatara Week, #1:

Unless you're a terminal-stage herpetology nerd like me, you probably think this animal is a lizard. It's not, though - it's a tuatara. The last living member species of a group of reptiles (the rhynchocephalians) that had its heyday some 245 million years ago, just a short while before the rise of the first dinosaurs.

There are *many* distinctively unlizardlike traits to a tuatara, and I'll cover some of my favourites throughout this week. And I'll start with the one that is most clearly evident without close examination: Their gait.

Tuataras move in a slow, distinctive "waddle" with a completely consistent diagonal footfall pattern; a trait they share with salamanders (and 400-million-year-old early tetrapods). They cannot change their gait at all - they can't trot or run, only walk. They bob up and down while walking (basically vaulting their centre of mass up and over their legs as they walk), with only relatively little lateral movement. Most lizards have at least 4 different gaits that they dynamically switch between as they pick up speed (over 50 species can do a fully bipedal sprint).

There are anatomical reasons for this. While their legs sprawl out sideways similar to those of lizards, they have much less flexible spines than lizards do - and they have a much longer ribcage, with rigid ribs all the way down into the abdominal area. Lizards throw their bodies from side to side in wave patterns (which is how you can maximize stride length if your legs face sideways) and usually keep their centre of gravity vertically constant, so more energy goes into going forward than up and down. Furthermore, tuataras have primitive single-chambered lungs without bronchia - basically mostly smooth air-filled bladders - and simple hearts without all the valves that allow for controlled blood flow during a sprint.

However, you won't see tuataras walk much. They live life very, very, *very* slowly. They're purely sit-and-wait ambush predators, and adults are (unbelievably) apex predators who never have to run to escape anything.