Datarama Tuatara Week, sidebar:

You're going to be seeing me say "primitive" *a lot* this week, and I might as well clear up what that actually means.

In zoology (and paleontology), a trait being "primitive" does not mean that it's crude or inferior or even simple - it simply means that it is a trait inherited from a distant ancestor with little change. It's the opposite of "derived", not the opposite of "sophisticated".

An example in mammals: Human hands vs. horse hooves. A human hand is a lot more complex than a horse's hoof - but it's also *a lot* more primitive. The basic gross anatomy of a human hand really isn't that far off from the five-toed forefoot of our distant tetrapod ancestors. A lot of the fine anatomy has changed, but the basic blueprint is strikingly similar.

The horse hoof, in contrast, is much more specialized! There is really nothing on any 300-million-year-old fossil that looks anything like a horse's hoof. Horses had five-toed ancestors, but as they adapted to being specialized grassland runners, they progressively shed unneeded complexity until they ended up with just one toe per leg. They even have tiny, vestigial remnants of side toes.

In fact, a human hand is more primitive than the hands of a *frog*. Frogs have only four digits, and a single forearm bone. But this is derived: Frogs and humans have a common ancestor with five digits and two forearm bones, and at some point after our lineages split, amphibians lost one digit on each hand, and fused their two forearm bones into one. These are derived adaptations because frog forelimbs are very highly specialized for shock absorption, and it turns out a simplified gross anatomy works really well for that.

So when I say that some tuatara trait is "primitive", I don't necessarily mean "crude" or "simple" or "shitty" - I mean that it's something tuataras share with their very distant ancestors, some of whom are also *our* very distant ancestors.

It just turns out tuataras have a lot of that kind of traits.