Yes, TUATARAS is a Scrabble word!

Letter values in Scrabble US: T 1, U 1, A 1, T 1, A 1, R 1, A 1, S 1.

Is it a valid word?

TUATARAS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

only extant member of the order Rhynchocephalia of large spiny lizard-like diapsid reptiles of coastal islands off New Zealand

Also: sphenodon punctatum.