Which of the fontalle is the last to close after birth
Ref. The Short Textbook of Pediatrics. Pg 550
 

Anterior fontanelle closes  around 10-18 months
Posterior fontanelle closes around 8 weeks
Persistent posterior fontanelles is earliest sign of hypothyroidism
Anterior fontanelle
Posterior fontanelle
Sphenoidal fontanelle
Mastoid fontanelle