Newborns and infants can open their mouths naturally (ie yawn, etc) but the presence of the extrusion reflex brings the tongue forward in the infants mouth to facilitate latch. When this reflex occurs the jaw also lowers further to support a nice, wide gape. This is why, when we consider the tongue function in context of tongue tie rule out we observe the degree to which the anterior tongue comes forward. I also train my eye to watch the jaw in this process.
The extrusion reflex of the tongue is suppressed around 4 months of age and serves as one of the readiness cues for spoon feeding. It’s suppression allows the jaw and tongue to remain in a more neutral position as the food in introduced with (less and quickly resolved) thrust pattern.