convert tool has a no-option, very simple way to access the first frame of an animated gif.
convert 'animated.gif' animated.first.gif
The square brackets after the file name above can contain any index for any frame of the image.
0 is the index of the first image.
To discover how many frames an animated gif has you can use:
Which will return a line for every frame in the animated gif. Those lines will look like this:
animated.gif GIF 736x521 756x594+4+70 8-bit sRGB 256c 421707B 0.000u 0:00.000