This is a two voice part, the note G in the upper voice is actually a double whole note (or a "brevis"- breve am.) of 8 beats. In a 4/4 measure it can't be notated otherwise than 2 tied whole notes. The second voice is containing 2 whole notes (semi brevis) each of 4 beats.
In music, a double whole note (American), breve (international), or double note (Baker 1895, 133; Burrowes 1874, 41) is a note lasting two times as long as a whole note (or semibreve). ... In "perfect" rhythmic mode, the brevis was a third of a longa, or in "imperfect" mode, half a longa (Hoppin 1978,).
So they obviously have to be played on the first beat of the measure - otherwise they wouldn't fit together in two bars.
Two voices and chords with intervals of second (as well the intervals of unison) can't be notated in such a narrow system without apparent "overlapping" it seems to be also evident and has been explained elsewhere:
this picture may demonstrate it: (regarding the unison and the seconds)
(when there are half notes or shorter ones, in unison the note head of both voices can be merged in one head in seconds the heads will look in different directions when the are added at one same stem, while when used two stems the upper voice is notated on the left side stem up - and the lower voice looks to the right side, whereby the stems can be stuck or not be stuck.)