Vestigial organ in man is

$A$ : Lycaenops is a connecting link between reptiles and mammals.
$R$ : In permian period there was origin of mammal like reptiles.

In the developmental history of mammalian heart, it is observed that it passes through a two-chambered fish-like heart, three-chambered frog-like heart and finally four-chambered stage. To which hypothesis can this above cited statement be approximated