What is an epicorus?

A kosher cow has 2 simanim. According to Oruch Hashulkhan YD 135.
Shmuel says he saw a shisua (siamese? ) cow, which cannot live more than a year, according to Rav. Shmuel assured that the shisua cow lived for more than 14 months.

Tora Tmima, in Re'e, ignoring Shmuel, says, "we (or he) are not sure what we're seeing"

Toro Tmima is a great authority, but anyone else who says that THEY did not know what that means is a good candidate for an epicorus.