Ancyra - Canon 16

Let those who have been or who are guilty of bestial lusts, if they have sinned while under twenty years of age, be prostrators fifteen years, and afterwards communicate in prayers; then, having passed five years in this communion, let them have a share in the oblation.  But let their life as prostrators be examined, and so let them receive indulgence; and if any have been insatiable in their crimes, then let their time of prostration be prolonged.  And if any who have passed this age and had wives, have fallen into this sin, let them be prostrators twenty-five years, and then communicate in prayers; and, after they have been five years in the communion of prayers, let them share the oblation.  And if any married men of more than fifty years of age have so sinned, let them be admitted to communion only at the point of death.

There were those who at some point had engaged in bestiality. Those teenagers that did so in the thralls of raging hormones were to be held back from full fellowship for twenty years.  If the person was more mature, the time was thirty years.  Lastly, if over fifty years, no communion was allowed until death was imminent.  During these probationary periods, penance could be shortened or elongated based on their conduct in relation to their past sinful practice.  Clearly, this sin was considered more grievous than any of the aforementioned worship of false gods, probably because it struck at the heart of something that should obviously separate Christians from pagans.