Hopefully someone else can find more context in the paper on left-to-right vs right-to-left sequencing (or animal-facing-direction or towards-the-head(?)-of-the-animal or ? sequencing).

The most relevant quote in the paper I could find is

>Figure 4 presents the position of <Y> in sequences, by analytical taxa. To determine the position of <Y>, we assumed that sequences were oriented in the same way as their associated animal depictions, i.e. with the animal the right way up.

But I don't see how to get a directionality from that quote.