Bless 'em; someone had the balls to admit to having no satisfactory explanation. Climate "Scientists" please note.

Could be a change in diet,more fish ?

I think on dienekes blog a paper showed that rounder heads had more brain capacity.Could increase in social competition require a more intelligent male ? Once social stabilty/order develops there is less need for intelligence and hence a change in head shape again.Or a change in employment eg fishing requires more spatial skills than farming ,increase in frontal lobe etc.Or a change in educational practice (men being educated differently,but not woman in both cases).??????

Or it could be a change in social status.Did the male heights also differ ?

"Or it could be a change in social status.Did the male heights also differ ? "

Good question about heights. But change in social status seems unlikely. The skeletons were apparently ordinary villagers - described as 'peasants'.

The 12th and 13th centuries in particular were periods of rising population, so there could have been pressures on food supplies, etc.

What about changes in whatever they wore on their heads when young? Early 20th century physical anthropologists assumed that the flat backs of heads found in some parts of the world were genetic, but later discovered that moms had strapped the infant's head to a board for convenience of carrying. See Carleton Coon's "Living Races of Man."

I always assumed my head was a product of my ancestor's hybridization with HR Giger's aliens. When predator eventually wiped them out the only remaining evidence was the shape of our heads and our bad breath.

Has anyone looked into the the way they took care of their infants? Putting them to sleep on their backs or their sides makes a big difference in head shape.

The 12th and 13th centuries in particular were periods of rising population, so there could have been pressures on food supplies, etc.

prolly less supply than the type of food. after the black death there was a lot more protein in the diet for a while until populations bounced back to pre-black death levels (which took centuries).

I suspect there's too little evidence to decide, but my imagination prompts me to believe that this is what a "founder effect" would look like, and that because it wasn't isolated from the larger population, it was lost in all the "interbreeding".

Feel free to correct my wording or refute my image.

Time span seems too short for selection to be at work (absent dramatic events that would have left a historical record). Diet does seem like the likely explanation. Could readily imagine that some technological advance allowed for a better diet for a while, followed by a regression when the population increased to the point where diet became bad again.