Yarrr, We Need To Talk About Pirates

TD;LR I didn’t like this article about pirates, because it wasn’t actually about pirates, so I wrote a blogpost three times as long as the actual article to tell you all about it.

I came across an article earlier this week via the Twittersphere: The Significance of Bone Mineral Density in the Depiction of Memento Mori in the Journal of Bone and Mineral Research – a Letter to the Editor by O’Keeffe, et al.

You can read the abstract at the above link. While it doesn’t actually set out the argument of their letter – it basically says: there’s a pirate cemetery on a island near Madagascar with ‘skull and crossbones’ iconography on tombs that is reminiscent of the ‘Jolly Roger’ flag – it was enough, along with the title, to pique my interest.

Something you may know about me: I am a human osteologist, currently studying the plague and associated funerary practices in the medieval period.

Something you may not know about me: I spent no less than six months writing and delivering a museum tour titled ‘Pirates: The Myth vs. The Reality’.*

This article was written for me to review it. Unfortunately, for the authors.**

EvilLaughWhen I went to access the full paper, which is… one page, I had every intention of providing a serious summary and interpretation of the results. However, I am afraid that I just cannot do that. Maybe one day I’ll make this into the proper academic blog it was always supposed to be.

Here is the gist of the letter (if you can get access, I recommend reading the full thing, it won’t take very long):

There is a supposed pirate cemetery on Ile Saint Marie, off the coast of Madagascar, that has “unique” tombs depicting the infamous ‘skull and crossbones’ iconography, which became the “universal symbol of piracy” via the Jolly Roger flags. The authors questioned why these particular bones became the symbol of piracy “and indeed death”. This prompted them to “review the academic literature to establish if there was any scientific reasoning behind the longevity of these bones”.

The authors go on to note that the skull and crossbones symbol exists beyond its use in piracy and is found all over the world and in many different periods – especially since the medieval period. Following this there are two short paragraphs that discuss the differences in bone mineralisation in various skeletal elements. Essentially, long bones (femur, tibia, humerus, etc) and the skull are mainly comprised of cortical bone (more solid) meaning they are more mineralised than other bones (vertebrae, ribs, sternum, etc), which include more cancellous bone (more spongy).

The letter wraps up with the authors suggesting that the higher mineralisation content of the long bones and skull would result in their surviving longer than other bones post-burial. In conclusion, these particular bones would become “the most visually potent reminder of our mortality”, leading to their use as a memento mori symbol.

I have so many issues with this article. First and foremost, look I know it’s a Letter to the Editor, but when someone says they are going to “review the academic literature” I expect them to cite more than FIVE academic papers (four of which are more than fifteen years old). Especially when I know there are some really good papers out there that specifically discuss the differential preservation of human skeletal remains.

HeadDeskSo, you know, aside from that. Then there’s the whole… pirate thing. We seriously need to talk about pirates. I know they make for a great hook, but they have LITERALLY NOTHING TO DO WITH THIS PAPER. This article actually proposes two questions, but only seeks to address the answer to one (I’m not going to give them credit in saying they answer it, because I don’t think they do). In the order they are presented in the introduction:

  • Why did the skull and crossbones become the universal symbol of piracy?
  • Is the prominence of the skull and crossbones as a symbol due to the preferential preservation of these bones?

I can answer question number one for you. It didn’t. This is a cliché. While yes, ‘Jolly Roger’ flags often do include the skull and crossbones iconography – they also include a lot of other symbols as well: entire skeletons, blood, hearts, spears, swords, hourglasses, etc. Each pirate had their own flag design. Some used the skull and crossbones, some didn’t.

Some examples of 'Jolly Roger' flags. From the Wikipedia article on: Jolly Roger. WIKIPEDIA!

Some examples of ‘Jolly Roger’ flags. From the Wikipedia article on: Jolly Roger. WIKIPEDIA!

However, even if we take the stance, that okay – the skull and crossbones seems to crop up a lot around pirates, pirates still have nothing to do with this paper, because the authors never address it again after the introduction. Never. This article is all about question number two.

But that doesn’t mean I’m going to stop talking about pirates.

I have to mention the ‘pirate graveyard’. Yes, the Ile Saint Marie was home to a lot of pirates back in the day. Yes, there is a cemetery on the Ile Saint Marie. Yes, there are probably some pirates buried in this cemetery. No, the skull and crossbones depictions on the tombs there are not “unique” – and it has nothing to do with pirates. This symbol is there because, as the authors note in their letter, it is incredibly ubiquitous, especially as a memento mori – and therefore you will see this symbol all over graveyards, tombstones, memorials, etc.

In addition, I can find evidence of exactly ONE instance of the skull and crossbones symbol in this cemetery (while this is from an admittedly quick search, it appears to be more than the authors conducted). It is on the tombstone of a French merchant who died in Ile Saint Marie in the early 19th century (link in French).

Skull. Crossbones. Umm...

Skull and crossbones and umm…

Not a pirate. I have no idea why this ‘pirate graveyard’ is in this paper. LITERALLY NO IDEA. What does it have to do with anything?


Back to the science bit about the differential bone preservation. The authors probably aren’t wrong in their suggestion that the long bones and the skull, with a higher mineral content and composition of cortical bone, are somewhat better preserved than other bones post-burial. However, I’d have liked to see them back it up with, you know, evidence.


This table (from Stojanowski et al.) shows the average preservation scores (API) from a modern reference sample. The correlation between the average weight of the skeletal element and the preservation was significant. This indicated the lighter elements (more cancellous bone) were less well preserved than the heavier bones (more cortical bone). This study also showed differential preservation within single elements, to account for varying degrees of bone density in different skeletal features. It’s a good paper. Go read it. Either way, even if you don’t, we can probably agree that the people who wrote this letter probably should have, eh?

The letter also briefly touches on taphonomy (the study of the processes that affect remains after death, especially decomposition and demineralisation)… in so far as mentioning it exists. But if you’re talking about skeletal preservation you SERIOUSLY need to address this topic. In human osteology and zooarchaeology (because animals have bones too, so their studies are useful here) there are a great deal of articles and books and blogs available on taphonomy and how it impacts skeletal preservation. It’s not hard to find them.


If the skull and crossbones symbol did originate in some way, shape, or form because of the preferential preservation of these skeletal elements and therefore an increased familiarity with them, neat. I remain to be convinced, because although these skeletal elements may be better preserved, I’m not sure it’s a significant enough difference – if you still have a recognisable skull and long bones, you still potentially have other recognisable bones too. There is also the added complicated matter of aesthetics, religion, anatomical knowledge, funerary rites, and oh so much more.

Ignoring the reasons for their creation in the first place, the reasons for the rise of certain symbolism over others is complicated. It’s not made very clear in the letter, but the skull and crossbones symbol is only one type of memento mori. It appears as early as the 14th century, sees a rise in the 15th century, and is firmly established in the lineage that led to its use in piracy in the post-Reformation period. ***

The relationship of the living to skeletonised remains at this time goes through a dramatic shift and you see a huge increase in the use of this type of imagery. In addition to the skull and crossbones there is a lot of other iconography out there, much of it that includes skeletal elements other than the skull, femurs, and tibiae.

The Danse Macabre - one of many.

The Danse Macabre – one of many.

I’m not sure whether the skull and crossbones in the most prevalent of these. But let’s just say it is, for the sake of going somewhere with this whole post. The question then becomes why this particular symbol and not the others? I’m not sure that it has anything to do with differential skeletal preservation.

And it certainly has nothing to do with pirates.


*at the risk of my credibility: sometimes in costume

**Look, I have nothing against the authors, but if you’re going to publish something (says the academic who’s never published something) maybe do your freaking homework?

***although I am sure some of you can name-drop earlier ones in the comments

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