Pachycephalosaur head butting

Pachy fight52Despite my interests in dinosaur behaviour I have rather managed to avoid the question of pachycephalosaurs so far and with a couple of nice photos on cue it seemed a good time to discuss this at least superficially. I don’t think this clade has actually even been mentioned here at any point so this is longer overdue.

Since I try to cover even the basics of archosaur palaeontology on here I should probably give a bit of background to these bone heads (as they are occasionally know – the literal translation of the name being thick headed reptiles). Pachycephalosaurs are a group of ornithischian dinosaurs closely allied to the ceratopsians (the horned dinosaurs) and with them make up the large and important clade the Marginocephalae. They were herbivorous bipeds that only spanned a relatively small range of sizes from small to medium (compared to many of their relatives) with the largest genus, Pachycephalosaurus, being up to around 5 m long.

Pachy2Obviously their most prominent characteristic is the massively thickened skull roof and the occasional fringe of spines and knobs that run around the crown of the skull. What these were actually used for has long been contested with the most obvious suggestion being that these were used to fight with, either with each other or to attack other animals (like predators). Evidence has gone backwards and forwards over this with papers saying the head could not have absorbed impacts of fighting, or could have done, that they would clash heads or would not and would target flanks and that these were ornamental or not. In short, the only real consensus is that there is no real consensus as yet.

This may come as a surprise as despite the obvious controversial nature of many questions in palaeontology many are at least close to a consensus or the evidence has started to tip decisively but here this is not really the case. Part of the problem is likely to be the sparsity of material – pachycephalosaurs are not known from many good specimens at all (half a dozen are known from only skulls, partial skulls, or just the domes) and some aspects of their anatomy are thus not well understood. Combined with the relative lack of interest in this clade (since almost everyone seems to prefer theropods) it is perhaps less of a surprise.

Pachy0532The lack of material in Europe especially and the fact that the group is not half as well known as the ‘classics’ like tyrannosaurs and ceratopsians, and their relative small size means that they rarely make it into dinosaur halls outside North America so I was pleased to see two different displays of them in Japan – the first time I’d actually seen any. At the top we have a butting pair from Tokyo and below the front/side and back of a skull from Fukui (both images used with permission). I hope more research goes into this area as it is genuinely fascinating and covers various aspects of mechanics, ecology and behaviour that integrate well and of course the application of data and studies from living animals would be especially useful.

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19 Responses to “Pachycephalosaur head butting”


  1. 1 Tor Bertin 21/08/2009 at 2:31 pm

    http://www.rmdrc.com/exhibits/exhibits.html

    Had a chance to talk to these guys on some field work I did with them earlier this summer–turns out they’ve got the first partial Pachycephalosaur skeleton ever discovered in their collections.

    Very neat.

  2. 2 Richard 21/08/2009 at 9:28 pm

    Tor: that can’t be quite true, seeing as partial postcrania are known for Wannanosaurus, Goyocephale, Homalocephale, Prenocephale and Stegoceras. Perhaps you mean “first partial Pachycephalosaurus skeleton”?

  3. 3 Tor Bertin 21/08/2009 at 10:11 pm

    Yes! Sorry about that, was half asleep when I wrote it. Good catch!

  4. 4 Michael 22/08/2009 at 2:01 am

    I’m really not sure what pachycephalosaurs were doing with those heads, but I find the “only for visual display” hypothesis a bit hard to swallow. I just don’t think that an animal walks around with 10 inches of solid bone in its skull just to show off to the ladies! I feel a structure such as a ceratopsian frill would be far more suited for that. They were using their heads actively, but for what? That is the question.

    Of course, this is all just my own personal, irrevelent, idiosyncratic opinion, but I thought I’d mention it anyway.

    Nice post Dave! :-)

    • 5 David Hone 22/08/2009 at 9:08 am

      Well I would *largely* agree with you, but the truth of course is that evolution throws up some incredible oddities from time to time. If females liked big heads then males will develop big heads, no matter how useless they may be for anything else (look at Asian elephants for example as Darren recently covered on Tet Zoo). Do not underestimate that power of selection to be really odd, though personally I do think they were likely fighting in some way, but I also think display plays a part in this. I have a paper in review that deals partly with this, so I’ll keep quiet on the details for now if that’s OK.

  5. 7 Tor Bertin 22/08/2009 at 3:11 am

    At least for Pachycephalosaurus, I’ve always liked the flank butting hypothesis–mostly just because of the tiny impact surface of the skull. From what I’ve seen of the post-cranial skeletal (admittedly in photos–haven’t had a chance to head to Colorado), its neck doesn’t lend itself to a harsh direct impact too well either.

    But head butting or not, it’s an awesome animal!

  6. 8 Tor Bertin 22/08/2009 at 3:12 am

    *Post cranial skeletal material. Should proofread first. ;-)

  7. 9 Dave B 25/08/2009 at 12:05 am

    The pachycephalosaurs definitely need more love in the popular press! I got to hold a piece of the head dome last year, and to my amateur hands it seemed like the original bone would have been really dense! I was quite impressed.

    I, too, find it hard to believe that an animal with such an impressive noggin wouldn’t find a use for it – even if all the she-pachys just liked men with thick skulls, wouldn’t those boneheads find some use for their natural endowments? Isn’t that what evolution is all about – co-opting existing structures for novel purposes?

    PS: Will said paper be available for enthusiasts like myself to download and read?

    • 10 David Hone 25/08/2009 at 8:12 pm

      All my papers are accessible in the you just have to ask and I’ll send out a copy of anyhting requested. But it has onlyjust gone for review so don’t expect it to be coming out for, well, probably anyhting up to 18 months at least.

      And yes a lot of evolution is about co-opting structures, but that does not mean they always *are* co-opted. You have to show that rather than assume it and really there is noting quite like these domes out there to act as an analogue (though some artiodactyls and some teleosts come close).

  8. 11 Zach Miller 26/08/2009 at 1:52 am

    Pachycephalosaurs definately don’t get the coverage they deserve, although the scarcity of good material is partially to blame. Have you seen Sereno’s new tiny bonehead, Mycocephalae? I don’t think it’s been formally announced, but HE announced it in a British video about pachycephalosaurs…you can see it here, at Ville’s blog.

    Cute little guy!

  9. 12 kattato Garu 01/05/2012 at 9:29 pm

    Hey – did your paper on the Pachycephalosaurs get published?
    Time for a headbutting revival – head on to Love in the Time of Chasmosaurs…

    • 13 David Hone 01/05/2012 at 9:47 pm

      If the ‘your’ is aimed at me then yes, it was the mutual sexual selection paper which did indeed (if very briefly) cover pachycepahlosaurs but obviously far more generally dealt with issues of selection and mate choice and functionality of such structures.

  10. 14 kattato Garu 02/05/2012 at 1:48 pm

    Ah thanks David. I now remember reading it at the time.


  1. 1 The other side of the Marginocephalae « Dave Hone’s Archosaur Musings Trackback on 23/08/2009 at 10:46 am
  2. 2 Weekly Wonders: Ulemosaurus « The Theatrical Tanystropheus Trackback on 27/01/2010 at 8:44 am
  3. 3 Guest post: when pachycephalosaurs attack. « Dave Hone's Archosaur Musings Trackback on 16/07/2011 at 11:38 pm
  4. 4 Pachycephalosaur heads « Dave Hone's Archosaur Musings Trackback on 10/12/2011 at 9:42 am
  5. 5 Butting Heads Over Skull Injuries and Dinosaur Head-Butts – Phenomena: Not Exactly Rocket Science Trackback on 19/07/2013 at 2:00 pm

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