Wednesday, April 10, 2013

What's A Monoclonius?

Hypothetical restoration of an adult Monoclonius crassus,
by Matt Martyniuk. All rights reserved.

Monoclonius crassus is an iconic ceratopsian, a fixture of many 1970s era dinosaur books, which owes its status almost completely to another species. 

I grew up with depictions of Monoclonius in media like Phil Tippet's short film Prehistoric Beast and toys like the DinoRiders figure. Like most representations of Monoclonius in popular culture, these were based on specimens now classified as Centrosaurus apertus (though, actually, that DinoRider looks like it has a genuinely Monoclonius-type frill, long, straight, and unadorned). 

Originally known only from teeth and a fragmentary frill and nasal horn, the Monoclonius was one of the first ceratopsians known to science, found by E.D. Cope in 1876 and named for its configuration of tooth roots ("single sprout" as opposed to the "double sprout" of Diclonius, now known to pertain to a hadrosaur). 

Like many of Cope's species, Monoclonius was not recognized for what it really was (a "horned dinosaur") until more complete remains from other ceratopsians likeTriceratops were found by Cope's rival O.C. Marsh. Monoclonius itself remaned enigmatic for many years, though the idea of a Triceratops-like ceratopsian with a single large nasal horn was used by Charles R. Knight in his famous painting of Cope's other dubious ceratopsian, Agathaumas. Knight also incorporated spiny dermal armor associated with some supposed Monoclonius remains, though at least some of this material was later shown to belong to ankylosaurs and pachycephalosaurs.

Monoclonius became iconic when complete skeletons of ceratopsians were found in the Judith River/Dinosaur Park Formation of Montana/Alberta. In the early 1900s, C.H. Sternberg (who had co-discovered the orgiinal Monoclonius fossils with Cope) established that complete specimens classified by Lawrence Lambe as Centrosaurus apertus (and some of which were considered to be Monoclonius and which had already been used to form a picture of that animal) were a distinct species. After this, the genus Monoclonius was dismantled, with former specimens re-assigned to either new or recently established centrosaurine genera.

Matters were complicated by the discovery of the drastic changes centrosaurines went through as they grew, and today the distinctive Monoclonius specimens are generally considered juvenile centrosaurines. Zach Miller has done an awesome rendering of a centrosaurine growth series showing where a traditional "Monoclonius" specimen fits into the sequence. 
Skull of the subadult Monoclonius lowei. Note the three prominent projections at the rear of the
 parietal frill. Incipient styracosaur-like spikes?

However, known specimens of Monoclonius aren't a perfect match for juveniles of the contemporary Einiosaurus, as Miller notes. The long, generally flattened frill with larger incipient spikes at the first three positions of the the parietal (Ryan 2006) are reminiscant of Styracosaurus and Einiosaurus, all of about the same geological age. The large size of a specimen sometimes referred to the distinct species Monoclonius lowei compares with some pachyrhinosaurs like the contemporary Achelousaurus, and while these do begin life with a small nasal horn that later develops into a boss, and though it isn't backward-cureved, such drastic changes during ontogony are known in other ceratopsians. It may be that Monoclonius is a juvenile form of (and therefore a senior synonym of) one of these centrosaurines, or it may be a valid species similar to both, possibly a transitional form between centrosaurin-type centrosaurs and pachyrhinosaurs. Ironically, though long mixed up with that genus, Monoclonius doesn't seem to be as great a match for Centrosaurus itself.

In my restoration of a hypothetical, mature Monoclonius (above), I made it generally styracosaur-like, though with more einiosaur-like parietal spikes, and these could alternately be seen as styracosaur parietal spikes which are not yet fully grown. In this way I've tried to hedge my bets: this Monoclonius could either be a mature, intermediate stage between styracosaurs and einiosaurs, or simply an immature but very large styracosaur. 

The nasal horn is restored as styracosaur-like as well, a conservative growth trajectory for the shorter, recurved nose horn seen in subadult specimens of M. crassus and M. lowei. However, it's entirely possible that as the nasal horn grew, it swept forward into the hook-like horn of Einiosaurus or even flattened and thickened into the nasal boss seen in Achelousaurus. Both of those pachyrhinosaurs have long parietal spikes like Monoclonius seems to have had, though both only had a single pair jutting from the back of the frill, while Monoclonius seems to have been developing at least three. Though, again, it's possible the transformation was more extreme than I'm assuming for my illustration, and that these incipient parietal horns were resorbed during growth like the epiparietals of chasmosaurines (e.g. Triceratops).

Rather than the centrosaur-like Monoclonius of my childhood, it looks like this fairly plain-looking ceratopsian grew up into something a bit more spectacular. But we'll need further study and, hopefully, more specimens to find out exactly what, and exactly how extreme, that transformation may have been.

* Ryan, M.J. (2006). "The status of the problematic taxon Monoclonius (Ornithischia: Ceratopsidae) and the recognition of adult-sized dinosaur taxa.Geological Society of America Abstracts with Programs38(4): 62.


  1. beautiful art, great article. Thanks, Matt!

  2. Excellent write up Matt, and a lovely image.

  3. I too like the picture.

    I'm noticing a sudden increase in large Ceratopsian depictions with those dermal horns/spine/spikes. John Conway has done both his All Yesterdays Triceratops with these, and a Styracosaur on his website with similar augmentation.

    Is this based off the Blackhill Triceratops skin? Where does one get a reference of it, as as far as I can find it is still completely unpublished.

    I'm just assuming you guys all have a similar source as the spins are all similarly spaced.

    So in addition to being a loving rendering, my interest in this detail is rather piqued.

    1. Yes, the skin (specimen nicknamed "Lane") is still unpublished, but you can find some good pics online by searching different combinations of Lane Triceratops Skin. Photos will probably increase now that a cast of the skin is on display in a museum:

      A lot of people are also basing their Triceratops skin on that depicted in Dinosaur Revolution/Dinotasia. David Krentz has stated on the DML I think that he and his animation team actually laser scanned the Lane skin impressions and mapped it to their CGI model!

      The spiny bits are based on the fact that some of the larger scales have "nipple"-like projections. Someone (Bakker?) speculated in an article a few years ago that this could represent anchor points for Psittacosaur-like quills/feathers. However, feathers grow from follicles in the skin, not from scales or other large dermal structures, so I restore them as simply spiny scales with keratinous projections.

      If these do indeed represent the same kind of thing as Psittacosaur quills, it would seem to me to conclusively show those are not related to feathers. However, the quills in Psittacosaurus seem to anchor somewhere below the epidermis, not from the surface of the skin, o I doubt they have anything to do with the Triceratops integument at all.

    2. Cool thanks,

      Someone funny enough posted a pic of that cast on FB this morning, and made me feel bad for potentially wasting your time...

      Though I have to say I hope you consider it not wasted. As you've fleshed out and connected all I'd heard about the Tric skin, and this has been very helpful. Thank you.

      Interesting. Up till now I'd only been hearing the "nipples" were possible quill sites. I'd taken that to mean they represented preserved bases of the quills.

      Very interesting that they seem to represent something different.

      I was going to do a post on ART Evolved how I thought Conway was about to (despite all his awesome rants against) start a new palaeo-meme. As he just released a third spiney ceratopsian (another Triceratops, from a new angle).

      Having seen it now, that is really interesting. Definitely not what one would expect on a Ceratopsian (specifically the nipples)

    3. No problem! And yeah, everyone seems to have latched on to the "quill base" thing based on comments in news articles, but there seems to be no attempt to critically compare the two structures. The quills in Psittacosaurus are definitely not arising from the middle of large polygonal scales, as far as what has been published. If Triceratops did have quills, and if quills are similar to feathers, I think they'd have to emerge from spaces in between the scales, not from the scales themselves, unless we've got feather development wrong. I don't know if this would even be preserved in skin impression molds, especially if the quills fell out after death, Montauk Monster style.