A two new horned dinos kind of day!

Although my work now is primarily on pterosaurs, I will always have a soft spot in my heart for ceratopsians after doing my (failed) work on Centrosaurus as an undergrad. So imagine my excitement when the most recent releases of new PLoS ONE papers included not one, but two new ceratopsids from the US! And in typical horned-dinosaur fashion, they are both awesomely weird.

The first one, Machairoceratops cronusi comes from the Middle Campanian of Utah. It’s known from skull fragments, including two orbital horns, a jugal, and portions of the parietosquamosal frill of a single individual, described by Lund et al. As is typical for ceratopsids, the unique feature of this animal is the frill which consists of two forward-facing, curved epiparietal bones, unlike the laterally-directed epiparietals of Diabloceratops, the other known ceratopsid from this formation. Also interesting is the complete lack of any other other epiossifications along any part of the frill. Ceratopsids often have a slightly scalloped look with a slightly wavy looking frill due to small bones that ossify to the lateral edges. However, Machairoceratops has a smooth frill edge. These features, especially the forward-facing epiparietals make for a very strange looking animal, as seen in the wonderful Mark Witton image below. This new species appears to sit at the bottom of the centrosaurine tree, one of the two groups of ceratopsids that includes Centrosaurus, Pachyrhinosaurus, and many more. It shows that even in early centrosaurine ceratopsids, the frill was highly diverse and a number of unique morphologies were present from early on. Machairoceratops also shows that we’re not anywhere near fully understanding the morphological diversity of ceratopsid frills, showing yet another completely new set up. What a weird new dude!

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A herd of Machairosaurus crossing a river. Image by Mark Witton.

 

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Bones known from the skull of Machairosaurus with an outline of the skull from Lund et al. (2016)

For ceratopsian number two, Mallon et al. introduce Spiclypeus shipporum (pronounced spick-LIP-ee-us according to Mallon), a chasmosaurine (rather than centrosaurine like Machairoceratops) ceratopsid. Spiclypeus comes from the Late Campanian Judith River Formation of Montana, a little younger than Machairoceratops, and is known from a partial skeleton including both cranial and postcranial remains. Like usual, it shows a unique combination of cranial features, with short nasal and orbital horns, and an elongate parietosquamosal frill with fused ossifications along the parietal, giving it the typical scalloped edge notedly absent in Machairoceratops. One thing I think is really cool is that Spiclypeus AKA Judith has some interesting pathologies on both the skull and the humerus. There is a hole in the squamosal that they attribute to some sort of combat, possibly from another Spiclypeus horncore. This wound must have become infected, later remodelling the bone. Another injury on the humerus shows sign of chronic infection, the cause of the infection is unclear, but could have been something like tuberculosis or a fungus. Whatever happened, this horned-dinosaur seemed to live a pretty painful life for the 10 years it was alive.

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Reconstructed skull of Spiclypeus from Mallon et al. (2016)

Two very cool new ceratopsians described in one day. Almost as good as two pterosaurs in one day! Congratulations to everyone involved!

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6 thoughts on “A two new horned dinos kind of day!

  1. Machairosaurus is cool looking, but is the new genus really warranted? I am admittedly no expert, but I personally would’ve named it as a new species of Diabloceratops. Not because I’m necessarily a lumper over a splitter, but this seems to fall into a similar range of variation compared to say, the 3 Pachyrhinosaurus species.

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    1. There are 2 significant differences in the frill between Machairosaurus and Diabloceratops – the anterior facing epiparietals, and the lack of an epiossifications on the parietal or squamosal. I think those are the two major things separating it from Diabloceratops. Of course you could maybe make the argument that the anteriorly-directed epiparietals were maybe some kind of taphonomic feature or maybe individual variation I suppose, but it’s not obviously the same as Diabloceratops. The lack of epiossifications could also just be taphonomic as much of the skull is missing.

      I suppose that the argument could be made that there isn’t really enough there to say for sure if it’s separate, but the present evidence does seem to separate it from Diabloceratops. Of course, people like naming new genera rather than species 🙂

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    2. The other thing to consider here is phylogeny. Generally speaking, it’s preferred that genera consist of only of species that form a single group with a close common ancestor (called a monophyletic group). Since the phylogenetic analysis performed for Machairoceratops did not recover such a relationship with Diabloceratops, erecting a new genus is justified. Of course, should a future analysis recover the two as sister taxa, you could make the case for them being the same genus, although it’s all pretty subjective at that level.

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