Eotriceratops xerinsularis

It sort of makes me mad that this is the only picture of Eotriceratops making the rounds on the web right now. It's a horrible picture, and clearly a sculpture rather than the actual fossil. I want to see the bones, dammit! But look at the size of that monster! E. xerinsularis was just published last week in the Canadian Journal of Earth Sciences, and its authors suggest that it belongs in a group including Triceratops, Torosaurus, and Diceratops. Eotriceratops is known from deposits significantly older than those ceratopsids, though. Its head is apparently the size of a European SmartCar, and is quite a bit larger than typical Triceratops skulls. What shocks me about the skull is that, despite its ridiculous absolute size (which approaches the current record-holders, Pentaceratops and Torosaurus), the proportions of the skull are similar to those of Triceratops. It's as if Eotriceratops is a scaled-up Triceratops.

Like every other well-known ceratopsid, Eotriceratops' diagnostic characters are in its head, and its unique bones include the premaxilla, nasal horn core, squamosal, and epijugal. Seeing as there are obvious similarities between Eotriceratops and Triceratops, one wonder what the former can tell us about that most problematic of ceratopsine taxons, Diceratops. That misnamed genus was named by Lull in 1905 on the basis of a basically complete, but poorly preserved, single skull. While originally named Diceratops, the animal eventually fell under the Triceratops moniker, ironically, by Lull in 1933. What made Diceratops distinct at all? It has small holes in its frill--features that are present in all other ceratopsians, but not in Triceratops.

By the by, the lack of fenestrae in Triceratops' frill is generally considered an automorphy of that genus. Although the frill's small, rounded construction brings to mind the centrosaurines, the rest of Triceratops' skull is clearly of ceratopsine affinities. Given its close relatives--Torosaurus, Arrhinoceratops, and Pentaceratops, the small, rounded frill of Triceratops is a bit of a puzzle. Yet even juveniles are fenestrae-less, so the Triceratops' frill is a very distinct feature.

At any rate, Diceratops' frill has small holes behind the horn cores, and, oddly, one more just behind each postorbital fenestrae. Lull attributed these holes to either pathology or injury, suggesting that 'Diceratops' merely represented an old individual of Triceratops. Other more minor oddities of Diceratops include nearly vertically-oriented orbital horn cores, a rounded nasal horn core, and a proportionately shorter snout than most Triceratops specimens. Of course, Triceratops itself shows incredible individual diversity, as more than a dozen species were once recognized, all based on minor individual variations. That number has now been knocked down to just two species (and even these may be the result of sexual dimorphism): T. horridus and T. prorsus.

Since Lull's 1933 suggestion, Diceratops' true relationships have continued to provide debate. It has been called a sister species to Triceratops, an ancestral species (or genus) of Triceratops, or an old/injured Triceratops. In his extremely informative summary of the Ceratopsia, The Horned Dinosaurs, Peter Dodson declined to say for sure whether Diceratops was a distinct taxon or not, but since that 1996 tome, I have continued to see Diceratops treated as a unique genus in ceratopsian literature, and I wonder if Eotriceratops will illuminate its taxonomic position at all.

Many thanks to Jerry and Louis for sending me a copy of Eotriceratops' description. Now I'll be able to answser my own question (hopefully!). If any of you readers would like a copy, feel free to email me, and I can send it along.