Torosaurus latus: Triceratops or Not?
Size: Roughly 25 feet (8 meters) long.
Time Period: The Maastrichtian Stage of the Late Cretaceous Period. This animal was one of the last of the ceratopsids, and one of the last dinosaurs in general.
Locale: The Javelina, Frenchman, Lance, and Hell Creek Formations, all found in the western United States of America.
Name: The generic name means “Perforated lizard,” in reference to the holes (fenestrae) in the animal’s frill. Though most people assume that the name means “Bull lizard (from the Latin noun Taurus),” such a meaning would entail a spelling such as “Taurusaurus” or “Taurosaurus,” the name is probably derived from the Greek verb toreo, which means “to perforate.” A lot of the confusion about the meaning of the name has to do with the fact that Othniel Charles Marsh (the original describer) wasn’t specific about the origin of the name.
Triceratops, one of the most famous dinosaurs, was a common animal in its time and place, and outclasses all Maastrichtian ceratopsids in range, population, and (of course) popularity. Animals like Anchiceratops, Arrhinoceratops, and Torosaurus were way more common, but still important. Anyway, Torosaurus was a very large ceratopsid discovered in 1891, two years after the initial discovery of Triceratops. It, unlike Triceratops and like most other known chasmosaurines, possessed a very long frill that had two large holes (also called fenestrae), which had no use in defense and was probably used for courtship displays.
Aside from being really flashy and cool-looking (probably the reason why Torosaurus was in Walking With Dinosaurs instead of Triceratops), there is a major controversy surrounding Torosaurus and its phylogeny. Since its discovery, Torosaurus has been recovered as a very derived member of the tribe Triceratopsini, and was most closely related to Eotriceratops and Triceratops. This pattern was shattered in 2010, when a histological study indicated that Torosaurus may have simply been the mature form of Triceratops. Jack Horner noted that ceratopsian skulls consist of a kind of bone that may lengthen or shorten over time, and may change from one shape to another over time. Part of the reassignment of Torosaurus is confusing, considering how much variety is seen in Triceratops skulls (which have historically been assigned to many genuses and species). Horner observed that roughly half of all known subadult Triceratops specimens possessed two thin areas in the frill that may have corresponded with the placement of the holes (FENESTRAE!!) in a Torosaurus’s frill. This might suggest that the holes developed to lighten the load of the skull as the animal (and its colossal frill) grew.
Other researchers are less sure about this idea than Horner and Scanella. I personally think that the supposed status of Torosaurus doesn’t explain some crucial facts, such as the extremely uncommon nature of Torosaurus remains relative to those of Triceratops. It’s also asserted that distinct juvenile specimens of Torosaurus were found in the Javelina Formation of Texas. These animals have been strongly identified as Torosaurus. In Triceratops, the thin areas of the frill actually differed in shape and position from the holes (fenestrae) found in the frills of Torosaurus. A 2011 analysis by Andrew Farke also noted that the development of Triceratops into Torosaurus would require unusual bone development and the unprecedented establishment of holes (fenestrae) in the frill late in the animal’s life.
In short, Torosaurus has sometimes been classified as an adult specimen of Triceratops. Even if this were true, the genus Triceratops would be valid (not ‘dead’ as discussed by the media in 2010), having been discovered 2 years prior to Torosaurus. Considering that the analyses of Andrew Farke in 2011 and of Nicholas Longrich in 2012 present data that outweighs the 2010 hypothesis, I’m going to assume that Torosaurus and Triceratops are distinct (though related) forms and leave it at that.
(I hope you forgive me for my copious use of the term fenestrae, incidentally.)