Torosaurus latus, T. utahensis

By Jack Wood on @thewoodparable

PLEASE support us on Patreon! We really do need all of your support to keep this blog running - any amount helps!

Name: Torosaurus latus, Torosaurus utahensis

Name Meaning; Bull Reptile

First Described: 1891

Described By: Marsh

Classification: Dinosauria, Ornithischia, Genasauria, Neornithischia, Cerapoda, Marginocephalia, Ceratopsia, Neoceratopsia, Coronosauria, Ceratopsoidea, Ceratopsidae, Chasmosaurinae, Triceratopsini

Torosaurus is a somewhat controversial genus of Ceratopsian from various formations in the Northwestern United States and Southern Canada, including the Lance Formation, the Hell Creek Formation, and others. It lived in the latest part of the Cretaceous, about 68 to 66 million years ago, in the Maastrichtian age. It was about 7.9 to 9 meters long and had one of the largest Ceratopsian skulls, with a distinctively long, smooth and rounded frill without notable osteoderms. It had very long brow horns and a short nose horn, and holes in its frill that may have been used for display with different colors or patterns. It’s remains were fairly variable, with the brow horns curving in different ways or not even curving at all, and the frill occasionally curving as well. All specimens of Torosaurus, however, are identical to Triceratops in every way, except for the frill - though Torosaurus lack long nasal horns, plenty of Triceratops also lack this feature. 

By José Carlos Cortés on @ryuukibart

So, what is the controversy? 

Torosaurus may be an adult form of Triceratops - or, at least, an old-adult form. First things first: if that is true, Triceratops isn’t dead - it was named first, so Torosaurus would no longer be it’s own genus, and would be called Triceratops. So what’s the evidence for and against? 

- The hypothesis is that, since dinosaurs didn’t reach full skeletal maturity until late in life, the “Torosaurus” morphotype for Triceratops would have only been found in some older individuals, rather than in typical adults. Since Triceratops has similarities to juvenile Ceratopsians, including it’s shorter frill, and given that Ceratopsians and other Marginocephalians (like Pachycephalosaurus) changed a lot as they grew, it seems reasonable that growing such a noticeably large frill would be a later stage in Triceratops growth. 

- However, this hypothesis is far from proven. It has been pointed out that the differences in the frill between Torosaurus and Triceratops are not ones that typically happen during the growth of Ceratopsians - Triceratops would have needed to change a lot late in life. However, it is still not outside the realm of possibility, given the amount of change seen in the frill otherwise in Ceratopsians, and changes seen in other dinosaurs. Also, every specimen of Torosaurus seems to come from old individuals. 

By Nobu Tamura, CC BY 3.0

- Torosaurus seems to be mainly found from the older parts of the Hell Creek Formation - in the same parts, or older parts than, Triceratops horridus, but it is older than Triceratops prorsus. It has also been proposed that Triceratops horridus really is two separate species: the oldest Hell Creek species, and the younger one. This would indicate that the Torosaurus in Hell Creek may represent the adult form of early Triceratops, with later Triceratops keeping their short frills in adulthood. 

- The oldest known Torosaurus fossils are the least like Triceratops and do not overlap with Triceratops, however; in addition, Torosaurus utahensis lived much earlier than Torosaurus latus or any Triceratops, however, it is very poorly known and might not even be Torosaurus. 

In the end, this is an ongoing debate - and one of the most interesting ones in Nonavian dinosaur paleontology. It’s really a toss up, and more studies are needed. Histological studies to look at the individual growth ages of various Torosaurus and Triceratops specimens - Stratigraphical studies to look at the temporal ages of the specimens and their spaciotemporal overlap - and studies into how much change is really reasonable for bones to undergo late in life. I personally think that Torosaurus is, indeed, the “old morph” for Triceratops - but the jury is out, and I encourage all of you to make your own conclusions by looking at the sources below. 

Thanks to @fezraptor for helping me to summarize all of this (I’m not having a very good mental health day today). 

Sources:

https://en.wikipedia.org/wiki/Torosaurus

Farke, A. A. 2011. Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A. PLoS One: 6 (1): e16196.

Fowler, D. W., 2016. A new correlation of the Cretaceous formations of the Western Interior of the United States, I: Santonian-Maastrichtian formations and dinosaur biostratigraphy. PeerJ Preprints. 

Longrich, N. R., and D. J. Field. 2012. Torosaurus is not Triceratops: Ontogeny in Chasmosaurine Ceratopsids as a Case Study in Dinosaur Taxonomy. PLoS One 7(2): e32623. 

Maiorino, L., A. A. Farke, T. Kotsakis, and P. Piras. 2013. Is Torosaurus Triceratops? Geometric Morphometric Evidence of Late Maastrichtian Ceratopsid Dinosaurs. PLoS One 8(11): e81608.

Scannella, J. B., and J. R. Horner. 2010. Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny. Journal of Vertebrate Paleontology 30 (4): 1157-1168

Scannella, J. B., and J. R. Horner. 2011. ‘Nedoceratops’: An Example of a Transitional Morphology. PLoS One 6(12): e28705.

Shout out goes to @rainbowbuttocks!