Torosaurus genus to be reclassified Triceratops. – [Retrospective Post]

2/3/2012 – A New Article has been published in the Journal PLoS ONE which refutes the claim that Torosaurus is Triceratops, well worth a read if you’re interested in this: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032623

Triceratops prorsus

Image via Wikipedia

John Scannella and Jack Horner, two researchers at the Museum of the Rockies, Montana have recently published a paper in the Journal of Vertebrate Paleontology entitled “Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny” which has caused a firestorm in the internet community thanks to the mainstream media headline writers not reading the articles they are headlining. We must forgive them however as they are out to sell papers and make money, not tell the truth!

The paper argues that the two genuses (Torosaurus and Triceratops) which have been separate entities for over a century are in fact the juvenile and adult growth stages of the same taxon – but why?

The discovery centres around the study of over 50 specimens of the two genuses and both macro-scale comparative anatomy and micro-scale histology (study of the bone structure) of the skulls of the animals.

The big hitting piece (or should that be most obvious) of evidence is the hypothesised opening up of the parietal fenestre found in Torosaurus which are not included in the usual image of Triceratops with a short, solid shield. The parietal fenestre are the holes visible in the shield at the back of the head. On closer examination, many of the available Triceratops specimens showed signs of an incipient fenestre forming initially at the margin of the shield and then “migrating” toward their later place in Torosaurus as the shield grew around them, the shape of the thinned region being near circular and expanding with growth.

Proposed Ontological sequence from Triceratops (a-i) through to Torosaurus (j,k) scale bars 10cm

Proposed Ontological sequence from Triceratops (a-i) through to Torosaurus (j,k) scale bars 10cm (from fig. 3 of Scannella & Horner, 2010)

Other evidence that bolsters the researchers’ hypothesis includes the fact that up until this point, no juvenile, or even infantile skulls of Torosaurus have been confirmed. Inclusion of the Triceratops juveniles and the proposed growth sequence does accommodate this observation.

What are the implications of this research? well first off this isn’t the first case of an ontogenic synonymy (two or more species being found to be one), not even within the one formation from which Triceratops is known, with a citation in the paper for another article by Horner and others regarding other Hell Creek Formation dinosaurs. (unfortunately I couldn’t find an online copy so cannot give details).

The research also means that there is more support for a decline in the diversity of the dinosauria in the mid to late cretaceous, as there is now one less species surviving to the end of the cretaceous and coming face to face with the dinosaur’s bolide nemesis.

What this article does illustrate though is how careful palaeontologists have to be when it comes to their research, as we only have the fossils or trace fossils to work with, and because of the extreme rarity of fossilisation we cannot be guaranteed a complete ontological sequence of skeletons. When this is combines with events such as the great bone rush (both Torosaurus and Triceratops were described by O.C. Marsh during this time.) it can be easy to pidgeon hole specimens to such an extent that you end up splitting one into two!

As to the name change, because Torosaurus was named two years after Triceratops and taxonomy is done according to the Linnean system, the first name is kept. Hence Triceratops gets to live on, while Torosaurus is no longer a valid genus name.

This Story Features in  PalaeoNews : Webisode 1 (28th July – 3rd Aug)

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