Torosaurus

*Torosaurus* was first named upon the description of two partial skulls by Othniel Charles Marsh all the way back in‭ ‬1891, ‭ ‬two years after he had named the much more famous *Triceratops*.‭ ‬The most common mistake regarding the name *Torosaurus* is the meaning,‭ ‬with many people misquoting it as meaning‭ ‘‬bull lizard‭’ ‬after the Spanish word‭ ‘‬toro‭’ ‬which means bull.‭ ‬However,‭ ‬Spanish is not a commonly used language in establishing binomial names,‭ ‬and in the late nineteenth century the two most commonly used languages were Latin and particularly Ancient Greek.‭ ‬In this respect *Torosaurus* is based upon the Ancient Greek words‭ ‘‬toreo‭’‬,‭ ‬which means‭ ‘‬perforate‭’ ‬or‭ ‘‬to pierce‭’ ‬and‭ ‘‬sauros‭’ ‬which means‭ ‘‬lizard‭’‬.
*Torosaurus* was a large ceratopsian dinosaur that lived on the North American continent towards the end of the Cretaceous.‭ ‬Like with others of its kind,‭ *‬Torosaurus* was an herbivore cropping low growing vegetation and may have lived in social groups.‭ *‬Torosaurus* is noted for having one of the largest skulls of not just any dinosaur but any land animal.‭ ‬Most of this is physical length formed by the neck frill which grows out from the back of the skull,‭ ‬which covers the neck,‭ ‬but was almost certainly for display as opposed for defence.‭ ‬The defence theory is no longer thought to be a primary function given to save weight the bone of the frill was relatively thin and perforated‭ (‬clue is in the name‭!) ‬with large openings.‭ ‬However,‭ ‬new skulls attributed to the genera *Pentaceratops* and *Titanoceratops* seem to be even larger,‭ ‬suggesting that *Torosaurus* while large may not have had‭ ‘‬the‭’ ‬biggest skull.‭ ‬In addition to this a *Triceratops* skull measuring‭ ‬2.8‭ ‬meters long and nicknamed Lung Wong‭ (‬Dragon King‭) ‬is now known.
       Currently the only valid species of *Torosaurus* is the type species *T.‭ ‬latus*,‭ ‬though as we will see,‭ ‬this may in fact be synonymous with *Triceratops*.‭ ‬A former species *T.‭ ‬gladius* has now been ascertained to be

synonymous with the type species.‭ ‬Fossils originally attributed as a species of the genus *Arrhinoceratops*,‭ *‬A.‭ ‬utahensis*,‭ ‬have now been credited by some researchers as representing a species of *Torosaurus*.‭ ‬However again,‭ ‬the debate about synonymy with *Triceratops* has cast this in doubt.

## The *Triceratops*/*Torosaurus* synonymy debate

       Around‭ ‬2009-2010‭ ‬new study into the skulls of *Torosaurus* and *Triceratops* by John Scanella and John R.‭ ‬Horner‭ (‬better known as Jack Horner‭) ‬led to the idea that the skulls of *Torosaurus* were actually the fully mature forms of *Triceratops*.‭ ‬This would mean that *Torosaurus* was not only a synonym,‭ ‬but reconstructions of *Triceratops* for over a hundred years had been slightly wrong,‭ ‬with a neck frill far too short.‭ ‬At the time this was big news with most online news outlets and many printed newspapers covering the story,‭ ‬and many erroneously reporting that‭ ‘*‬Triceratops* never existed‭’‬,‭ ‬though if the theory were true then it would technically be the other way around given that *Triceratops* was named first.
       The theory is quite detailed but the finer points are this.‭ ‬Ceratopsian dinosaur bones are known to be composed of large amounts of metaplastic bone,‭ ‬and as an animal matures this metaplastic bone can change in both size and shape‭ (‬its why little baby ceratopsian dinosaurs have short stubby neck frills,‭ ‬they wouldn’t fit into the egg otherwise‭!)‬.‭ ‬Scanella and Horner noted that all the known specimens of *Torosaurus* were of very old and mature adults,‭ ‬while those of *Triceratops* were of sub adults and young adults. ‭ ‬They also noted that while known *Triceratops* skulls don’t have holes in the neck frill,‭ ‬they do have areas of thin bone.‭ ‬Their theory was that *Torosaurus* skulls represented the true adult form of fully mature *Triceratops*,‭ ‬with the thin areas of bone giving way to the holes that we see in *Torosaurus* neck frills.‭ ‬This also led to the phrase‭ ‘‬toromorph‭’ ‬to describe the *Torosaurus* skulls as fully mature *Triceratops* skulls.
       The theory was however was not perfect,‭ ‬and there were still some areas that were blank.‭ ‬First it’s that even after over a hundred years of study and dozens of skulls,‭ ‬no actual transitional form showing the change of a *Triceratops* skull to the toromorph form had been found.‭ ‬However in‭ ‬2007‭ ‬a‭ ‬ceratopsian dinosaur skull was used to establish a new ceratopsian genus called *Nedoceratops*.‭ ‬Scanella and Horner considered this skull to possibly be a missing transitional form given that it appeared to show the development of holes and reduction in nasal horn on an otherwise *Triceratops* skull.‭ ‬Scanella and Horner also addressed the issues of epoccipitals,‭ ‬the osteoderms that grow along the edges of the neck frill.‭ *‬Triceratops* skulls average around five epoccipitals with one centred along the midline of the skull.‭ *‬Torosaurus* however are noted for having ten to twelve epoccipitals with none centred on the midline.‭ ‬Scanella and Horner noted however that the number of epoccipitals in some *Triceratops* skulls does vary from the norm,‭ ‬and at least one has no midline epoccipital.‭ ‬Scanella and Horner also proposed that the epoccipitals in *Triceratops* may have each split in half allowing for a ten count as seen in some *Torosaurus*.
       Since their theory was published,‭ ‬other palaeontologists have not recognised the study as‭ ‬correct,‭ ‬and indeed some have even published counter studies to test this theory with the conclusion that *Torosaurus* skulls can’t be those of *Triceratops*.‭ ‬To start *Nedoceratops* was‭ ‬re-described in‭ ‬2011‭ ‬by Andrew Farke who noted that the holes in the *Nedoceratops* holotype were surrounded by thicker bone growths,‭ ‬leading him to conclude that the holes were a result of injury and/or disease with possible infection.‭ ‬Therefore according to this study,‭ ‬the holes in the *Nedoceratops* skull were not formed by the beginning of a new growth stage,‭ ‬and so it cannot be heralded as a transitional form.‭ ‬Since this Scanella and Horner have conceded that the *Nedoceratops* skull is not an ideal candidate for a transitional form but yet they considered it to represent a diseased *Triceratops* and not a distinct genus.
       In‭ ‬2012‭ ‬Nicholas Longrich and D.‭ ‬J.‭ ‬Field tested Scanella’s and Horner’s theory upon the basis of three predictions that should all be proven true if correct.‭ ‬First is that both *Triceratops* and *Torosaurus* should being found from the same locations,‭ ‬but in depth study of the currently known locations of both genera show that‭ ‬while close,‭ ‬very little overlap occurs.‭ ‬However the fossil record will never be complete,‭ ‬and only a relatively rare few animals will be preserved.‭ ‬Older individuals may have also shifted to different parts within the ecosystem,‭ ‬and the difference in the length of the snout of *Torosaurus* as opposed to *Triceratops* may indicate a different feeding and by extension ecological placement.‭ ‬In short however,‭ ‬this information‭ ‬cannot conclusively prove or disprove Scanella’s and Horner’s theory.
       Second is that all *Torosaurus* skulls should be of very old and mature individuals while those of *Triceratops* should be no older than just beyond sub adult.‭ ‬Horner did state that all *Triceratops* skulls that were tested had a sub adult bone structure,‭ ‬however,‭ ‬not all known *Triceratops* skulls were tested.‭ ‬When *Triceratops* skulls from other locations were investigated many were concluded to be older than sub adult,‭ ‬and some seemingly quite old,‭ ‬with at least ten being of the same level of maturity as older *Torosaurus*.‭ ‬Also,‭ ‬while all the *Torosaurus* skulls were thought to be of very old individuals,‭ ‬at least two *Torosaurus* skulls are now known to have come from much younger individuals,‭ ‬with a lack of fusion in some parts of the skull indicating that they themselves were not much past the sub adult level when then died.‭ ‬These younger *Torosaurus* skulls already show an extended neck frill with established openings far beyond that of similarly aged *Triceratops*.‭ ‬Furthermore,‭ ‬one of these skulls is also missing the epoccipitals,‭ ‬showing that this individual was so young when it died that the epoccipitals had not even fused to the main neck frill.‭ ‬In the second part,‭ ‬not only is there no evidence to establish an age/maturity difference,‭ ‬but the available fossils seem to support the opposite.
       The third prediction was that there should be at least some transitional forms that show a *Triceratops* skull growing into the toromorph.‭ ‬At the time of writing there are no known skulls that show us this change happening,‭ ‬and again,‭ ‬what fossils we do have seem to show that *Triceratops* and *Torosaurus* should be separate.‭ ‬Firstly,‭ ‬while *Triceratops* skulls often show slight depressions,‭ ‬these seem to be surrounded by a slight thickening of bone,‭ ‬while the holes in *Torosaurus* are surrounded only by thin bone.‭ ‬Also,‭ ‬the depressions in *Triceratops* while mostly on the parietal bone of the skull also extend to the squamosal bone.‭ ‬In *Torosaurus* the holes are only on the parietal bone.‭ ‬Out of these three predictions proposed by Longrich,‭ ‬one is neutral,‭ ‬neither confirming of denying the theory,‭ ‬while two conclude that *Triceratops* and *Torosaurus* are separate species.
       The differences in the number of epoccipitals has also been discredited.‭ ‬Firstly,‭ ‬the numbers of epoccipitals between members of the same species has been known to vary,‭ ‬meaning that identification of a ceratopsian species by counting epoccipitals can only be used as a very rough guide at best.‭ ‬At the time of writing there are no known cases of epoccipitals doubling themselves by splitting.‭ ‬If anything,‭ ‬the epoccipitals should proportionately increase in size with age.
       Although ceratopsian dinosaur skulls are known to have metaplastic bone which changes,‭ ‬it has been noted that due to the age of some *Triceratops* skulls,‭ ‬this bone would have already matured and hardened to hold its shape.‭ ‬If these individuals were to be capable of forming a toromorph skull,‭ ‬this bone would have had to have been rejuvenated to be able to morph again,‭ ‬before finally setting once more into the new form.‭ ‬This is a sequence that currently has no known precedence,‭ ‬and is seen as further support to keep *Torosaurus* and *Triceratops* separate.
       2013‭ ‬saw the publication of another paper,‭ ‬this time by Andrew Farke and Leonardo Maiorino,‭ ‬this time involving morphometric research upon the two main‭ *‬Triceratops* species,‭ *‬T.‭ ‬horridus* and *T.‭ ‬prorsus*,‭ *‬Torosaurus* and *Nedoceratops*.‭ ‬The conclusions were that *T.‭ ‬horridus* and *T.‭ ‬prorsus* overlapped one another in development,‭ ‬as would be expected within two species of the same genus.‭ ‬*Torosaurus* data was limited due to the much lower number of known *Torosaurus* remains when counted against *Triceratops*,‭ ‬but those that were able to be tested showed that the *Torosaurus* skulls did not overlap with those of *Triceratops*.‭ ‬When *Nedoceratops* was included,‭ ‬it was shown that it could not be a transitional form between *Triceratops* and *Torosaurus*.‭ ‬One interesting side theory from this study however is that *Triceratops* and *Torosaurus* could form a chronospecies.‭ ‬If correct then this would mean a direct familial relation between *Triceratops* and *Torosaurus* with them both being on the same line.
       It should also be noted however that fully grown *Torosaurus* seem to have reached total lengths of just over seven and a half meters.‭ ‬Large *Triceratops* by comparison are known to have ranged between eight and nine metres in length.‭ ‬It would be unprecedented for a large land vertebrate to grow large and then actually reduce in body length as it matured.‭ ‬The largest *Triceratops* skulls are also known to have reached up to two hundred and eighty centimetres in length‭ (‬length of the specimen nicknamed‭ ‬Lung Wong,‭ ‬a.k.a Dragon King‭)‬,‭ ‬just a little bit longer that large *Torosaurus* skulls.‭ ‬The discovery of such a large skull counts a lot against the theory that *Triceratops* grew into toromorphs to save on skull weight,‭ ‬as here is one individual that obviously didn’t have to.

       So what is likely to happen in the future‭? ‬At the time of writing there are three distinct possibilities.‭ ‬One is that future research and discoveries will prove that *Torosaurus* and *Triceratops* are one and the same,‭ ‬and if so then this will mean that the *Torosaurus* genus is attributed to one of the *Triceratops* species.‭ ‬Two is that *Torosaurus* is proven to not represent a mature form of *Triceratops*,‭ ‬but may still be moved to the *Triceratops* genus as a separate species to those we currently know.‭ ‬Third,‭ *‬Torosaurus* and *Triceratops* continue to be regarded as distinct species and genera,‭ ‬and things go on like they have done for over a hundred years now.‭ ‬Indeed,‭ ‬most palaeontologists and researchers continue to regard *Triceratops* and *Torosaurus* as distinct genera.

Torosaurus BodyTorosaurus face and beakTorosaurus Frill and Horns