Torosaurus

***Torosaurus*** ("perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous ceratopsid dinosaur that lived during the late Maastrichtian stage of the Cretaceous period, between 68 and 66 million years ago, though it is possible that the species range might extend to as far as 69 million years ago.[1] Fossils have been discovered across the Western Interior of North America, from Saskatchewan to southern Texas.

*Torosaurus* possessed one of the largest skulls of any known land animal. The frilled skull reached up to 2.77 metres (9.1 ft) in length. From head to tail, *Torosaurus* is thought to have measured about 8 to 9 m (26 to 30 ft) long and weighed four to six tonnes. *Torosaurus* is distinguished from the contemporary *Triceratops* by an elongate frill with large openings (fenestrae), long squamosal bones of the frill with a trough on their upper surface, and the presence of five or more pairs of hornlets (epoccipitals) on the back of the frill.[4] *Torosaurus* also lacked the long nose horn seen in *Triceratops prorsus*, and instead resembled the earlier and more basal *Triceratops horridus* in having a short nose horn.[4] Three species have been named, *Torosaurus latus*, *T. gladius* and *T. utahensis*. *T. gladius* is no longer considered a valid species, however.

In 2010, the validity of *Torosaurus* was disputed.[5] A study of fossil bone histology combined with an investigation of frill shape concluded that *Torosaurus* probably represented the mature form of *Triceratops*, with the bones of typical *Triceratops* specimens still immature and showing signs of a first development of distinct *Torosaurus* frill holes. During maturation, the skull frill would have been greatly lengthened and holes would have appeared in it. In 2011, 2012 and 2013 however, studies of external features of known specimens have claimed that morphological differences between the two genera preclude their synonymy. The main problems are a lack of good transitional forms, the apparent existence of authentic *Torosaurus* subadults, different skull proportions independent of maturation and the assertion that hole formation at an adult stage is not part of a normal ceratopsian maturation sequence. The individuals referred to *Torosaurus* are all large, comparable to the largest *Triceratops* specimens. Due to the elongated frill, especially the skull length is considerable. Hatcher estimated the skull of YPM 1830 at 2.2 metres, of YPM 1831 at 2.35 metres.[20] In 1933 Richard Swann Lull increased this to 2.4 metres and 2.57 metres respectively.[21] Based on this, *Torosaurus* was seen as having the longest skull of any known land animal. However, in 1998 Thomas Lehman claimed that a *Pentaceratops* specimen possessed a partial skull that would have been 2.9 metres long in life.[22] This was again doubted by Nicholas Longrich who in 2011 named this exemplar as a separate genus *Titanoceratops* and concluded its skull had been reconstructed as too long.[23] Furthermore, in 2006 Andrew Farke had pointed out that the new skulls described by him were on average even longer than Hatcher's original two: MOR 1122 has a length of 252 centimetres and MOR 981 of 277 centimetres.

Farke in 2006 established some diagnostic traits of *Torosaurus*. The frill is extremely long in comparison to the remainder of the skull. The rear, parietal, edge of the frill bears ten or more epiparietals, triangular osteoderms. A midline epiparietal is absent; likewise no osteoderm straddles the parietal-squamosal boundary. The parietal bone is thin. It is pierced by parietal *fenestrae* in the form of circular or transversely oval openings. The parietal bone is about 20% wider than long. Farke identified a single trait in which *T. latus* differed from both *Triceratops horridus* and *T. utahensis*: its squamosal bore a conspicuous ridge on the edge with the parietal combined with a deep longitudinal trough parallel to it.[24]

Farke pointed out that the known *Torosaurus* specimens are rather variable. The orbital "brow" horns are sometimes large and curved to the front, as with MOR 981, sometimes short and straight as shown by MOR 1122 and ANSP 15191. Also the position of these horns differs: often they are located directly on top of the eye socket but with YPM 1831 they originate at the rear edge of the orbit. Likewise there is a variation in the form of the nose horn. YPM 1831 and to a lesser extent YPM 1830 have a straight upright nasal horn but MOR 981, ANSP 15192 and especially MOR 1122 at most possess a low bump. The frill too differs. ANSP 15192 and YPM 1830 have a shield curving upwards at the rear, but the frill of YPM 1831 is nearly flat, though this could be an artefact of restoration. The frill of YPM 1831 is also heart-shaped, with a clear mideline notch, whereas the rear edge of the other specimens is straight. The frill proportions are quite variable: with YPM 1831 the length-width ratio is 1.26 but MOR 981 has a shield 2.28 times longer than wide. The number of epiparietals is difficult to assess as most fossils seem to have lost them. MOR 981 and MOR 1122 have ten and twelve epiparietals respectively. YPM 1831 has been restored with a fontanelle in the skull roof, which possibly is authentic. Farke also concluded that the degree of variability did not exceed that shown by related genera.

Farke stressed that, apart from the frill, no systematic differences could be found between *Torosaurus* and *Triceratops*. All *Torosaurus* specimens are similar in that they lack a truly long nasal horn and a horizontal arterial groove at the front base of that horn, but *Triceratops* fossils with the same combination of traits are not uncommon.[24] Hunt in 2008 concluded that *T. utahensis*, contrary to *T. latus* but similar to *Triceratops*, possessed a midline epiparietal.

one species of torosaurus is a light grey with dark grey strips and frill with blue coloring with yellow and black spots

another species is regular grey with black on its back and red on its frill

another species is green with a red frill with yellow colors