Torosaurus

Torosaurus (meaning "perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous chasmosaurine ceratopsian dinosaur which lived during the Maastrichtian Stage of the Cretaceous Period between 68 and 66 million years ago, although it is possible that the species range might extend back as far back as 69 million years ago. Fossils which have been definitively identified as Torosaurus or which might belong to it have been discovered across the Western Interior of North America, from as far north as Saskatchewan to as far south as Texas. Measuring between 7.5 and 9 m (25 and 30 ft) and weighing around 8 t (18,000 lb), Torosaurus possessed the longest skull of any known land animal, with the frilled skull reaching 2.77 metres (9.1 ft) in length. Torosaurus is thought to have been the same size as the contemporary Triceratops, but is distinguished by an elongated frill with large oval shaped openings, long squamosal bones of the frill with a trough on their upper surface, and the presence of five or more pairs of hornlets on the back of the frill. Torosaurus possessed a short upright nose horn similar to that seen in Triceratops horridus. Two species of Torosaurus are presently considered valid: T. latus and T. utahensis. Torosaurus gladius is no longer considered a valid species, being now considered a synonym of T. latus. In 2010, the validity of Torosaurus was disputed. 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,...