Chasmosaurus

Discovery

Chasmosaurus ("cleft lizard") fossils were first recovered in 1902, but were thought to be from a previously-known short-frilled ceratopsian - Monoclonius. However, in 1913, Charles Sternberg and his sons found several complete skulls of what is now known as Chasmosaurus, in Alberta, Canada. These were finally described in 1914 by Lawrence Lambe of the Canadian Geological Survey. Since that date, more skulls have been found. There are some differences across these skulls, for reasons we shall return to in a moment.

Description

Ceratopsians are frequently split into two categories by taxonomists; those with short frills, such as Triceratops, and those with long frills, of whom Chasmosaurus was one. In addition to the larger frill, the long-frilled ceratopsians typically had longer faces and jaws, and it is suggested by some paleontologists that they were more selective about the plants they ate. Chasmosaurus is interesting because it is the earliest of the known long-frilled dinosaurs. Long frills were a late development for the dinosaurs, since even Chasmosaurus dates from the late Cretaceous period, 76 to 70 million years ago. Chasmosaurus' frill has been described as "heart-shaped", since its bone structure consists of two large "loops" from a central bone. Some finds include a number of smaller spikes which may have grown from the perimeter of the frill. The frill may also have been brightly coloured, to draw attention to its size or as part of mating display. However, the frill was so large and yet so flimsy (since it was mainly skin stretched between the bones) that it could not have provided much functional defence. It is possible that it was simply used to appear imposing or conceivably for thermoregulation. If a chasmosaur herd was attacked by one of the carnivores of the day, the males could have formed a ring and, with all the frills facing outwards, would have presented a formidably sight.

Like many ceratopsians, chasmosaurus had three main facial horns - one on the nose and two on the brow. Different fossils finds have produced inconclusive results - one species of Chasmosaurus, named C. kaiseni, bore long brow horns, while C. belli had only short ones. Although these were initially named as different species, it now seems possible that the long horns belonged to males and the shorter horns to females.

With a length of 5 - 6 metres and a weight of 3.6 tonnes, Chasmosaurus was a ceratopsian of average size. Like all ceratopsians, it was purely herbivorous.

Interestingly, paleontologists have recovered some fossilized skin from a Chasmosaurus. The skin appears to have had many boney knobs, with five or six sides each. Unfortunately, nothing more can be learned from these samples - the colour of dinosaurs remains a mystery.

Classification

• Order - Ornithischia
• Sub-order - Ceratopsia
• Infra-order - Coronosauria
• Super-family - Ceratopsinae
• Family - Ceratopsia