Chasmosaurus
Encyclopedia
Chasmosaurus is a genus
of ceratopsid
dinosaur
from the Upper Cretaceous
Period of North America
. Its name means 'opening lizard', referring to the large openings (fenestrae
) in its frill (Greek
chasma meaning 'opening' or 'hollow' or 'gulf' and sauros meaning 'lizard'). With a length of 5–6 m (16.4–19.7 ft) and a weight of 3.6 tonne, Chasmosaurus was a ceratopsian of average size. Like all ceratopsians, it was purely herbivorous
. It was initially to be called Protorosaurus
, but this name had been previously published for another animal. All specimens of Chasmosaurus were collected from the Dinosaur Park Formation
of the Dinosaur Provincial Park
of Alberta, Canada
. C. russelli comes from the lower beds of the formation while C. belli comes from middle and upper beds.
In 1898, Lawrence M. Lambe
of the Geological Survey of Canada made the first discovery of Chasmosaurus remains- part of a neck frill. Although recognizing that his find represented a new species, Lambe thought to be from a previously-known short-frilled ceratopsian genus- Monoclonius
. He erected the new species Monoclonius belli to describe his finding.
However, in 1913, Charles Sternberg
and his sons found several complete "M. belli" skulls in the middle Dinosaur Park Formation
of Alberta
, Canada
. These were finally described as the new genus Chasmosaurus in 1914, again by Lawrence Lambe.
Since that date, more Chasmosaurus remains, including skulls, have been found. There appears to be morphological variation among the known sample of Chasmosaurus skulls, so there are a number of known species
of Chasmosaurus. Lambe's original C. belli ('Bell's cleft lizard') was joined by C. canadensis ('from Canada') in the same year. The latter species had been described as Eoceratops canadensis by Lambe but was later reclassified as a chasmosaur by Thomas M. Lehman. Eoceratops and the long-horned Chasmosaurus kaiseni are now provisionally thought to be examples of Mojoceratops
. Lull named an unusual, short-muzzled skull, collected in 1926, C. brevirostris. C. M. Sternberg added C. russelli, in 1940, from southwestern Alberta (lower Dinosaur Park Formation
). Thomas Lehman described C. mariscalensis in 1989 from Texas
, which has now been renamed Agujaceratops
. The most recently described species is C. irvinensis, which stems from the uppermost beds of the Dinosaur Park Formation
. This species was given its own genus, Vagaceratops
, in 2010.
; those with short frills (centrosaurines), such as Centrosaurus
and those with long frills (chasmosaurines), of which 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. Long frills were a relatively late development in dinosaur evolution
, since even Chasmosaurus dates from the late Cretaceous
Period, 76.5 to 75.5 million years ago. The frill of Chasmosaurus 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 ossifications (called epoccipitals), which may have grown from the perimeter of the frill. The frill may also have been brightly colored, 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 defense. It is possible that it was simply used to appear imposing or conceivably for thermoregulation
.
Like many ceratopsians, chasmosaurs had three main facial horn
s - one on the nose and two on the brow. Different fossil 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.
Interestingly, a Chasmosaurus specimen recovered by Sternberg was accompanied by fossilized skin
. The skin appears to have had many large scales in evenly spaced rows among smaller scales, with five or six sides per knob. Unfortunately, nothing can be learned about the coloration of Chasmosaurus from the known fossil skin samples.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of ceratopsid
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Upper Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Its name means 'opening lizard', referring to the large openings (fenestrae
Fenestrae
Fenestræ is a Latin word that means "window".* In histology, fenestræ are small pores in endothelial cells that allow for rapid exchange of molecules between sinusoid blood vessels and surrounding tissue...
) in its frill (Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
chasma meaning 'opening' or 'hollow' or 'gulf' and sauros meaning 'lizard'). With a length of 5–6 m (16.4–19.7 ft) and a weight of 3.6 tonne, Chasmosaurus was a ceratopsian of average size. Like all ceratopsians, it was purely herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
. It was initially to be called Protorosaurus
Protorosaurus
Protorosaurus , a lizard-like reptile of the order Prolacertiformes, is the earliest known archosauromorph. It lived during the Late Permian period in Germany. In 1914, a new ceratopsian dinosaur found by Lawrence Lambe was again given the name Protorosaurus...
, but this name had been previously published for another animal. All specimens of Chasmosaurus were collected from the Dinosaur Park Formation
Dinosaur Park Formation
The Dinosaur Park Formation is the uppermost member of the Judith River Group, a major geologic unit in southern Alberta. It was laid down over a period of time between about 76.5 and 75 million years ago. The formation is made up of deposits of a high-sinuosity fluvial system, and is capped...
of the Dinosaur Provincial Park
Dinosaur Provincial Park
Dinosaur Provincial Park is a UNESCO World Heritage Site located about two and a half hours drive southeast of Calgary, Alberta, Canada or , about a half hour drive, northeast of Brooks....
of Alberta, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. C. russelli comes from the lower beds of the formation while C. belli comes from middle and upper beds.
Discoveries and species
Lawrence Lambe
Lawrence Morris Lambe was a Canadian geologist and palaeontologist from the Geological Survey of Canada .His published work, describing the diverse and plentiful dinosaur discoveries from the fossil beds in Alberta, did much to bring dinosaurs into the public eye and helped usher in the Golden...
of the Geological Survey of Canada made the first discovery of Chasmosaurus remains- part of a neck frill. Although recognizing that his find represented a new species, Lambe thought to be from a previously-known short-frilled ceratopsian genus- Monoclonius
Monoclonius
Monoclonius was a ceratopsian dinosaur from the Judith River Formation of Late Cretaceous Montana and Canada. It is often confused with Centrosaurus, a similar genus of ceratopsian . Monoclonius was described by Edward Drinker Cope in 1876...
. He erected the new species Monoclonius belli to describe his finding.
However, in 1913, Charles Sternberg
Charles Hazelius Sternberg
Charles Hazelius Sternberg , was an American fossil collector and amateur paleontologist. His older brother, Dr. George M. Sternberg was a military surgeon assigned to Fort Harker near Ellsworth, Kansas and brought the rest of Sternberg family to Kansas to live on his ranch about 1868...
and his sons found several complete "M. belli" skulls in the middle Dinosaur Park Formation
Dinosaur Park Formation
The Dinosaur Park Formation is the uppermost member of the Judith River Group, a major geologic unit in southern Alberta. It was laid down over a period of time between about 76.5 and 75 million years ago. The formation is made up of deposits of a high-sinuosity fluvial system, and is capped...
of Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. These were finally described as the new genus Chasmosaurus in 1914, again by Lawrence Lambe.
Since that date, more Chasmosaurus remains, including skulls, have been found. There appears to be morphological variation among the known sample of Chasmosaurus skulls, so there are a number of known species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of Chasmosaurus. Lambe's original C. belli ('Bell's cleft lizard') was joined by C. canadensis ('from Canada') in the same year. The latter species had been described as Eoceratops canadensis by Lambe but was later reclassified as a chasmosaur by Thomas M. Lehman. Eoceratops and the long-horned Chasmosaurus kaiseni are now provisionally thought to be examples of Mojoceratops
Mojoceratops
Mojoceratops is a genus of ceratopsian dinosaur. It is a chasmosaurine ceratopsian which lived during the Late Cretaceous period in what is now Western Canada...
. Lull named an unusual, short-muzzled skull, collected in 1926, C. brevirostris. C. M. Sternberg added C. russelli, in 1940, from southwestern Alberta (lower Dinosaur Park Formation
Dinosaur Park Formation
The Dinosaur Park Formation is the uppermost member of the Judith River Group, a major geologic unit in southern Alberta. It was laid down over a period of time between about 76.5 and 75 million years ago. The formation is made up of deposits of a high-sinuosity fluvial system, and is capped...
). Thomas Lehman described C. mariscalensis in 1989 from Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, which has now been renamed Agujaceratops
Agujaceratops
Agujaceratops is a genus of herbivorous ceratopsian dinosaur. It is a chasmosaurine ceratopsian which lived during the Late Cretaceous period in what is now Texas. Originally known as Chasmosaurus mariscalensis and described by Lehman in 1989, it was moved to a new genus by Lucas, Sullivan and...
. The most recently described species is C. irvinensis, which stems from the uppermost beds of the Dinosaur Park Formation
Dinosaur Park Formation
The Dinosaur Park Formation is the uppermost member of the Judith River Group, a major geologic unit in southern Alberta. It was laid down over a period of time between about 76.5 and 75 million years ago. The formation is made up of deposits of a high-sinuosity fluvial system, and is capped...
. This species was given its own genus, Vagaceratops
Vagaceratops
Vagaceratops is a genus of herbivorous ceratopsian dinosaur. It is a chasmosaurine ceratopsian which lived during the Late Cretaceous period in what is now Alberta. Its fossils have been recovered from the Upper Dinosaur Park Formation...
, in 2010.
Description
Ceratopsians are split into two subfamilies by taxonomistsTaxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
; those with short frills (centrosaurines), such as Centrosaurus
Centrosaurus
Centrosaurus is a genus of herbivorous ceratopsian dinosaurs from the late Cretaceous of Canada. Their remains have been found in the Dinosaur Park Formation and uppermost Oldman Formation, dating from 76.5 to 75.5 million years ago....
and those with long frills (chasmosaurines), of which 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. Long frills were a relatively late development in dinosaur evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
, since even Chasmosaurus dates from the late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period, 76.5 to 75.5 million years ago. The frill of Chasmosaurus 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 ossifications (called epoccipitals), which may have grown from the perimeter of the frill. The frill may also have been brightly colored, 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 defense. It is possible that it was simply used to appear imposing or conceivably for thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
.
Like many ceratopsians, chasmosaurs had three main facial horn
Horn (anatomy)
A horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...
s - one on the nose and two on the brow. Different fossil 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.
Interestingly, a Chasmosaurus specimen recovered by Sternberg was accompanied by fossilized skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
. The skin appears to have had many large scales in evenly spaced rows among smaller scales, with five or six sides per knob. Unfortunately, nothing can be learned about the coloration of Chasmosaurus from the known fossil skin samples.