Dinosaurs – Species Encycolpedia


Saturday, November 19, 2016

Centrosaurus apertus specimen ROM 767. Exhibit in the Royal Ontario Museum, Toronto, Ontario, Canada.

Centrosaurus is a genus of herbivorous ceratopsian dinosaurs from the late Cretaceous of Canada. Their remains have been found in the Dinosaur Park Formation, dating from 76.5 to 75.5 million years ago.

The massive bodies of Centrosaurus were borne by stocky limbs, although at up to 6 m (19.7 ft) they were not particularly large dinosaurs. Like other centrosaurines, Centrosaurus bore single large horns over their noses. These horns curved forwards or backwards depending on the specimen. Skull ornamentation was reduced as animals aged.

Centrosaurus is distinguished by having two large hornlets which hook forwards over the frill. A pair of small upwards directed horns is also found over the eyes. The frills of Centrosaurus were moderately long, with fairly large fenestrae and small hornlets along the outer edges.

Centrosaurus, which moved on all fours, had powerful front limbs that would have enhanced the animal’s speed and agility. A ball-and-socket joint in the neck would also have been useful in defense. it allowed Centrosaurus to turn its head swiftly and bring its sharp horn into play against large predators, such as Tyrannosaurus, that attacked from the rear.

Complete skulls arranged in ontogenetic order. Complete skulls arranged in ontogenetic order. Complete Centrosaurus skulls in lateral view arranged in ontogenetic order from the relatively least mature to the relatively most mature specimens, based on the reduced multistate tree. Skulls are not to scale. (A) TMP 1992.082.0001; (B) ROM 767; (C) TMP 1994.182.0001, (D) AMNH FARB 5351, (E) CMN 348; (F) UALVP 11735; (G) USNM 8897; (H) TMP 1997.085.0001; (I) CMN 8795; (J) YPM 2015. Images of TMP 1994.182.0001, AMNH FARB 5351, and CMN 8795 are reversed (mirrored). AMNH FARB 5351 and TMP 1997.085.0001 are represented here by casts. Division of Vertebrate Paleontology, YPM 2015. Courtesy of the Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA. Joseph A. Frederickson​, Allison R. Tumarkin-Deratzian



The genus Centrosaurus gives its name to the Centrosaurinae subfamily. These were large North American horned dinosaurs characterized by their “prominent nasal horns, subordinate brow horns, short squamosals in a short frill, a tall, deep face relative to the chasmosaurines, and a projection into the rear of the nasal fenestra.” Its closest relatives appear to be Styracosaurus and Monoclonius. It so closely resembles the latter of these that some paleontologists have considered them to represent the same animal.

This cladogram follows the phylogenetic analysis performed by Ryan et al. (2016)



Saturday, November 19, 2016


Ceratosaurus (from Greek keras/keratos meaning “horn” and σαυρος/sauros meaning “lizard”), was a large predatory theropod dinosaur from the Late Jurassic Period (Kimmeridgian to Tithonian), found in the Morrison Formation of North America, and the Lourinhã Formation of Portugal (and possibly the Tendaguru Formation in Tanzania). It was characterized by large jaws with blade-like teeth, a large, blade-like horn on the snout and a pair of hornlets over the eyes. The forelimbs were powerfully built but very short. The bones of the sacrum were fused (synsacrum) and the pelvic bones were fused together and to this structure (i.e. similar to modern birds). A row of small osteoderms was present down the middle of the back.

Ceratosaurus, at first glance, looked like a fairly typical theropod, however its skull was quite large in proportion to the rest of its body, and large nasal and brow horns and possessed a prominent nose horn formed from protuberances of the nasal bones. In addition to the large nasal horn, Ceratosaurus possessed smaller hornlike ridges in front of each eye, similar to those of Allosaurus, these ridges were formed by enlargement of the lacrimal bones. Uniquely among theropods, Ceratosauruspossessed dermal armor, in the form of small osteoderms running down the middle of its back. Its tail comprised about half of the body’s total length and was thin and flexible with high vertebral spines.

The type specimen was an individual about 18 feet (5.5 m) long; it is not clear whether this animal was fully grown. David B. Norman (1985) estimated that the maximum length of Ceratosaurus was 20 ft (6.1 m), an assessment supported by a particularly large Ceratosaurus specimen from the Cleveland-Lloyd Dinosaur Quarry (UMNH 5728), discovered in the mid-1960s, which may have been 22 ft (6.7 m) long assuming similar proportions to the holotype.

Ceratosaurus is known from the Cleveland-Lloyd Dinosaur Quarry in central Utah and the Dry Mesa Quarry in Colorado. The type species, described by O. C. Marsh in 1884 and redescribed by Gilmore in 1920, is Ceratosaurus nasicornis. The first skeleton was excavated by rancher Marshall Parker Felch in 1883.

Artist's impression of C. nasicornis


Relatives of Ceratosaurus include GenyodectesElaphrosaurus, and the abelisaurs, such as Carnotaurus. The classification of Ceratosaurus and its immediate relatives has been under intense debate. Ceratosaurs are unique in their characters; they share some primitive traits with coelophysoids, but also share some derived traits with tetanuran theropods not found in coelophysians. Its closest relatives appear to be the abelisaurs.

In the past, Ceratosaurus, the abelisaurs, and the primitive coelophysoids were all grouped together and called Ceratosauria, defined as “theropods closer to Ceratosaurus than to Aves”. Recent evidence, however, has shown large distinctions between the later, larger and more advanced ceratosaurs and earlier forms like Coelophysis. While considered distant from birds among the theropods, Ceratosaurus and its kin were still very bird-like, and even had a more avian tarsus (ankle joint) than Allosaurus.


Saturday, November 19, 2016


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 4.3–4.8 metres (14.1–15.7 ft) and a weight of 1.5–2 tonnes (1.7–2.2 short tons), 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.

Chasmosaurus was a medium-size ceratopsid. In 2010 G.S. Paul estimated the length of C. belli at 4.8 metres, its weight at two tonnes; C. russelli would have been 4.3 metres long and weighed 1.5 tonnes. The known differences between the two species mainly pertain to the horn and frill shape, as the postcrania of C. russelli are poorly known. Like many ceratopsians, Chasmosaurus had three main facial horns – one on the nose and two on the brow. In both species these horns are quite short, but with C. russelli they are somewhat longer, especially the brow horns, and more curved backwards. The frill of Chasmosaurus is very elongated and broader at the rear than at the front. It is hardly elevated from the plane of the snout. With C. belli the rear of the frill is V-shaped and its sides are straight. With C. russelli the rear edge is shaped as a shallow U, and the sides are more convex. The sides were adorned by six to nine smaller skin ossifications (called episquamosals) or osteoderms, which attached to the squamosal bone. The corner of the frill featured two larger osteoderms on the parietal bone. With C. russelli the outer one was the largest, with C. belli the inner one. The remainder of the rear edge lacked osteoderms. The parietal bones of the frill were pierced by very large openings, after which the genus was named: the parietal fenestrae. These were not oval in shape, as with most relatives, but triangular, with one point orientated towards the frill corner.

Depiction of the mega-herbivores in the Dinosaur Park Formation, C. belli on the left


Chasmosaurus was in 1915 by Lambe within the Ceratopsia assigned to the Chasmosaurinae. The Chasmosaurinae usually have long frills, like Chasmosaurus itself, whereas their sister-group the Centrosaurinae typically have shorter frills. Most cladistic analyses show that Chasmosaurus has a basal position in the Chasmosaurinae.


Monday, November 14, 2016

Mounted skeleton (NCSM 14345) at the North Carolina Museum of Natural Sciences.

Acrocanthosaurus (meaning “high-spined lizard”) is a genus of theropod dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. Its fossil remains are found mainly in the U.S. states of Oklahoma, Texas, and Wyoming, although teeth attributed to Acrocanthosaurus have been found as far east as Maryland.

Acrocanthosaurus was a bipedal predator. As the name suggests, it is best known for the high neural spines on many of its vertebrae, which most likely supported a ridge of muscle over the animal’s neck, back and hips. Acrocanthosaurus was one of the largest theropods, reaching 11.5 m (38 ft) in length, and weighing up to 6.2 tonnes (6.8 short tons). Large theropod footprints discovered in Texas may have been made by Acrocanthosaurus, although there is no direct association with skeletal remains.

Recent discoveries have elucidated many details of its anatomy, allowing for specialized studies focusing on its brain structure and forelimb function. Acrocanthosaurus was the largest theropod in its ecosystem and likely an apex predator which preyed on sauropods, ornithopods, and ankylosaurs.

Acrocanthosaurus was big for its time,‭ ‬a family trait that is shared with‭ ‬some other carcharodontosaurids such as Carcharodontosaurus and Giganotosaurus.‭ ‬At‭ ‬eleven and a half‭ ‬meters,‭ ‬Acrocanthosaurus would have been the largest predator of its time and locale.‭ ‬Its diet as a result probably consisted of hadrosaurs and smaller sauropods,‭ ‬dinosaurs that were large enough to provide sufficient sustenance,‭ ‬while being too slow to escape.‭ ‬Study of the area that the main Acrocanthosaurusremains come from suggest that it was probably the apex predator of its location,‭ ‬with most other predators such as Deinonychus being much smaller.

The skull of Acrocanthosaurus featured large fenestra,‭ ‬a necessary adaptation to reduce the weight of its huge skull that could approach up to a‭ ‬one hundred and thirty‭ centi‬meters long.‭ ‬The teeth of Acrocanthosaurus were curved and serrated like other members of the carcharodontosaurid group.‭ ‬The maxilla and premaxilla contained‭ ‬a total of around thirty-eight teeth.‭ ‬The teeth in the lower jaw are generally smaller than those above and can approach up to thirty in number.‭ ‬Another carcharodontosaurid trait is the bony brow ridge above the eye,‭ ‬formed by the lacrimal and postorbital bones coming together.

Artist's impression of a pair of Acrocanthosaurs on the move.

Computer reconstruction of the inner ear has shown that the‭ ‘‬resting position‭’ ‬of the head of Acrocanthosaurus was twenty-five degrees below zero horizontal.‭ ‬This may give the impression that Acrocanthosaurus usually walked around looking slightly towards the ground.

Reconstruction of an Acrocanthosaurus forelimb suggests that there would have been large amounts of cartilage between the bones.‭ ‬This comes from the fact that bones themselves do not make perfect joints and would need the extra cartilage in order to articulate properly.‭ ‬The arms of Acrocanthosaurus did not have a huge range of motions.‭ ‬The arm could not fully extend and could only manage limited flexing.‭ ‬The humerus could retract back quite away,‭ ‬as if Acrocanthosaurus was pulling something towards its chest.‭ ‬As is commonly seen in larger theropods,‭ ‬the fore arm could not twist like a human arm can.‭ ‬When at rest the arms would have faced medially inwards,‭ ‬like when you clap your hands together.‭ ‬Acrocanthosaurus had three digits on the end of its arms with the first and second claws probably being permanently flexed.‭ ‬The third and smallest claw may have been able to retract as well.

Altogether,‭ ‬Acrocanthosaurus may have grabbed large prey such as sauropods like Paluxysaurus with its jaws and then latched onto it with its claws. ‭The neck vertebrae also interlocked together for greater rigidity which means that Acrocanthosauruscould hold onto large prey with its jaws without sustaining injury to the neck. ‬Lighter prey such as ornithopod dinosaurs like Tenontosaurus may have been pulled towards Acrocanthosaurus while it continued to work with its jaws,‭ ‬whereas it would probably have to pull itself onto heavier prey.‭ ‬Alternatively it may have held its prey with its jaws while repeatedly slashing at it with its claws,‭ ‬the more the prey struggled,‭ ‬the worse its wounds became.

One usual feature of Acrocanthosaurus is the large neural spines on the vertebrae of the neck, back, hips and upper tail. It is not thought that it had a sail on its back like Spinosaurus (which was unrelated, and had much larger neural spines), but rather it is thought the spines had attachments for powerful muscles, similar to those found in modern bison. Its not entirely clear what the purpose of these spines and muscles were – possibilities include fat storage, communication, or temperature regulation.

Acrocanthosaurus was a carnivore, but is not believed to have been a fast runner. Its forelimbs and shoulders are also unusual, and seem to have been very strong, had lots of cartilage, but been quite stiff with very limited movement. It is thought that the forelimbs hung down and inwards, and would not have been used for seizing prey. Acrocanthosaurus may instead have seized prey with its jaws, and used its forelimbs to prevent the prey escaping. It is also possible that Acrocanthosaurus may have held the prey in its jaws, and used the claws in its forelimbs to tear gashes into the prey.