Carcharodontosaurus

Carcharodontosaurus

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Carcharodontosaurus was a gigantic carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

 carcharodontosaurid
Carcharodontosauridae
Carcharodontosaurids were a group of carnivorous theropod dinosaurs. In 1931 Ernst Stromer named Carcharodontosauridae as a family, in modern paleontology this name indicates a clade within Carnosauria...

 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...

 that lived around 100 to 93 million years ago, during the late Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...

 to early Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...

 stages of the mid-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. It was discovered to be the second largest predatory dinosaur, larger than Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...

and Giganotosaurus
Giganotosaurus
Giganotosaurus is a genus of carcharodontosaurid dinosaur that lived around 97 million years ago during the early Cenomanian stage of the Late Cretaceous Period. It included some of the largest known terrestrial carnivores, slightly larger than the largest Tyrannosaurus, but smaller than the...

, but not as large as Spinosaurus
Spinosaurus
Spinosaurus is a genus of theropod dinosaur which lived in what is now North Africa, from the lower Albian to lower Cenomanian stages of the Cretaceous period, about 112 to 97 million years ago. This genus was first known from Egyptian remains discovered in 1912 and described by German...

.

The Carcharodontosaurus is named after the shark genus Carcharodon (from the 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...

 καρχαρο karcharo meaning "jagged" or "sharp" and οδοντο odonto meaning "teeth", and σαυρος sauros, meaning "lizard") — "jagged-toothed lizard" or "sharp-toothed lizard".

Description



Carcharodontosaurus is one of the longest and heaviest known carnivorous dinosaurs, with various scientists proposing length estimates ranging between 12 and 13 m (39-43.5 ft) and weight estimates between 6 and 15 metric tons.

Carcharodontosaurus was a carnivore, with enormous jaws and long, serrated teeth up to eight inches long. Paleontologists
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...

 once thought that Carcharodontosaurus had the longest skull of any of the theropod
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...

 dinosaurs. However, the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

 and quadrate bones were missing from the original African skull, which led to misinterpretation of its actual size by researchers. A more modest length of 1.6 meters (5.2 ft) has now been proposed for C. saharicus, and the skull of C. iguidensis is reported to have been slightly larger at 1.75 m in length (5.5 ft). Currently, the largest known theropod skull belongs to another huge carcharodontosaurid
Carcharodontosauridae
Carcharodontosaurids were a group of carnivorous theropod dinosaurs. In 1931 Ernst Stromer named Carcharodontosauridae as a family, in modern paleontology this name indicates a clade within Carnosauria...

 dinosaur, the closely related Giganotosaurus
Giganotosaurus
Giganotosaurus is a genus of carcharodontosaurid dinosaur that lived around 97 million years ago during the early Cenomanian stage of the Late Cretaceous Period. It included some of the largest known terrestrial carnivores, slightly larger than the largest Tyrannosaurus, but smaller than the...

(with skull length estimates up to 1.95 m) (6.3 ft).

Brain and inner ear


In 2001, Hans C. E. Larsson published a description of the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...

 and endocranium
Endocranium
For internal cast of the cranium, see Endocast.The endocranium in comparative anatomy is a part of the skull base in vertebrates and represent the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy.-Basic structure:Structurally, the...

 of Carcharodontosaurus saharicus. Larsson observed that the C. saharicus braincase "completely encloses the endocranial region." This "high degree of ossification
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

" made his analysis of its anatomy significantly easier to perform. The C. saharicus endocast is similar to that of a related dinosaur, Allosaurus fragilis. Larsson describes the olfactory bulbs and peduncles
Cerebral peduncle
Mainly, the three common areas that give rise to the cerebral peduncles are the cortex, the spinal cord and the cerebellum. The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. The region includes the midbrain tegmentum, crus cerebri and pretectum...

 as lying "on approximately the same horizontal plane as the forebrain." The midbrain is angled downwards and towards the rear of the animal, while the hind brain is roughly parallel to the forebrain. The cephalic flexure
Cephalic flexure
The mesencephalic flexure or cephalic flexure is the first flexure, or bend, of the embryonic brain; it appears in the region of the mid-brain...

, the bend between the fore- and midbrain, has an angle of 45 degrees. The pontine flexure
Pontine flexure
The pontine flexure is a bend in the axis of the embryological central nervous system . This flexure marks the junction between the metencephalon and the myelencephalon. The division of the rhombencephalon into the metencephalon and the myelencephalon occurs at the 7th week of development...

, the bend between the mid- and hindbrain has an angle of about 40 degrees. Carcharodontosaurus had a large optic (II) nerve. The C. saharicus vena capitis dorsalis "drains the anterior neck muscles through a pair of long canals on the posterior surface of the endocast." This configuration is found in Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...

and Dromaeosaurus albertensis, although in C. saharicus and Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...

"the transverse sinus probably drained into a middle cerebral vein
Middle cerebral vein
The superficial middle cerebral vein begins on the lateral surface of the hemisphere, and, running along the lateral cerebral sulcus, ends in the cavernous or the sphenoparietal sinus.-Relations:It is connected:...

 that exited the brain in the ridge present on the dorsal edge of the trigeminal foramen."


The three semicircular canals of the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...

 of Carcharodontosaurus saharicus, when viewed from the side, had a subtriangular outline. This subtriangular inner ear configuration is present in Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...

, lizards, turtles, but not in birds. The pointed apex "at the junction of the anterior and posterior semicircular canals" is caused by the near linearity of the canals and closely resembles the condition of modern crocodiles. The subtriangular configuration may be the basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 condition of archosauromorphs. A recess which would have held the floccular lobe of the brain projects into the area surrounded by the semicircular canals. This condition is also present in other non-avian theropods, birds, and pterosaurs. The orientation of the lagena
Lagena
The extremities of the ductus cochlearis are closed; the upper is termed the lagena and is attached to the cupula at the upper part of the helicotrema; the lower is lodged in the recessus cochlearis of the vestibule.- In fish and amphibians :...

 of C. saharicus resembles the condition in crocodilians and some birds. The extent of its perilymphatic duct
Perilymphatic duct
The perilymphatic duct is where the perlyphatic space is connected to the subarachnoid space. This works as a type of shunt to eliminate excess perilymph fluid from the perlymphatic space around the cochlea of the ear. Perilymph is continuous with cerebrospinal fluid in the subarachnoid space...

 resembled those of Varanus, crocodilians, and birds. The crista
Crista ampullaris
The crista ampullaris is the sensory organ of rotation located in the semicircular canal of the inner ear. The function of the crista ampullaris is to sense angular acceleration and deceleration.-Background:...

 which would have supported the secondary tympanic membrane in C. saharicus was either absent, or not preserved. This contrasts with Troodon, whose crista were ossified at least in their dorsal and ventral regions and their remaining portions either cartilaginous or too delicate to be preserved. The metotic strut of C. saharicus is reduced and medial compared to the "laterally hypertrophied" condition of non-avian maniraptors like Dromaeosaurus and Troodon, as well as primitive birds like Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...

and Hesperornis
Hesperornis
Hesperornis is a genus of flightless aquatic birds that spanned the first half of the Campanian age of the Late Cretaceous period . One of the lesser-known discoveries of the paleontologist O. C. Marsh in the late 19th century Bone Wars, it was an important early find in the history of avian...

.

Traditional comparisons of brain volume to body mass has estimated brain size as the volume of the endocast. However, the brain of Sphenodon fills only about half of its endocranial volume. Some paleontologists used the fifty percent estimate to ascertain the brain size of dinosaur endocasts. Other workers have observed that details on the endocranial surface indicates that some fossil reptiles had brains that occupied a much larger portion of the endocranium. Larsson notes that the transition from reptiles to birds prevents using a set ratio from being a valid approach to estimating the volume of the endocranium occupied by a dinosaur's brain.

Adding difficulty to examining the ratio of the brain volume of a dinosaur to its body mass is the wide range of estimates for live mass. Larsson observes that one study which estimated the live masses for many dinosaur genera typically had a fourfold range. Larsson laments that "[t]he broad ranges of body mass estimates, combined with the ambiguous ratio of endocranial volume occupied by the brain, present a high degree of uncertainty for [creating an] index of brain size." Consequently, he attempted to minimize errors in his study by making a different kind of comparison.

Noting that while it is difficult to estimate the absolute volume of the brain, the proportions of its various regions should the same in the endocast as it was in the large brain Larsson's study compared the ratio of the cerebrum, which is highly demarcated, to the rest of the endocast's volume. However, if the thickness of the dura
Dura
Dura may refer to:* Dura , a Palestinian town in the southern West Bank located eleven kilometers southwest of Hebron in the Hebron Governorate* Dura language, a critically endangered language of Nepal...

 covering the various parts of the brain itself differed, then that could alter the relative proportions within the endocast. In Caiman the dura covering the medullary region seemed to increase proportionally in thickness compared to the dura covering the forebrain, although this might not impact the ratio between the regions. Nevertheless, Larsson reaffirmed the superiority of his technique to traditional comparisons of brain volume to estimated live body mass.

"As brain mass increases, cerebral mass increases with slight negative allometry in nonavian reptiles," Larsson concludes, larger nonavian reptile have proportionately smaller cerebra than smaller ones. Further, the opposite is true in birds, larger avian brains have cerebra which are slightly larger, proportionally speaking. Larsson found that both C. saharicus and Allosaurus lie within the 95% confidence limits of the nonavian reptile ratio, while Tyrannosaurus lies just outside it in the direction of a more avian proportion. The extinct crocodile Sebecus
Sebecus
Sebecus is an extinct genus of sebecid crocodylomorph from the Eocene of South America. Fossils have been found in Patagonia. Like other sebecosuchians, it was entirely terrestrial and carnivorous. The genus is currently represented by a single species, the type S. icaeorhinus...

had a ratio similar to those of the non-coelurosaurian theropods studied. Since tyrannosaurs are coelurosaurs, this is evidence that the advent of the Coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...

 marks the beginning of trend in theropod brain enlargement.

Pathology



SGM-Din 1, a Carcharodontosaurus saharicus skull, has a circular puncture wound in the nasal and "an abnormal projection of bone on the antorbital rim".

Discovery, etymology and taxonomic history



Carcharodontosaurus fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s were first found by Charles Depéret and J. Savornin in the Continental intercalaire of Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...

 (dating to the Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...

 stage) in 1927. Originally called Megalosaurus saharicus (many theropods were once erroneously referred to as Megalosaurus
Megalosaurus
Megalosaurus is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic period of Europe...

), its name was changed in 1931 by Ernst Stromer von Reichenbach to that used today. Stromer named Carcharodontosaurus "for its mainly Carcharodon-like teeth", which were "not recurved, almost bilaterally symmetrical but with convex edges." Further fossils were collected from the Baharija Formation of Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

, dating to the slightly later Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...

 stage. These first fossils of Carcharodontosaurus were destroyed during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. However, cranial material from a Carcharodontosaurus was again discovered in the Kem Kem Formation of Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

 in 1995 by paleontologist Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...

. Stephen Brusatte and Paul Sereno reported a second species of Carcharodontosaurus, found in the Echkar Formation of Niger
Niger
Niger , officially named the Republic of Niger, is a landlocked country in Western Africa, named after the Niger River. It borders Nigeria and Benin to the south, Burkina Faso and Mali to the west, Algeria and Libya to the north and Chad to the east...

, differing from C. saharicus in some aspects of the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 and braincase. This second species, which was discovered in Niger
Niger
Niger , officially named the Republic of Niger, is a landlocked country in Western Africa, named after the Niger River. It borders Nigeria and Benin to the south, Burkina Faso and Mali to the west, Algeria and Libya to the north and Chad to the east...

in 1997, was named C. iguidensis in December 2007.

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