Megalosaurus

Megalosaurus (meaning "great lizard", from Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic Epoch (Bathonian stage, 166 million years ago) of southern England. Although fossils from other areas have been assigned to the genus, the only certain remains of Megalosaurus come from Oxfordshire and date to the late Middle Jurassic.

The earliest remains of Megalosaurus were described in the 17th century, and were initially interpreted as the remains of elephants or giants. Megalosaurus was named in 1824 by William Buckland, becoming the first genus of dinosaur to be validly named (other than birds, not then recognized as dinosaurs). The type species is M. bucklandii, named in 1827 by Gideon Mantell, after Buckland. In 1842, Megalosaurus was one of three genera on which Richard Owen based his Dinosauria, along with Iguanodon and Hylaeosaurus. On Owen's directions a model was made as one of the Crystal Palace Dinosaurs, which greatly increased the public interest for prehistoric reptiles. Over 50 other species would eventually be classified under the genus; at first, this was because so few types of dinosaur had been identified, but the practice continued even into the 20th century after many other dinosaurs had been discovered. Today it is understood that none of these additional species was directly related to M. bucklandii, which is the only true Megalosaurus species. Because a complete skeleton of it has never been found, much is still unclear about its build.

The first naturalists who investigated Megalosaurus mistook it for a gigantic quadrupedal lizard in length. In 1842, Owen concluded that it was no longer than . Modern scientists were able to obtain a more accurate picture, by comparing Megalosaurus with its direct relatives in the Megalosauridae. Megalosaurus was about long, weighing about . It was bipedal, walking on stout hindlimbs, its horizontal torso balanced by a horizontal tail. Its forelimbs were short, though very robust. Megalosaurus had a rather large head, equipped with long curved teeth. It was generally a robust and heavily muscled animal.

At the time Megalosaurus lived, Europe formed an island archipelago bounded by then narrow Atlantic Ocean and Tethys Ocean, with Megalosaurus inhabiting an island formed by the London–Brabant Massif, where it likely served as the apex predator of its ecosystem, coexisting with other dinosaurs like the large sauropod Cetiosaurus, stegosaurs, ankylosaurs, and heterodontosaurids.

Discovery and naming

Edward Lhuyd's tooth (specimen OU 1328)

thumb|upright|Possible Megalosaurus tooth OU 1328

In 1699, Edward Lhuyd described what he believed to have been a fish tooth (called Plectronites), later believed to be part of a belemnite, that was illustrated alongside the holotype tooth of the sauropod "Rutellum impicatum" and another tooth, from a theropod, in 1699. Later studies found that the theropod tooth, known as specimen 1328 (University of Oxford coll. #1328; lost?) almost certainly was a tooth crown that belonged to an unknown species of Megalosaurus. OU 1328 has since been lost and it was not confidently assigned to Megalosaurus until the tooth was re-described by Delair & Sarjeant (2002). after "Scrotum humanum" in 1677 and "Rutellum impicatum" in 1699.

"Scrotum humanum"

Megalosaurus may have been the first non-avian dinosaur to be described in the scientific literature. The earliest possible fossil of the genus, from the Taynton Limestone Formation, was the lower part of a femur, discovered in the 17th century. Part of a bone was recovered from the Taynton Limestone Formation of Stonesfield limestone quarry, Oxfordshire in 1676. Sir Thomas Pennyson gave the fragment to naturalist Robert Plot, who published a description and illustration in his Natural History of Oxfordshire in 1676. It was the first illustration of a dinosaur bone published. Plot correctly identified the bone as the lower extremity of the thighbone or femur of a large animal and he recognized that it was too large to belong to any species known to be living in England. He therefore at first concluded it to be the thigh bone of a Roman war elephant and later that of a giant human, such as those mentioned in the Bible. The bone has since been lost, but the illustration is detailed enough that some have since identified it as that of Megalosaurus.

thumb|upright|left|Plot's illustration of the lower extremity of the femur dubbed "Scrotum humanum"

It has also been argued that this possible Megalosaurus bone was given the very first species name ever applied to an extinct dinosaur. Plot's engraving of the Cornwell bone was again used in a book by Richard Brookes in 1763. Brookes, in a caption, called it "Scrotum humanum", apparently comparing its appearance to a pair of "human testicles". However, it is possible that the attribution of this name stemmed from illustrator error, not Richard Brookes. In 1970, paleontologist Lambert Beverly Halstead pointed out that the similarity of Scrotum humanum to a modern species name, a so-called Linnaean "binomen" that has two parts, was not a coincidence. Linnaeus, the founder of modern taxonomy, had in the eighteenth century not merely devised a system for naming living creatures, but also for classifying geological objects. The book by Brookes was all about applying this latter system to curious stones found in England. According to Halstead, Brookes thus had deliberately used binomial nomenclature, and had in fact indicated the possible type specimen of a new biological genus. According to the rules of the International Code of Zoological Nomenclature (ICZN), the name Scrotum humanum in principle had priority over Megalosaurus because it was published first. That Brookes understood that the stone did not actually represent a pair of petrified testicles was irrelevant. Merely the fact that the name had not been used in subsequent literature meant that it could be removed from competition for priority, because the ICZN states that if a name has never been considered valid after 1899, it can be made a nomen oblitum, an invalid "forgotten name".

In 1993, after the death of Halstead, his friend William A.S. Sarjeant submitted a petition to the International Commission on Zoological Nomenclature to formally suppress the name Scrotum in favour of Megalosaurus. He wrote that the supposed junior synonym Megalosaurus bucklandii should be made a conserved name to ensure its priority. However, the Executive Secretary of the ICZN at the time, Philip K. Tubbs, did not consider the petition to be admissible, concluding that the term "Scrotum humanum", published merely as a label for an illustration, did not constitute the valid creation of a new name, and stated that there was no evidence it was ever intended as such. Furthermore, the partial femur was too incomplete to definitely be referred to Megalosaurus and not a different, contemporary theropod.

Buckland's research

thumb|right|Lithography from [[William Buckland's "Notice on the Megalosaurus or great Fossil Lizard of Stonesfield", 1824. Caption reads "anterior extremity of the right lower jaw of the Megalosaurus from Stonesfield near Oxford".]]

During the last part of the eighteenth century, the number of fossils in British collections quickly increased. According to a hypothesis published by science historian Robert Gunther in 1925, among them was a partial lower jaw of Megalosaurus. It was discovered about underground in a Stonesfield Slate mine during the early 1790s and was acquired in October 1797 by Christopher Pegge for 10s.6d. and added to the collection of the Anatomy School of Christ Church, Oxford.

In the early nineteenth century, more discoveries were made. In 1815, John Kidd reported the find of bones of giant tetrapods, again at the Stonesfield quarry. The layers there are currently considered part of the Taynton Limestone Formation, dating to the mid-Bathonian stage of the Jurassic Period. The bones were apparently acquired by William Buckland, Professor of Geology at the University of Oxford and fellow of Corpus Christi. Buckland also studied a lower jaw, according to Gunther the one bought by Pegge. Buckland did not know to what animal the bones belonged but, in 1818, after the Napoleonic Wars, the French comparative anatomist Georges Cuvier visited Buckland in Oxford and realized that they were those of a giant lizard-like creature. Buckland further studied the remains with Mary Morland (later his wife), and his friend William Conybeare who in 1821 referred to them as the "Huge Lizard". In 1822 Buckland and Conybeare, in a joint article to be included in Cuvier's Ossemens, intended to provide scientific names for both gigantic lizard-like creatures known at the time: the remains found near Maastricht would be named Mosasaurus – then seen as a land-dwelling animal – while for the British lizard Conybeare had devised the name "Megalosaurus", from the Greek μέγας, megas, "large". That year a publication failed to occur, but the physician James Parkinson already in 1822 announced the name "Megalosaurus", illustrating one of the teeth and revealing the creature was 40 feet long and eight feet high. It is generally considered that the name in 1822 was still a nomen nudum ("naked name"). Buckland, urged on by an impatient Cuvier, continued to work on the subject during 1823. Mary provided drawings of the bones, that were to be the basis of illustrating lithographies. Finally, on 20 February 1824, during the same meeting of the Geological Society of London in which Conybeare described a very complete specimen of Plesiosaurus, Buckland formally announced Megalosaurus. The descriptions of the bones in the Transactions of the Geological Society, in 1824, constitute a valid publication of the name.

thumb|Referred tail vertebra, NHMUK PV R9672. The top of its neural spine has broken off, which would have been about twice as long

By 1824, the material available to Buckland consisted of specimen OUM J13505, a piece of a right lower jaw with a single erupted tooth; OUM J13577, a posterior dorsal vertebra; OUM J13579, an anterior caudal vertebra; OUM J13576, a sacrum of five sacral vertebrae; OUM J13585, a cervical rib; OUM J13580, a rib; OUM J29881, an ilium of the pelvis, OUM J13563, a piece of the pubic bone; OUM J13565, a part of the ischium; OUM J13561, a thigh bone and OUM J13572, the lower part of a second metatarsal. As he himself was aware, these did not all belong to the same individual; only the sacrum was articulated. Because they represented several individuals, the described fossils formed a syntype series. By modern standards, from these a single specimen has to be selected to serve as the type specimen on which the name is based. In 1990, Ralph Molnar chose the famous dentary (front part of the lower jaw), OUM J13505, as such a lectotype. Because he was unaccustomed to the deep dinosaurian pelvis, much taller than with typical reptiles, Buckland misidentified several bones, interpreting the pubic bone as a fibula and mistaking the ischium for a clavicle. Buckland identified the organism as being a giant animal belonging to the Sauria – the Lizards, at the time seen as including the crocodiles - and he placed it in the new genus Megalosaurus, repeating an estimate by Cuvier that the largest pieces he described, indicated an animal 12 meters long in life.

Etymology

Buckland had not provided a specific name, as was not uncommon in the early nineteenth century, when the genus was still seen as the more essential concept. which however was not much used by later authors and is now considered a nomen oblitum. A year later, in 1827, Gideon Mantell included Megalosaurus in his geological survey of southeastern England, and assigned the species its current valid binomial name, Megalosaurus bucklandii. Until recently, the form Megalosaurus bucklandi was often used, a variant first published in 1832 by Christian Erich Hermann von Meyer – and sometimes erroneously ascribed to von Ritgen – but the more original M. bucklandii has priority.

Early reconstructions

thumb|1854 reconstruction in [[The Crystal Palace Dinosaurs|Crystal Palace Park guided by Richard Owen presents Megalosaurus as a quadruped; modern reconstructions make it bipedal, like most theropods]]

The first reconstruction was given by Buckland himself. He considered Megalosaurus to be a quadruped. He thought it was an "amphibian", i.e. an animal capable of both swimming in the sea and walking on land. Generally, in his mind Megalosaurus resembled a gigantic lizard, but Buckland already understood from the form of the thigh bone head that the legs were not so much sprawling as held rather upright. In the original description of 1824, Buckland repeated Cuvier's size estimate that Megalosaurus would have been 40 feet long with the weight of a seven foot tall elephant. However, this had been based on the remains present at Oxford. Buckland had also been hurried into naming his new reptile by a visit he had made to the fossil collection of Mantell, who during the lecture announced to have acquired a fossil thigh bone of enormous magnitude, twice as long as that just described. Today, this is known to have belonged to Iguanodon, or at least some iguanodontid, but at the time both men assumed this bone belonged to Megalosaurus also. Even taking into account the effects of allometry, heavier animals having relatively stouter bones, Buckland was forced in the printed version of his lecture to estimate the maximum length of Megalosaurus at 60 to 70 feet.

thumb|left|[[Édouard Riou's 1863 depiction of herbivore Iguanodon battling Megalosaurus]]

Around 1840, it became fashionable in England to espouse the concept of the transmutation of species as part of a general progressive development through time, as expressed in the work of Robert Chambers. In reaction, on 2 August 1841 Richard Owen during a lecture to the British Association for the Advancement of Science claimed that certain prehistoric reptilian groups had already attained the organisational level of present mammals, implying there had been no progress. Owen presented three examples of such higher level reptiles: Iguanodon, Hylaeosaurus and Megalosaurus. For these, the "lizard model" was entirely abandoned: they would have had an upright stance and a high metabolism. This also meant that earlier size estimates had been exaggerated. By simply adding the known length of the vertebrae, instead of extrapolating from a lizard, Owen arrived at a total body length for Megalosaurus of 30 feet. In the printed version of the lecture published in 1842, Owen united the three reptiles into a separate group: the Dinosauria. Megalosaurus was thus one of the three original dinosaurs.

thumb|Von Meyer's restoration of Megalosaurus from before 1897; showing it bipedal with long neural spines

In 1852, Benjamin Waterhouse Hawkins was commissioned to build a life-sized concrete model of Megalosaurus for the exhibition of prehistoric animals at the Crystal Palace Park in Sydenham, where it remains to this day. Hawkins worked under the direction of Owen and the statue reflected Owen's ideas that Megalosaurus would have been a mammal-like quadruped. The sculpture in Crystal Palace Park shows a conspicuous hump on the shoulders and it has been suggested this was inspired by a set of high vertebral spines acquired by Owen in the early 1850s. Today, they are seen as a separate genus Becklespinax, but Owen referred them to Megalosaurus. The models at the exhibition created a general public awareness for the first time, at least in England, that ancient reptiles had existed.

The presumption that carnivorous dinosaurs, like Megalosaurus, were quadrupeds was first challenged by the find of Compsognathus in 1859. That, however, was a very small animal, the significance of which for gigantic forms could be denied. In 1870, near Oxford, the type specimen of Eustreptospondylus was discovered – the first reasonably intact skeleton of a large theropod. It was clearly bipedal. Shortly afterwards, John Phillips created the first public display of a theropod skeleton in Oxford, arranging the known Megalosaurus bones, held by recesses in cardboard sheets, in a more or less natural position.

Later finds of Megalosaurus bucklandii

thumb|upright|left|Replica of theropod footprints attributed to Megalosaurus at the [[Oxford University Museum of Natural History.]]

The quarries at Stonesfield, which were worked until 1911, continued to produce Megalosaurus bucklandii fossils, mostly single bones from the pelvis and hindlimbs. Vertebrae and skull bones are rare. In 2010, Roger Benson counted a total of 103 specimens from the Stonesfield Slate, from a minimum of seven individuals. In 2008 Benson favoured this idea, In 1992 Robert Thomas Bakker claimed it represented a member of the Sinraptoridae; in 2007, Darren Naish thought it was a separate species belonging to the Abelisauroidea. In 2010, Benson pointed out that the fragment was basically indistinguishable from other known M. bucklandii maxillae, to which it had in fact not been compared by the other authors. Though the age disparity makes it problematic to assume an identity with Megalosaurus bucklandii, in 2009 Benson could not establish any relevant anatomical differences with M. bucklandii among the remains found at one site, the New Park Quarry, and therefore affirmed the reference to that species. However, in another site, the Oakham Quarry, the material contained one bone, an ilium, that was clearly dissimilar. According to Benson, such referrals are unprovable, as the tracks show no traits unique to Megalosaurus. Certainly they should be limited to finds that are of the same age as Megalosaurus bucklandii.

Finds from sites outside England, especially in France, have in the nineteenth and twentieth century been referred to M. bucklandii. In 2010 Benson considered these as either clearly different or too fragmentary to establish an identity.

Size and general build

left|thumb|Diagram showing known bones; with the [[lectotype and paralectotype material in white, and elements from other specimens in blue]]

Traditionally, most texts, following Owen's estimate of 1841, give a body length of 30 feet or nine meters for Megalosaurus. Gregory S. Paul in 1988 estimated the weight tentatively at 1.1 tons, given a thigh bone 76 centimeters long. The trend in the early twenty-first century to limit the material to the lectotype inspired even lower estimates, disregarding outliers of uncertain identity. Paul in 2010 estimated the size of Megalosaurus at in length and . However, the same year Benson claimed that Megalosaurus, though medium-sized, was still among the largest of Middle Jurassic theropods. Specimen NHMUK PV OR 31806, a thigh bone 803 millimeters long, would indicate a body weight of 943 kilograms, using the extrapolation method of J.F. Anderson - which method, optimized for mammals, tends to underestimate theropod masses by at least a third. Furthermore, thigh bone specimen OUM J13561 has a length of about 86 centimeters. The skeleton of Megalosaurus is highly ossified, indicating a robust and muscular animal, though the lower leg was not as heavily built as that of Torvosaurus, a close relative.

The Stonesfield Slate material contains no neck vertebrae; but a single broken anterior cervical vertebra is known from the New Park Quarry, specimen NHMUK PV R9674. The breakage reveals large internal air chambers. The vertebra is also otherwise heavily pneumatized, with large pleurocoels, pneumatic excavations, on its sides. The rear facet of the centrum is strongly concave. The neck ribs are short. The front dorsal vertebrae are slightly opisthocoelous, with convex front centrum facets and concave rear centrum facets. They are also deeply keeled, with the ridge on the underside representing about 50% of the total centrum height. The front dorsals perhaps have a pleurocoel above the diapophysis, the lower rib joint process. The rear dorsal vertebrae, according to Benson, are not pneumatized. They are slightly amphicoelous, with hollow centrum facets. They have secondary joint processes, forming a hyposphene–hypantrum complex, the hyposphene having a triangular transverse cross-section. The height of the dorsal spines of the rear dorsals is unknown, but a high spine on a tail vertebra of the New Park Quarry material, specimen NHMUK PV R9677, suggests the presence of a crest on the hip area. The spines of the five vertebrae of the sacrum form a supraneural plate, fused at the top. The undersides of the sacral vertebrae are rounded but the second sacral is keeled; normally it is the third or fourth sacral having a ridge. The sacral vertebrae seem not to be pneumatized but have excavations at their sides. The tail vertebrae are slightly amphicoelous, with hollow centrum facets on both the front and rear side. They have excavations at their sides and a longitudinal groove on the underside. The neural spines of the tail basis are transversely thin and tall, representing more than half of the total vertebral height. However, a comprehensive study by Roger Benson and colleagues in 2008, and several related analyses published in subsequent years, overturned the previous consensus by identifying several autapomorphies, or unique distinguishing characteristics, in the lower jaw that could be used to separate Megalosaurus from other megalosaurids.

Phylogeny

thumb|upright|Referred tibia, lateral view (left), posterior view (right). Lithograph drawn by James Erxleben in the 19th century

In 1824, Buckland assigned Megalosaurus to the Sauria, assuming within the Sauria a close affinity with modern lizards, more than with crocodiles. For a long time, the precise relationships of Megalosaurus remained vague. It was seen as a "primitive" member of the Carnosauria, the group in which most large theropods were united.

In the late 20th century the new method of cladistics allowed for the first time to exactly calculate how closely various taxa were related to each other. In 2012, Matthew Carrano et al. showed that Megalosaurus was the sister species of Torvosaurus within the Megalosaurinae, giving this cladogram:

Paleobiology

thumb|Map of Europe during the preceding [[Bajocian period, which had a broadly similar paleogeography to the Bathonian when Megalosaurus lived. The London-Brabant Massif is labelled "LBM", while the Armorican Massif is labelled "AM"]]

Megalosaurus lived in what is now Europe during the Bathonian stage of the Middle Jurassic (~166-168 million years ago). Repeated descriptions during the nineteenth and early twentieth century of Megalosaurus hunting Iguanodon (another of the earliest dinosaurs named) through the forests that then covered the continent are now known to be inaccurate, because Iguanodon skeletons are found in much younger Early Cretaceous formations. The only specimens belonging to Megalosaurus bucklandii are from the Lower/Middle Bathonian of Oxfordshire and Gloucestershire. Other roughly contemporaneous dinosaur species known from the Bathonian of Britain include the theropods Cruxicheiros (a large sized taxon), indeterminate ornithischians primarily known from teeth, including heterodontosaurids, stegosaurs, and ankylosaurs, and the sauropods Cardiodon (only known from teeth) with the seaway across England being very shallow, and showing evidence of at times being temporarily transformed into lagoons and terrestrial environments during the Bathonian. Plant fossils from the Taynton Limestone Formation from which many Megalosaurus fossils originate, representing the nearshore vegetation are largely dominated by conifers (including the living family Araucariaceae and the extinct family Cheirolepidiaceae) as well as the extinct seed plant group Bennettitales, with other plants including cycads (Ctenis), ferns (Phlebopteris, Coniopteris) Caytoniales, the living genus Ginkgo, and the seed ferns Pachypteris and Komlopteris, representing a probably seasonally dry coastal environment including mangroves.

Paleopathology

thumb|upright|Ribs and pelvic elements. The left rib fragment shows a healed fracture at the underside of the base of the capitulum. Work from the 1800s drawn by James Erxleben

A Megalosaurus rib figured in 1856 and 1884 by Sir Richard Owen has a pathological swollen spot near the base of its capitular process. The swollen spot appears to have been caused by a healed fracture and is located at the point where it would have articulated with its vertebra.

Species and synonyms

During the later nineteenth century, Megalosaurus was seen as the typical carnivorous dinosaur. If remains were found that were not deemed sufficiently distinct to warrant a separate genus, often single teeth, these were classified under Megalosaurus, which thus began to function as a wastebasket taxon, a sort of default genus. the "frightening one", a genus based on teeth. In 1858, Friedrich August Quenstedt named Megalosaurus cloacinus, based on a probable Late Triassic theropod tooth found near Bebenhausen, specimen SMNH 52457. It is a nomen dubium. In 1869 Eugène Eudes-Deslongchamps named Megalosaurus insignis, the "significant", based on a theropod tooth found near La Hève in Normandy that was 12 centimeters long, a third longer than the teeth of M. bucklandii. The name at first remained a nomen nudum, but a description was provided, in 1870, by Gustave Lennier. Today, it is considered a nomen dubium, an indeterminate member of the Theropoda, Today, this is either referred to Amanzia, Ceratosaurus or seen as a nomen dubium, an indeterminate member of the Ceratosauria. It is a nomen nudum, the fossils possibly belonging to Dakosaurus maximus. It is a nomen dubium, perhaps a theropod or some indeterminate predatory archosaur. The specific name refers to Pannonia. It is a nomen dubium, possibly an indeterminate member of the Dromaeosauridae or Tyrannosauroidea. In 1932, this was made a separate genus Betasuchus by Friedrich von Huene. In 1923, this became the genus Erectopus. In 1923, this was made a separate genus Altispinax. Today the renaming is generally rejected. In 1889, Richard Lydekker named Megalosaurus oweni, the specific name honouring Owen, based on a series of metatarsals from the Early Cretaceous, specimen BMNH R?2556?. In 1991, this was made a separate genus Valdoraptor. This had been largely motivated by a desire to annoy his rival Othniel Charles Marsh and the name has found no acceptance. In 1896, Charles Jean Julien Depéret named Megalosaurus crenatissimus, "the much crenelated", based on remains from the Late Cretaceous found in Madagascar. In 1955 this was made a separate genus Majungasaurus. The generic name Laelaps, used by Cope to denote a theropod, had been preoccupied by a mite. Marsh had therefore provided the replacement name Dryptosaurus, but Henry Fairfield Osborn, a partisan of Cope, rejected this replacement and thus in 1898 renamed Laelaps aquilunguis Cope 1866 into Megalosaurus aquilunguis.

Species named in the 20th century

thumb|Claw of Megalosaurus lonzeensis

In 1901 Baron Franz Nopcsa renamed Laelaps trihedrodon Cope 1877 into Megalosaurus trihedrodon. In the same publication Nopcsa renamed Poekilopleuron valens Leidy 1870 into Megalosaurus valens; this probably represents fossil material of Allosaurus. In 1902, Nopcsa named Megalosaurus hungaricus based on two teeth found in Transylvania, then part of the Kingdom of Hungary. The specimens, MAFI ob. 3106, were later lost. It represents an indeterminate theropod. He had first reported this claw in 1883, and as a result some sources by mistake indicate this year as the date of the naming. It perhaps represents a member of the Noasauridae, or an indeterminate member of the Coelurosauria. This is today seen as a nomen dubium, an indeterminate member of the Tetanurae. In 1909, Richard Lydekker named Megalosaurus woodwardi, based on a maxilla with tooth, specimen NHMUK PV OR 41352. This is today seen as a nomen dubium, an indeterminate member of the Theropoda. In 1926, this was made a separate genus Proceratosaurus. In 1920, Werner Janensch named Megalosaurus ingens, "the enormous", based on specimen MB R 1050, a 12 centimeter long tooth from German East Africa. It possibly represents a large member of the Carcharodontosauridae; Carrano e.a. saw it as an indeterminate member of the Tetanurae. Today, the genus Poekilopleuron is generally seen as valid. In the same publication, von Huene named two additional Megalosaurus species. The first was Megalosaurus parkeri, its specific name honouring William Kitchen Parker and based on a pelvis, leg bones and vertebrae from the Late Cretaceous. This was made the separate genus Metriacanthosaurus in 1964. The second was Megalosaurus nethercombensis, named after its provenance from Nethercombe and based on two dentaries, leg bones, a pelvis and vertebrae from the Middle Jurassic, which von Huene himself in 1932 made the separate genus Magnosaurus. In 1931/1932 this was made the separate genus Carcharodontosaurus. In 1956 von Huene by mistake named the same species as Megalosaurus africanus, intending to base it on remains from Morocco but referring the Algerian teeth; this implies that M. africanus is a junior objective synonym of M. saharicus. In 1926, von Huene named Megalosaurus lydekkeri, its specific name honouring Richard Lydekker, based on NHMUK OR 41352, i.e. the same specimen that had already been made the holotype of M. woodwardi (Lydekker, 1909). This implies that M. lydekkeri is a junior objective synonym of M. woodwardi. It is likewise seen as a nomen dubium. In 1932, a work by von Huene mentioned a Megalosaurus (Magnosaurus) woodwardi, a synonym of Magnosaurus woodwardi named in the same book. Its type specimen is differing from the earlier Megalosaurus woodwardi (Lydekker, 1909), the two names are not synonyms. In 1954 Samuel Welles named Megalosaurus wetherilli. This species is exceptional in being based on a rather complete skeleton, found in Arizona, from the Early Jurassic. Its specific name honours John Wetherill. In 1970, Welles made this the separate genus Dilophosaurus. In 1955, Albert-Félix de Lapparent named Megalosaurus mersensis based on a series of 23 vertebrae found near Tizi n'Juillerh in a layer of the El Mers Formation of Morocco. This probably represents a member of the Mesosuchia. In 1956, Alfred Sherwood Romer renamed Aggiosaurus nicaeensis Ambayrac 1913, based on a lower jaw found near Nice, on the authority of von Huene into Megalosaurus nicaeensis. Originally it had been considered to be some crocodilian; present opinion confirms this. Today it is seen as a nomen dubium, an indeterminate member of the Theropoda. It is a nomen dubium based on the tooth of some indeterminate predatory Triassic archosaur, found in Silesia, perhaps a theropod. It might represent a member of the Carcharodontosauridae. In 1970, Rodney Steel named two Megalosaurus species. Firstly, he renamed Iliosuchus incognitus Huene 1932 into Megalosaurus incognitus. Secondly, he renamed Nuthetes destructor Owen 1854 into Megalosaurus destructor. Both genera are today seen as not identical to Megalosaurus. Indeed, Sarcosaurus andrewsi is today by some scientists not seen as directly related to the type species of Sarcosaurus: Sarcosaurus woodi. Del Corro in 1974 named Megalosaurus chubutensis, based on specimen MACN 18.189, a tooth found in Chubut Province. It is a nomen dubium, a possible carcharodontosaurid, or a very large abelisaurid. He had earlier mentioned these species in an unpublished dissertation of 1983, implying they initially were invalid nomina ex dissertatione. However, his 1985 publication did not contain descriptions so the names are still nomina nuda. This is a nomen dubium, a possible member of the Abelisauridae. The change has found no acceptance. In 1973, Anatoly Konstantinovich Rozhdestvensky had renamed Poekilopleuron schmidti Kiprijanow 1883 into a Megalosaurus sp. However, as it is formally impossible to change a named species into an unnamed one, George Olshevsky in 1991 used the new combination Megalosaurus schmidti. It is a chimaera. In 1993, Ernst Probst and Raymund Windolf by mistake renamed Plateosaurus ornatus Huene 1905 into Megalosaurus ornatus by mentioning the latter name in a species list. This can be seen as a nomen vanum. The same publication listed the ichnospecies Megalosauropus teutonicus Kaever & Lapparent 1974 as a Megalosaurus teutonicus. In 1997, Windolf renamed Saurocephalus monasterii Münster 1846, based on a tooth found near Hannover, into Megalosaurus monasterii. It is a nomen dubium, an indeterminate member of the Theropoda. which was later followed by Peter Galton in 1998. It is a senior synonym of Gressylosaurus cambrensis Olshevsky 1991. or some other predatory archosaur.

Species list

The complex naming history can be summarized in a formal species list. The naming authors are directly mentioned behind the name. If the name has been changed, they are placed in parentheses and the authors of the changed name are mentioned behind them. The list also indicates whether a name has been insufficiently described (nomen nudum), is not taxonomically identifiable at the generic level (nomen dubium), or fallen out of use (nomen oblitum). Reclassifications under a different genus are mentioned behind the "=" sign; if the reclassification is today considered valid, it is listed under Reassigned species.

References

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Sources

• Carrano, M.T.; Benson, R.B.J.; & Sampson, S.D. (2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology 10(2): 211–300