| Megalosaurus | |
|---|---|
 | |
| Fossil specimens referred toM. bucklandii,Oxford University Museum of Natural History. The display shows most of the originalsyntype series, including thelectotype dentary, identified byBuckland in 1824 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Megalosauridae |
| Subfamily: | †Megalosaurinae |
| Genus: | †Megalosaurus Buckland, 1824 |
| Species: | †M. bucklandii |
| Binomial name | |
| †Megalosaurus bucklandii Mantell, 1827 | |
| Synonyms | |
| |
Megalosaurus (meaning "great lizard", fromGreekμέγας,megas, meaning 'big', 'tall' or 'great' andσαῦρος,sauros, meaning 'lizard') is an extinctgenus of large carnivoroustheropoddinosaurs of the MiddleJurassicEpoch (Bathonian stage, 166 million years ago) of southernEngland. Although fossils from other areas have been assigned to the genus, the only certain remains ofMegalosaurus come fromOxfordshire and date to the lateMiddle Jurassic.
The earliest remains ofMegalosaurus were described in the 17th century, and were initially interpreted as the remains of elephants or giants.Megalosaurus was named in 1824 byWilliam Buckland, becoming the first genus of (non-avian) dinosaur to be validly named. Thetype species isM. bucklandii, named in 1827 byGideon Mantell, after Buckland.[1] In 1842,Megalosaurus was one of three genera on whichRichard Owen based hisDinosauria, along withIguanodon andHylaeosaurus. On Owen's directions a model was made as one of theCrystal 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 toM. bucklandii, which is the only trueMegalosaurus species. Because a complete skeleton of it has never been found, much is still unclear about its build.
The first naturalists who investigatedMegalosaurus mistook it for a gigantic quadrupedal lizard 20 metres (66 ft) in length. In 1842, Owen concluded that it was no longer than 9 metres (30 ft). Modern scientists were able to obtain a more accurate picture, by comparingMegalosaurus with its direct relatives in theMegalosauridae.Megalosaurus was about 6 metres (20 ft) long, weighing about 700 kilograms (1,500 lb). 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 timeMegalosaurus lived, Europe formed an islandarchipelago bounded by then narrowAtlantic Ocean andTethys Ocean, withMegalosaurus inhabiting an island formed by theLondon–Brabant Massif, where it likely served as theapex predator of its ecosystem, coexisting with other dinosaurs like the large sauropodCetiosaurus,stegosaurs,ankylosaurs, andheterodontosaurids.
In 1699,Edward Lhuyd described what he believed to have been afish tooth (calledPlectronites), later believed to be part of abelemnite, that was illustrated alongside the holotypetooth of thesauropod "Rutellum impicatum" and another tooth, from atheropod, in 1699.[2][3] 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 ofMegalosaurus.[4] OU 1328 has since been lost and it was not confidently assigned toMegalosaurus until the tooth was re-described by Delair & Sarjeant (2002).[4]
OU 1328 was collected near Caswell, nearWitney,Oxfordshire sometime during the 17th century and became the third dinosaur fossil to ever be illustrated,[5] after "Scrotum humanum" in 1677 and "Rutellum impicatum" in 1699.
Megalosaurus may have been the first nonaviandinosaur to be described in the scientific literature. The earliest possible fossil of the genus, from theTaynton Limestone Formation, was the lower part of afemur, discovered in the 17th century. Part of a bone was recovered from the Taynton Limestone Formation ofStonesfield limestone quarry,Oxfordshire in 1676. Sir Thomas Pennyson gave the fragment to naturalistRobert Plot, who published a description and illustration in hisNatural History of Oxfordshire in 1676.[6] It was the first illustration of a dinosaur bone published.[7] Plot correctly identified the bone as the lower extremity of thethighbone orfemur 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 aRoman war elephant and later that of a giant human, such as those mentioned in the Bible.[8] The bone has since been lost, but the illustration is detailed enough that some have since identified it as that ofMegalosaurus.[9]
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It has also been argued that this possibleMegalosaurus bone was given the very firstspecies name ever applied to an extinct dinosaur. Plot's engraving of the Cornwell bone was again used in a book byRichard Brookes in 1763. Brookes, in a caption, called it "Scrotum humanum", apparently comparing its appearance to a pair of "humantesticles".[10] However, it is possible that the attribution of this name stemmed from illustrator error, not Richard Brookes.[11] In 1970, paleontologistLambert Beverly Halstead pointed out that the similarity ofScrotum humanum to a modern species name, a so-called Linnaean "binomen" that has two parts, was not a coincidence.Linnaeus, the founder of moderntaxonomy, 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 usedbinomial nomenclature, and had in fact indicated the possibletype specimen of a new biological genus. According to the rules of theInternational Code of Zoological Nomenclature (ICZN), the nameScrotum humanum in principle had priority overMegalosaurus 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 anomen oblitum, an invalid "forgotten name".[12]
In 1993, after the death of Halstead, his friend William A.S. Sarjeant submitted a petition to theInternational Commission on Zoological Nomenclature to formally suppress the nameScrotum in favour ofMegalosaurus. He wrote that the supposed junior synonymMegalosaurus bucklandii should be made aconserved 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 toMegalosaurus and not a different, contemporary theropod.[13]
During the last part of the eighteenth century, the number of fossils in British collections quickly increased. According to a hypothesis published byscience historianRobert Gunther in 1925, among them was a partial lower jaw ofMegalosaurus. It was discovered about 40 feet (12 m) underground in aStonesfield Slate mine during the early 1790s and was acquired in October 1797 byChristopher Pegge for10s.6d. and added to the collection of the Anatomy School ofChrist Church, Oxford.[14]
In the early nineteenth century, more discoveries were made. In 1815,John Kidd reported the find of bones of giant tetrapods, again at theStonesfield quarry. The layers there are currently considered part of the Taynton Limestone Formation, dating to the mid-Bathonian stage of theJurassic Period.[15] The bones were apparently acquired byWilliam Buckland, Professor of Geology at the University of Oxford and fellow ofCorpus 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 theNapoleonic Wars, theFrench comparative anatomistGeorges Cuvier visited Buckland in Oxford and realized that they were those of a giantlizard-like creature.[16] Buckland further studied the remains withMary Morland (later his wife),[17] and his friendWilliam 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'sOssemens, intended to provide scientific names for both gigantic lizard-like creatures known at the time: the remains found nearMaastricht would be namedMosasaurus – then seen as a land-dwelling animal – while for the British lizard Conybeare had devised the name "Megalosaurus", from the Greek μέγας,megas, "large"[citation needed]. That year a publication failed to occur, but the physicianJames 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.[18] It is generally considered that the name in 1822 was still anomen nudum ("naked name").[19] Buckland, urged on by an impatient Cuvier, continued to work on the subject during 1823.Mary provide drawings of the bones, that were to be the basis of illustratinglithographies. Finally, on 20 February 1824, during the same meeting of theGeological Society of London in which Conybeare described a very complete specimen ofPlesiosaurus, Buckland formally announcedMegalosaurus. The descriptions of the bones in theTransactions of the Geological Society, in 1824, constitute a valid publication of the name.[9][20]Megalosaurus was the first non-avian dinosaur genus named; the first of which the remains had with certainty been scientifically described wasStreptospondylus, in 1808 by Cuvier.[21]
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 dorsalvertebra; OUM J13579, an anterior caudal vertebra; OUM J13576, asacrum of five sacral vertebrae; OUM J13585, a cervical rib; OUM J13580, a rib; OUM J29881, anilium of thepelvis, OUM J13563, a piece of thepubic bone; OUM J13565, a part of theischium; OUM J13561, a thigh bone and OUM J13572, the lower part of a secondmetatarsal. 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 asyntype 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 famousdentary (front part of the lower jaw),OUM J13505, as such alectotype.[22] Because he was unaccustomed to the deep dinosaurian pelvis, much taller than with typical reptiles, Buckland misidentified several bones, interpreting the pubic bone as afibula and mistaking the ischium for aclavicle. Buckland identified the organism as being a giant animal belonging to theSauria – the Lizards, at the time seen as including the crocodiles - and he placed it in the new genusMegalosaurus, repeating an estimate by Cuvier that the largest pieces he described, indicated an animal 12 meters long in life.[20]
Buckland had not provided aspecific name, as was not uncommon in the early nineteenth century, when the genus was still seen as the more essential concept.[1] In 1826,Ferdinand von Ritgen gave this dinosaur a complete binomial,Megalosaurus conybeari,[23] which however was not much used by later authors and is now considered anomen oblitum. A year later, in 1827,Gideon Mantell includedMegalosaurus in his geological survey of southeastern England, and assigned the species its current valid binomial name,Megalosaurus bucklandii.[24] Until recently, the formMegalosaurus bucklandi was often used, a variant first published in 1832 byChristian Erich Hermann von Meyer[25] – and sometimes erroneously ascribed to von Ritgen – but the more originalM. bucklandii has priority.
The first reconstruction was given by Buckland himself. He consideredMegalosaurus 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 mindMegalosaurus 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 thatMegalosaurus 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 toIguanodon, or at least someiguanodontid, but at the time both men assumed this bone belonged toMegalosaurus also. Even taking into account the effects ofallometry, heavier animals having relatively stouter bones, Buckland was forced in the printed version of his lecture to estimate the maximum length ofMegalosaurus at 60 to 70 feet.[20] The existence ofMegalosaurus posed some problems for Christianorthodoxy, which typically held that suffering and death had only come into the world throughOriginal Sin, which seemed irreconcilable with the presence of a gigantic devouring reptile during apre-Adamitic phase of history. Buckland rejected the usual solution, that such carnivores would originally have been peaceful vegetarians, as infantile and claimed in one of theBridgewater Treatises thatMegalosaurus had played a beneficial role in creation by ending the lives of old and ill animals, "to diminish the aggregate amount of animal suffering".[26]
Around 1840, it became fashionable in England to espouse the concept of thetransmutation of species as part of a general progressive development through time, as expressed in the work ofRobert Chambers. In reaction, on 2 August 1841Richard Owen during a lecture to theBritish 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 andMegalosaurus. 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 forMegalosaurus 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.[27]
In 1852,Benjamin Waterhouse Hawkins was commissioned to build a life-sized concrete model ofMegalosaurus for theexhibition 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 thatMegalosaurus 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 genusBecklespinax, but Owen referred them toMegalosaurus.[28][29] The models at the exhibition created a general public awareness for the first time, at least in England, that ancient reptiles had existed.[30]
The presumption that carnivorous dinosaurs, likeMegalosaurus, were quadrupeds was first challenged by the find ofCompsognathus 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 ofEustreptospondylus 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 knownMegalosaurus bones, held by recesses in cardboard sheets, in a more or less natural position.[28] During the 1870s,North American discoveries of large theropods, likeAllosaurus, confirmed that they were bipedal. TheOxford University Museum of Natural History display contains most of the specimens from the original description by Buckland.[31]
The quarries atStonesfield, which were worked until 1911, continued to produceMegalosaurus bucklandii fossils, mostly single bones from thepelvis andhindlimbs. 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.[33] It has been contentious whether this material represents just a singletaxon. In 2004,Julia Day andPaul Barrett claimed that there were twomorphotypes present, based on small differences in the thighbones.[34] In 2008 Benson favoured this idea,[35] but in 2010 concluded the differences were illusory.[33] A maxilla fragment, specimen OUM J13506, was, in 1869 assigned, byThomas Huxley, toM. bucklandii.[36] In 1992Robert Thomas Bakker claimed it represented a member of theSinraptoridae;[37] in 2007,Darren Naish thought it was a separate species belonging to theAbelisauroidea.[28] In 2010, Benson pointed out that the fragment was basically indistinguishable from other knownM. bucklandii maxillae, to which it had in fact not been compared by the other authors.[33]
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Apart from the finds in theTaynton Limestone Formation, in 1939Sidney Hugh Reynolds referred remains toMegalosaurus that had been found in the olderChipping Norton Limestone Formation dating from the earlyBathonian, about 30 single teeth and bones.[38][39] Though the age disparity makes it problematic to assume an identity withMegalosaurus bucklandii, in 2009 Benson could not establish any relevant anatomical differences withM. 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.[15]
Sometimestrace fossils have been referred toMegalosaurus or to theichnogenusMegalosauripus. In 1997, a famous group offossilized footprints (ichnites) was found in a limestone quarry atArdley, 20 kilometers northeast ofOxford. They were thought to have been made byMegalosaurus and possibly also some left byCetiosaurus. There are replicas of some of these footprints, set across the lawn of theOxford University Museum of Natural History. One track was of a theropod accelerating from walking to running.[40] According to Benson, such referrals are unprovable, as the tracks show no traits unique toMegalosaurus. Certainly they should be limited to finds that are of the same age asMegalosaurus bucklandii.[33]In 2024 five more sets of tracks were discovered at a nearbyBicester quarry, with one of them showing clear features of largetridactyl theropod feet distinctive ofMegalosaurus.[41]
Finds from sites outside England, especially in France, have in the nineteenth and twentieth century been referred toM. bucklandii. In 2010 Benson considered these as either clearly different or too fragmentary to establish an identity.[33]
Since the first finds, many otherMegalosaurus bones have been recovered; however, no complete skeleton has yet been found. Therefore, the details of its physical appearance cannot be certain. However, a fullosteology of all known material was published in 2010 by Benson.[33]
Traditionally, most texts, following Owen's estimate of 1841, give a body length of 30 feet or nine meters forMegalosaurus.[42] The lack of an articulated dorsal vertebral series makes it difficult to determine an exact size.David Bruce Norman in 1984 thoughtMegalosaurus was seven to eight meters long.[43] Gregory S. Paul in 1988 estimated the weight tentatively at 1.1 tons, given a thigh bone 76 centimeters long.[44] 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 ofMegalosaurus at 6 meters (20 ft) in length and 700 kilograms (1,500 lb).[45] However, the same year Benson claimed thatMegalosaurus, 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.[33]
In general,Megalosaurus had the typical build of a large theropod. It was bipedal, the horizontal torso being balanced by a long horizontal tail. The hindlimbs were long and strong with three forward-facing weight-bearing toes, the forelimbs relatively short but exceptionally robust and probably carrying three digits. Being acarnivore, its large elongated head bore long dagger-like teeth to slice the flesh of its prey.[42] The skeleton ofMegalosaurus is highly ossified, indicating a robust and muscular animal, though the lower leg was not as heavily built as that ofTorvosaurus, a close relative.[33]
The skull ofMegalosaurus is poorly known. The discovered skull elements are generally rather large in relation to the rest of the material. This can either be coincidental or indicate thatMegalosaurus had an uncommonly large head. Thepraemaxilla is not known, making it impossible to determine whether the snout profile was curved or rectangular. A rather stubby snout is suggested by the fact that the front branch of themaxilla was short. In the depression around theantorbital fenestra to the front, a smaller non-piercing hollowing can be seen that is probably homologous to thefenestra maxillaris. The maxilla bears 13 teeth. The teeth are relatively large, with a crown length up to seven centimeters. The teeth are supported from behind by tall, triangular, unfused interdental plates. The cutting edges bear 18 to 20denticula per centimeter. The tooth formula is probably 4, 13-14/13-14. Thejugal bone is pneumatized, pierced by a large foramen from the direction of the antorbital fenestra. It was probably hollowed out by an outgrowth of anair sac in thenasal bone. Such a level of pneumatisation of the jugal is not known from other megalosaurids and might represent a separateautapomorphy.[33]
The lower jaw is rather robust. It is also straight in top view, without much expansion at the jaw tip, suggesting the lower jaws as a pair, themandibula, were narrow. Several traits in 2008 identified as autapomorphies, later transpired to have been the result of damage. However, a unique combination of traits is present in the wide longitudinal groove on the outer side (shared withTorvosaurus), the small third dentary tooth and a vascular channel, below the row of interdental plates, that only is closed from the fifth tooth position onwards. The number of dentary teeth was probably 13 or 14, though the preserved damaged specimens show at most 11 tooth sockets. The interdental plates have smooth inner sides, whereas those of the maxilla are vertically grooved; the same combination is shown byPiatnitzkysaurus. Thesurangular has no bony shelf, or even ridge, on its outer side. There is laterally an oval opening present in front of the jaw joint, aforamen surangulare posterior, but a secondforamen surangulare anterior to the front of it is lacking.[33]
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Although the exact numbers are unknown, thevertebral column ofMegalosaurus was probably divided into 10 neck vertebrae, 13 dorsal vertebrae, five sacral vertebrae and 50 to 60 tail vertebrae, as is common for basalTetanurae.[46]
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 largepleurocoels, pneumatic excavations, on its sides. The rear facet of the centrum is strongly concave. The neck ribs are short. The front dorsal vertebrae are slightlyopisthocoelous, 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 thediapophysis, 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 ahyposphene–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.[33]
The shoulderblade orscapula is short and wide, its length about 6.8 times the minimum width; this is a rare and basal trait within Tetanurae. Its top curves slightly to the rear in side view. On the lower outer side of the blade a broad ridge is present, running from just below the shoulder joint to about mid-length where it gradually merges with the blade surface. The middle front edge over about 30% of its length is thinned, forming a slightly protruding crest. The scapula constitutes about half of the shoulder joint, which is orientated obliquely sideways and to below. Thecoracoid is in all known specimens fused with the scapula into ascapulocoracoid, lacking a visiblesuture. The coracoid as such is an oval bone plate, with its longest side attached to the scapula. It is pierced by a large ovalforamen but the usual boss for the attachment of the upper arm muscles is lacking.[33]
Thehumerus is very robust with strongly expanded upper and lower ends. Humerus specimen OUMNH J.13575 has a length of 388 millimeters. Its shaft circumference equals about half of the total humerus length. The humerus head continues to the front and the rear into large bosses, together forming a massive bone plate. On the front outer side of the shaft a large triangulardeltopectoral crest is present, the attachment for theMusculus pectoralis major and theMusculus deltoideus. It covers about the upper half of the shaft length, its apex positioned rather low. Theulna is extremely robust, for its absolute size more heavily built than with any other known member of the Tetanurae. The only known specimen, NHMUK PV OR 36585, has a length of 232 millimeters and a minimal shaft circumference of 142 millimeters. The ulna is straight in front view and has a largeolecranon, the attachment process for theMusculus triceps brachii.Radius, wrist and hand are unknown.[33]
In the pelvis, theilium is long and low, with a convex upper profile. Its front blade is triangular and rather short; at the front end there is a small drooping point, separated by a notch from the pubic peduncle. The rear blade is roughly rectangular. The outer side of the ilium is concave, serving as an attachment surface for theMusculus iliofemoralis, the main thigh muscle. Above the hip joint, on this surface a low vertical ridge is present with conspicuous vertical grooves. The bottom of the rear blade is excavated by a narrow but deep trough forming a bony shelf for the attachment of theMusculus caudofemoralis brevis. The outer side of the rear blade does not match the inner side, which thus can be seen as a separate "medial blade" that in side view is visible in two places: in the corner between outer side and the ischial peduncle and as a small surface behind the extreme rear tip of the outer side of the rear blade. The pubic bone is straight. The pubic bones of both pelvis halves are connected via narrow bony skirts that originated at a rather high position on the rear side and continued downwards to a point low on the front side of the shaft. The ischium is S-shaped in side view, showing at the transition point between the two curvatures a rough boss on the outer side. On the front edge of the ischial shaft an obturator process is present in the form of a low ridge, at its top separated from the shaft by a notch. To below, this ridge continues into an exceptionally thick bony skirt at the inner rear side of the shaft, covering over half of its length. Towards the end of the shaft, this skirt gradually merges with it. The shaft eventually ends in a sizeable "foot" with a convex lower profile.[33]
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The thigh bone is straight in front view. Seen from the same direction its head is perpendicular to the shaft, seen from above it is orientated 20° to the front. Thegreater trochanter is relatively wide and separated from the robustlesser trochanter in front of it, by a fissure. At the front base of the lesser trochanter a low accessory trochanter is present. At the lower end of the thigh bone a distinct front, extensor, groove separates thecondyles. At the upper inner side of this groove a rough area is present continuing inwards into a longitudinal ridge, a typical megalosauroid trait. Theshinbone, ortibia, is relatively straight, slightly curving inwards. To below, its shaft progressively flattens from front to rear, resulting in a generally oval cross-section. For about an eighth of its length the front lower end of the shaft is covered by a vertical branch of theastragalus. Of the foot, only the second, third and fourthmetatarsals are known, the bone elements that were connected to the three weight-bearing toes. They are straight and robust, showing ligament pits at their lower sides. The third metatarsal has no clear condyles at its lower end, resulting in a more flexible joint, allowing for a modicum of horizontal movement. The top inner side of the third metatarsal carries a unique ridge that fits into a groove along the top outer side of the second metatarsal, causing a tighter connection.[33]
For decades after its discovery,Megalosaurus was seen by researchers as the definitive or typical large carnivorous dinosaur. As a result, it began to function as a "wastebasket taxon", and many large or small carnivorous dinosaurs from Europe and elsewhere were assigned to the genus. This slowly changed during the 20th century, when it became common to restrict the genus to fossils found in the middle Jurassic of England. Further restriction occurred in the late 20th and early 21st centuries, researchers such asRonan Allain andDan Chure suggesting that the Stonesfield Slate fossils perhaps belonged to several, possibly not directly related, species of theropod dinosaur. Subsequent research seemed to confirm this hypothesis, and the genusMegalosaurus and speciesM. bucklandii became generally regarded as limited to the taxon having produced the lectotype, the dentary of the lower jaw. Furthermore, several researchers failed to find any characteristics in that jaw that could be used to distinguishMegalosaurus from its relatives, which would mean the genus were anomen dubium.[35] 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 severalautapomorphies, or unique distinguishing characteristics, in the lower jaw that could be used to separateMegalosaurus from other megalosaurids.[35]
Various distinguishing traits of the lower jaw have been established. The longitudinal groove on the outer surface of the dentary is wide. The third tooth socket of the dentary is not enlarged. Seen from above, the dentary is straight without an expanded jaw tip. The interdental plates, reinforcing the teeth from behind, of the lower jaw are tall. Benson also concluded it would be mostparsimonious to assume that the Stonesfield Slate material represents a single species. If so, several additional distinctive traits can be observed in other parts of the skeleton. The low vertical ridge on the outer side of the ilium, above the hip joint, shows parallel vertical grooves. The bony skirts between the shafts of the ischia are thick and touch each other forming an almost flat surface. There is a boss present on the lower outer side of the ischium shaft with a rough surface. The underside of the second sacral vertebra has an angular longitudinal keel. A ridge on the upper side of the third metatarsal connected to a groove in the side of the second metatarsal. The middle of the front edge of the scapula forms a thin crest.[47]
In 1824, Buckland assignedMegalosaurus to the Sauria, assuming within the Sauria a close affinity with modern lizards, more than with crocodiles.[20] In 1842, Owen madeMegalosaurus one of the first three genera placed in theDinosauria.[27] In 1850, PrinceCharles Lucien Bonaparte coined a separate familyMegalosauridae withMegalosaurus as thetype genus.[48] For a long time, the precise relationships ofMegalosaurus remained vague. It was seen as a "primitive" member of theCarnosauria, the group in which most large theropods were united.[49]
In the late 20th century the new method ofcladistics allowed for the first time to exactly calculate how closely various taxa were related to each other. In 2012, Matthew Carranoet al. showed thatMegalosaurus was thesister species ofTorvosaurus within theMegalosaurinae,[50] giving thiscladogram:[51]
Megalosaurus lived in what is now Europe during theBathonian stage of theMiddle Jurassic (~166-168 million years ago). Repeated descriptions during the nineteenth and early twentieth century ofMegalosaurus huntingIguanodon (another of the earliest dinosaurs named) through the forests that then covered the continent are now known to be inaccurate, becauseIguanodon skeletons are found in much younger EarlyCretaceous formations. The only specimens belonging toMegalosaurus bucklandii are from the Lower/Middle Bathonian of Oxfordshire and Gloucestershire.[46] No material from outside the Bathonian formations of England can be referred toMegalosaurus.[52] Other roughly contemporaneous dinosaur species known from the Bathonian of Britain include the theropodsCruxicheiros (a large sized taxon),[52]Iliosuchus (a dubious taxon only known from fragmentary remains), the small tyrannosauroidProceratosaurus, and other indeterminate theropods known from teeth, suggested to includedromaeosaurs,troodontids, andtherizinosaurs,[53] indeterminateornithischians primarily known from teeth, includingheterodontosaurids,stegosaurs, andankylosaurs,[54] and the sauropodsCardiodon (only known from teeth)[46] andCetiosaurus.[45]Megalosaurus may have hunted stegosaurs and sauropods.[42]
Benson in 2010 concluded from its size and common distribution thatMegalosaurus was theapex predator of itshabitat. He saw the absence ofCetiosaurus on the FrenchArmorican Massif as an indication thatMegalosaurus too did not live on that island and was limited to theLondon-Brabant Massif,[33] atectonic high that during this period formed an island landmass including parts of southern Britain and adjacent areas of northern France, the Netherlands, Belgium and western Germany, suggested to be comparable in size to Cuba with an area of around 100,000 square kilometres (39,000 sq mi). It has been questioned why the dinosaurs of the island did not experienceinsular dwarfism, as would be expected for an island of this size. A possible explanation for this is that the island remained ecologically connected to the much larger landmass comprising northern Britain (the Scottish Massif), theFennoscandian Shield and the now submerged region in theNorth Sea between them,[55] 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.[56] Plant fossils from theTaynton Limestone Formation from which manyMegalosaurus fossils originate, representing the nearshore vegetation are largely dominated by conifers (including the living familyAraucariaceae and the extinct familyCheirolepidiaceae) as well as the extinct seed plant groupBennettitales, with other plants includingcycads (Ctenis), ferns (Phlebopteris,Coniopteris)Caytoniales, the living genusGinkgo, and theseed fernsPachypteris andKomlopteris, representing a probably seasonally dry coastal environment includingmangroves.[57]
AMegalosaurus rib figured in 1856 and 1884 bySir Richard Owen has a pathological swollen spot near the base of itscapitular 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.[58]
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 underMegalosaurus, which thus began to function as awastebasket taxon, a sort of default genus.[42] Eventually,Megalosaurus contained more species than any other non-avian dinosaur genus,[19] most of them of dubious validity. During the twentieth century, this practice was gradually discontinued; but scientists discovering theropods that had been mistakenly classified under a different animal group in older literature, still felt themselves forced to rename them, again choosingMegalosaurus as the default generic name.[15]
In 1857,Joseph Leidy renamedDeinodon horridus (Leidy, 1856) intoMegalosaurus horridus,[59] the "frightening one", a genus based on teeth. In 1858,Friedrich August Quenstedt namedMegalosaurus cloacinus,[60] based on a probable Late Triassic theropod tooth found nearBebenhausen, specimen SMNH 52457. It is anomen dubium.[61] In 1869Eugène Eudes-Deslongchamps namedMegalosaurus insignis, the "significant", based on a theropod tooth found nearLa Hève inNormandy that was 12 centimeters long, a third longer than the teeth ofM. bucklandii.[62] The name at first remained anomen nudum, but a description was provided, in 1870, byGustave Lennier.[63] Today, it is considered anomen dubium, an indeterminate member of the Theropoda,[64] the specimen having in 1944 been destroyed by a bombardment. In 1870,Jean-Baptiste Greppin namedMegalosaurus meriani based on specimen MH 350, a premaxillary tooth found nearMoutier and part of the collection ofPeter Merian.[65] Today, this is either referred toAmanzia,Ceratosaurus or seen as anomen dubium, an indeterminate member of theCeratosauria.[64] In 1871,Emanuel Bunzel named remains found nearSchnaitheimMegalosaurus schnaitheimi.[66] It is anomen nudum, the fossils possibly belonging toDakosaurus maximus.[67] In 1876, J. Henry, a science teacher atBesançon, in a published dissertation named four Late Triassic possible dinosaur teeth found nearMoisseyMegalosaurus obtusus, "the blunt one".[68] It is anomen dubium, perhaps a theropod or some indeterminate predatoryarchosaur.[67] In 1881,Harry Govier Seeley named two possible theropod teeth found inAustriaMegalosaurus pannoniensis.[69] The specific name refers toPannonia. It is anomen dubium, possibly an indeterminate member of theDromaeosauridae orTyrannosauroidea.[67] In 1883, Seeley namedMegalosaurus bredai, based on a thigh bone, specimen NHMUK PV OR 42997 found near Maastricht, theNetherlands. The specific name honoursJacob Gijsbertus Samuël van Breda.[70] In 1932, this was made a separate genusBetasuchus byFriedrich von Huene.[71]
In 1882,Henri-Émile Sauvage named remains found atLouppy-le-Château, teeth and vertebrae from the Early Cretaceous,Megalosaurus superbus, "the proud one".[72] In 1923, this became the genusErectopus.[73] In 1884/1885,Wilhelm Barnim Dames, based on specimen UM 84, a tooth from the Early Cretaceous, namedMegalosaurus dunkeri, the specific name honouringWilhelm Dunker.[74] In 1923, this was made a separate genusAltispinax.[73] In 1885,Joseph Henri Ferdinand Douvillé renamedDakosaurus gracilis Quenstedt 1885 intoMegalosaurus gracilis.[75] Today the renaming is generally rejected. In 1889,Richard Lydekker namedMegalosaurus oweni, the specific name honouring Owen, based on a series of metatarsals from the Early Cretaceous, specimen BMNH R?2556?.[76] In 1991, this was made a separate genusValdoraptor.[77] In 1892,Edward Drinker Cope renamedCeratosaurus nasicornis Marsh 1884 intoMegalosaurus nasicornis.[78] This had been largely motivated by a desire to annoy his rivalOthniel Charles Marsh and the name has found no acceptance. In 1896,Charles Jean Julien Depéret namedMegalosaurus crenatissimus, "the much crenelated", based on remains from the Late Cretaceous found inMadagascar.[79] In 1955 this was made a separate genusMajungasaurus.[80] The generic nameLaelaps, used by Cope to denote a theropod, had been preoccupied by amite. Marsh had therefore provided the replacement nameDryptosaurus, butHenry Fairfield Osborn, a partisan of Cope, rejected this replacement and thus in 1898 renamedLaelaps aquilunguis Cope 1866 intoMegalosaurus aquilunguis.[81]
In 1901 BaronFranz Nopcsa renamedLaelaps trihedrodon Cope 1877 intoMegalosaurus trihedrodon.[82] In the same publication Nopcsa renamedPoekilopleuron valens Leidy 1870 intoMegalosaurus valens; this probably represents fossil material ofAllosaurus.[83] In 1902, Nopcsa namedMegalosaurus hungaricus based on two teeth found inTransylvania,[84] then part of theKingdom of Hungary. The specimens, MAFI ob. 3106, were later lost. It represents an indeterminate theropod.[61] In 1903,Louis Dollo namedMegalosaurus lonzeensis based on a manual claw found nearLonzee inBelgium.[85] He had first reported this claw in 1883,[86] and as a result some sources by mistake indicate this year as the date of the naming. It perhaps represents a member of theNoasauridae, or an indeterminate member of theCoelurosauria.[64] In 1907 or 1908, von Huene renamedStreptospondylus cuvieri, based on a presently lost partial vertebra, intoMegalosaurus cuvieri.[87] This is today seen as anomen dubium, an indeterminate member of the Tetanurae.[88] In 1909,Richard Lydekker namedMegalosaurus woodwardi, based on a maxilla with tooth, specimen NHMUK PV OR 41352.[89] This is today seen as anomen dubium, an indeterminate member of the Theropoda.[64]
In 1910,Arthur Smith Woodward namedMegalosaurus bradleyi based on a skull from the Middle Jurassic, the specific name honouring the collector F. Lewis Bradley.[90] In 1926, this was made a separate genusProceratosaurus.[91] In 1920,Werner Janensch namedMegalosaurus ingens, "the enormous", based on specimen MB R 1050, a 12 centimeter long tooth fromGerman East Africa.[92] It possibly represents a large member of theCarcharodontosauridae; Carrano e.a. saw it as an indeterminate member of the Tetanurae.[64]M. ingens is now seen as a specimen ofTorvosaurus. In 1923, von Huene renamedPoekilopleuron bucklandii Eudes-Deslongchamps 1838 intoMegalosaurus poikilopleuron.[73] Today, the genusPoekilopleuron is generally seen as valid.[93] In the same publication, von Huene named two additionalMegalosaurus species. The first wasMegalosaurus parkeri, its specific name honouringWilliam Kitchen Parker and based on a pelvis, leg bones and vertebrae from the Late Cretaceous. This was made the separate genusMetriacanthosaurus in 1964.[94] The second wasMegalosaurus nethercombensis, named after its provenance fromNethercombe and based on two dentaries, leg bones, a pelvis and vertebrae from the Middle Jurassic, which von Huene himself in 1932 made the separate genusMagnosaurus.[71] In 1925, Depéret, based on two teeth fromAlgeria, namedMegalosaurus saharicus.[95] In 1931/1932 this was made the separate genusCarcharodontosaurus.[96] In 1956 von Huene by mistake named the same species asMegalosaurus africanus, intending to base it on remains fromMorocco but referring the Algerian teeth;[97] this implies thatM. africanus is ajunior objective synonym ofM. saharicus. In 1926, von Huene namedMegalosaurus lydekkeri, its specific name honouring Richard Lydekker, based on NHMUK OR 41352, i.e. the same specimen that had already been made theholotype ofM. woodwardi (Lydekker, 1909).[98] This implies thatM. lydekkeri is a junior objective synonym ofM. woodwardi. It is likewise seen as anomen dubium.[64]
In the same publication von Huene namedMegalosaurus terquemi based on three teeth found nearHettingen, its specific name honouringOlry Terquem. It is seen as anomen dubium, the fossil material probably representing some member of thePhytosauria or some other archosaur.[99] In 1932, a work by von Huene mentioned aMegalosaurus (Magnosaurus) woodwardi, a synonym ofMagnosaurus woodwardi named in the same book.[71] Its type specimen is differing from the earlierMegalosaurus woodwardi (Lydekker, 1909), the two names are not synonyms. In 1954Samuel Welles namedMegalosaurus wetherilli. This species is exceptional in being based on a rather complete skeleton, found inArizona, from the Early Jurassic. Its specific name honours John Wetherill.[100] In 1970, Welles made this the separate genusDilophosaurus.[101] In 1955,Albert-Félix de Lapparent namedMegalosaurus mersensis based on a series of 23 vertebrae found nearTizi n'Juillerh in a layer of theEl Mers Formation of Morocco.[102] This probably represents a member of theMesosuchia.[67] In 1956,Alfred Sherwood Romer renamedAggiosaurus nicaeensis Ambayrac 1913, based on a lower jaw found nearNice, on the authority of von Huene intoMegalosaurus nicaeensis.[103] Originally it had been considered to be some crocodilian; present opinion confirms this.[67] In 1957, de Lapparent namedMegalosaurus pombali based on three teeth found nearPombal in the Jurassic ofPortugal.[104] Today it is seen as anomen dubium, an indeterminate member of the Theropoda.[67]
In 1965,Oskar Kuhn renamedZanclodon silesiacus Jaekel 1910 intoMegalosaurus? silesiacus.[105] It is anomen dubium based on the tooth of some indeterminate predatory Triassic archosaur, found inSilesia, perhaps a theropod.[67] In 1966,Guillermo del Corro namedMegalosaurus inexpectatus, named "the unexpected" as it was discovered on a sauropod site with remains ofChubutisaurus, based on specimen MACN 18.172, a tooth found inArgentina.[106] It might represent a member of the Carcharodontosauridae.[64] In 1970,Rodney Steel named twoMegalosaurus species.[107] Firstly, he renamedIliosuchus incognitus Huene 1932 intoMegalosaurus incognitus. Secondly, he renamedNuthetes destructor Owen 1854 intoMegalosaurus destructor. Both genera are today seen as not identical toMegalosaurus.[83]Michael Waldman in 1974 renamedSarcosaurus andrewsi Huene 1932 intoMegalosaurus andrewsi.[108] Indeed,Sarcosaurus andrewsi is today by some scientists not seen as directly related to thetype species ofSarcosaurus:Sarcosaurus woodi.[28] In the same publication Waldman namedMegalosaurus hesperis, "the western one", based on skull fragments from the Middle Jurassic. In 2008 this was made the separate genusDuriavenator.[109] Del Corro in 1974 namedMegalosaurus chubutensis, based on specimen MACN 18.189, a tooth found inChubut Province.[110] It is anomen dubium, a possible carcharodontosaurid,[111] or a very largeabelisaurid.[61]
In 1985,Zhao Xijin named twoMegalosaurus species found inTibet.[112] He had earlier mentioned these species in an unpublisheddissertation of 1983, implying they initially were invalidnomina ex dissertatione. However, his 1985 publication did not contain descriptions so the names are stillnomina nuda.[61] The first species wasMegalosaurus "dapukaensis", named for theDapuka Group. It was, in the second edition ofThe Dinosauria, by mistake spelled asMegalosaurus cachuensis.[46] The second species wasMegalosaurus "tibetensis". In 1987/1988,Monique Vianey-Liaud renamedMassospondylus rawesi (Lydekker, 1890), based on specimen NHMUK R4190, a tooth from theMaastrichtian ofIndia, intoMegalosaurus rawesi.[113] This is anomen dubium, a possible member of theAbelisauridae.[67] In 1988,Gregory S. Paul renamedTorvosaurus tanneri Galton & Jensen 1979 intoMegalosaurus tanneri.[114] The change has found no acceptance. In 1973,Anatoly Konstantinovich Rozhdestvensky had renamedPoekilopleuron schmidti Kiprijanow 1883 into aMegalosaurus sp. However, as it is formally impossible to change a named species into an unnamed one, George Olshevsky in 1991 used thenew combinationMegalosaurus schmidti.[77] It is achimaera. In 1993,Ernst Probst andRaymund Windolf by mistake renamedPlateosaurus ornatus Huene 1905 intoMegalosaurus ornatus by mentioning the latter name in a species list.[115] This can be seen as anomen vanum. The same publication listed theichnospeciesMegalosauropus teutonicus Kaever & Lapparent 1974 as aMegalosaurus teutonicus. In 1997, Windolf renamedSaurocephalus monasterii Münster 1846, based on a tooth found nearHannover, intoMegalosaurus monasterii.[116] It is anomen dubium, an indeterminate member of the Theropoda.[67] In 1990,Ralph Molnar renamed "Zanclodon" cambrensis Newton 1899, based on a left lower jaw, specimen BGS 6532 found atBridgend, Wales, United Kingdom, into ?Megalosaurus cambrensis,[117] which was later followed byPeter Galton in 1998.[118] It is a senior synonym ofGressylosaurus cambrensis Olshevsky 1991.[77] The specific name refers toCambria, the Latin name ofWales. It was suggested to probably represents a member of theCoelophysoidea,[119] or some other predatory archosaur.[61] In 2025, it was formally described asNewtonsaurus cambrensis, in a study that demonstrated unambiguously that it was a relatively primitive theropod dinosaur, a possibly coelophysoid member ofNeotheropoda outside ofAverostra.[120]
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.
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