Majungasaurus description by Deperet, описание Маджунгазавра Деперетом - Ceratosauria Цератозавры - Tetrapods Taxa (Таксоны тетрапод) - Articles (Статьи) - DINOWEB

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Majungasaurus description by Deperet, описание Маджунгазавра Деперетом
First description Megalosaurus crenatissimus, by Deperet:
Descriptions. — I attribute the following elements to a megalosaurid of moderate size:
1st. Two teeth, of which one is nearly complete up to the base of the crown, and the other is larger but incomplete below. These teeth show the typical characters of megalosaurid teeth: a transversely compressed shape with two sharp ridges anteriorly and posteriorly, the latter more trenchant than the anterior: a recurved posterior profile in the shape of a saber blade; fine transverse serrations on the trenchant ridges: these serrations extend along the entire length of the anterior edge. The enamel is finely striated lengthwise.
2nd. An ungual phalanx in the shape of a recurved claw, unfortunately broken near the point. A blunt ridge that runs over the convex or superior edge along its entire length separates two oblique lateral faces, of which one – doubtless located on the external side – is more developed than the other: this asymmetry of the phalanx makes it possible to think that it is the claw of a lateral digit. Each of the two faces is covered near the base by a wide, curved vascular groove that leaves the inferior edge and moves while rising towards the terminal point of the claw. The posterior or articular face shows indications of two shallow articular excavations, the external being wider, separated by a slightly vertical ridge.
3rd. Two sacral vertebrae are compressed in the middle of the centrum, according to the ordinary type of megalosaurids.
4th. A very elongated caudal vertebra, clearly amphicoelous, whose centrum shows a quadrangular cross-section, higher than wide. A slight median longitudinal crest is visible below, bordered by two weakly marked grooves. The neural arch is inserted along nearly the entire length of the centrum, only a centimeter of which is free posteriorly. A median longitudinal ridge represents the only indication of a spinous process. No surface for the chevrons is seen, which permits attributing this element to the post-median region of the tail. There is an extremely straight neural canal, of elliptical shape. The anterior and posterior zygapophyses are broken. 
Relationships and differences. — The characters drawn together from the teeth, the ungual phalanx, and the amphicoelous caudal vertebra described above do not allow any doubt regarding the existence of a predatory dinosaur in Madagascar close to Megalosaurus Buckland from the Jurassic and Cretaceous of Europe, and of a genus near Dryptosaurus Marsh (Laelaps Cope) from the Cretaceous of the United States. 
If the elements from Madagascar are compared with those of the type species, Megalosaurus bucklandi Meyer from the Lower Jurassic of England and France, important differences are recognized: the mandibular teeth (1) are higher, but straighter, with much coarser serrations on the posterior edge, and above all on the anterior edge where they exist only on the superior part of the crown; this character is important to note, because the teeth from Madagascar, that of Fig. 4 in particular whose crown is less nearly complete, show serrations along the entire visible part of the anterior edge. The upper teeth of M. bucklandi (2) are similar to the lowers; the serrations only appear less marked. The sacral vertebrae of this species (3) clearly have the short, compressed shape in the middle of the centrum shown by the Malagasy vertebrae; these are only much smaller. The caudal vertebrae from Madagascar entirely resemble the caudal vertebrae of M. bucklandi (4) in their general shape and details; it is only still of more elongate proportions and smaller dimensions by about a quarter. Finally, the ungual phalanx is less transversely compressed and more flattened dorsoventrally than in M. bucklandi (5); it differs further because the lateral groove ends behind the inferior edge of the bone much earlier than in the European species, where this short groove parallels the inferior edge nearly up to the proximal end of the phalanx. 
Megalosaurus insignis Desl. from the Upper Jurassic of England and France (1) is a very large species whose teeth have the same straight, elongated form as those of M. bucklandi; they are less strongly recurved posteriorly than in the Malagasy species, the serrations of the trenchant anterior edge are weaker and cease on the inferior third of the length of the crown.
In M. dunkeri Koken (2) from the Wealden of England and Germany, the form of the teeth is likewise straighter and more elongated than in the Malagasy species; but the serrations are already finer and more closely resemble those of this latter type; however they disappear near the middle of the anterior ridge, as in the other European species, and are attenuated fairly easily by use along the entire length of this edge. The ungual phalanges of M. dunkeri (3) are more slender and more transversely compressed than those of the Malagasy species, and the lateral groove remains parallel to the inferior edge instead of recurving below near the posterior third.
Mr. Seeley has described (4) two teeth from the Upper Cretaceous beds of Neue Welt, near Vienna, under the name Megalosaurus pannoniensis that are much closer to the Malagasy teeth in the shape of the crown, which is shorter and wider at the base, and more finely serrated anteroposteriorly than in the other European species. However the posterior curvature is weaker than in the Malagasy species and the serrations cease on the inferior third of the anterior ridge instead of continuing along the entire length of this edge. I do not think that they could be attributed to the same species.
Above all, it is the species from the Arrialoor Group of Trichinopoly (British India), figured by Mr. Lydekker (5) without specific designation, that the Malagasy teeth resemble entirely in shape, which is short, wide at the base, and strongly posteriorly recurved, and in the fineness of the serrations, which are likewise extended along the entire length of the anterior edge. Except for the much greater dimensions of the Indian type, no appreciable difference can be found with the Malagasy form, and this difference of size can be due either to the age of the subject or to the positional order of the tooth in the jaws. Therefore I think that I can join these two types together, and I will give the name Megalosaurus crenatissimus n. sp. to the species because of the serrations which are extended along the entire length of the two trenchant ridges of the teeth.
Some genera from the Jurassic and Cretaceous of America show great affinities with Megalosaurus. The best known is Dryptosaurus Marsh (= Laelaps Cope) (1) from the Upper Cretaceous of New Jersey. The type species D. aquilunguis Cope is very large, attaining the size of M. bucklandi; the teeth differ entirely from those of Megalosaurus in the serrations of the anterior edge, which are extended along the entire length of this edge to near the root, instead of being limited to the upper part of the crown. It is interesting to note that this character is found exactly in the Malagasy and Indian form, therefore the attribution to the genus Dryptosaurus is shown as entirely probable. It is true to add that Leidy expressed the opinion that the American genus was close enough to Megalosaurus of Europe not to be distinguished from it, and this opinion is all the more probable because that the known parts of the skeleton of Dryptosaurus are extremely similar to those of Megalosaurus. Therefore I will attribute the Malagasy species to the large genus Megalosaurus, while emphasizing its affinities with the species from the Upper Cretaceous of America distinguished under the name Dryptosaurus. 
Megalosaurus crenatissimus, n. sp. — A predatory dinosaur is represented by two small, compressed teeth, anteroposteriorly recurved in the shape of a saber blade, of the typical form of Megalosaurus but shorter and wider than in all the European species of this genus and characterized above all by fine serrations that ornament the two trenchant ridges anterior and posterior to the crown, extended along the entire length of the anterior edge instead of only occupying part or two thirds of this trenchant edge. The name Megalosaurus crenatissimus, n. sp., is intended to emphasize this character, which
is found in a Megalosaurus sp. noted by Mr. Lydekker in the Upper Cretaceous of India, and also in Dryptosaurus Marsh (Laelaps Cope) from the Upper Cretaceous of the United States. I am thus brought to refer the type from Madagascar to the genus Dryptosaurus, which it is doubtless better to consider as a simple section of the large genus Megalosaurus.
The other elements of M. crenatissimus are: a sacral vertebra, a caudal of more elongate form than M. bucklandi, and finally an ungual phalanx in the shape of a recurved claw, less transversely compressed than in other Megalosaurus, and furnished with a lateral groove that is less prolonged posteriorly than in the described species (Deperet, 1896).
4-8. — "Megalosaurus" crenatissimus, n. sp.
4. Tooth whose crown is a little near complete, from the side. The figure is enlarged by a quarter.
4a. Same tooth; cross-section at the base.
5. Another tooth, incomplete at the base of the crown, from the side. Enlarged by a quarter.
5a. Same tooth; cross-section at the base.
6. Centrum of one of the sacral vertebrae. 2/3 natural size.
7. Amphicoelous caudal vertebra, from the side. 2/3 natural size.
8. Ungual phalanx of a lateral digit, side view. 2/3 natural size.
8a. Same phalanx, proximal articular view (modified from Deperet, 1896).

Dr. Decorse has sent to the Museum a megalosaur tooth found at Maevarano. It is larger than the type figured by Deperet; but it probably belongs to the same species, because it is finely crenulated along the entire length of the anterior edge, though also on the posterior edge. Analogous teeth are known from the Cretaceous of India (1) and Austria (2). They show some similarity to the teeth of Laelaps (Dryptosaurus) from the Cretaceous of North America (3).
The same explorer collected fragments of thin hollow bones probably belonging to the same animal, but all poorly preserved. Mr. Bastard has found, in the same locality, biplanar or gently amphicoelous vertebrae with the body is strongly narrowed in the middle; these vertebrae can be attributed to the same bipedal carnivorous dinosaur as the preceding teeth (Thevenin, 1907). 
17, 17a. - MEGALOSAURUS CRENATISSIMUS Deperet. - Tooth; profile, lateral face and section. - Same locality.
18. - Ibid. - Caudal vertebra; profile. - Same locality (modified from Lavocat, 1955).
A considerable number of teeth recovered in the Upper Cretaceous of Berivotro and Ambalakidy indicate the presence of a theropod of moderate size to which DEPERET gave the name of Megalosaurus. I possess a portion of mandible from this theropod, in the form of a nearly complete right dentary. This bone was found complete one month before our trip by an inhabitant of the countryside looking for yams, and unfortunately broken by him. Questioned by chance on whether he knew if it had teeth such as those that I showed him, he signaled to me at once as having found some "with the bone.” A visit to the place fortunately permitted collecting most of the pieces and several teeth. It seems that this is the first dentary of a theropod known from Madagascar. According to the Europeans in Marovoay, a mandible was found at another time in the vicinity of this village, but until now it had been impossible to find a trace of it. Without being able yet to give a definitive study of this bone here, I can now note its thin and rather long form (length: around 25 cm) and indicate that the form of the dentary in its posterior region seems to differ markedly from that of Megalosaurus from England, such as it is described by English authors (Lavocat, 1955).
Категория: Ceratosauria Цератозавры | Добавил: dinoweb (2013-07-16)
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