| Magyarosaurus | |
|---|---|
 | |
| Titanosaur remains used to erectMagyarosaurus dacus, including thelectotype (A-F) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Titanosauria |
| Genus: | †Magyarosaurus von Huene,1932 |
| Species: | †M. dacus |
| Binomial name | |
| †Magyarosaurus dacus | |
| Synonyms[1] | |
| |
Magyarosaurus ("Hungarian lizard") is agenus ofdwarfsauropoddinosaur from lateCretaceousPeriod (early to lateMaastrichtian) inRomania. It is one of the smallest-known adult sauropods, measuring less than 3 m (9.8 ft) long and weighing less than 1,000 kg (2,200 lb). Thetype andonly species isMagyarosaurus dacus. It has been found to be a close relative ofRapetosaurus in the familySaltasauridae in the sauropod cladeTitanosauria in a 2005 study.[2]
Remains belonging to at least ten individuals have been recovered since 1895 from theHunedoara region (Sânpetru Formation) in the area which was, at the time of their discovery, Hungary, but is now western Romania. Initially they were namedTitanosaurus dacus, the specific name referring to theDacians (who had lived in that place about 2000 years ago), byBaron Nopcsa in 1915.[3] In 1932,Friedrich von Huene reassigned this taxon to a new genus,Magyarosaurus, and he also named two other species within the genus:M. hungaricus andM. transsylvanicus.[4] However,M. transsylvanicus represents achimera and some material belongs toM. dacus, whileM. hungaricus is now reassigned to a distinct genusPetrustitan with some previously referred material now being the specimens of another genusUriash.[5]
Thelectotype ofM. dacus is the anterior caudal vertebraSZTFH Ob.3091, and other specimens (SZTFH Ob.4215 and SZTFH Ob.3098) are also referred toM. dacus to erect this taxon.[5] Numerous other bones have been found, mainly caudal vertebrae but also dorsals and elements of the appendicular skeleton. No remains of skulls are known. There has been a discovery of 14fossil eggs which have been attributed toMagyarosaurus.[6]
Paleontology investigations have been carried out atRâpa Roșie nearSebeș, on the southwestern side of the Transylvanian Basin. The investigations were started in 1969.Dinosaur bones were reported in earlier investigations. Based on the investigations carried out by Codrea and Dica in 2005, they have assigned the age of these formations to theMaastrichtian-Miocene age (also conjectured as of Eggenburgian-Ottnangian age). Some of the rare fossils found here are also vertebrates and one of these is ofsauropod caudal vertebra. Paleontologists involved with the studies at Râpa Roșie have also opined that this is the onlysauropodgenus reported at any time in the latestCretaceousMaastrichtian formations in Romania, which could be stated asMagyarosaurus.[1]
Magyarosaurus was a relatively small sauropod, with specimens currently referrable toM. dacus measuring 2.16–2.82 m (7.1–9.3 ft) long and weighing up to 660–972 kg (1,455–2,143 lb).[5] Its small size is a distinguishing autapomorphy, for none of its close relatives had such a reduced size.[7]Magyarosaurus is also notable for the presence of dermal armour.[8][9]
A distal caudal vertebrae was referred to the genus by Codreaet al. (2008). It was probably from near the middle of the tail as it has transitional features. Before it was definitively buried, the neural arch was broken off, probably by repositioning of the vertebrae from its original position. Its centrum is elongated, and measures 105 millimetres (4.1 in) long. Both sides that would have articulated with vertebrae were severely damaged. It is assigned toMagyarosaurus on the basis that no other sauropods are known from the region it was found in, and the fact that it is located between the two vertebrae compared with it because of its intermediate morphology.[1]
The islands it inhabited led toMagyarosaurus becoming a product ofinsular dwarfism as a result of selective pressures presented by limited food supplies and a lack of predators, all favoring a smaller body size.[7] This is seen in many other dinosaurs existing at the time, including theornithopodRhabdodon and thenodosaurStruthiosaurus. Nopcsa was the first to suggest island dwarfism as an explanation for the small size ofMagyarosaurus compared to other sauropods. Later researchers doubted his conclusions, suggesting instead that the knownMagyarosaurus fossil represented juveniles. However, a detailed study of bone growth patterns published in 2010 supported Nopcsa's original hypothesis, showing that the smallMagyarosaurus individuals were adults.[7][10] Island dwarfism has been suggested to have led to isolated genera retaining more primitive characteristics.[8]
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In 2010,Koen Steinet al. studied the histology ofMagyarosaurus. They found that even the smallest individuals appeared to be adults. They also retained "M."hungaricus to represent the larger specimens that were too big to be variations of the smaller specimens. The histology ofMagyarosaurus showed that it had a very reduced growth rate, but even so, had a high metabolic rate.[7]
An osteoderm discovered in the "La Cãrare" locality. The locality is near Sînpetru village, in theHațeg Basin ofRomania. The osteoderm was assigned toMagyarosaurus dacus. This shows that dermal armour had a wide distribution in these Late Cretaceous sauropods.[9] The osteoderms was peculiar in shape and size,[9] and led to eggs being assigned to its family,Nemegtosauridae, and possibly toMagyarosaurus.[8]
Lithostrotian eggs have been assigned toNemegtosauridae. The eggs possibly belong to eitherMagyarosaurus dacus orPaludititan, the former being more likely.[8] The Hațeg Basin was a large nesting place in the late Cretaceous, and is served as that for hadrosaurids, and titanosaurs. 11 eggs have been assigned toNemegtosauridae, all from the Sânpetru Formation.[8] Embryos were preserved inside the eggs, and one egg shows proof of dermal armouring.[8]
The eggs were uncovered in 2001, during a field expedition by a Belgo-Romanian team. They were originally identified as in nests, but now it has been shown that no nesting structures has been preserved.[8]
During the earlyMaastrichtian, the Hațeg Basin was subhumid, and had seasonal precipitation. However, during the later age of the formation, a large-scale paleoenvironmental change occurred, the region transformed into an extensive wetland.[11]
Magyarosaurus dacus is known from the early Maastrichtian of the Sânpetru Formation, part of the Hațeg Basin in Romania.[11][2][12] Also known from the Hațeg Basin are the small, basalhadrosauridTelmatosaurus;[7] the smallnodosauridStruthiosaurus;[13] themaniraptoransBalaur,Bradycneme, andElopteryx;[13] thepterosaurHatzegopteryx;[10][14] and the two species of theeuornithopodZalmoxes.[7]
M. sp. is known from a vertebra. The vertebra was found in the latest Cretaceous of theSebeș Formation, although it was probably eroded from theȘard Formation and placed there. AlongsideMagyarosaurus existedKallokibotion, an ancientturtle;[1]Balaur, a two-clawedavialan;[13] andEurazhdarcho, anazhdarchid.[14] AlongsideMagyarosaurus,Telmatosaurus andZalmoxes also are dwarfed genera, as proven by their histology.[7]
