Magyarosaurus was a small sauropod from the late Cretaceous measuring only 5-6 meters in length and was first discovered by Nopcsa in 1915 in the Haţeg region. When compared to the 7 metre long Saltasaurus and the 20-25m long Argentinosaurus to which it's related to it's clearly a lot smaller. Research conducted by Jianu and Weishampel (1999), found the humeri of Magyarosaurus was similar to subadults of other taxa rather than the adults which suggested that dwarfing was apomorphic and was achieved by paedomorphosis.

As an adult Magyrosaurus would have been only half the length of its main land relative therefore there would have been a corresponding reduction in its body mass to one eighth. The same is seen in Telmatosaurus.

All the dinosaurs in the Haţeg Region generally occupy the basal positions of their respective cladograms. They all existed during the Maastrichtian period of the late Cretaceous and they are viewed as "living fossils" within the paleontological world they existed in as they showed more primitive features than some of there more derived counterparts. Magyrosaurus dacus currently sits basally in the "Rapetosaurus clade" which is currently poorly supported and includes a mix of early and late Cretaceous taxa, creating the problem that if Magyrosaurus is truely basal then it would post date many "older" relatives suggesting it needs anatomical revision within the cladogram.

An ontogenetic series of Magyrosaurus dacus long bones (Figure: 1) showed a histology that is only seen in older, larger members of the sauropoda. The cortex of even the smallest specimen, which only 45% of its maximum size (Figure: 1a) is dominated by secondary osteons, where the bone has been "recycled" as part of the process of secondary remodelling, leaving only a few areas of lamellar primary fibrolamellar bone with strong lamellar component in the bone matrix (Figure: 2 a-d).

Whilst the only way to completely certain your dealing with an adult specimen is the presence of an external fundamental system (Introduction: Figure: 1c) in the outer bone cortex. Though there wasn't any observed in the entire set, there was advanced secondary remodelling which is typical of the oldest histological ontogenetic stages of larger sauropods (Klein and Sander, 2008). A completely remodelled long bone cortex is only found in the oldest and largest examples of Apatosaurus and Supersaurus suggest that Magyrosaurus was indeed a small adult and not a juvenile.

Growth Rate in Magyrosaurus dacus

Secondary bone remodelling completely "destroyed" the primary growth record in the long bones of M.datus with it any LAGs or other growth marks making it diffcult to accurately estimate Magyrosaurus growth rate. Because of the strong lamellar component of the remaining primary bone when compared with the bones of larger sauropods suggests however that the growth rate of M.dacus was much slower than its larger counterparts (Figure: 2e) but still faster than endothermic reptiles that have a lamellar-zonal bone dominated cortex (Figure: 9f).

The extensive remodelling and remainate priamry bone suggests that the largest examples of M.dacus had reached full size and that it had done so by slowing the growth rate. (Stein et al)

Artwork: Magyarosaurus dacus

Kindly provided by Mihai Dumbrava

Literature cited

• Jianu, C.-M., Weishampel, D.B., 1999. The smallest of the largest: a new look at possible dwarfing in sauropod dinosaurs. Geologie en Mijnbouw 78, 335-343.
• Klein, N., Sander, M., 2008. Ontogenetic stages in the long bone histology of sauropod dinosaurs. Paleobiology 34, 248-264.
• Stein, K., Csiki, Z., Curry Rogers, K., Weishampel, D.B, Redelstorff, R., Sander, M.P., submitted for publication. Insular nanism in Magyarosaurus dacus (Sauropoda: Titanosauria): unique bone histology indicates that Baron Franz von Nopcsa was right. Proceedings of the National Academy of Sciences