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Zalmoxes

From the Haţeg fauna there have been two named species of the genus Zalmoxes, Z. robustus which reached 3 m in length and Z. shqiperorum which was 4.0-4.5 m long, both date from the Maastrichtian stage of the late Cretaceous. The genus name derives from the name of a freed slave of Pythagoras, who later was deified by the Dacians as amoungst others god of the Underworld, thus it was chosen due to the subterranean origin of the bones as well as the bones county of discovery (Modern Romania is geographically in the same area as ancient Dacia).

In life Zalmoxes was a herbivorous dinosaur living upon the sub-tropical island of Haţeg surrounded by the remains of the Tethys ocean. Unlike some other dinosaurs from Haţeg (eg the Hadrosaur Telmatosaurus), the types of preservation environment for the fossil bones of Zalmoxes have been widespread, with examples of fossils being found in channel-related sediments as well as in oxidized/poorly-drained floodplain deposits (Weishampel et al. 2003).

Zalmoxes is of the order Ornithischia ('bird hipped') which has a extensive history stetching back at least until the Late Triassic and contains some of the most iconic dinosaurs including Stegosaurus, Triceratops and Iguanadon, to name but a few. Of these the closest relative to Zalmoxes is Iguanadon, indeed in cladistical analysis performed by Weishampel et al. (2003) they found that the two species of Zalmoxes when grouped with Rhabdodon ("fluted tooth") , known from the Campanian and Maastrichtian of France and Spain formed a new family Rhabdodontidae which was sister clade to the Iguanadontia. However the Iguanadontia date to the early cretaceous whereas the Rhabdodontidae date to the Late Cretaceous, implying a Ghost lineage, where there there is as yet no fossil evidence, of 73 My connecting these late Cretaceous dinosaurs to their closest early Cretaceous relatives. the primitiveness of Zalmoxes is not unique to Haţeg island, indeed it seems that the entire Ornithopod fauna of Europe in the Late Cretaceous appears to be a relic, with instead of being dominated by the Hadrosaurids as seen elsewhere in the Northern Hemisphere instead consisting of derived non-Iguanodontian ornithopods, with some rare Hadrosaurids (Benton et al. 2010).

Zalmoxes - Dwarf Dinosaur?

There are a number of features that an animal must possess inorder to be called an island dwarf, namely they must be an isolated island dwelling species with a reduced adult-size in comparison to mainland relatives. Therefore for Zalmoxes to be called a island dwarf it must fit this description.

Using Palaeogeographic reconstructions of Haţeg during the late Cretaceous it is probable that it existed as an island, and so shows that Zalmoxes would have been isolated from the mainland.

Next the small fossils of Zalmoxes must be shown to be adults; for this bone histology, or the microscopic sudy of bone cells and tissues, can be used to find charactoristic features in order to distinguish the fossils of small adults from those of large juveniles. Studies such as by Benton et al. (2010) have been done upon Zalmoxes for this very reason, samples were taken from adult (Figure 1: a-b) and sub-adult fossil (Figure 1: c-d) femora and humeri. Zalmoxes themselves have a remarkable late onset of secondary remodeling, a process where bone is replaced in the skeleton, when sub-adult (Figure 1: c-d), in adults (Figure 1: a-b) this remodeling is restricted to the inner cortex, around blood vessels in the middle cortex and completely absent in the outmost cortex. In all specimens however the vascular canals opening to the bone surface have in all sample specimens indicate that a fully grown state had not been reached, despite this decause of the high number of growth marks (up to 13 in Z. robustus and 7 in Z. shqiperorum) a juvenile origin of the bones can be ruled out. Bone histology can also be used to show that at the same age of development Z. robustus is larger than Z. shqiperorum. Therefore bone histology it is able to show that the small specimens were small adults rather than juveniles.

The final feature to show that Zalmoxes was an isand dwarf is a reducted sized when compared with mainland relatives, however this is not simple. This is because when compared to their basal relatives it can be seen that some are smaller - Hypsilophodon from the Early Cretaceous (2.3 m long), some equivolent in size - Thescelosaurus from the Late Cretaceous (3-4 m long) and others were much larger - Camptosaurus from the Late Jurassic (5-7 m long) (Benton et al. 2010). However it may be better to compare the femur lengths of Z. robustus (250 - 320 mm) and Z. shqiperorumit (333 - 355 mm) to the femurs of other Euornithopods, e.g. Tenontosaurus tilletti (400mm) (Forster, 1990), 544 mm in the small iguanodontid Camptosaurus dispar (544 mm) (Paul, 2008), and Rhabdodon priscus (600m) (Garcia et al., 1999). In this comparison we can see that the Zalmoxes species are in all cases smaller than these their closest relatives and so it does fit the defination of an island dwarf.

This evidence from bone histologies, Palaeogeographical reconstructions as well from comparisons of the bones themselves seems to point towards the two Zalmoxes species having indeed undergone island dwarfing.


Zalmoxes_3

Artwork: Zalmoxes

Kindly provided by Mihai Dumbrava


Literature cited

  • Benton M. J., Csiki Z., Grigorescu D., Redelstorff R., Sander P. M., Stein K. and Weishampel D. B., 2010, Dinosaurs and the island rule: The dwarfed dinosaurs from Hateg Island, Palaeogeography, Palaeoclimatology, Palaeoecology, Article in Press
  • Forster, C.A., 1990. The postcranial skeleton of the ornithopod dinosaur Tenontosaurus tilletti. Journal of Vertebrate Paleontology 10, 273-294.
  • Garcia, G., Pincemaille, M., Vianey-Liaud, M., Marandat, B., Lorenz, E., Cheylan, G., Cappetta, H., Michaux, J., Sudre, J., 1999. Découverte du premier squelette presque complet de Rhabdodon priscus (Dinosauria, Ornithopoda) du Maastrichtien inférieur de Provence. Comptes rendus de l'Académie des Sciences de Paris 328, 415-421.
  • Paul, G.S., 2008. A revised taxonomy of the iguanodontid dinosaur genera and species. Cretaceous Research 29, 192-216.
  • Weishampel, D.B., Jianu, C.-M., Csiki, Z., Norman, D.B., 2003. Osteology and phylogeny of Zalmoxes (n. g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania. Journal of Systematic Palaeontology 1, 65-123.
 Zalmoxes


Latin Name:

Zalmoxes robustus (1899)

Zalmoxes shqiperorum (2003)

Order: Ornithischia

Suborder: Ornithopoda

Infraorder: Iguanodontia

Family: Rhabdodontidae

Length: 2/3 metres (Z.robustus)

4/4.5 metres (Z.shqiperorum)

Late Cretaceous


 
Zalmoxes_2lg

Figure 1: Histology of the long bones of the ornithopods Zalmoxes shqiperorum (a-b), and Z. robustus (c-d).

(a-b) Long bone histology of Z. shqiperorum. The femur (length 16.4 cm) of the subadult specimen FGGUB R.1088 shows that secondary remodelling is restricted to the inner cortex indicating a late onset of remodelling. Primary osteons occur in longitudinal and reticular organization. Vascular canals open to the bone surface indicating active growth at the time of death. (b) - Same view in polarized light. (c-d) - Bone histology in the femur of Zalmoxes robustus FGGUB R.1382 (estimate of femur length 28 cm). The high number of growth marks (11; only 7 seen in this view) indicates an adult stage of this specimen. Remodelling is dense in the inner cortex and scattered in the middle cortex. (d) - Same view in polarized light.

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Authored by Tom Baird and Richard Conium

Dicynodon Illustration courtesy of John Sibbick.
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