Europasaurus

Taxobox |
name = "Europasaurus"
fossil_range = Upper Jurassic

---

image_width = 200px
image_caption = Life restoration of "Europasaurus holgeri".
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Sauropodomorpha
unranked_familia = Macronaria
genus = "Europasaurus"
species = "E. holgeri"
binomial = "Europasaurus holgeri"
binomial_authority = Mateus, Laven, & Knötschke "vide" Sander "et al.", 2006

"Europasaurus" Sander, P. M., Mateus, O., Laven, T., Knötschke, N. 2006. Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur. "Nature" 441: 739-741.] is a basal macronarian sauropod, a form of quadrapedal herbivorous dinosaur. It lived during the Upper Jurassic (Kimmeridgian) of northern Germany, and has been identified as an example of insular dwarfism resulting from the isolation of a sauropod population on an island within the Lower Saxony basin. Remains of both adults and juveniles have been recovered from marine carbonate beds ("bed 93"), representing more than eleven individuals ranging from 1.7 to 6.2 meters in total body length. The genus name means "lizard from Europe" (Europe + Greek "sauros" = lizard), and the species is named in honor of Holger Lüdtke, who discovered the first fossils of the taxa. The holotype specimen (DFMMh/FV 291; Dinosaurier-Freilichtmuseum Münchehagen/Verein zur Förderung der Niedersächsischen Paläontologie) consists of portions of a disarticulated skull, along with cervical and sacral vertebrae, derived from a single individual. This specimen and all others referred to the taxon were collected from "bed 93" at the Langenberg quarry, Oker near Goslar, Lower Saxony (Niedersachsen).

Phylogeny

A cladistic analysis of "Europasaurus holgeri" indicates that the species' dwarfism is a derived characteristic, and that this taxon is a more derived macronarian than "Camarasaurus", and should be regarded as the sister group of the Brachiosauridae and all more derived members of the Titanosauriformes.

Dwarfism and Histology

It has been suggested that the ancestor of "Europasaurus" would have "dwarfed rapidly" after immigrating to a paleo-island , as even the largest of these islands in the Lower Saxony basin (a landmass <2,000 square kilometers) would not have possessed sufficient food for a population of large sauropods. Other examples of insular dwarfism among dinosaurs have been cited from the Maastrichtian (latest Cretaceous) Haţeg Island in Romania, namely the sauropod "Magyarosaurus"Nopsca, F. 1914. Über das Vorkommen der Dinosaurier in Siebenbürgen. "Ver. Zool. Bot. Ges. Wien." 54: 12-14.] and the hadrosaur "Telmatosaurus" Weishampel, D., Norman, D. B. et Grigorescu, D. 1993. "Telmatosaurus transsylvanicus" from the Late Cretaceous of Romania: the most basal hadrosaurid dinosaur. "Palaeontology" 36: 361-385.] . In these two examples, paleogeography and paleoecology have been employed to explain the evolution of new and miniature versions of larger species. These fossils were determined to represent a dwarf species, and not merely juveniles of a large macronarian species, by studying the histology of the fossil bones. Likewise, by comparing the long-bone histology of a typical large-bodied sauropod, "Camarasaurus", paleontologists have concluded that the diminutive size of "Europasaurus" resulted from a decreased growth rate. This phenomenon is a reversal of the accelerated growth responsible for gigantism in other sauropod dinosaurs . Dwarfism among macronarians seems especially remarkable as this clade includes some of the largest known dinosaurs, such as the brachiosaurs "Brachiosaurus" and "Sauroposeidon".

Diagnosis and Comparative Morphology

"Europasaurus holgeri" exhibits the following unambiguous autapomorphic states : "nasal process of premaxillary projecting anterodorsally; medial notch is posterior dorsal margin of cervical vertebral centra; scapular acromion with a prominent posterior projection; and transverse width of astragalus twice its dorsoventral height and anteroposterior width." In comparing "Europasaurus" with "Camarasaurus" , "Europasaurus" differs "in the wing-shaped posterior process of the postorbital being slightly longer and wider than the anterior process, whereas it is much shorter in "Camarasaurus"." Other differences include "Europasaurus"' shorter nasal-frontal contact and a parietal bone which is rectangular in posterior view. Unlike "Camarasaurus", the neural spines of the presacral vertebrae are undivided. In comparing "Europasaurus" with "Brachiosaurus" , the former genus differs from the latter by having a shorter muzzle, a quadratojugal which makes contact with the squamosal, and an anteromedially flattened humerus possessing unaligned proximal and distal epiphyses. "Europasaurus" was also compared with the macronarians "Lusotitan" and "Cetiosaurus" humerocristatus" and found to be distinct from both those forms. Finally, "Europasaurus" can be distinguished from most known members of the Neosauropoda by its very small adult body size.

References