Europasaurus
5468113
223111758
2008-07-02T16:57:36Z
192.165.213.18
hu:Europasaurus
{{Taxobox |
| name = ''Europasaurus''
| fossil_range = [[Upper Jurassic]]
| image = Europasaurus_holgeri_detail.png
| image_width = 200px
| image_caption = Life restoration of ''Europasaurus holgeri''.
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
| classis = [[Reptile|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''''' <ref name="Sander ''et al.'', 2006">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.</ref> is a basal [[macronaria]]n [[sauropod]], a form of [[quadraped]]al [[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 language|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'' <ref name="Sander ''et al.'', 2006"/> 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 ==
[[Image:Europasaurus skull.JPG|thumb|left|''Europasaurus'' skull]]
It has been suggested that the ancestor of ''Europasaurus'' would have "dwarfed rapidly" after immigrating to a paleo-island <ref name="Sander ''et al.'', 2006"/>, 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]]''<ref name="Nopsca, 1914">[[Franz Nopcsa|Nopsca, F.]] 1914. Über das Vorkommen der Dinosaurier in Siebenbürgen. ''Ver. Zool. Bot. Ges. Wien.'' '''54''': 12-14.</ref> and the [[hadrosaur]] ''[[Telmatosaurus]]'' <ref name="Weishampel ''et al.'', 1993">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.</ref>. 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'', [[paleontologist]]s 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 <ref name="Sander ''et al.'', 2006"/>. 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 ==
[[Image:Europasaurus.png|thumb|left|Size comparisons of adult and juvenile ''Europasaurus'' with human for scale.]]
''Europasaurus holgeri'' exhibits the following unambiguous autapomorphic states <ref name="Sander ''et al.'', 2006"/>: "[[nasal]] process of [[premaxilla]]ry projecting anterodorsally; [[medial]] notch is posterior [[Dorsum (biology)|dorsal]] margin of cervical vertebral [[centra]]; [[scapula]]r [[acromion]] with a prominent posterior projection; and [[transverse]] width of [[talus bone|astragalus]] twice its dorsoventral height and anteroposterior width." In comparing ''Europasaurus'' with ''Camarasaurus'' <ref name="Sander ''et al.'', 2006"/>, ''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'' <ref name="Sander ''et al.'', 2006"/>, 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 ==
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{{portalpar|Dinosaurs}}
[[Category:Dinosaurs of Europe]]
[[Category:Jurassic dinosaurs]]
[[Category:Sauropods]]
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