This lineage includes some of the most primitive of the great Sauropods. Some forms, like Shunosaurus, still retained many prosauropod features. Yet even at this early evolutionary stage they had already become specialised, developing ankylosaurid-like clubbed tails as protection against predators (and maybe also a sexual display device), and - in later forms - amazingly long necks. The lineage culminates in the 22 meter Mamenchosaurus, which has the longest neck for any animal.
Euhelopids have been drawn like dinosaurian giraffes, with the head held high in the air. In fact - as with the barosaurs and brachiosaurs - this pose is physiologically impossible. There is no way the heart could of pumped blood to the head against the force of gravity. A more reasonable explanation is that the neck was held stiffly in front of the body, and swung from side to side as the creature grazed on ferns and other herbacous plants.
The following is a tentative classification of the group.
family Euhelopodidae (=Mamenchisauridae)
length: 8 metres
weight: 1 to 2 tonnes
Bathonian or Callovian of China
Euhelopodidae and Mamenchisauridae by Dinogeorge
Isalo Formation, (Bathonian age)
Majungar, Madagascar (north-central Gondwana)
Several disarticulated by very well preserved juvenile skeltons [Dinosauria, pp.382-3].
Although this species was originally classified under the genus Bothriosponylus, family Brachiosauridae, the South American paleontologist Jose Bonaparte argues that it, along with the late Callovian age Volkheimeria chubutensis, possess a more primitive form of vertebrae, charac-terised by flat neural spines, structually intermediate between that of Vulcanodon (which has flat prosauropod-like vertebrae) and typical Cetiosaurids such as Braposaurus, Cetiosaurus, and Patagosaurus (with high neural spines consisting of four diverg-ing laminae) [Jose F. Bonaparte, "The early radiation and phylogenetic relationships of the Jurassic sauropod dinosaurs, based on vertebral anatomy"]. If this is a valid criteria, then Lapparentosaurus and Volkheimeria, despite their otherwise advanced brachiosaur-like structure, actually represent a persisting primitive lineage of sauropods that independently evolved brachiosaurid features.MEASUREMENTS LENGTH: 14 m to 18 m see also: World Records TIME C. medius: Bajocian "C." conybearei: Valanginian C. mogrebiensis: Bajocian to Bathonian C. oxonensis: Bajocian to Bathonian see also: Ages of the MesozoicCetiosaurus Owen, 1842 [nomen conservandum] TYPE SPECIES: C. medius Owen, 1842 [nomen conservandum] OTHER SPECIES: ?C. mogrebiensis de Lapparent, 1955 C. oxonensis Phillips, 1871 C. phillipsi Sauvage, 1880 [nomen nudum] PLACE C. medius: England "C." conybearei: England C. mogrebiensis: Morocco & Algeria? C. oxonensis: England see also: Paleo-Maps REMAINS C. medius vertebrae, limb elements "C." conybearei caudal vertebrae, chevron C. mogrebiensis several skeletons C. oxonensis 2 partial postcrania, vertebrae, limb elements
This smallish sauropod was unusual in that it was a survivor of the very primitive Cetiosauroid line, existing as a sort of "living fossil" alongside its more advanced descendants. It probably should be grouped with Cetiosaurus, which it resembles, in the family Cetiosauridae, although Jose Bonaparte argues it should be placed in a distinct family because of its unusual and more advanced vertebral structure [J.F.Bonaparte, "Jurassic Sauropod Dinosaurs..." in The Beginning of the Age of Dinosaurs, ed K.Padian] (rather implausably, Bonaparte classes Haplocanthosaurus with Dicraeosaurus - which shows a similiar vertebral form but is otherwise a very different type of sauropod - in the Dicraeosauridae); the upper spine of each vertebra was single, not forked as in most sauropods [Field Guide to Dinosaurs, p.115]. Haplocanthosaurus resembled Brachiosaurus in its high shoulders, fairly long neck, and short tail, but this was the result of parallel evolution and adaptation to a giraffe-like high-feeding lifestyle, not direct relationship. The back was quite long, containing 14 vertebrae.
Haplocanthosaurus delfsi McIntosh
et Williams 1988
Morrison Formation; Colorado, United States
Partial skeleton lacking skull
Length: 21.5 metres; Weight about 25 tonnes
A huge and rare Haplocanthosaur, the last and one of the largest of the Cetiosaurids. Although "Cetiosaurus" has supposedly been reported from the early Cretaceous of england, those isolated postcrania would actually belong to other sauropods of that time. It seems that this family, once so successful and widespread, did not survive the mid-Tithonian extinction.
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page historypage uploaded 6 May 1999