Hypselosaurus

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Hypselosaurus
Temporal range:
Ma
↓
Holotype material including femur, tibia, fibula and vertebrae
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Clade: †Macronaria
Clade: †Titanosauria
Genus: †Hypselosaurus
Matheron, 1869[1]
Species:
†H. priscus
Binomial name
†Hypselosaurus priscus
Matheron, 1869[1]

Hypselosaurus (meaning 'highest lizard', from

Rhodanosaurus
, as well as indeterminate bones from other groups.

Discovery

Restoration

In 1846,

caudal vertebrae, as the holotype specimen of a new taxon, Hypselosaurus priscus.[1] Among the bones, portions of the femur shaft are not preserved, along with a majority of the tibia, while both the fibula and vertebrae are entirely preserved.[1] The layer the fossils came from is likely from the late Late Cretaceous, specifically 70 million years ago.[3][4]

Since its original description, several specimens have been referred to Hypselosaurus. One of these, originally described in 1957 by Albert de Lapparent, includes a caudal vertebra, as well as another vertebra described in 1960 by Bataller.[5] In 1993, a review of European sauropods stated that Hypselosaurus was a nomen dubium, and that its holotype could not be verifiably distinguished from other sauropods in the same, and many other, regions. Based on this, the material that was referred to Hypselosaurus by several other authors would have to be considered an intermediate titanosaur.[6]

In addition to the holotype skeleton, Matheron described two fragments of a spherical or ellipsoid fossil in 1869. These fragments were studied for some time by Matheron and his contemporary French paleontologists, and the only probable conclusion was that they were fragments of eggshells. The eggs were proposed to have been significantly larger than those of Aepyornis when complete, and Matheron suggested that they either were a very large bird egg, or belonged to Hypselosaurus.[1]

When originally named, Matheron proposed that Hypselosaurus was an aquatic crocodile, as was suggested for similar taxa like

medullary bone, and thus proposed that it could not have been terrestrial like Iguanodon.[1]

The discoveries of new material from the Rognac area of France has led to the suggestion that Hypselosaurus may be the same taxon as Atsinganosaurus, which requires further material with overlap to confirm or deny.[7]

Description

Scale diagram

Hypselosaurus was a proposed to be 15 m (49 ft) in length, when it was considered a crocodilian, which would have made it one of the largest of the group.[8] However, a modern estimate as a titanosaur has put Hypselosaurus at around 12.0 m (39.4 ft), with a very rough weight estimate of 7.3–14.5 t (8–16 short tons).[9] One of the smaller titanosaurs, Neuquensaurus, measures only 7.5 m (25 ft) long.[10]

Limb bones

The left femur of Hypselosaurus, at 80 cm (31 in) in length, is quite eroded, with both the femoral head and the distal condyles being eroded and distorted by sediment. The femur is slightly sinuous, and narrows antero-posteriorly, becoming a subquadrangular oval 17 cm (6.7 in) wide and only 7 cm (2.8 in) long. The internal shaft is fairly spongey, although the internal bone is only loosely attached, and the femur clearly lacks a medullary canal.[1]

As preserved, the left tibia is largely incomplete, with only a small section of the shaft, just proximal to the distal condyles, known. Like the femur, there is no medullary canal present, and the spongey internal bone is asymmetrically dense. Few other features can be identified, among those the dimensions and cross-section of the bone. The tibia is ovoid in cross-section, with the anterior diameter 11 cm (4.3 in) long, and 5.5 cm (2.2 in) wide.[1]

The fibula, at 55 cm (22 in) in length, corresponds well with the size of the femur and tibia. The fibula is approximately an equilateral triangle in cross-section, with the inner face slightly concave and outer face convex. The flatter surface of the fibula is 18 cm (7.1 in) wide, and opposite ridge protrudes 7 cm (2.8 in) from this.[1]

Vertebrae

Two caudal vertebrae were preserved, although there would have been a much larger number in the tail. Both bones are nearly identical in every feature, but the anterior has is slightly larger dimensions. The vertebrae are not compressed

zygapophyses, articular processes that connect the consecutive vertebrae. The vertebrae are overall very similar to those of Pelorosaurus[1]

Palaeobiology

Eggs

Referred eggs at the National Museum of Natural History, France

Eggs attributed to Hypselosaurus by Matheron and

Age determination studies performed on the fossilized remains have been inconclusive, with results ranging from a few decades to several hundred years.[11]

Eggs with abnormally thin shells have been attributed to Hypselosaurus priscus. Some experts have speculated that this was the cause of the species' extinction, with vegetation changes, climatic change and overcrowding being the original impetus for the shell thinning. However, there are alternative explanations for the thin eggshell not dependent on pathology. Later researchers found evidence that the eggs in question successfully hatched. Some researchers postulated that the thinner "Hypselosaurus priscus" eggshells came from different taxa than the thicker eggshells, and subsequent researchers have come to support this idea. Another potential explanation for variation in eggshell thickness is that the thinner eggs were laid by younger individuals than the thicker shell eggs laid by older individuals or that it was a consequence of natural variations of eggshell thickness within a single species.[12]

Most Hypselosaurus egg are in collections and museums in France, but an egg is on display in the Life on Earth gallery at Leeds City Museum, United Kingdom,[13] and a rock slab with twelve eggs is on display at the Museum of Evolution in Knuthenborg Safaripark, Denmark.[14]

Ecology

Hypselosaurus has been found only in the

dorsal vertebrae.[17] There are also indeterminate crocodilians known from the same strata as Hypselosaurus, although they are only represented by unnamed fragments.[1]

References

  1. ^ a b c d e f g h i j k Matheron, P.M. (1869). "Notice sur les reptiles fossiles des dépots fluvio-lacustres Crétacés du bassin a lignite de Fuveau". Extrait des Mémoires de l'Académie des Sciences, Belles-Lettres, et Arts de Marseille (in French): 345–379.
  2. ^ Matheron, P. (1846). "Sur les terrains traversés par le souterrain de la Nerthe, près Marseille". Bulletin de la Société Géologique de France. 4 (2): 261–269.
  3. ^
    ISBN 0-520-24209-2
    .
  4. ISBN 2-88124-906-X
    .
  5. ^ Superbiola, P.X.; Ruiz-Omeñaca, J.I (2001). "Un dinosaurio saurópodo (Titanosauria) en el Cretácico superior del Cubilla, Soria (España)" (PDF). Geogaceta. 30 (2001): 175–178.
  6. doi:10.1016/j.annpal.2012.12.002
    .
  7. ^ Tortosa, T.; Dutour, Y.; Cheylan, G.; Buffetaut, E. (2012). "New discovery of titanosaurs (Dinosauria: Sauropoda) from Provence (SE France): implications on local paleobiodiversity". 10th Annual Meeting of the European Association of Vertebrate Palaeontologists. ¡Fundamental!: 259–262.
  8. ^ Matheron, P.M. (1891). "Sur les animaux vertébrés dans les couches d'eau douce Crétacées du Midi de la France". Compte Rendu de la 20me Session, Seconde Parte. Notes et Extraits (in French). Association Française pour l'Avancement des Sciences Fusionnée avec l'Association Scientifique de France, Reconnues d'utilité publique. pp. 382–383.
  9. ^ Holtz, T.R. Jr. (2012). "Genus List for Holtz (2007) Dinosaurs" (PDF). University of Maryland. p. 34. Retrieved 11 October 2017.
  10. ^ Paul, G.S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 213.
  11. doi:10.1017/s0094837300006023
    .
  12. ^ Hirsch, K.F. (2001). "Pathological amniote eggshell - fossil and modern". In Tanke, Darren H.; Carpenter, Kenneth (eds.). Mesozoic Vertebrate Life. Indiana University Press. pp. 378–392.
  13. ^ "Object of the week Hypselosaurus egg". Leeds City Council. Retrieved 11 December 2020.
  14. ^ "Knuthenborgs sjældne dinosauræg undersøgt - svaret overrasker". TV2. 17 October 2023. Retrieved 17 October 2023.
  15. ^ Pereda-Suberbiola, X.; Galton, P.M. (2001). "Reappraisal of the nodosaurid ankylosaur Struthiosaurus austriacus Bunzel, 1871 from the Upper Cretaceous Gosau Beds of Austria". In Carpenter, K. (ed.). The Armored Dinosaurs. Indiana University Press. pp. 173–210.
  16. doi:10.2113/gssgfbull.180.2.145
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  17. doi:10.2113/gssgfbull.181.3.269
    .
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