Glacialisaurus
Glacialisaurus | |
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holotype specimen FMNH PR1823)
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | †Sauropodomorpha |
Family: | †Massospondylidae |
Genus: | †Glacialisaurus Smith & Pol, 2007 |
Type species | |
†Glacialisaurus hammeri Smith & Pol, 2007
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Glacialisaurus is a
This dinosaur has been classified as a massospondylid, a group of medium-sized, basal (early diverging or "primitive") sauropodomorphs that existed during the Late Triassic and Early Jurassic on every continent except Australia. Its length has been estimated at 6.2 m (20 ft). Glacialisaurus was a large herbivorous dinosaur, though it was average sized for a massospondylid. Glacialisaurus was distinct from other sauropodomorphs in features such as having a robust medial epicondylar ridge on the lower femur, a robust adductor ridge extending from the upper end of the femoral medial condyle, and a second metatarsal with a front border that is weakly convex in the upper end.
Discovery and naming
Fossils of a
Several other fossils were collected from the same site, including fossils of the carnivorous
The fossils were described by the paleontologists Nathan Smith and Diego Pol, who named the new genus and species Glacialisaurus hammeri, with FMNH PR1823 as
Description
While few remains are known of Glacialisaurus, its leg bones show it was a robust basal (early diverging or "primitive") sauropodomorph. The femur fragment is the larger of the two known specimens, measuring 300 mm (0.98 ft) as preserved, with an estimated total length when intact of 600 mm (2.0 ft).[3] Glacialisaurus is estimated to have been about 6.2 m (20 ft) long.[5] As a basal sauropodomorph, Glacialisaurus would have had a long neck and a proportionally small head with leaf-shaped teeth. The hand would have been short, wide, and robust with a large claw on the thumb.[6]
Leg bones
The
The astragalus is low and elongate from across side to side and the medial portion lacks the craniocaudally broadening compared to the lateral portion, a trait found in most non-eusauropods. The astragalus is weakly convex at the lower end, though this is not as extreme as in Blikanasaurus and Lessemsaurus. The upper surface of the astragalus is softly convex because it is where the lower end of the tibia (shin bone) articulates with the astragalus. This surface is pierced by two fossae (small openings in bone) that have been interpreted as vascular fossae. The ascending process (protrusion of bone) is mound shaped and its upper articular surface faces proximomedially. The distal tarsals have a laterally elongated triangular shape in when seen from their top ends. The corners of the tarsals are rounded and bulbous, especially in the posteromedial corner. The medial distal tarsal is not confined solely to metatarsal III, but also barely contacts the proximal end of metatarsal II, like in Saturnalia. The lateral distal tarsal has a quadrangular shape and was likely longer mediolaterally than proximodistally.[3]
Metatarsal I is roughly 3/4 the length of metatarsal II, as in most basal sauropodomorphs. Metatarsal I has a broad and short shaft that is ellipse shaped, more so than in most other basal sauropodomorphs. The upper portion of the small posterior groove separating the two distal
The diagnostic traits (characteristics that distinguish a taxon from others) of the second metatarsals include: a front border that is weakly convex in proximal aspect; a hypertrophied lateral plantar flange on the proximal end (present, but less developed in many basal sauropodomorphs, e.g., Saturnalia, Plateosaurus); and a medial distal condyle that is more robust and well−developed than the lateral distal condyle. The third metatarsal lacks much preserved detail, but has a trapezoidal upper end with a straight to concave front border and a slightly convex medial border for articulation with metatarsal II. The hind edge is narrower from side toside than the front one, but is not acute or rounded, causing the upper outline of metatarsal III to be almost trapezoidal, as in Lufengosaurus, Gyposaurus, and Coloradisaurus. On the contrary, most non-eusauropod sauropodomorphs have almost triangular upper outlines. Only the upper portion of the metatarsal IV is preserved, but preserves an upper outline akin to that of Lufengosaurus that has a broad anterior face and a finger−like posteromedial projection. This finger-like process is slightly convex and would have articulated with metatarsal III.[3]
Classification
The phylogenetic position of Glacialisaurus is unstable due to its fragmentary nature, but it is frequently found to be a member of the family
The paleontologist Oliver W. M. Rauhut and colleagues found Lufengosaurus tobe the sister taxon of Glacialisaurus in 2020, and the following cladogram shows the placement they recovered for Glacialisaurus within the sauropodomorph group Massopoda:[10]
Massopoda |
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The discovery of Glacialisaurus is important to the study of the early distribution of sauropod dinosaurs.[3] The presence of this primitive sauropodomorph in the Hanson Formation (which has also yielded remains attributed to true sauropods) shows that both primitive and advanced members of this lineage existed side by side in the early Jurassic Period.[13][3]
Paleoenvironment
Glacialisaurus is known from the Hanson Formation, which is one of only two major dinosaur-bearing rock formations found on Antarctica. The specimens were discovered in
Models of Jurassic air flow indicate that coastal areas probably never dropped much below freezing, although more extreme conditions existed inland.
See also
References
- ^ a b Hammer, W. R., & Hickerson, W. J. (1996). Implications of an Early Jurassic vertebrate fauna from Antarctica. The Continental Jurassic, 215–218.
- ^ S2CID 38933265.
- ^ a b c d e f g h i j k l m n o p q r s t u Smith, Nathan D.; Pol, Diego (2007). "Anatomy of a basal sauropodomorph dinosaur from the Early Jurassic Hanson Formation of Antarctica". Acta Palaeontologica Polonica. 52 (4): 657–674.
- ^ a b c Smith, N. D., Makovicky, P. J., Hammer, W. R., & Currie, P. J. (2007). Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society, 151(2), 377–421.
- ^ Holtz Jr., Thomas R. (2012). "Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Appendix" (PDF). Retrieved January 12, 2012.
- ^ ISBN 978-0-375-82419-7.
- ^ ISBN 978-987-95849-7-2.
- ^ S2CID 85851161.
- ^ PMID 20926438.
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- ^ S2CID 209575985.
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- S2CID 18921496.
- ^ a b c Hammer, W.R.; Hickerson, W.J. (1999). Tomida, Y.; Rich, T.H.; Vickers-Rich, Y. (eds.). "Gondwana Dinosaurs from the Jurassic of Antarctica". Proceedings of the Second Gondwana Dinosaur Symposium National Science Museum Monographs. 15: 211–217.
- ^ a b c Smith, N.D; Hammer, W.R.; Makovicky, P.J. (2013). "New Dinosaurs from the Early Jurassic Hanson Formation of Antarctica, and Patterns of Diversity and Biogeography in Early Jurassic Sauropodomorphs". Geological Society of America Abstracts with Programs. 45 (7): 405–406.
- ^ ISBN 978-0-12-226810-6.
- ^ S2CID 130084588.
- ^ Chandler, M. A.; Rind, D.; Ruedy, R. (1992). "Pangaean climate during the Early Jurassic: GCM simulations and the sedimentary record of paleoclimate". Geological Society of America Bulletin. 104 (5): 543.
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- ISBN 978-0-691-16766-4.