Isanosaurus

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Isanosaurus
Temporal range: Late Triassic
~214–201 Ma
Isanosaurus attavipachi femur.JPG
Isanosaurus attavipachi thigh bone
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Clade: Sauropoda
Genus: Isanosaurus
Buffetaut et al. 2000
Species:
I. attavipachi
Binomial name
Isanosaurus attavipachi
Buffetaut et al. 2000

Isanosaurus (meaning "Isan [north-eastern Thailand] lizard") was one of the first sauropod dinosaurs. It lived approximately 210 million years ago during the Late Triassic (late Norian to Rhaetian stages) in Thailand; the only species is Isanosaurus attavipachi. Though important for the understanding of sauropod origin and early evolution, Isanosaurus is poorly known. Exact relationships to other early sauropods remain unresolved.[1]

Description[edit]

Models in Poland

The only specimen includes a neck vertebra, a back vertebra and part of a second, six tail vertebra, two chevrons, fragmentary ribs, the right sternal plate, the right shoulder blade, and the left thigh bone (femur);[1] this individual may have measured 6.5 metres (21 ft) when alive; the thigh bone measures 76 centimetres in length.[1] However, the vertebral neural arches have been found separated from the vertebral centra, indicating that these elements were not fused with each other; thus, this individual probably was not fully grown.[1]

Early sauropodomorphs were primitively bipedal (two-legged). Isanosaurus, being one of the first sauropods known, already shows a quadrupedal locomotion (with all four legs on the ground);[1] the legs were column-like, as indicated by the robust and straight thigh bone.[1] In prosauropods, but also in the very basal sauropod Antetonitrus, the thigh bone was slightly sigmoidal (S-curved).[2] Also, like in other sauropods, bony processes of the femur were reduced in Isanosaurus; most notably, the lesser trochanter was lacking.[1]

Additional important features can be found in the vertebrae; the neck vertebrae were distinctly opisthocoelous (convex at the front and hollow at the back), forming ball-and-socket joints with neighbouring vertebrae. The tail vertebrae, on the other hand, were amphicoelous (concave at both ends);[1] the dorsal neural spines were very high, like those of some later sauropods, unlike the low prosauropod neural spines.[1] The lateral sides of the vertebrae were concave, but not deeply excavated (a structure known as pleurocoels) as in later sauropods.[1]

Discovery[edit]

The specimen was found in dark red sandstone of the Nam Phong Formation near the village of Ban Non Thaworn, in Chaiyaphum Province;[1] when discovered in 1998, the skeleton had unfortunately been mostly eroded away.[1] With regard to vertebrate fossils, the Nam Phong Formation is poorly explored: besides Isanosaurus, only two articulated ischia were found. Whether these ischia belong to Isanosaurus is unclear, because no pelvic bones are preserved in the holotype specimen.[1]

Isanosaurus was described by French palaeontologist Éric Buffetaut and colleagues in 2000;[1] the name is derived from Isan (north-eastern Thailand); the species name honours P. Attavipach, a supporter of palaeontological research in Thailand and former Director General of the Thai Department of Mineral Resources.[1]

References[edit]

  1. ^ a b c d e f g h i j k l m n o Buffetaut, E.; Suteethorn, V.; Cuny, G.; Tong, H.; Le Loeuff, J.; Khansubha, S.; Jongautchariyakul, S. (2000). "The earliest known sauropod dinosaur". Nature. 407 (6800): 72–74. doi:10.1038/35024060. PMID 10993074.
  2. ^ Yates, A.M. & Kitching, J.W. 2003. The earliest known sauropod dinosaur and the first steps towards sauropod locomotion. Proceedings of the Royal Society of London B: Biological Sciences 270: 1753-1758.

External links[edit]