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''Isanosaurus'' means "North-eastern thailand lizard" was a
sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', ' lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23  million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is ...
from
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
. It was originally dated to approximately 210 
million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
during the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
(late
Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic ...
to
Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...
stages), which would make it one of the oldest known sauropods. Its age was later considered uncertain, and may be as young as
Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the nam ...
. 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.


Description

The only specimen includes a neck
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
, a back vertebra and part of a second, six tail vertebra, two
chevrons Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock l ...
, fragmentary ribs, the right sternal plate, the right shoulder blade, and the left
thigh bone The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with t ...
(femur). This individual may have measured when alive; the thigh bone measures 76 centimetres in length. However, the vertebral neural arches have been found separated from the vertebral
centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different ...
, indicating that these elements were not fused with each other; thus, this individual probably was not fully grown. Early
sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
s were primitively
bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...
(two-legged). ''Isanosaurus'', being one of the first sauropods known, already shows a
quadruped Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor ...
al locomotion (with all four legs on the ground). The legs were column-like, as indicated by the robust and straight thigh bone. In
prosauropod Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
s, but also in the very basal sauropod ''
Antetonitrus ''Antetonitrus'' is a genus of sauropod dinosaur found in the Early Jurassic Elliot Formation of South Africa. The only species is ''Antetonitrus ingenipes''. As one of the oldest known sauropods, it is crucial for the understanding of the origin ...
'', the thigh bone was slightly sigmoidal (S-curved). Also, like in other sauropods, bony processes of the femur were reduced in ''Isanosaurus''; most notably, the
lesser trochanter The lesser trochanter is a conical posteromedial bony projection of the femoral shaft. it serves as the principal insertion site of the iliopsoas muscle. Structure The lesser trochanter is a conical posteromedial projection of the shaft of the f ...
was lacking. 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 joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...
s with neighbouring vertebrae. The tail vertebrae, on the other hand, were amphicoelous (concave at both ends). The dorsal neural spines were very high, like those of some later sauropods, unlike the low prosauropod neural spines. The lateral sides of the vertebrae were concave, but not deeply excavated (a structure known as pleurocoels) as in later sauropods.


Discovery

The specimen was found in dark red
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
of the Nam Phong Formation near the village of Ban Non Thaworn, in
Chaiyaphum Province Chaiyaphum ( th, ชัยภูมิ, ) is one of Thailand's seventy-six provinces (''changwat''), located in central northeastern Thailand , also called Isan. Neighboring provinces are (from north clockwise) Khon Kaen, Nakhon Ratchasima, Lop ...
. When discovered in 1998, the skeleton had unfortunately been mostly eroded away. With regard to vertebrate fossils, the Nam Phong Formation is poorly explored: besides ''Isanosaurus'', only two articulated
ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to we ...
were found. Whether these ischia belong to ''Isanosaurus'' is unclear, because no pelvic bones are preserved in the
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
specimen. ''Isanosaurus'' was described by French palaeontologist Éric Buffetaut and colleagues in 2000. The name is derived from
Isan Northeast Thailand or Isan ( Isan/ th, อีสาน, ; lo, ອີສານ; also written as Isaan, Isarn, Issarn, Issan, Esan, or Esarn; from Pali ''īsānna'' or Sanskrit ईशान्य ''īśānya'' "northeast") consists of 20 provi ...
(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.


Phylogeny

The following cladogram shows the position of ''Isanosaurus'' within Massopoda, according to Oliver W. M. Rauhut and colleagues, 2020:


References

Peyre de Fabrègues, C. & Allain, R. 2020. ''Kholumolumo ellenbergerorum'', gen. et sp. nov., a new early sauropodomorph from the lower Elliot Formation (Upper Triassic) of Maphutseng, Lesotho. ''Journal of Vertebrate Paleontology'' e1732996. DOI: 10.1080/02724634.2019.1732996 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


Restoration and discussion
of ''Isanosaurus'', by noted paleoartist Luis Rey. {{Taxonbar, from=Q1555632 Sauropods Norian life Rhaetian life Late Triassic dinosaurs of Asia Fossils of Thailand Fossil taxa described in 2000 Taxa named by Éric Buffetaut