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''Phuwiangosaurus'' (meaning "Phu Wiang lizard") is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
from the Early
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
(
Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...
-
Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.6 ± 2 Ma and 125.77 (million years ago). The Hauterivian is preceded by the Valangi ...
)
Sao Khua Formation The Sao Khua Formation () is a middle member of the Khorat Group. It consists of an alteration of pale red to yellowish-gray, fine to medium-grained sandstone and grayish-reddish brown siltstone and clay. Rare pale red to light gray conglomerates ...
of
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
. The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''P. sirindhornae'', was described by Martin, Buffetaut, and Suteethorn in a 1993 press release and was formally named in 1994. The species was named to honor
Princess Maha Chakri Sirindhorn Maha Chakri Sirindhorn, Princess Royal () (born 2 April 1955) is a member of the Thai royal family. She is the second daughter of King Bhumibol Adulyadej and Queen Sirikit, and the younger sister of King Vajiralongkorn. Early life Birth Si ...
of
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
, who was interested in the
geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
and
palaeontology Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geo ...
of Thailand, while the genus was named after the Phu Wiang area, where the fossil was discovered. The precise affinities of ''Phuwiangosaurus'' among
titanosauriform Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...
sauropods are uncertain, though several studies have classified it as a
euhelopodid Euhelopodidae is a family of sauropod dinosaurs of disputed membership and affinities, which contains '' Euhelopus'' and its close relatives. Most proposed euhelopodids are from East Asia. Euhelopodidae was first recognized by Carl Wiman in 192 ...
.


Discovery and naming

The type specimen of ''Phuwiangosaurus sirindhornae'' was discovered in Phu Wiang National Park in 1982, and excavated and prepared over the next several years. The specimen was described as representing a new genus and species, ''Phuwiangosaurus sirindhornae'', by Valérie Martin, Eric Buffetaut, and Varavudh Suteethorn in 1994. The genus name refers to its discovery in Phu Wiang, and the species name honors
Princess Maha Chakri Sirindhorn Maha Chakri Sirindhorn, Princess Royal () (born 2 April 1955) is a member of the Thai royal family. She is the second daughter of King Bhumibol Adulyadej and Queen Sirikit, and the younger sister of King Vajiralongkorn. Early life Birth Si ...
of
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
for her interest in the paleontology of the country.


Fossil specimens

''Phuwiangosaurus sirindhornae'' is known from several specimens, all of which were found in the
Sao Khua Formation The Sao Khua Formation () is a middle member of the Khorat Group. It consists of an alteration of pale red to yellowish-gray, fine to medium-grained sandstone and grayish-reddish brown siltstone and clay. Rare pale red to light gray conglomerates ...
of Thailand. The
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
, SM PW 1, is a partial skeleton of an adult individual, which consists of three cervical vertebrae, three dorsal vertebrae, ribs, a chevron, both scapulae, a coracoid, the left humerus, the left ulna, both ilia, ischia, pubes, and femora, and the left fibula. A dorsal vertebra and a caudal vertebra excavated at the same site years later probably belong to the same specimen. The most complete skeleton, SM K11, represents a half-grown individual and is about 60% complete, including a partial skull. Other partial skeletons and isolated bones have been described as well. In 2020, Cashmore et al. calculated that, overall, 65% of the skeletal anatomy of ''Phuwiangosaurus sirindhornae'' was known. Numerous bones of baby ''Phuwiangosaurus'' have been found, which is a rarity for sauropods. Though specimens of a wide range of ages are known, no old individuals that had reached their maximum body size are known.


Description

''Phuwiangosaurus'' was a mid-sized sauropod, roughly long. Its mass has been estimated at 17 tonnes. The teeth are slender and peg-like, with the tooth height from base to tip being on average over four times greater than the width of the base of the tooth. They are slenderer than the teeth of other euhelopodids, with their proportions more closely resembling the teeth of diplodocoids and
titanosaurs Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of Sauropoda, sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with tax ...
. The braincase of ''Phuwiangosaurus'' exhibits characteristics intermediate between those of basal somphospondyls and titanosaurs. The neck of ''Phuwiangosaurus'' was probably composed of 13 vertebrae. The lengths of the vertebrae increase up to the middle of the neck, with the eighth cervical vertebra being the longest, and then decrease again. The cervical neural spines are bifurcated from the seventh cervical vertebra onward. The
sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
was composed of five vertebrae.


Classification

''Phuwiangosaurus'' was originally assigned to
Titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of Sauropoda, sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with tax ...
, but more recent studies have placed it in a more basal position within the Titanosauriformes. Phylogenetic analyses presented by D'Emic (2012), Mannion ''et al.'' (2013), and Mocho ''et al.'' (2014) resolve ''Phuwiangosaurus'' within the
Euhelopodidae Euhelopodidae is a family of sauropod dinosaurs of disputed membership and affinities, which contains '' Euhelopus'' and its close relatives. Most proposed euhelopodids are from East Asia. Euhelopodidae was first recognized by Carl Wiman in 1929 ...
, alongside genera such as ''
Euhelopus ''Euhelopus'' is a genus of sauropod dinosaur that lived between 145 and 133 million years ago during the Berriasian and Valanginian ages of the Early Cretaceous in what is now Shandong Province in China. It was a large quadrupedal herbivore. Lik ...
'' and ''
Tangvayosaurus ''Tangvayosaurus'' (meaning "Tang Vay lizard") is a genus of sauropod dinosaur from the Aptian-Albian age Lower Cretaceous Gres superieurs Formation of Savannakhet Province, Laos. It was a basal somphospondylan, about 15 m long, and is kno ...
''. Other analyses have failed to find support for such a grouping, including some finding it to be
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
at the base of Somphospondyli.


Paleoecology

The Sao Khua Formation, where fossils of ''Phuwiangosaurus'' have been found, was deposited 133.6 to 132.1 million years ago, and represents a floodplain environment in a humid, subtropical climate. The Sao Khua dinosaur assemblage includes the large theropods ''
Siamotyrannus ''Siamotyrannus'' (meaning "Siamese tyrant") is a genus of theropod dinosaur from the early Cretaceous of Thailand. Discovery and naming In 1993, Somchai Traimwichanon found a partial skeleton of a large theropod at the Phu Wiang 9 site in Khon K ...
'', ''
Phuwiangvenator ''Phuwiangvenator'' () is an extinct genus of megaraptoran Theropoda, theropod that lived during the Early Cretaceous period in what is now Thailand. It contains only the type species, ''P. yaemniyomi''. The genus, generic name of ''Phuwiangven ...
'', ''
Vayuraptor ''Vayuraptor'' (meaning "wind thief") is a genus of basal coelurosaurian (possibly megaraptoran) theropod dinosaur that lived in the Early Cretaceous (Barremian) Sao Khua Formation of Thailand. The genus contains a single species, ''V. nongbual ...
'', and ''
Siamosaurus ''Siamosaurus'' (meaning "Siam lizard") is a potentially nomen dubium, dubious genus of Spinosauridae, spinosaurid dinosaur that lived in what is now known as China and Thailand during the Early Cretaceous Period (geologic time), period (Barr ...
'', and the ornithomimosaur ''
Kinnareemimus ''Kinnareemimus'' (, meaning "Kinnara#Thailand, Kinnaree mimic", after a figure from Thai folklore) is an extinct genus of ornithomimosaurian theropod dinosaur that was discovered in the Early Cretaceous Sao Khua Formation in what is now Thailand. ...
''. Other unidentified sauropods, different from ''Phuwiangosaurus'', were present in the ecosystem. These sauropods include a ''Euhelopus''-like taxon and a possible brachiosaurid.
Ornithischian Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...
dinosaurs are not known from the Sao Khua Formation, although they are known from roughly contemporary environments in other parts of Asia. Non-dinosaurian members of the fauna included crocodilians, turtles, fish, and sharks. There is evidence that theropods fed on ''Phuwiangosaurus''.


References


Works cited

* * * * * * * * * * * * {{Taxonbar, from=Q135641 Macronaria Dinosaur genera Valanginian dinosaurs Hauterivian dinosaurs Taxa named by Éric Buffetaut Taxa named by Varavudh Suteethorn Fossil taxa described in 1994 Dinosaurs of Thailand