''Sirindhorna'' 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 ...

hadrosauroid Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or Hadrosauridae, and all dinosaurs more closely related to them than to ''Iguanodon''. Their remains have been recovered in Asia, Euro ...

ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

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

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

deposits of northeastern

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 ...

Discovery and naming

In 2007, the Fukui Prefectural Dinosaur Museum (FPDM) approached the Northeastern Research Institute of Petrified Woods and Mineral Resources, Nakhon Ratchasima Rajabhat University (NRRU) and associated Khorat Fossil Museum on the possibility of a collaboration. The motivation for such an effort was because of the similar age of rocks in Suranaree Subdistrict, Nakhon Ratchasima Province,

and Katsuayama,

Fukui Prefecture is a Prefectures of Japan, prefecture of Japan located in the Chūbu region of Honshū. Fukui Prefecture has a population of 737,229 (1 January 2025) and has a geographic area of 4,190 Square kilometre, km2 (1,617 sq mi). Fukui Prefecture border ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. Similar dinosaurs are known from the formations of both locales, and so the researchers wanted to collaborate in research to be able to more deeply compare the prehistory of both countries. The collaboration was approved as the Japan-Thailand Dinosaur Project (JTDP), and this contributed to the basis of the founding of the Asia Dinosaur Association in 2013, by which time over 30,000 fossils had been found by the joint effort. The fossils of ''Sirindhorna'' were collected as part of the JTDP, at the Ban Saphan Hin site of the

Khok Kruat Formation The Khok Kruat Formation () is a geological formation, rock formation found in northeastern Thailand. It is the uppermost formation of the Khorat Group. It is dated to the Aptian Geological stage, stage of the Early Cretaceous Geological period, ...

; the dating of the formation is uncertain (as index fossils have proven rare), but it's thought to mostly likely date the

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the late

Period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

, between 125 and 112

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

. The formation does not usually crop out in the Nakhon Ratchasima province, where the geologic features are covered in a layer of thin red soil (local legend claims this colour is from the blood of dinosaurs);

bedrock in Suranaree is generally found around a metre below ground level. The locality of the ''Sirindhorna'' bonebed is usually used for farming of

corn Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout Poaceae, grass that produces cereal grain. It was domesticated by indigenous peoples of Mexico, indigenous peoples in southern Mexico about 9,000 years ago ...

and

tapioca Tapioca (; ) is a starch extracted from the tubers of the cassava plant (''Manihot esculenta,'' also known as manioc), a species native to the North Region, Brazil, North and Northeast Region, Brazil, Northeast regions of Brazil, but which has ...

. Digging to make a reservoir, farmers happened upon dinosaur fossils. Researchers re-identified the bonebed's location and gathered information on

taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientis ...

and other fossils found there, pertaining to various vertebrates but not any plants or invertebrates. Farming was not conducted while fossil excavation was conducted. Described in

2015 2015 was designated by the United Nations as: * International Year of Light * International Year of Soil __TOC__ Events January * January 1 – Lithuania officially adopts the euro as its currency, replacing the litas, and becomes ...

by Thai

palaeontologists 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 geolo ...

Masateru Shibata, Pratueng Jintasakul, Yoichi Azuma and Hai-Lu You, ''Sirindhorna'' was one of eighteen dinosaur taxa from the year to be described in an

open access Open access (OA) is a set of principles and a range of practices through which nominally copyrightable publications are delivered to readers free of access charges or other barriers. With open access strictly defined (according to the 2001 de ...

or free-to-read journal. It's the third species of

iguanodont Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivore, herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and rel ...

found in Thailand, following '' Siamodon'' and '' Ratchasimasaurus'', both known from poorer material, and the first

from

Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

to have a well-preserved skull. The

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

and only species of the genus is ''Sirindhorna khoratensis''. The

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

is known from the

holotype specimen A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was Species description, formally described. It is either the single such physical example (or illus ...

NRRU3001-166, an articulated

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

, as well as a number of disarticulated referred specimens. The material known from these referred specimens consists of three more partial braincases, one with an articulated postorbital, one right premaxilla, a left and right maxilla, a right jugal, surangular, and quadrate, one predentary, a right and left dentary, and assorted teeth. The generic name is dedication to

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 ...

for her contribution to the support and encouragement of palaeontology in Thailand. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

is derived from Khorat, the informal name of Nakhon Ratchasima Province. The ilium and ischium of ''S. khoratensis'' still remains undescribed.

References

{{Taxonbar, from=Q21945702 Hadrosauroidea Dinosaur genera Aptian dinosaurs Taxa named by Hailu You Fossil taxa described in 2015 Dinosaurs of Thailand