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Ratchasimasaurus, Early CretaceousKhok Kruat Formation, Thailand · named 2011
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Ratchasimasaurus

"Ratchasima lizard"

Lived
121 to 113 million years ago, Early Cretaceous
Diet
Herbivore
Group
Ornithopods
Found in
Thailand
Named by
Shibata et al. 2011

Where its fossils were found

The evidence

Today

1 find

115 million years ago

Map: C. R. Scotese, PALEOMAP

Habitat

Winding rivers crossed a floodplain in what is now Thailand. The Khok Kruat Formation also contains Siamodon, Sirindhorna and Siamraptor.

Field notes

About Ratchasimasaurus

What it was like

Ratchasimasaurus was a plant eater related to Iguanodon. It is known from a lower jaw bone.

Its world

It lived in the Early Cretaceous in what is now Thailand. Its bones come from the Khok Kruat Formation, where it shared the land with the plant eaters Siamodon and Sirindhorna and the predator Siamraptor.

How it was found

Shibata and colleagues named it in 2011. It is named after the province where it was found.

Field gallery

More views of Ratchasimasaurus

Scenes reconstructed from the available fossil evidence.

Ratchasimasaurus in its habitat, photo 1

1 of 3

Lived alongside

Found in the same rock formations

A rock formation can hold fossils laid down millions of years apart, so not every animal here met Ratchasimasaurus.

The evidence

The science behind Ratchasimasaurus

Which parts of the picture come from its own bones, and which come from its relatives.

From its own fossils

  • It is known from a single toothless lower jaw bone, long and low, with a row of empty tooth sockets.
  • A shelf separates the tooth row from the tall process where jaw muscles attached, and that process leans backward.
  • Its jaw is longer and shallower than the jaw of Sirindhorna from the same rocks. Jaws in this group grow longer with age, so it is unlikely to be a young Sirindhorna.

Borrowed from relatives

  • Its upper skull is unknown, so restorations borrow a broad toothless beak and a low skull roof from Eolambia, a North American relative.
  • The neck, body, limbs and tail also follow Eolambia, because Ratchasimasaurus is known only from its jaw.

Still unknown

  • Whether its jaw features are distinctive enough to define a genus. Some experts see them as unique, while others find them in many related plant eaters.
  • Whether it is the same animal as Siamodon from the same rocks. The two are known from different bones, so they cannot be compared.
  • Its age at death, its complete skull and body, and its skin.

Discovery timeline

  1. 2011Named itSHIBATA, JINTASAKUL & AZUMA
  2. 2015Close relativeShibata et al.
  3. 2019Same rocksChokchaloemwong et al.
  4. 2022Family treePoole

Key papers

The research behind what we know of Ratchasimasaurus

Close relatives

Other members of Hadrosauroidea

Sources: Wikidata