AI imageNote: This dinosaur is known from only part of a skeleton. The image fills in the missing parts from close relatives, so the real animal may have looked quite different.
Match with prompt
89% (8/9 items)
Where the image differs from the prompt
- Hands dangle with claws pointing downShould be: Palms facing each other, not turned down or dangling
See the checklist, prompt and sources
- ✓Bipedal, back horizontal, tail held straight out off the ground
- ✓Mouth closed, lips covering the teeth so none are visible
- ✕Palms facing each other, not turned down or danglingHands dangle with claws pointing down
- ✓Three weight-bearing toes on each foot
- ✓Long allosaur-like skull, not a tyrannosaur despite the name
- ✓Medium-sized, about 6–7 m long, three-fingered arms, small scales
- ✓Whole animal visible in side view
- ✓Scene matches the period and the fossil site
- ✓No text, people or modern objects
Checked by Claude Opus 5.5 (checked item by item from the image) on Oct 28, 2026. The score is the share of checklist items the image gets right; it is not an expert scientific review.
Prompt used to create the image
Scientifically accurate paleoart of Siamotyrannus, a carnivore Metriacanthosauridae dinosaur from Barremian times (125.77–121.4 million years ago). Bipedal with the back held roughly horizontal and the tail held straight out behind for balance, never dragging on the ground. NOT standing upright like a kangaroo. Mouth closed with all teeth fully hidden behind scaly lips, like a monitor lizard. NO visible teeth. A long, fairly narrow skull of an allosaur-like predator, NOT a tyrannosaur despite its name. Reference: Siamotyrannus is a genus of possibly allosauroid theropod dinosaur from the Early Cretaceous Sao Khua Formation of Thailand. Anatomy: hands held with palms facing each other (not pronated, not palms-down, not dangling); three main weight-bearing toes on each foot; medium-sized, about 6–7 meters long, three-fingered arms, skin of small scales. Full body in side view, whole animal visible, standing in an Early Cretaceous river floodplain like the Sao Khua Formation of northeastern Thailand, warm and semi-arid with conifers, cycads and ferns along meandering rivers, no grass and no flowering plants. Natural history museum illustration style, realistic textures and natural daylight, muted natural colors. No text, no labels, no humans, no modern objects.
Facts in the prompt come from Wikipedia (en) and Paleobiology Database
Siamotyrannus
Name meaning: Means "tyrant of Siam".
📏 About 6–7 m long, roughly half the length of Tyrannosaurus rex.
📐 Compare its size with other dinosaurs →Find it in a game
In Cretaceous Survival, Sao Khua Formation · opens the game at play.dinocodex.com
Play as Siamotyrannus
Siamotyrannus was a medium-sized meat-eater from the Sao Khua Formation in Khon Kaen. When it was named in 1996 it was thought to be an early tyrannosaur relative, but current research places it among the allosauroids, a separate lineage of predators.
Fun facts
- Its name means "tyrant of Siam", the old name of Thailand, even though it is no longer considered a close relative of Tyrannosaurus.
- Siamotyrannus shows how dinosaur classifications can change as new fossils and methods appear.
Who lived alongside it
Dinosaurs found in the same rock formation as Siamotyrannus (Sao Khua), so they lived in the same region at roughly the same time.
Phuwiangosaurus
Phuwiangvenator
Kinnareemimus
Vayuraptor
Formation data from the Paleobiology Database, counting only each genus's main formations. One formation can span hundreds of thousands to millions of years, so this doesn't mean any two of them ever met.
Scientific details
- Classification
- Theropod (two-legged predators)
- Family
- Metriacanthosauridae
- When it lived
- 121.4–125.77 million years ago
- Geologic stages
- Barremian
- Named by
- Buffetaut et al., 1996
- Fossil occurrences
- 1 sites
🦴 Known fossil material
Parts found as fossils
- Back vertebrae
- Sacrum (hip vertebrae)
- Tail vertebrae
- Pelvis
Holotype: the rear of the body, with the left half of the pelvis, the sacrum, five back vertebrae and thirteen front tail vertebrae. A shin bone and some teeth were referred to it in 1998; this diagram shows only the holotype.
Coloured areas are parts of the skeleton with fossil bones found so far (sometimes just one bone in that area); faint areas have not been found. The outline is a general shape for its group, not this dinosaur's real body.
Compiled from published descriptions; not yet checked against the original papers by a specialist. Sources: Wikipedia (en): Siamotyrannus
Countries with fossils
- Thailand
Data from Paleobiology Database and Wikidata