An Ultimate Guide to Siamosaurus: The Lizard of Thailand

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Name Meaning“Lizard of Thailand”Height3-4 meters (10-13 feet)
PronunciationSigh-ah-moh-SAW-rusLength8-10 meters (26-33 feet)
EraMesozoicEarly CretaceousWeight1 to 2 tons (2,000-4,000lbs)
ClassificationDinosauria,‭ Saurischia & TheropodaLocationThailand

Siamosaurus Pictures

Siamosaurus suteethorni – License

The Siamosaurus

Gage Beasley Prehistoric's Siamosaurus Concept
Gage Beasley Prehistoric’s Siamosaurus Concept

The Siamosaurus (“The Lizard of Thailand”) is an intriguing dinosaur that inhabited the Earth in the late Cretaceous Period.

This huge theropod, belonging to the Spinosauridae family, has captured the public’s attention due to its unusual appearance and the uncertainty surrounding its origins. 

Finding a Siamosaurus specimen in Thailand, a country not often connected with dinosaur fossils is quite exciting.

Its unique characteristics, including its long snout and narrow, crocodile-like jaws filled with sharp teeth, set it apart from any other known dinosaur.

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

It was also one of the biggest carnivorous dinosaurs, with a possible length of up to 12 meters. 

Scientists have pieced together a wealth of information about the Siamosaurus by meticulously examining the available fossil record, even though it is inadequate.

Explore the Siamosaur’s environment in more detail as we learn more about its anatomy, behavior, habitat, and importance in the context of ancient ecosystems.

Physical Characteristics

Gage Beasley Prehistoric's Siamosaurus Size Comparison Chart
Gage Beasley Prehistoric’s Siamosaurus Size Comparison Chart

The morphological traits of Siamosaurus, sometimes known as the “Lizard of Thailand,” set it apart from other theropod dinosaurs.

Due to the lack of full fossils, its precise size is unknown, although experts believe it was between 6 and 9 meters (20 and 30 feet) long and weighed between 1 and 2 tons.

The extended and narrow snout of Siamosaurus was one of the dinosaur’s most distinctive traits.

The similarity of this feature to modern-day crocodilians suggests a preference for watery habitats where capturing prey is easier.

Siamosaurus’s long, narrow snout may have helped it swim quickly and efficiently through the water.

Sharp, conical teeth lined its nose, making it well-suited for grabbing and shredding apart prey.

Five spinosaurid teeth that have been found in various parts of Asia
Five spinosaurid teeth that have been found in various parts of Asia -PaleoGeekSquared – License

Siamosaurus possessed a tall and slender head, with its upper jaw adorned by a row of tiny, recurved teeth.

The head size of the Siamosaurus was unusually tiny for such a massive dinosaur.

The placement of its eyes on the side of its head suggested a broad field of vision, which would have been an advantage while hunting and spotting danger. 

The dinosaur’s long, muscular hind legs suggested it could move quickly and effectively.

Researchers believe that Siamosaurus had the ability to sprint at high speeds, enabling it to effectively pursue its prey.

Siamosaurus likely had well-adapted legs for terrestrial mobility, suggesting that it could move efficiently both on land and in the water.

However, Siamosaurus’s forelimbs were noticeably shorter than its rear limbs.

The presence of claws on the forelimbs indicates that Siamosaurus used them to capture and grasp onto its prey.

The forelimbs may have helped with propulsion when swimming or navigating aquatic surroundings, albeit this is a less well-established theory.

Life reconstruction of Siamosaurus suteethorni
Life reconstruction of Siamosaurus suteethorni | Connor Ashbridge via License

Due to a lack of fossils, our understanding of Siamosaurus’s anatomy is hazy at best.

However, we assume that its physique was slim and well-proportioned.

Swimming more efficiently and with less effort might have been possible with such a body design.

Siamosaurus probably swam with the help of its long, muscular tail, which provided both propulsion and stability while doing so.

Siamosaurus’s anatomical make-up as a whole implies it was a predator that made use of its watery or semi-aquatic environment.

Its streamlined shape and lengthened snout suggest it hunted fish and other aquatic animals in river and lake habitats.

It is possible that Siamosaurus may have moved quickly both on land and in water, making it a dangerous predator in its day.

Habitat and Distribution

There is a lot of conjecture and active investigation on the Siamosaurus’s potential habitat and range.

Siamosaurus, as its name implies, was first discovered in Thailand, more precisely in the Khok Kruat Formation, which is around 125 million years old and hence belongs to the early Cretaceous era.

This discovery prompted doubts regarding the long-standing belief that spinosaurid dinosaurs were confined to regions such as Africa and South America.

Scientists believe that the Siamosaurus lived in a biodiverse ecosystem that included rivers, floodplains, and lush tropical forests based on the geological setting of its finding.

Other fossilized remains, such as those of fish, turtles, crocodiles, and numerous plant species, discovered in the same location lend credence to this view.

According to experts, the Siamosaurus had the swimming and navigational skills necessary for an amphibious existence.

The long snout and pointed, conical teeth were ideal for snatching fish and other aquatic creatures out of the water.

Siamosaurus’s precise range is unknown, however, it is speculated that it may have extended outside Thailand.

Siamosaurus in the Sao Khua Formation palaeoenvironment
Siamosaurus in the Sao Khua Formation palaeoenvironment | Offy & PaleoGeekSquared via License

Researchers have uncovered spinosaurid dinosaur fossils in various regions worldwide, including Europe, Africa, and South America, indicating a potential global distribution.

However, additional excavations are necessary to fully understand the extent of Siamosaurus‘ distribution and geographic range due to the limited availability of fossils.

Behavior and Diet

Siamosauruses seem to have specialized in the capture and consumption of fish and other aquatic prey due to their extended snouts and sharp, interlocking teeth.

Its crocodile-like jaws and conical teeth indicate a piscivorous diet, as they are specialized for capturing and impaling slippery prey.

This feature shows that the Siamosaurus was a skilled aquatic predator, waiting patiently along the water’s edge or perhaps partly submerged to attack unwary fish.

Although the Siamosaurus is often thought to have lived in the water and fed mostly on fish and other aquatic food, it is likely that, when it roamed the land, it also ate terrestrial species.

Although we don’t have a lot of hard data, we can get some idea of what this dinosaur would have eaten on land by comparing it to other spinosaurids and learning more about its ecological niche.

Spinosaurus, like Siamosaurus, were massive theropods with strong heads and conical teeth that they used to grasp and hold their food.

Opportunities to hunt and scavenge smaller terrestrial creatures, such as ill, juvenile, and elderly dinosaurs, turtles, and other animals that went near water sources, were presumably taken by the Siamosaurus.

This opportunistic feeding habit is corroborated by the discovery of remains of tiny dinosaurs and other animals in locations where spinosaurids have been discovered.

Siamosaurus suteethorni after a day of feeding
Siamosaurus suteethorni after a day of feeding – DinoThaiThai Chatchy – License

In addition, the Siamosaurus possessed robust forelimbs with formidable claws, suggesting the capability of gripping and manipulating prey items on land.

Because of this, it’s possible that it might have captured and subdued tiny to medium-sized terrestrial prey before delivering a lethal bite with its sharp teeth.

Siamosaurus probably demonstrated some nutritional flexibility, adjusting its eating habits to the accessible food supplies in both aquatic and terrestrial habitats, while the exact ratios of its diet on land compared to in water remain unknown.

The Siamosaurus probably used both two- and four-legged movement strategies, depending on the circumstances.

Like other theropod dinosaurs, it would have moved on the ground using its strong hind limbs.

Perhaps it paddled or swam well, thanks to its powerful forelimbs and webbed fingers.

Life Cycle

Due to a lack of fossil evidence about its reproductive and developmental phases, the Siamosaurus‘ spinosaurid family life cycle is poorly understood.

Their life cycle is a mystery, but we may make educated guesses by looking at that of other theropod dinosaurs and living reptiles.

Like other dinosaurs, spinosaurus, like the Siamosaurus, probably reproduced by depositing eggs.

Females probably hid their eggs in sand or other safe places before laying them.

Spinosaur babies would have been delicate newborns after hatching from their eggs.

Spinosaurs’ young would have needed protection and care from their parents when they first hatched.

Illustration of an adult and a young Spinosaurus (dinosaur species) isolated on a white background
Spinosaurus’ family life cycle was likely similar to Siamosaurus – XiaImages via Istock

During those early phases of development, they would have needed help from their parents or other mature members of their species to survive.

Like contemporary birds, adult spinosaurus would have cared for their young by feeding and protecting them from predators until they were old enough to fend for themselves.

The juvenile dinosaurs would have experienced a period of fast development as they matured, growing in size and taking on adult characteristics.

Adult Siamosaurus developed lengthened snouts and sharp teeth, which were likely a result of tooth replacement and bone hardening during this period of growth.

The time to sexual maturity and overall life span in spinosaurids is unknown and possibly varied across different species.

Spinosaurs’ growth and survival rates during their life cycle would have been affected by factors including nutrition, environmental circumstances, and predation pressures.

Evolution and History

The first Siamosaur fossils were found in the Sao Khua Formation of the Khorat Group.

The age of the formation is determined to be between 129.4 and 125 million years old, during the Barremian epoch of the Early Cretaceous era.

Fossil teeth were discovered in the Phu Wiang region of Khon Kaen Province, and in 1983, French paleontologist Éric Buffetaut and his Thai colleague Rucha Ingavat reported these fossils.

It was concluded that the bones “belonged either to an unusual theropod dinosaur or to some unknown crocodilian,” but no firm conclusions were drawn. 

In 1986, the same scientists reexamined the fossils and determined that they belonged to a previously undescribed species of spinosaurid theropod they called Siamosaurus suteethorni.

The generic title references the historical name of Thailand, “Siam”, and incorporates the Ancient Greek word (sauros), meaning “lizard” or “reptile.”

Reconstruction of the terrestrial paleoenvironmental setting of the Sao Khua
Reconstruction of the terrestrial paleoenvironmental setting of the Sao Khua | Renata Cunha via License

The specific name is an homage to Varavudh Suteethorn, a paleontologist and geologist from Thailand who made important discoveries in the country’s vertebrate fossil record.

Excavators discovered the fragmentary skeleton in an outcrop of the Khok Kruat Formation near the city of Khon Kaen in 2004.

The SM-KK 14 specimen includes parts of the pelvis, a potential metacarpal (long bone of the hand), and a chevron from the tail.

It also includes cervical and dorsal vertebrae, a 60-centimeter (24-inch) high neural spine (upward-extending process from the top of vertebra).

The distinguishing features of spinosaurids include an extended neural spine and a pelvis and cervical vertebrae that closely resemble those of the European Spinosaurus, Baryonyx walkeri.

An adjacent Siamosaurus tooth suggests the skeleton is from the same species. However, this may just be the result of scavenging.

Interactions with Other Species

Siamosaurus probably had interactions with creatures from all around its environment.

Siamosaurus was likely a predator of fish, turtles, and other aquatic animals due to its watery lifestyle.

Its large snout and pointed teeth suited it for hunting watery creatures.

Siamosaurus may have faced off against other huge theropods or aquatic carnivores, like Baryonyx or Suchomimus, that inhabited the same bodies of water. 

Gage Beasley Prehistoric's Baryonyx Concept
Siamosaurus likely had a few meetings with Baryonyx

These interactions would have altered the balance of predators and prey in aquatic ecosystems, as well as the distribution of available resources. 

Siamosaurus may have also reduced the variety and number of its prey by applying predation pressure.

Cultural Significance

When compared to other well-known dinosaurs, the Siamosaurus has received less attention in mainstream culture.

Perhaps the lack of fossils and the unfamiliarity with the Siamosaurus have led to its underrepresentation in the media. 

However, it’s important to keep in mind that popular culture is ever-evolving, so the Siamosaurus may show up in novels, movies, or other kinds of media in the future based on new findings or interpretations.

As scientific understanding expands and the public’s interest in obscure dinosaurs grows, the Siamosaurus may eventually come to get greater attention and publicity in mainstream media.

Siamosaurus suteethorni skeleton at Bangkok River city
Siamosaurus suteethorni skeleton at Bangkok River city – by Pescov – License

However, the group of Spinosaurids has gained cultural prominence and frequently appears in various forms of media.

Their extraordinary qualities and size have sparked the interest of audiences everywhere, leading to their prominent feature in a variety of media.


The Siamosaurus is a fascinating spinosaurid dinosaur that had exceptional adaptations and a long and eventful history of evolutionary development.

In spite of the fact that its life cycle and cultural value are still being investigated, the fossils it has left behind give very helpful information on the ancient ecosystems that formerly existed in Thailand.

The mysterious dinosaur and its significance in the world of the ancient era may be better understood if studies are carried on, and further discoveries are made in the future.


What caused the Siamosaurus‘ extinction?

Siamosaurus became extinct around 66 million years ago.

The Cretaceous-Paleogene extinction event took place due to an asteroid impact, volcanic activity, and climate change.

About 75% of Earth’s species, including the dominant dinosaurs, went extinct due to these circumstances.

What other dinosaurs were unearthed in Thailand?

Researchers have found dinosaur fossils in Thailand, providing valuable insights into the ecosystems of bygone eras.

Among the dinosaurs unearthed in Thailand are Phuwiangosaurus, Siamotyrannus, and Psittacosaurus, to name just a few.

How many species of Siamosaurus are there?

Science presently accepts Siamosaurus suteethorni as the only species of Siamosaurus.


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