Imagine the country's northeast as lush, green floodplains canopied by giant trees. Dinosaurs roamed free near a large river with a complex system of tributaries, islands and islets.
What today is Kalasin province was part of thriving ecological network dating back 150 million years.
Those huge waterways became ideal natural traps for the carcasses of enormous beasts, their remains enclosed in layers of sediment over the centuries.
That was until 2008, when Thai palaeontologist Varavudh Suteethorn and his French colleague Eric Buffetaut led a team to excavate the country's most prominent Mesozoic fossil excavation site, Phu Noi.
About 20 dinosaur bone fragments were found initially. But in the following years, the team uncovered more than 1,000 bone fragments from sauropods, a family of long-necked dinosaurs; the jaw of a carnosauria, a predatory dinosaur; fragments of ancient mammal bones; remains of late-Jurassic turtles; and the teeth of a freshwater shark.
Plant fossils with stems measuring more than one metre in diameter were also found. The discovery allowed local scientists to conclude that modern-day Isan, during the Mesozoic period, was abundant with water.
Yet the more Mr Varavudh digs in search of answers, the more mystery he encounters.
Dinosaurs appeared on the Earth about 225 million years ago and roamed the planet for some 150 million years before their eventual extinction, with the most accepted theory suggesting a major asteroid strike contributed to their decline.
But the fossils that have been found in Thailand all date back to more than 100 million years ago, indicating that dinosaurs may have disappeared here long before the period of worldwide extinction.
Perhaps the bones of more recent dinosaurs are yet to be found, Mr Varavudh says -- or maybe there are none to be found.
At least some of the answers may lie in the more than 10,000 bone fragments recovered from digs in the Northeast, many of which are still awaiting proper analysis. But while there is a small team of experts trying to unveil the mysteries of what happened to the dinosaurs in Thailand, so far little is known.
IN SEARCH OF GIANTS
Studies on fossils found in Thailand -- one of the richest sources of high-quality dinosaur fossils in the region -- could go a long way to helping understand the evolution of dinosaurs in Asia, and paint a much more detailed picture of dinosaur history as a whole.
Directed by Mr Varavudh, a study from Mahasarakham University's Paleontological Research and Education Centre points out that Thailand has good records of non-marine dinosaurs from the Mesozoic era, which spanned the Triassic (252-200 million years ago), Jurassic (200-145 million years ago) and Cretaceous (145-65 million years ago) periods.
Several parts of the country have yielded fossils of plants, invertebrates and vertebrates. Many important excavation sites have been explored, with bones discovered in Phu Wiang district in Khon Kean, and Phu Kum Khao district and Phu Noi Hill in Kalasin.
Major contributions came from collaborations with Thai and French experts who participated with Mr Varavudh, a geologist turned palaeontologist.
They discovered several important specimens at the Phu Wiang excavation site, including a new species of Cretaceous sauropod which they named Phuwiangosaurus sirindhornae, after Princess Maha Chakri Sirindhorn, and the new tyrannosaurus species Siamotyrannus isanensis.
They also discovered teeth from a new species of carnosauria, which was later named after Mr Varavudh as Siamosaurus suteethorni.
"There are still many of them buried underground. We can keep digging for another hundred years and keep making fresh discoveries," Mr Varavudh said.
Now 68, Mr Varavudh doesn't have a century left to keep digging, but he has no plans to retire from fossil excavation any time soon.
He is on a perpetual quest for new potential fossil sites, even though most can't be opened for excavation at this stage. He said about 20 sites have been marked and are visited regularly by his team.
Mr Varavudh believes there is high potential that dinosaur remains can be found in areas spanning around 100,000 square kilometres.
"We can always have new discoveries in this field. It's fun and an exciting experience for me to be here," he said while handling the skull of an ancient crocodile.
"Dinosaurs lived on the Earth very successfully for a very long period of time. But they went extinct eventually. That should serve as a warning for us, as humans, to look at the way we are living, to look at the way we are trying to change the course of nature."
Geological evidence shows that the disappearance of dinosaurs from what is modern-day Thailand may have been caused by environmental changes, perhaps driven by climate change, said Mr Varavudh.
Sudden drought -- severe enough to turn the once abundant northeastern floodplains to barren desert -- swept across the region in the late Cretaceous period, creating a harsh environment for large plants and animals.
There is also evidence that the Northeast may have experienced major flooding caused by rising sea levels at some point, said Mr Varavudh. The event caused salt water to become locked in the Northeast's lowlands, creating a kind of salt lake.
He said similarities have been found in some late-Jurassic period dinosaur bones found in Phu Noi and bones found in China, indicating that the beasts might have been forced to migrate north from Thailand.
Mr Varavudh and his team have also found fragments of mammal bones aged between 10,000 and 100,000 years in a cave in Chaiyaphum. Among those are teeth of an orangutan, a hyena and a panda, which today are not found in Thailand. He said this highlights the possibility that environmental changes had driven them away.
CLOSE TO THE BONES
Fossil research in Thailand has made significant progress since the Fossil Protection Act was introduced in 2008, authorising officials to enforce laws for the protection of dinosaur bones.
Prior to the law becoming effective, fossils from Thailand were regularly smuggled onto the international black market, or made into amulets by local people who stumbled across them.
In one well-known case, a Korean collector purchased five Thai dinosaur bones from smugglers. He later offered to sell each piece for 10 million baht to Thai officials.
The government baulked at the high price, and the pieces were never returned.
Tawsaporn Nuchanong, director-general of the Department of Mineral Resources (DMR), said it's difficult to estimate how many bones have been lost to smugglers prior to the law being implemented.
But the 2008 law has played a major role in progressing palaeontological research, as it allows the government to set budgets to hire more experts, fund research and build fossil museums.
The DRM ranks Thailand as an "excellent" fossil site in Asia in terms of quantity of discovered fossils and their quality.
Early discoveries in Southeast Asia were limited, and included the bones of a 100-million-year-old sauropod in Laos prior to World War II, and fossilised mammals found in Myanmar. But the fossilised remains of more than 100 species have now been found in Thailand, including at least nine species of dinosaurs. In Phu Noi alone, the DMR was able to register more than 1,600 fossil specimens into its database.
Yet only 20% of those have been analysed to classify species and age.
Thousands of other specimens are also awaiting analysis from other government offices and researchers.
The DMR now has the budget to take care of seven fossil museums across the country, while the number of palaeontological experts has risen from seven prior to 2008 to about 30 today.
"There are still very few human resources if we want to develop palaeontological research. We have a lot more to dig out," said Mr Tawsaporn.
Palaeontology is usually limited to a subject in undergraduate geology studies at Thai universities. Many geology students prefer to focus on mineral and petroleum surveys and extraction, specialities which can earn them much higher incomes after graduation.
Only Mahasarakham University and Nakhon Ratchasima Rajabhat University offer master's degrees in palaeontology. The other option is to study palaeontology abroad. But with limited career options, it is a path few Thai parents condone.
"Fossil museums should be a part of the Thai education system. Instead of department stores, museums should be a meeting place for families to cultivate knowledge and interest in palaeontology," said Mr Tawsaporn.
But attracting visitors to fossil museums is a challenge -- most government-run dinosaur museums report small visitor numbers.
Sirindhorn Museum, close to the Phu Kum Khao dinosaur excavation site in Kalasin, is touted as one of the best fossil museums in Thailand. Local authorities have marketed it as a "must visit". But it's a long journey for budding young natural historians in Bangkok.
On the other hand, theme parks such as Dinosaur Planet, which opened earlier this year on Sukhumvit Road, have proved popular for tourists and locals, but place their focus on entertainment over education.
Improving government museums to compete with the likes of Dinosaur Planet requires a significant investment. But Mr Tawsaporn believes that money is not the only answer -- just as important, he says, is generating creative content and multi-sector involvement.
He pointed to the Bangkok Art and Culture Centre, where cafe operators, art gallery owners and artists all play a part in filling space inside. Exhibitions come from various sources and themes change regularly, encouraging repeat visits.
Some palaeontologists, including Mr Varavudh, dream of establishing a natural-history museum in Thailand, which would be able to collect the fossils that are scattered around the country while offering a more complete history of dinosaurs, nature and humanity.
The arrival of monsoon rains forced the temporary closure of Phu Noi in the third week of June. A day before this announcement, Mr Varavudh and his staff carried many large fossiliferous rocks from Phu Noi to their PRC lab.
The rocks were wrapped in sacks coated with white plaster to prevent possible damage. Some were almost two metres in length. It will take at least two months to expose these fossils, and many months more to determine their species and age. Excavation will continue after the annual rains subside, and many new specimens are expected to be recovered.
Despite more than three decades passing since the dawn of Thai palaeontological research, the PRC estimates it has uncovered less than 1% of the fossils hidden underground.
Even still, the PRC lab is packed with thousands of Mesozoic fossil specimens ranging from bone fragments to teeth, fish scales and whole backbones of a herbivorous dinosaurs.
Despite having such a large area awaiting excavation, Mr Varavudh's staff is a small and eclectic one, and includes his own son, Suravech Suteethorn, along with researchers, a veterinarian and several interns.
Mr Suravech, 34, said he had followed his father to fossil excavation sites since he was a child, and in the process had developed a passion for dinosaurs.
Now an academic at Mahasarakham University, he's trying to encourage young students to see the value of fossils through his teaching, site visits and training programme.
Recently, his department has been able to use CT scans on fossiliferous rocks to model dinosaurs' bones and brain function, and use 3D printers to replicate the structure of their bodies.
"Palaeontology may have few job opportunities. But it's an important field, and a necessary one, because the study of natural history will go on for a long time," said Mr Suravech.
Taking after his father, the junior palaeontologist believes the study of dinosaurs will help humans better understand the planet and our relationship with the natural environment.
He is particularly interested in the ability of some dinosaur species to grow rapidly, in some cases from 1kg at birth to over 40 tonnes after 10 years. He said understanding this ability could unlock new methods for livestock production that could help feed a growing global population.
"The extinction of the dinosaurs may not be the most severe. It took around 1,000 years for them to reach extinction. Humans may be at a point that lead to mass extinction much sooner," he said.
"If we can unlock the mystery of the dinosaurs, we may be able to adapt and survive."
You old fossil: The jaw of Jurassic carnosauria found in 2012 at Phu Noi, Kalasin.
Many species: From left, a hypsilophodont fossil, the teeth of a panda dating back to 10,000-100,000 years from a cave in Chaiyaphum and the skull of an ancient crocodile in the university's collection.
Massive collection: Palaeontologist Varavudh Suteethorn at his lab at Mahasarakham University, where many specimens are waiting to be classified.
Grey matter: A Mahasarakham University staff member works on a 3D model of a dinosaur's brain.
Set in stone: A Paleontological Research and Education Centre staff member uses tools to remove a layer of rock from dinosaur fossils.
PERIOD: Late Cretaceous
LENGTH: 15-20 metres
FOUND IN: Khon Kean, Kalasin, Sakhon Nakhon and Nongbua Lamphu Phuwiangosaurus sirindhornae was the first sauropod discovered in Thailand. A medium-sized herbivore, it was named after Princess Maha Chakri Sirindhorn.
ERIOD: Late CretaceousLength: Seven metresFound in: Khon Kean, Kalasin, Sakhon Nakhon, Mukdahan, Nakhon Ratchasima and Ubon Ratchathani Siamosaurus suteethorni was discovered in 1986 by French palaeontologist Eric Buffetaut. It's a theropod — a group of lizard-like dinosaurs — with teeth similar to those of a crocodile, which means it most likely used to eat fish. It was named after Thai palaeontologist Varavudh Suteethorn.
Period: Early CretaceousLength: Seven meters
Location found: Khon Kean, Kalasin, Sakhon Nakhon, Udon Thani and Nakhon Ratchasima Siamotyrannus isanensis is a medium-sized carnivorous theropod which would walk and run on two legs. It falls under the genus tyrannosaurus, which means 'tyrant lizard'.