Today, the land near Ban Saphan Hin in central Thailand is dusted with thin reddish soil where local farmers plant maize and tapioca. But more than 113 million years ago, this region hosted ancient floodplains terrorized by a terrifying dinosaur with shark-like teeth.
Today described in the journal PLOS One the new-found predator – called Siamraptor suwati – is the most complete dinosaur of its type and age ever found in Southeast Asia. The legs of the 25-foot animal add a string of large dinosaur finds from the region, and they reveal new insights into how a large group of predator dinosaurs spread across the ancient world.
"It's one of the most important Thai dinosaurs ever found," said Steve Brusatte, a University of Edinburgh paleontologist who reviewed the study for publication, in an email.
For example, a team led by Duangsuda Chokchaloemwong, a researcher at Thai Nakhon Ratchasima Rajabhat University, pored over the bones and found that the skeleton was shot through with air sacs, which would have made the dinosaur's frame easier and perhaps helped it breathe faster, an idea that future scans of the bones could test. 19659002] "It would have been a hard, fast, dynamic animal," says Brusatte.
19659008] Teeth like a shark
Tens of millions of years before giant bulls nnosaurs that T. rex arrived on the scene, another group of large predator dinosaurs reigned: the allosauroids. Among these carnivorous heavyweights was a group called the carcharodontosaurs (kar-KA-ro-DON-toe-SORES), which were the best predators for most of the chalk.
"It was only with the decline of carcharodontosaurs that small tyrannosaurs became large and moved into the top of the predator role," says Brusatte.
Evidence that the group first emerged from the Egyptian Sahara in 1914, when an expedition funded by German palaeontologist Ernst Stromer found dinosaur teeth that were looking like frying knives. The prohibitive chompers reminded Stromer of the Carcharodon shark genus that includes the great white shark, so in 1931 he named the dinosaur Carcharodontosaurus saharicus .
In the following decades, paleontologists found more relatives of Stromer's shark-toothed dinosaurs, including some of the largest predator dinosaurs ever lived. But until recently, no well-preserved carcharodontosaurs had been found in Southeast Asia. Was this gap the sign of a real absence, or had their remains simply not yet been discovered? To find out, researchers needed to start digging.
Excavating a dinosaur
In recent decades, Thai paleontologists have found much fossil material from the dinosaur era. Since 2007, an international team named Japan-Thailand Dinosaur Project has found two new herbivorous dinosaurs named Ratchasimasaurus and Sirindhorna as well as an old relative of alligators and crocodiles.  "This project is strikingly important for revealing the evolutionary history of dinosaurs during the early Cretaceous period," study officer Soki Hattori, a paleontologist at Japan's Fukui Prefectural Dinosaur Museum, said in an email. "The comparison of early Cretaceous dinosaurs from Japan and Thailand allows us to understand deeply about them, such as the history of the dinosaurs' geographic radiation."
The researchers found that herbivorous Sirindhorna near Ban Saphan Hin, a village in Nakhon Ratchasima province, within a rock layer believed to have formed about 113 to 125 million years ago. The heights reached 95 degrees Fahrenheit as the team dug, and the site rang out with the constant dress of stone knocking stone.
The hard work was worth it: In addition to looking up Sirindhorna the excavation revealed 22 disarticulated pieces of a predator dinosaur. The fossils were from at least four different individuals and included some backbones, parts of the limbs and hips and fragments of the skull, including a well preserved lower right jaw. Chokchaloemwong and her colleagues pored over the legs and found that they belonged to a carcharodontosaur.
The discovery shows that carcharodontosaurs were widespread throughout the earth during the early Cretaceous period. Many other dinosaur groups, including other allosauroids, also expanded their ranges at that time. Then North America was connected to Europe and Asia, which allowed the dinosaurs of the three continents to mix and mingle.
Siamraptor also has significance for Thailand itself, says Chokchaloemwong: "I hope this discovery will make Thai people realize that our country has so many fossils [we] that still need the young generation to discover. "