Ancestor of Asian Turtles – Basilochelyes macrobios
Scientists have announced the discovery of the fossil of a previously unknown turtle species dating from the Jurassic period near Phupan mountain in the eastern Thailand province of Mukdahan. Analysis of the shape of the carapace (shell) and the backbone of this animal indicate that this species was the ancestor of several extant species of turtle found in south-east Asia today.
Thailand is proving itself to be an important country for palaeontologists and geologists studying life in the early Mesozoic. The fossils of one of the first species of Chelonians, Proganochelys; have been found close to the city of Khon Kaen in the northeast of the country. Proganochelys was approximately one metre long and had a box-like carapace. Unlike modern species, it could not retract its neck fully into its shell. Instead the neck was protected by rows of spikes, important to protect this vulnerable part of its body from attacks as there were a number of early theropod dinosaurs (coelurosaurs) around during this particular time in Earth’s history.
Proganochelys (P. quenstedii) lived close to freshwater lakes and rivers. It probably was semi-aquatic. Unlike extant species, this primitive tortoise had small teeth in the roof of its mouth. Modern species of tortoise/turtle have not teeth in their jaws. Proganochelys shared its watery environment with a number of bizarre creatures, the heavy rhynchosaurs with their powerful beaks, the unusual Gerrothorax and the huge, carnivorous amphibian Mastodonsaurus.
This new species of extinct turtle dates from the Late Jurassic (approximately 150 million years ago), this part of Thailand was a lush, lowland area with many lakes and rivers crossing it. In fact the environment was quite similar to the environment in which Proganochelys flourished sixty million years earlier.
The turtle discovery confirms the geological importance of the north-eastern region of Thailand, where many other fossils of Mesozoic animals have been found. Two pieces of turtle fossil measuring 80 cm by 90 cm were discovered by geologists in 2005 in Mukdahan province. A number of important fossils have been discovered in the area, ancient fish, primitive crocodiles and dinosaurs.
Dinosaurs discovered in Thailand include titanosaurs and large meat-eating dinosaurs, members of the Allosauroidae.
To read an article about the discovery of the largest meat-eating dinosaur known to date from Thailand: Allosaurus Fossils Discovered in Thailand.
Chinese experts worked with the geologists and the paper on this new species was published earlier this year in the London-based scientific paper, the Journal of the Geological Society. This new species has been named Basilochelyes macrobios.
Turtles and tortoises possess a shell, their most distinctive feature. The shell is actually a modified ribcage covered in armour plates. Unlike other vertebrates (animals with backbones), Chelonians have a modified skeleton so that their shoulder and hip girdles are inside the ribcage. An armoured shell is not unique in the fossil record, some placodonts, part of the Sauropterygia reptile group also developed a turtle-like shell. Animals such as the Triassic Henodus, for example, a one metre long reptile; lived in lagoons and shallow seas. It also lacked teeth, like modern tortoises and may have filtered its food living on phytoplankton and other small organisms.