The Thar Desert today is a scorching region in western India’s Rajasthan state. But in the Mesozoic Era, it was a tropical shoreline along the Tethys Ocean, inhabited by dinosaurs and marine creatures.
The latest find from that desert, dated to 167 million years ago, was from a dinosaur group called the dicraeosaurids, which munched on plant life with long necks (although not as long as some of their close relatives). It is the first of that group discovered in India, and the oldest ever found in the world’s fossil record.
The all-Indian team that discovered the species named it Tharosaurus indicus, referencing the Thar Desert, and its country of origin. They described the find earlier this month in the journal Scientific Reports, and argue that it underscores the importance of studying fossils from the Indian subcontinent to more broadly understand our planet’s prehistory.
Dicraeosaurids like Tharosaurus indicus are part of a larger group called diplodocoid sauropods. These dinosaurs are characterized by their elongated bodies and necks. They are ubiquitous among fossil beds from the Middle Jurassic to Early Cretaceous periods. The dicraeosaurids are distinguished by spikes on the back of their necks, and have been unearthed in Africa, the Americas and China. But no such fossils had been documented in India before, said Sunil Bajpai, a vertebrate paleontologist at the Indian Institute of Technology Roorkee and an author of the study. Earlier theories suggested that India was inhabited only by the predecessors of diplodocoids.
But Dr. Bajpai and other researchers wondered if there was more to the story. In 2018, the Geological Survey of India and IIT Roorkee began a collaboration aimed at systematically exploring and excavating fossils near Jaisalmer, a major city in the Thar Desert. Initial finds included now-extinct hybodont sharks and marine bony fish. Then in 2019, the excavation of dinosaur fossils got underway, yielding the eventual discovery of Tharosaurus indicus.
The dinosaur was distinctive from others of its group, with elongated depressions on the neck bones’ sides, neural spines with deep divisions that might have resembled upward spikes on the neck, and a heart-shaped front surface on its tail bones. It also provides evidence for an alternative viewpoint on which sauropods lived in what is now India.
“It represents the earliest global record of not only dicraeosaurids but also of diplodocoids,” said Debajit Datta, a postdoctoral earth sciences researcher at IIT Roorkee and a co-author of the study.
Together with other primitive dinosaur findings like Barapasaurus and Kotasaurus from the Early Jurassic Kota Formation in central India, the discovery of Tharosaurus strongly suggests that what is now India played a significant role in the emergence and diversification of neosauropods, a group of long-necked vegetarian dinosaurs that thrived as the largest land animals. This conclusion is further supported when considering the arrangement of continents during the Middle Jurassic period, Dr. Datta said.
Dr. Bajpai also pointed to other discoveries that demonstrated that the Indian landmass was an important location in the origin and evolutionary history of other vertebrate groups. Notable examples include fossils of Indohyus and Cambaytherium, which have played crucial roles in tracing the origins of whales and horses.
“We still do not know so much about the prehistory of India,” said Andrej Čerňanský, a vertebrate paleontologist at Comenius University in Bratislava, Slovakia. “Finds such as this new fossil are therefore crucial to our understanding, as they convey important information about the evolution of the animals of the subcontinent, and its different paleogeography during the past.”
Dr. Bajpai said that although India possessed valuable fossils of different ages, there were not enough vertebrate paleontologists to comprehensively study them. The field’s advancement, he said, is hampered by restricted access to certain fossil sites because of mining operations, dense forest cover, insufficient funding and limited job opportunities.
But he said he was optimistic that recent federal proposals would help in the protection and conservation of geoheritage sites in the country, including important fossil sites.