Similar to an average house cat, it measured about 5 feet (1.5 meters) long and weighed only 9 to 15 lbs (4-7kg).
The dinosaur likely walked upright on its back legs through a steamy landscape about 100 million years ago.
The fossilized remains were discovered near a dam in Patagonia’s Ro Negro province’s La Buitrera palaeontological zone (LBPA) over the last decade.
Sebastián Apestegua and his colleagues uncovered a partial Jakapil skeleton, as well as 15 tooth fragments with a leaf-like shape, similar to iguana teeth.
Jakapil resembled a primitive form of thyreophoran that lived much earlier, making its Cretaceous age surprising.
“Never before had such a thyreophoran been dug up anywhere in the southern hemisphere,” Apesteguía said.
The report noted that most fossils in the LBPA were found between beds of migrating dunes.
The remains were found disarticulated and with a slight southwestern-northeastern orientation due to dune transport.
Jakapil’s discovery was first published in the journal Scientific Reports.
Thyreophorans are distinguished by the presence of body armor arranged in longitudinal rows along their bodies.
Primitive forms possessed simple, low, keeled scutes or osteoderms, whereas more derived forms possessed more elaborate structures such as spikes and plates.
Most thyreophorans were herbivorous and had tiny brains in comparison to their body size.