The species, named Laquintasaura venezuelae, was identified with the help of 200-million-year-old fossils from the La Quinta Formation in Venezuela.
Bones from at least four Laquintasaura were found together, with individuals ranging in age from three to approximately 12 years old.
It is possible they lived in small groups, making it the earliest example of social behaviour in ornithischians, 'bird-hipped' dinosaurs, a group which includes species such as Stegosaurus and Iguanodon.
Laquintasaura walked on two hind-legs and was about the size of a small dog, measuring one metre in length and 25 centimetres at the hip, according to scientists from the Natural History Museum in the UK and the University of Zurich.
More From This Section
"Laquintasaura lived very soon after the major extinction at the end of the Triassic Period, 201 million years ago, showing dinosaurs bounced back quickly after this event," said Dr Paul Barrett, lead author and palaeontologist at the Natural History Museum.
"It is fascinating and unexpected to see they lived in herds, something we have little evidence of so far in dinosaurs from this time.
"The fact that it is from completely new and early taxon means we can fill some of the gaps in our understanding of when different groups of dinosaurs evolved," Barrett said.
The study was published in Proceedings of the Royal Society B.