The remains of a 230-million-year-old marine reptile with fangs and a long neck have been found in southeast China.
The creature's 1.7m-long neck was almost twice as long as its trunk which measured less than one metre in length.
The creature, Dinocephalosaurus orientalis, is the first reported fully marine member of a diverse group of reptiles called the protorosaurs.
Its discovery is reported in Science magazine by Chun Li, from the Chinese Academy of Sciences, and colleagues.
Protorosaurs were characterised by their long necks and elongated neck vertebrae.
It is possible, say the researchers, that D. orientalis's small head and stretched neck allowed it to sneak up and lunge at prey before its full profile scared them off.
They also suggest that the animal's specialized neck ribs may have flared outward before an attack, allowing it to swallow the pressure waves created in the water of its shallow-sea habitat.
These waves would otherwise alert the prey to the approaching predator.
The fangs were a couple of cm in length
Dinocephalosaurus orientalis means "terrible headed lizard from the Orient". The remains were found in 2002 in the Guanling geological formation in China's Guizhou Province.
"This is important research because we have finally explained the functional purpose of this strange, long neck," said Dr Olivier Rieppel, a co-author of the Science paper, from the Field Museum in Chicago, US.
"It allowed an almost perfect strike at prey, which usually consisted of elusive fish and squid."
Scientists say the remains will be compared with similar creatures from the Middle East and Europe to gain insights into protorosaur hunting strategies, evolution and diversity during the Triassic Period.