In Sidmouth, a coastal city in southern England, paleontologists have identified a new prehistoric species after examining fossilized bones discovered in 2015 at the Helsby Sandstone Formation. The find is described as the oldest known lizard relative, dating back about 241 million years to the Triassic period.
Researchers extracted a block of stone from the coastline that contained nearly complete remains of a rhynchocephalian, an ancient reptile. According to a Sept. 10 study published in Nature, “A recently discovered thin sandstone bed located near the top of the Otter Sandstone on the coast west of Sidmouth, east Devon, has produced an abundance of vertebrate fossils. Among these often remarkably well-preserved remains is the nearly complete skull and skeleton of a rhynchocephalian, described here, which was excavated as a block … from a temporarily exposed foreshore exposure beneath Peak Hill.”
The exceptional preservation may have resulted from a severe rainstorm causing river overflow and rapid burial in sediment. The fossil belongs to Lepidosauria, which includes ancient snakes and lizards. This specimen predates previously found lepidosaurs by 3 to 7 million years.
Named Agriodontosaurus helsbypetrae, or “fierce-toothed lizard,” it represents both a new species and genus. Study author Dan Marke stated in a news release from the Natural History Museum of London: “Agriodontosaurus helsbypetrae is unlike anything yet discovered and has made us all think again about the evolution of the lizard, snakes and the tuatara. This specimen not only provides important information about the ancestral skull of all lepidosaurs but also builds on growing knowledge of the tuatara. While often called a ‘living fossil,’ this animal belongs to a once-diverse order of ancient reptiles with a rich evolutionary history.”
Modern tuataras are found only in New Zealand and are considered remnants of their lineage. Researchers said Agriodontosaurus’s name references its notable large teeth—“agrio” for fierce (from Greek), “donto” for tooth, and “saurus” for lizard—while its species name combines Helsby (the site) with “petraea,” meaning rock.
According to researchers, tuataras use their teeth to pierce insect exoskeletons; Agriodontosaurus likely hunted similar prey such as cockroaches and grasshoppers using its large eyes for tracking.
Earlier assumptions suggested that ancient lizard relatives possessed certain skull features for eating larger prey: partially hinged skulls or palate teeth among them. Marke noted: “The fossil shows almost none of the characters we expected,” adding: “It has no teeth on its palate and no sign of any hinging, just an open temporal bar.” This suggests these evolutionary traits may have developed multiple times rather than from one common ancestor.
The quality of this fossil is unusual because delicate bones like these are rarely so well preserved. The discovery adds to more than 12,000 known lepidosaur species—a major group among land vertebrates.
Devon, where Sidmouth is located, lies roughly 170 miles southeast of London.
The research team included Dan Marke along with David I. Whiteside, Thitiwoot Sethapanichsakul, Robert A. Coram, Vincent Fernandez, Alexander Liptak, Elis Newham and Michael J. Benton.
