PNAS has an interesting news feature about the origin of the dinosaurs. When and where did they first appear? Evidence points to an amimal known as Lewisuchus admixtus that lived in what is now Argentina about 236 million years ago.

There’s a small, but fierce, jawbone in Argentina’s national natural science museum in Buenos Aires. It’s 6 inches long and studded with backward-curving fangs that would have hooked into flesh to rip it open—teeth not unlike those of the fearsome Komodo dragon, says paleontologist Martín Ezcurra, a researcher at the museum.

But this jaw is 236 million years old. It belonged to an extinct reptile called Lewisuchus admixtus that ran across Triassic northern Argentina, a world of cycads and ferns that thrived long before grass existed. Lewisuchus stood about knee-high, was roughly 5 feet long nose to tail, and hunted the cousins of early mammals. It lived about 30 million years before the well-known dinosaurs featured in museum gift shops first roamed the Argentine plains.

So was Lewisuchus a very early dinosaur? Or was it a cousin of the dinosaurs, one of many reptile groups skittering over Earth at the time?

Lewisuchus is embroiled in an ongoing debate that could help to resolve enduring mysteries about the dawn of the dinosaurs. Placing these and related reptiles on the tree of life could reveal the early steps in dinosaur evolution, how their rise was shaped by their body plans, and how they interacted with other species. Ultimately, says vertebrate paleontologist Sterling Nesbitt at Virginia Tech in Blacksburg, research could answer some of the most fundamental questions about creatures that dominated our world for 180 million years: “What is a dinosaur? And why did they take over the planet?”