Labrujasuchus expectatus: The Toothless Two-Legged Witch Croc

The crocodile body shape seems as though it was perfected long ago and then left unchanged. It stays close to the ground on four stubby legs, with jaws made to clamp shut with tremendous force. It has the appearance of an animal that discovered a winning design and never needed to try another.

This newly identified species took a very different route. Although it belonged to the same major family branch, it walked upright on two legs, had arms so small they were almost insignificant, and possessed a beak instead of teeth.

Naming Labrujasuchus expectatus

Palaeontologists have at last given one of these animals a name. They have called it Labrujasuchus expectatus – the “Witch Croc” – after its discovery in the rust-coloured badlands of Ghost Ranch, northern New Mexico.

The research was led by Dr Alan Turner of Stony Brook University (SBU), working with Dr Nate Smith of the Natural History Museum of Los Angeles County (NHMLAC).

Their group assembled a partial skeleton from bones found at the Hayden Quarry, a Late Triassic excavation at Ghost Ranch that has yielded new species for over 20 years.

The creature lived more than 200 million years ago, during the Late Triassic, an unusual period in which the modern animal groups familiar today were only beginning to take shape.

More ostrich than crocodile

If it were alive today, Labrujasuchus expectatus might easily be mistaken for a small, lanky dinosaur. Its form strongly resembles that of an ornithomimosaur, the long-legged, ostrich-like dinosaurs of the Cretaceous.

Yet it was not a dinosaur. It belonged to the evolutionary branch that eventually produced modern crocodiles, animals with heavy, low-slung bodies and four legs. Labrujasuchus instead adopted a two-legged way of moving.

Its powerful hind legs dwarfed its very small arms. It had a beak rather than teeth. Put it next to a living crocodile, and their shared ancestry would be almost impossible to guess.

This croc skipped teeth

Its lack of teeth is among the discovery’s most unexpected features. Most crocodile relatives, past and present, use jaws filled with conical teeth to seize and rip apart prey. Labrujasuchus gave up that arrangement completely.

Exactly what it consumed using its beak remains unknown. Other shuvosaurs, the family to which it belonged, have been associated with diets rich in plants but also including small animals.

Rather than biting, its beak may have been useful for clipping or stripping food.

Toothless beaks have appeared repeatedly in separate evolutionary lines. Birds are the best-known examples, although numerous dinosaurs and several ancient marine reptiles also had them. An early cousin of crocodiles can now be added to that group.

The missing cousin appears

Before this find, just five species from this family had been described. Two were known from the same region of New Mexico, with one dating from earlier in the Late Triassic and the other from later in the period. The interval between them was conspicuous.

Where older and younger relatives occur in the same area, an intermediate form will often be preserved in the rocks. The researchers’ expectation has now proved correct. Labrujasuchus expectatus fits precisely into that previously vacant middle position.

Each part of its Latin name has significance. Labrujasuchus joins “la bruja” – Spanish for witch – with the Greek term for crocodile, referring to Ghost Ranch’s former name. Expectatus recognises the intermediate relative that palaeontologists had expected to uncover.

Connecting the family tree

This same kind of body form appears again and again among unrelated groups. Long legs, a lightweight frame and a pointed beak probably suit an animal that travels swiftly over open terrain while feeding on whatever its surroundings provide.

Scientists describe this process as convergent evolution. Animals without close relationships can develop similar appearances when they face comparable challenges and arrive at similar solutions. Sharks and dolphins provide the well-known example.

Labrujasuchus illustrates the phenomenon plainly. It descended from the crocodile lineage but had an ostrich-like build.

A previous paper called this form of convergence “extreme” while examining a comparable animal from Ghost Ranch.

Turner regards the discovery as useful supporting evidence. Different lineages repeatedly developed a bipedal posture, probably because it brought genuine ecological benefits. “It obviously worked for these animals,” he said.

Evolution keeps repeating itself

Ghost Ranch lies amid northern New Mexico’s reddish hills, badlands made famous by the artist Georgia O’Keeffe. Underneath the vividly coloured rock is one of the world’s most productive Triassic fossil localities.

Teams from the Los Angeles museum have excavated the area every summer for two decades. This summer is the 20th anniversary of their work at the Hayden Quarry.

Earlier research found that the site preserves early dinosaurs together with their crocodile-line relatives from the same era.

It offers a glimpse of the point at which dinosaurs were beginning to dominate. Every fossil recovered adds definition to that view.

Lessons from Labrujasuchus expectatus

Prior to Labrujasuchus, palaeontologists had recognised only four shuvosaurid species, alongside strong evidence that additional forms must have existed between them. That expectation is now represented by a confirmed animal with a partial skeleton, a beak and an established place in the family tree.

The find underlines the extraordinary diversity among crocodile relatives before their lineage became restricted to the forms seen today.

A beaked, toothless, two-legged cousin of crocodiles was not an isolated evolutionary curiosity. It belonged to a successful evolutionary experiment that continued for millions of years.

For scientists investigating Late Triassic rocks, the discovery is encouraging. Gaps remain in the crocodile-and-dinosaur family tree, and Ghost Ranch continues to fill them.

The next unusual animal may already be partly visible somewhere, awaiting the right hammer.