Small-Arm Terrors

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Small and nearly useless arms did not deter the mighty Tyrannosaurus rex from terrorizing the planet millions of years ago.

They also did not appear to have impacted another apex predator, the horned Carnotaurus sastrei that lived around what is now South America’s Patagonia region.

And now a new study has found that a newly discovered close relative of the C. sastrei remained a fearsome beast, despite having punier arms than the T. rex.

Named Koleken inakayali, this carnivorous, bipedal dino was a member of the abelisaurid family – which also includes C. sastrei – known for their distinctive, short-snouted faces, really short arms and fearsome predatory habits.

Found in Argentina’s La Colonia geological formation, the K. inakayali measured 16 feet in length and lived near the end of the dinosaur era around 70 million years ago.

“These guys were the apex predator in that part of the world,” study co-author Michael Pittman told Live Science. “They were occupying the same role that T. rex would have been doing in parts of ancient North America.”

The research team was able to identify the creature after piecing together a treasure trove of fossilized bones, including parts of the skull, a nearly complete backbone, some tail vertebrae and almost complete hind limbs.

Although they did not find arm bones, they suggested that the K. inakayali’s upper limbs resembled those of the C. sastrei – both of which were smaller than those of the T. rex. What set apart the two extinct beasts was the K. inakayali’s smaller stature and lack of horns above the eyes.

Scholars are still wondering why these abelisaurids and other big dinos sported these dinky arms: Some suggest that they had a purpose in capturing prey, while others believe they were leftovers from evolution.

Still, K. inkayali had a formidable skull and jaw to make up for its puny appendages, with the authors explaining that the findings hint at abelisaurids having experienced rapid skull evolution compared with other dinosaurs.

“This finding sheds light on the diversity of abelisaurid theropods in Patagonia right before the mass extinction event,” lead author Diego Pol told National Geographic. “It expands what we know about abelisaurids living in this area during the Cretaceous Period and shows that they were more diverse than previously understood.”