Armless--or nearly so. Why?

They've found another tiny-armed dinosaur, one of the Abelisaurus-types

Those arms are relatively smaller than T-Rex's, and T-Rex's arm's look pretty useless.

When I looked at the illustration of a Carnotaurus at the first link, my first thought was "vulnerable belly."

Suppose the thing ate large critters. I don't see attacking with a biting or slashing head attack as wise--though it does have plenty of place to hang strong neck muscles on. If it's close enough for that, it's close enough for the target to get a side swipe at its belly, which might be a tad uncomfortable. It could slash with its feet, sure. Batter with its tail, sure--that'd be a pretty deadly club. But attack with its head?

This dinosaur model seems to have been a popular and successful enough that there's probably a way to use the head without risking too much, and make it a three-threat predator. The neck is long, which helps--suppose there were something like heavy scales or keratin layers on the belly. It would slow it down a tad, but ... T-Rex had "gastrailia" which they think might have helped Sue breathe, but maybe they also helped with stiffening the flesh to hold the "armor". Bone plates would be way too stiff and heavy, but "leather belt armor" might work to stave off "mule kicks". And if slashing kicks from prospective victims were a regular risk, Carny would have two options with his arms--make them big and strong enough to hold their own, or small enough to be out of the way.