Brontomerus literally means "thunder thighs" in Greek, and this particular dinosaur definitely earns the name. It had extremely strong back legs, allowing it to unleash devastating kicks on rivals or predators, as you can see in this absolutely incredible illustration.
As a member of the sauropods, brontomerus was already among the largest land animals in our planet's history. But its gigantic thighs are what set it apart. Two partial skeletons of the dinosaur were discovered in Utah back in 1994, and we can now confidently say that, in the words of paleontologist Mike Taylor, "this specimen just leaps out at you and looks weird."
The two skeletons, one adult and one juvenile, were found together, and there's some thought they were mother and son. The adult was forty-two feet long and weighed 13,200 pounds, while the younger Brontomerus was just fourteen feet long and a piffling 440 pounds. A hip bone discovered among the various fossils had a very wide surface projecting out from the hip socket. This large surface area provided tons of room for leg muscles, which means Brontomerus likely had much stronger leg muscles than its sauropod peers.
Taylor explains what purpose this might have served:
"The best we can work out, it could project its leg forward very powerfully - in short, for kicking. We think the most likely reason this evolved was over competition for mates, with males fighting each other or just showing off to win affection of females. [But] it would be bizarre if it wasn't also used in predator defense."
Brontomerus was around about 110 million years ago, meaning its predators included various raptors and the T. rex cousin Acrocanthosaurus. You can see Brontomerus delivering a swift kick to a raptor in the illustration above, which honestly just gets more and more awesome every time I look at it.
Still, though its back legs have attracted the most attention, paleontologist Matt Wedel suspects the forelimbs of Brontomerus were just as powerful, as its shoulder blades appeared to have bumps that mark the locations of various muscle attachments. Beyond the kicks, Wedel speculates Brontomerus was just tougher than the average sauropod:
"It's possible that Brontomerus mcintoshi was more athletic than most other sauropods. It is well established that far from being swamp-bound hippo-like animals, sauropods preferred drier, upland areas, so perhaps Brontomerus lived in rough, hilly terrain and the powerful leg muscles were a sort of dinosaur four-wheel drive,"