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| Earth on Mar 01, 2011

A new dinosaur nicknamed Thunder Thighs

A new dinosaur species discovered in Utah has been nicknamed “Thunder Thighs” for its enormously powerful thigh muscles.

“Thunder Thighs” is the nickname bestowed on a new species of dinosaur, Brontomerus mcintoshi, that had very large and powerful thigh muscles. Fossil remains of these behemoths, found in Utah, were the subject of a study by scientists from the UK and US that was recently published in Acta Palaeontologica Polonica. This new dinosaur species lived 100 million years ago in the early part of the Cretaceous period.

Brontomerus mcintoshi was an enormous long-necked plant-eater known as a sauropod. Other well-known sauropods are Brachiosaurus and Diplodocus. Features of Brontomerus’s hip bones reveal that they had the most powerful legs of any known sauropod. Very few sauropods from the Cretaceous period have ever been found, which makes the discovery of this new dinosaur species all the more significant.

The unique feature of Brontomerus mcintoshi is its powerful thighs. Its strong muscular legs, the most powerful ever seen in a sauropod, may have enabled it to traverse hilly terrain. Those legs could also have delivered well-aimed defensive blows at the kinds of small, fierce carnivorous dinosaurs that lived at the same time, such as Utahraptor and Deinonychus.

Mike Taylor, the lead author of the paper, from the Department of Earth Sciences at University College London, said in a press release,

Brontomerus mcintoshi is a charismatic dinosaur and an exciting discovery for us. When we recognised the weird shape of the hip, we wondered what its significance might be, but we concluded that kicking was the most likely. The kick would probably have been used when two males fought over a female, but given that the mechanics were all in place it would be bizarre if it wasn’t also used in predator defense.

Brontomerus is not known from a complete skeleton, but from a selection of bones: some from the shoulder and hip, some ribs, some vertebrae, and some unidentifiable fragments. This photograph shows all of the known material. Image Credit: Mike Taylor.

Incomplete fossilized skeletons of two Brontomerus mcintoshi individuals were found in a quarry in eastern Utah. The scientists believe that the site had previously been vandalized because some segments of the recovered bones were missing; the remaining accessible fossils were “rescued” by researchers at the Sam Noble Museum. In studying the bones that were recovered, which included shoulder, hip, ribs, and vertebrae, scientists concluded that the remains belonged to an adult and a juvenile, possibly a mother and child. The adult, 14 meters (46 feet) long, would have weighed about 6 metric tons (13,228 lbs), as heavy as an elephant. The youngster was about 4.5 meters (15 feet) long, weighing in around 200 kilograms (440 pounds), about the weight of a pony.

The hip bone was of particular interest. It is much larger than those seen in sauropods of comparable size. A wide blade-shaped bone that projected ahead of the hip socket was the attachment site of large, powerful muscles. Based on its size and features, the scientists inferred that this new species had the largest muscles ever known in a sauropod, a distinction that earned Brontomerus mcintoshi the nickname “Thunder Thighs.”

Photo of Brontomerus mcintoshi

In the press release, one of the paper’s authors, Matt Wedel of the Western University of Health Sciences in Pomona, California, also commented about detailed features seen in the shoulder bones.

The shoulder blade of Brontomerus has unusual bumps that probably mark the boundaries of muscle attachments, suggesting that Brontomerus had powerful forelimb muscles as well. 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.

Besides holding the record for most extreme muscular legs in a sauropod, this new dinosaur species was also distinctive for when it lived. Weidel explained,

Because sauropods were the most abundant dinosaurs found during the Jurassic period and the rarest during the Early Cretaceous, there’s long been the perception that sauropods were successful in the Jurassic and were replaced by duckbills and horned dinosaurs in the Cretaceous. In the past 20 years, however, we are finding more sauropods from the Early Cretaceous period, and the picture is changing. It now seems that sauropods may have been every bit as diverse as they were during the Jurassic, but much less abundant and so much less likely to be found.

A skeletal reconstruction of Brontomerus mcintoshi. The hip bone projects a long way forward from the leg socket: in life, muscles would have run down to the leg from the whole length of the hip bone, hence the name Thunder Thighs. Image Credit: Scott Hartman, with modifications by Mike Taylor.

A video featuring the paper’s lead author, Dr. Mike Taylor, of the University College of London Department of Earth Sciences, explaining the new dinosaur species at the Grant Museum of Comparative Zoology. Filmed and edited by Rob Eagle for University College London.

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It’s remarkable that in over 300 years of dinosaur research, scientists are still finding new species, a indication of the amazing diversity of dinosaurs. “Thunder Thighs” captures our imagination and awe in its record-holding powerful legs, and for its presence in a time when sauropod species were previously thought to be close to extinction. The partial skeletons of a Brontomerus mcintoshi adult and juvenile, perhaps a mother and child, lay hidden in the rocks for 100 million years. Their discovery compels us to ponder their lives as a family during the age of the dinosaurs and wonder how they met their end.

In this artist's depiction, a mother

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