Siats meekerorum: Remains of top predator before T. rex discovered in Utah

Paleontologists say that they have discovered the fossil remains of one of the largest prehistoric predators to have roamed North America. Named Siats meekerorum, the new dinosaur species, is believed to have lived around 98 million years ago during the Late Cretaceous period. The find is significant as Siats may have been North America’s dominant carnivore – or apex predator – before Tyrannosaurus rex arrived on the scene a few million years later.

Several bones of the giant carcharodontosaur were originally uncovered in Utah’s Cedar Mountains in 2008. “It’s been 63 years since a predator of this size has been named from North America,” said Lindsay Zanno, a palaeontologist at North Carolina State University and lead author of a paper detailing the identification of the new species. “You can’t imagine how thrilled we were to see the bones of this behemoth poking out of the hillside.” The previous find of this type was back in 1950, when remains were unearthed of Acrocanthosaurus, a carcharodontosaur that lived about ten million years before Siats meekerorum.

The unusual name comes from a man-eating monster from Ute legends (which is pronounced see-atch) and the Meeker family, which provided great support to Lindsay Zanno and several other palaeontologists.

Zanno and her team also found evidence of three new smaller dinosaurs during the Utah dig, which they say are tyrannosaurs “about the size of a large dog.” But it is Siats which is making news in the scientific community. Although the Utah discovery is only a partial skeleton, scientists are confident that they have a fairly clear picture of the long-dead creature. Working with vertebrae and bones from the hip, shin and foot, the paleontologists have determined that it is a type of predator called a neovenatorid, named for a cousin of the Allosaurus first discovered on the Isle of Wight in 1998.

Based on comparisons with similar dinosaurs, they say that it probably had a more angular head than the big tyrannosaurs and a three-clawed, longer arm than that of T. rex. Zanno’s team estimates that Siats may have been about 30 feet long – the length of a school bus – and weighed at least 4 tons, which, although impressive, is about half the size of a mature T. rex.  Nevertheless, this still makes Siats meekerorum the third largest predator found in North America, and as the fossil remains are that of a juvenile, later studies may reveal that it might have rivalled the Acrocanthosaurus in size.

The discovery helps to fill in a 25 million year gap between the predatory allosaurids and the reign of the famed and fearsome tyrannosaurs. Further research and a more comprehensive fossil record may allow scientists to understand whether Siats was out-competed or whether it went extinct, allowing larger tyrannosaurs to evolve into the dominant predator.

At this stage, the smart money is on the latter. According to Peter Makovicky from Chicago’s Field Museum of Natural History, smaller tyrannosaurs such as those found near the Siats fossil would have been no threat to the massive carcharodontosaur, and that they “only evolved into enormous apex predators after the carcharodontosaurs disappeared.”

Lindsay Zanno agrees. “Contemporary tyrannosaurs would have been no more than a nuisance to Siats, like jackals at a lion kill. It wasn’t until carcharodontosaurs bowed out that the stage could be set for the evolution of T. rex,” she says.

The full study has been published by Nature Communications, an online journal.