A newly found, meat-eating Cretaceous dinosaur is now on the list of the top three largest North American predatory dinosaurs.
As paleontologists increasingly unearth evidence of feathers in prehistoric fossils, our conceptions of what dinosaurs looked like when they roamed the earth has gradually evolved.
Instead of the reptilian appearance we all recognize from childhood toys and films like Jurassic Park, many dinosaurs in fact more closely resembled birds, kind of like this recently discovered little guy, Eosinopteryx brevipenna, a flightless theropod dinosaur that roamed China during the Middle/Late Jurassic period.
Archaeopteryx, also known as Urvogel, the German word for "original bird" or "first bird," was first discovered in 1860 and later fossils of this species presented some of the earliest evidence of flight in these prehistoric animals.
An intermediate creature that was not quite dinosaur but not exactly a bird either when it lived 150 million years ago, Archaeopteryx had teeth, a long tail, and wings capable of flight with claws at the end for grabbing prey.
A century after the discovery of Archaeopteryx, paleobiologists increasingly found anatomical connections between birds and dinosaurs. In the 1970s, artists began to portray dinosaurs with feathers based on accumulating evidence.
Megapnosaurus, shown here, was another species with whom researchers began early to identify with feathers. A lightweight animal that could reach up to 10 feet in length and roamed Jurassic Zimbabwe, Megapnosaurus, also known as Syntarsus, traveled in packs and preyed on small reptiles and fish.
Many of the fossils unearthed that provided evidence of feathers had deteriotated over the eons they remained buried. It wasn't until 2010 that researchers identified color pigments in feathers from dinosaurs and early birds.
Sinosauropteryx, illustrated here, was a theropod dinosaur that had "simple bristles -- precursors of feathers -- in alternate orange and white rings down its tail," according to a description of the study's findings.
Given that so many feathered dinosaurs were in fact flightless, the purpose of the feathers has been a subject of debate. Some dinosaurs may have evolved feathers for social signaling; others had plumage to provide insulation.
In the cases of some dinosaurs, such as the two oviraptors, herbivores related to T. rex that lived during the Cretaceous period, researchers believe the feathers were used for mating displays, similar to modern-day peacocks and turkeys.
Jason Brougham/University of Texas
You might be fooled into thinking the animals in this illustration are something between a murder of crows and a band of blue jays. In fact they are Microraptors that lives more than 130 million years ago.
These four-winged, plumed dinosaurs were no larger than modern-day pigeons and sported iridescent tail feathers.
Researchers believe the shimmering plumage was likely used in mating and other social interactions.
Like the diversity among birds today, not all feathered dinosaurs were lightweight, agile animals. A massive tyrannosaur that lived in China until about 65 million years ago, Yutyrannus huali, meaning "beautiful feathered tyrant," grew up to 30 feet long and could weigh more than 3,000 pounds.
This titanic tyrannosaur, as it was described, significantly increases the size range for feathered dinosaurs.
In a stunning find published in the journal Science in 2011, paleontologists uncovered dinosaur feather preserved in amber that dated back some 79 million years ago.
This discovery provided scientists a new window into the evolution of feathers in terms of structure in the evolutionary timeline from dinosaurs to birds. Even shades of color remained well preserved in the amber.
A newly discovered predatory dinosaur from Utah is so large that it may represent the biggest species of meat-eating dino that ever lived in North America.
The dinosaur, Siats meekerorum a.k.a. "Man Eating Monster," is described in the latest issue of Nature Communications. The specimen was just a juvenile, but conservatively it measured at least 30 feet long and weighed 9,000 pounds.
The name Siats pays homage to a human-chomping monster from legends of the Ute native tribe of Utah.
"Siats still had a lot of room to grow, and there is only a 4-inch difference between the estimated femur length of a juvenile Siats and an adult Acrocanthosaurus (the second largest predator in North America), so we think a safe estimate for an adult Siats is that it at least vied with Acrocanthosaurus (11,000 pounds) for the No. 2 slot," lead author Lindsay Zanno told Discovery News.
"However, our upper estimate on Siats is a body mass larger than T. rex (currently in the No. 1 spot), so future material may reveal Siats grew up to be one of the biggest predators known around the globe," added Zanno, who is director of the Paleontology and Geology Research Laboratory at the North Carolina Museum of Natural Sciences.
Zanno, who is also an assistant professor of biology at North Carolina State University, co-authored the paper with Peter Makovicky of the Field Museum of Natural History.
The researchers analyzed the remains for Siats, which were unearthed at the Dakota Formation in Emery County, Utah. The fossils reveal that the huge dinosaur lived approximately 98 million years ago at the dawn of the Late Cretaceous.
It was a carcharodontosaur, which refers to a type of enormous carnivorous dinosaur known, not just for their size, but also for their jagged, sharp teeth.
A newly found, meat-eating Cretaceous dinosaur is now on the list of the top three largest North American predatory dinosaurs.Julio Lacerda
Zanno and Makovicky believe that the mere existence of these apex predators prevented tyrannosaurs at the time from evolving into even larger beasts. It was only when Siats and other carcharodontosaurs mysteriously died out that tyrannosaurs like T. rex emerged.
"In the rock beds that contain the colossal bones of Siats we also find the teeth of relatively tiny tyrannosaurs about the size of a large dog," Zanno said. "This is a clear indication that tyrannosaurs were living in the shadows and carcharodontosaurs like Siats reigned at the dawn of the Late Cretaceous in North America."
She thinks it's possible that Siats even ate these small tyrannosaurs, although it probably went after less aggressive prey, such as large, plant-eating long-necked dinosaurs and primitive duckbilled dinos.
These and other animals, including crocodiles, turtles and mammals, all lived in a lush, wet coastal plain environment not far from a shallow sea that was then spreading over central North America. The sea divided the continent into smaller island landmasses.
Roger Benson, a paleobiologist at the University of Oxford, told Discovery News that the finding of Siats shows that extremely large predatory dinosaurs were present in North America at the time and that “their presence would have excluded tyrannosaurs from evolving to multi-ton sizes.”
Stephen Brusatte, a Chancellor's Fellow at the University of Edinburgh's School of GeoSciences said that it also raises the question: Why did Siats and its relatives die out?
"They were the largest predators for tens of millions of years, and then they suddenly seem to die out, which allowed tyrannosauroids to assume the apex role," Brusatte told Discovery News. "But why?"
He continued, "This is a major question that we need to figure out, and continued exploration of middle-early Late Cretaceous rocks in North America should provide some important clues."