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.
It's generally believed that Earth's earliest animals were not very big, but discovery of a huge new fish that lived around 423 million years ago has scientists rethinking what life was like close to 200 million years before the first dinosaurs emerged.
The fish, named Big Mouth Blunt Tooth (Megamastax amblyodus), is described in the latest issue of Scientific Reports. For its time, the toothy and lobe-finned fish was in the number one spot on the food chain.
"At 1 meter (3.3 feet) in length or greater, it was vastly larger than any other animal," lead author Brian Choo told Discovery News, adding that Big Mouth was "likely the earliest vertebrate (backboned) apex predator in the fossil record."
Choo, a paleontologist at the Chinese Academy of Sciences and Flinders University, and his colleagues analyzed Big Mouth's remains, which were unearthed at the Kuanti Formation in Yunnan, southwestern China. During the fish's lifetime, a period known as the Silurian, this region was part of the South China Sea. It is where the marine ancestors of all jawed animals, including humans, first evolved.
Equipped with both piercing and crushing teeth, Big Mouth likely preyed upon hard-shelled moving species, such as mollusks and armored fishes. The second largest animal at the time, Guiyu onerios -- aka Ghost Fish, was a mere one-third of Big Mouth's size.
Why then was Big Mouth so big?
One reason, according to the researchers, is that competition among fish appears to have been fierce.
Co-author Min Zhu explained, "During the Silurian period, the South China Sea, then at the equator, was the cradle of early jawed vertebrates, thus the ecological competition among these creatures was very intense."
Another reason is that Big Mouth probably had plenty of oxygen. Modern fish are generally worse off in low oxygen conditions, and big fish require more oxygen than small ones, Choo said. Big Mouth therefore could not have existed unless sufficient oxygen was present.
Fossils of Megamastax amblyodus compared with those of other early fish.Min Zhu
This has major implications because, as it stands, there are two major theories about what Earth's oxygen level was like during the Silurian. One holds that near-modern oxygen levels occurred around 420 million years ago, while another holds that they did not occur until 20 million years later.
Big Mouth provides strong evidence that near-modern oxygen levels occurred at least 420 million years ago, which Choo said was "a likely byproduct of the spread of plants on land."
"There was life on land during the Silurian, but it certainly wasn't nearly as diverse as today," he continued. "There would have been a variety of low-growing primitive plants growing in moist areas. While there were no trees, there was a towering organism called Prototaxites, possibly a giant fungus, which grew up to 8 meters (26.3 feet) tall."
The only animals on land were backbone-less ones, such as huge sea scorpions that scuttled along the beaches and swamps. There were no flying animals at this time, and sharks weren't around yet either. If additional Big Mouth-sized (or larger) animals did exist, they were probably other fish.
Paleontologist Per Ahlberg is a professor of evolutionary organism biology at Uppsala University. He recently saw the fossils for Big Mouth, and was impressed.
"This is a remarkably large, and very early, lobe-finned fish," Ahlberg told Discovery News. "It underscores the extraordinary importance of the Silurian fish faunas of Yunnan for our understanding of early vertebrate evolution."
For a time, Big Mouth was Earth's largest supreme predator, but it would have been dwarfed by what was to come. Members of its group -- the lobe-finned fishes -- later evolved into limbed animals that settled on land. By 95 million years ago, dinosaurs up to 130 feet tall, or roughly the height of a 13-story building, were in existence.