Fossils of the Cretaceous

Frog
Mesophryne
Splayed out like a dissected animal in a high school biology class, this fossil leaves little doubt as to what kind of creature it once was. Frogs are extremely ancient, dating back some 250 million years. By the time this animal lived, more than 100 million years later, numerous species of frogs likely rested on the muddy shores of Liaoning's lakes, though fossil hunters have yet identified only a few. Some of these species appear closely akin to frogs now hopping about Asia, Europe, and North Africa—and even savored as culinary treats in modern-day Liaoning.

Turtle
Ordosemys
While this particular animal lived at the time of Microraptor, turtles evolved at least 230 million years ago, long before the Liaoning fossil time. Even the earliest turtles, with their characteristic shells, resembled modern ones. The fossils of Liaoning are of two kinds: soft-shell turtles related to species living today, and—brace yourself—nanhsiungchelyids, which Mark Norell notes "have lumpy shells, huge noses (the largest in turtledom), long tails, and a very hard-to-pronounce name coined after the locality where these animals were first found."

Dragonfly
Aeschnidium
The tissue-thin membranes of this dragonfly's wings are so immaculately preserved that it's easy to picture the insect skimming along the surface of a lake at dusk 130 million years ago. Perhaps the toxic gas of a volcanic eruption suffocated it, and a fine coating of volcanic ash protected its fragile remains. Unlike their comparatively colossal ancient forbears, which had wingspans stretching over two feet, dragonflies of the Early Cretaceous were similar in size and anatomy to those flying through wetlands today.

Hornet
This fossil, likely that of a primitive hornet, belongs to a group of stinging insects called Hymenoptera. Insects evolved into the general types we see today about 250 million years ago, when dinosaurs and small mammals first appeared. It wasn't until the Early Cretaceous, however, that groups such as Hymenoptera began to diversify—a process linked to the evolution of the earliest flowering plants. When this hornet lived, for instance, its cousin the honeybee had yet to make its evolutionary appearance.

Fern
Botrychites
If you were suddenly transported into a Liaoning forest 130 million years ago, you would likely see a variety of ferns in the understory, including this one, and be surrounded by gingko trees and conifers similar to modern pines and firs. Along the shores of lakes, you might step through horsetails and other marsh plants, and possibly catch a glimpse of the oldest known flowering plant, called Archaefructus or "ancient fruit," which may have spread its pollen via water. (Like all early flowering plants, it lacked showy, colorful blossoms to attract insects and other animal pollinators.)

Mammal
Maotherium
Mark Norell may not be wowed by this specimen, which he compares to "a flat rat on a New York street." But even this seasoned paleontologist agrees that the fossil's details are exceptional. Perhaps most striking is the aura-like fringe of fur surrounding the skeleton. Small mammals are as ancient as dinosaurs. In fact, until the demise of traditional (non-avian) dinosaurs at the end of the Cretaceous, most mammals remained small, hunting insects, scavenging nests, and living in the shadow of dominant reptiles.

Champsosaur and fish
Monjurosuchus & Lycoptera
Like many Liaoning fossils, this one captures the remnants of several animals that died simultaneously, perhaps killed by a volcanic event. The champsosaur, a superficially crocodile-like reptile, is about a foot long. Fish are the most common backboned animals in the fossil beds, and the most prevalent are herring-like Lycoptera. Fossil hunters have discovered thousands of specimens in a single layer of sedimentary rock. Aquatic animals and plants, in general, often became spectacular fossils, as fine-grained sediments were likely to drift to the bottoms of lakes and ponds.

Champsosaur skin impression
Notice the scales on the skin (around the "knee") and webbing between the toes. The flesh appears like a ghostly halo, while the vertebrae and other bones are sharp and three-dimensional. This reflects the different ways in which hard parts (bone and teeth) and soft tissue (such as skin and internal organs) are fossilized. Bones become fossils as minerals replace organic structures on a molecular level. In contrast, bacteria create the blurry traces of soft tissue. As the bacteria consume skin, fur, feathers, and other soft tissue, they leave metabolic deposits in the shapes of their meals.

Dinosaur with proto-feathers
Sinosauropteryx
The full name of this animal, Sinosauropteryx prima, means "first Chinese winged lizard." Its discovery in the mid-1990s delighted many paleontologists who suspected that birds are close kin to dinosaurs. This fossil offered evidence in the form of downy, short feathers all along the animal's head, back, and tail. A carnivorous dinosaur about the size of a greyhound, Sinosauropteryx likely ran swiftly on its two hind legs. With fuzzy feathers just a few millimeters long, it is unlikely that it ever flew. The feathers could, however, help keep the dinosaur warm through cool nights in the temperate forest.

Ancient bird
Confuciusornis
When feathered dinosaurs roamed the land, true birds soared through the Liaoning skies. Some were as big as albatrosses; others, such as this Confuciusornis, were more the size of pigeons. This fossil, dating to about 120 million years ago, reveals characteristics that make Confuciusornis a mix of primitive (more dinosaur-like) and advanced (modern bird-like) traits: Like dinosaurs and the oldest known bird, Archaeopteryx, it has three fingers that are not fused into a single element, but like modern birds, it has a toothless beak and a well-developed shoulder girdle to power flight.

Pterosaur
Dendrorynchoides
The true masters of the Liaoning skies were pterosaurs, flying reptiles that preyed upon birds, mammals, small dinosaurs, and fish. Museum dioramas often depict them as giants, but some pterosaurs, like this specimen, were no bigger than swallows. A single, very elongated fourth finger formed the leading edge and support for the pterosaur's wing. The skin membrane stretched from wrist to ankle and even between the hind limbs. This fossil reveals an astounding covering of fuzz, suggesting that proto-feathers may have evolved in an animal that was a common ancestor to both pterosaurs and dinosaurs.

Feathered dinosaur
Sinornithosaurus
When his Chinese colleague Ji Qiang first showed Mark Norell this fossil in 1999, Norell thought it was the greatest dinosaur specimen he had ever seen. The feathers on this small dinosaur, which Norell affectionately calls "Dave," are much more pronounced than those on the "first feathered dinosaur," Sinosauropteryx prima. Dave's feathers also come in three types: simple hair-like fibers (primarily on the head and tail), sprays of fibers (apparent on the hind limbs and shoulders), and asymmetrical feathers like those of a modern bird (on the trailing edge of the arm).

Four-winged dinosaur
Microraptor
Like other great discoveries in Liaoning over the past two decades, Microraptor has transformed scientific understanding and pop-culture imagery of what dinosaurs of the Early Cretaceous looked like. Whereas we once might have envisioned smooth-skinned reptiles plodding along the ground, we now can imagine sprightly, feathered creatures gliding from tree to tree. Microraptor's ability to glide, and its exact flying form, are still debated, but the notion of a flying feathered dinosaur isn't as outlandish as it may have seemed a few decades ago.