June 2017

Vol. 45, No. 3

About Books: An Exquisite Ancient Menagerie

Mark Lynch

Birds of Stone: Chinese Avian Fossils from the Age of Dinosaurs. Luis M. Chiappe and Meng Qingjin. 2016. Baltimore, Maryland: Johns Hopkins University Press

“China’s newly discovered ancient menagerie has transformed our understanding of the kinds of birds that lived during the Mesozoic.” (p. 8)

The Beneski Museum of Natural History at Amherst College hosts a large collection of fossils and geological specimens, many collected in the Connecticut River Valley. Among the displays is a unique “rock book.” Edward Hitchcock, geologist and paleontologist at the college, split a book-sized fossil-bearing rock specimen into its horizontal layers. He then bound the layers together so that a viewer could actually turn the heavy rock pages and proceed through time to read the geological history of the minerals like a book. He called these pages his “stony library.”

In China, north of Beijing, there is a veritable Library of Alexandria written on thousands of layers of rock. Three regions converge here: western Liaoning Province, northeastern Hebei Province, and the eastern Inner Mongolia Autonomous Region. There are a number of deposits of beautiful fine-grained shales that have dramatically changed our understanding of the evolution of birds.

Numerous fossils of Mesozoic birds have been unearthed from sites around the world, but nowhere in such abundance, diversity, or superb state of preservation as in northeastern China during the past three decades. Thousands of exquisite fossils have been collected there. This remarkable fossil aviary, together with the well-preserved remains of many other animals and plants, is known as the Jehol Biota, a historic reference to the name of the ancient region that centuries ago was the seat of the powerful Khitan Empire. (p. 5–6)

During the Mesozoic Era (~252–66 million years ago) this area had numerous lakes and wetlands. It was also the location of several active volcanoes, which occasionally erupted as volcanoes will do. Sometimes an eruption would cause a pyroclastic flow, a rapidly moving deadly cloud of gas, ash, and debris that would devastate life in the area and lead to mass mortality. Many birds instantly fell dead into the lakes and were quickly covered by ash. These occurrences explain the abundance of detailed fossils from this region of China. Some unearthed slabs of shale contain multiple fossils of the same species of birds. The shales are so fine that many fossils are accompanied by a perfect mirror-image fossil when the rock is split. Photographs of these shale outcroppings look like tall piles of densely stacked books waiting to be pulled out and read. It is a fossil-a-palooza.

Today there are dozens of quarries in the area, and since the 1980s paleontologists have uncovered thousands of fossils. The detail captured in these fossils is breathtaking, and that is what is celebrated in Birds of Stone by Luis M. Chiappe and Meng Qingjin. Luis M. Chiappe is the vice president for research and collections at the Natural History Museum of Los Angeles County, where he directs the museum’s Dinosaur Institute. He is also an adjunct professor at the University of Southern California and one of the great “explainers” of the science of paleontology. Meng Qingjin is the Director of the Beijing Museum of Natural History and vice chairman of the Chinese Association of Natural Science Museums and the Beijing Zoological Society. He is almost always “in the field” and is one of the giants of Chinese paleontology.

Birds of Stone is a large format, sumptuous book filled with full color photographs of the fossils of the Mesozoic birds of the Jehol Biota. The high quality of the photographs is due to the efforts of Maureen Walsh and Stephanie Abramowicz, who spent weeks in China preparing and photographing the fossils. Many of the photographs are full page, with a number of two-page spreads. The accompanying text by the authors is thorough and fascinating. This text introduces the reader to many unique aspects of these ancient birds and what we can learn from the fossils. It is nothing less than an introductory course in Mesozoic ornithology and contemporary paleontology. Many of the birds found in the Jehol Biota are enantiornithines. Other species are ornithuromorphs, a more primitive group. The enantiornithines were an abundant and diverse group of Mesozoic birds. Thousands of fossils of these birds, more than 30 species, have been found in the Jehol Biota deposits. These Chinese enantiornithines ranged in size from that of a crow to something closer to a Western Sandpiper. Unlike modern birds, many enantiornithines had teeth, which gave some species quite a fierce look. The variety of dentition found in the fossils shown in Birds of Stone indicate that some species ate fruit, others caught fish or crushed seeds, and some probably probed in the mud for invertebrates.

Enantiornithines had clawed fingers on each wing, and like modern birds, they had alulas, the small group of feathers found at the bend of the wing that aid in flight. It used to be thought that enantiornithines could not fly well, but the evidence of the Jehol Biota fossils, as well as fossils unearthed elsewhere, indicates that some enantiornithines did achieve aerial competence, although their flight style may have been unlike that of modern birds. Some species may have flown, while others may simply have launched themselves from branch to branch. The feet of some species show that they could grasp a branch and perch; they even had a long hind toe like some modern birds. No fossil eggs of birds have been found from Jehol, and only one fossil embryo has been uncovered so far. Based on anatomical differences of adults, it has been theorized that some species laid small clutches of large eggs while other species laid large clutches of small eggs. You might be wondering if these birds sang. Because a syrinx is not present in any of these species, the vocalizations would not have been as complex as those of a warbler or thrush, but they likely made some kind of call like most non-songbirds do today. Overall, enantiornithines look more like modern birds than Archaeopteryx lithographica, but with a number of key differences.

The detailed pictures of feathers in some of the fossils (p. 21 and many other pages) certainly look like the feathers of modern birds at first glance, but again, there are some differences. There are many fossils in the Jehol of the primitive Confuciusornis sanctus. This large bird had a strong, massive toothless beak and likely ate tough seeds and fruit. Confuciusornis sanctus probably did not fly much but spent most of its life on the ground. What is most striking about this bird are the two, very long tail feathers that will remind you of a Fork-tailed Flycatcher or some species of motmot. But these feathers are not attached to a pygostyle, that fleshy and bony area at the end of the body sometimes colloquially known as the “Pope’s nose.” Furthermore, the shaft that runs the length of these long feathers looks more like a belt than a shaft. The feathers of many of these birds lack a shaft. Since fossils of some adult Confuciusornis sanctus have been found without these unique tail feathers, it has been suggested that this may be one of the earliest known examples of sexual dimorphism in birds.

Some of the fossils in the photographs in Birds of Stone are so detailed that they show the microstructure of the birds’ bones and allow us to age the specimens. As to the coloration of these species, paleontologists are now looking at the distribution of minute melanosome capsules in the fossils to indicate what areas of the body were darker than others. It is amazing what a wealth of information is contained in every shale slab.

Of course, life other than birds is also preserved in the Jehol Biota, and several examples are shown in Birds of Stone. Fossils from this area include plants, numerous frogs, fish, salamanders, and turtles. There are a number of fossils of mouse-sized mammals. There are also fossils of invertebrates, including many wonderfully preserved mayfly nymphs (Ephemeropsis trisetalis).

Birds of Stone is an eye-opening introduction to an actual Lost World of birds. The last third of this book is a thorough account of the early evolution of birds beyond those found in the Jehol. This includes the evolution of feathers in non-avian dinosaurs. What this book does not have is any artist’s paintings of what the living birds may have looked like. The visual focus is always on the actual fossils themselves and what they show us. The one exception is a simple painting of the Changyuraptor yangi, the “largest flying non-avian dinosaur” (p. 246), which because of its heavily feathered legs, looks like it “flew” with four wings. Imagine what that would look like in flight. Birds of Stone is a visual feast and one of the most beautiful books published on fossils, written by two experts in the field. In this book we are witness to another chapter in the evolution of the birds we are familiar with today.

Like no other fossils, the spectacular avifauna from the Jehol Biota has brightened our understanding of the lives of a thriving diversity of ancient birds, which study has transformed our knowledge about some of the earliest relatives of present day birds and has greatly clarified key aspects of the evolution of these remarkable animals. (p. 188)

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