The Liaoning fossils

In the early 1990s, feathered theropod dinosaurs from 124 Ma in Liaoning Province, China, began to be recovered. The fossil-rich rocks of Liaoning look superficially like those of Solnhofen in Bavaria. Preservation is spectacular; the specimens are generally complete and completely articulated, and the fine mudstones in which they are preserved show not only the impressions of the animals' coverings but also some darkened staining, possibly representing

4. Many paleontologists, including us in the first edition of our book (1996) predicted that non-flying theropods that used feathers for insulation would be found.

Figure 10.9. Sequential stages in the evolution of feathers. Type 1: simple, hollow, cylindrical filaments. Type 2: tufts of elongate, multiple filaments, attached at one end. Type 3: filament tufts align in a single plane (Type 3a) while also developing barbs and barbules (Type 3b). Eventually, a new planar (vaned) barbed form evolves (Type 3a+b). Type 4: vane becomes "closed"; that is, tiny hooks on the barbule attach to grooves on adjacent barbules, producing an integrated semi-rigid vane that does not allow much air to pass through. Type 5: vane becomes asymmetrical (for example, a flight feather).

Figure 10.9. Sequential stages in the evolution of feathers. Type 1: simple, hollow, cylindrical filaments. Type 2: tufts of elongate, multiple filaments, attached at one end. Type 3: filament tufts align in a single plane (Type 3a) while also developing barbs and barbules (Type 3b). Eventually, a new planar (vaned) barbed form evolves (Type 3a+b). Type 4: vane becomes "closed"; that is, tiny hooks on the barbule attach to grooves on adjacent barbules, producing an integrated semi-rigid vane that does not allow much air to pass through. Type 5: vane becomes asymmetrical (for example, a flight feather).

the original organic matter (Figure 10.10). With such superb preservation, there is little room for doubt about the nature of these dinosaurs or their feathers.

First there was the 1997 discovery of Sinosauropteryx, a small coelurosaur whose design was such that it obviously didn't fly. Yet it was covered with barb-like filaments, a very primitive downy coat insulating a clearly non-flying theropod. Next came the somewhat larger, toothless Caudipteryx, once thought to be a flightless bird but then clearly revealed to be an oviraptorosaur. Caudipteryx bears feathers with well-developed barbs,

Figure 10.10. Feathered non-flying dinosaurs from Liaoning Province, China. Clockwise from upper left-hand corner: (a) Protarchaeopteryx; (b) Sinor-nithosaurus; (c) Caudipteryx; (d) juvenile Sinosauropteryx; and center (e) an unnamed feathered dromaeosaur.

barbules, and symmetrical vanes. Even more startling was Beipiasaurus, a very large (ostrich-sized) therizinosauroid (see Chapter 9), also with no obvious ability to fly. Beipiasaurus has relatively primitive feathers with only barbules. A non-flying deinonychosaur was also found: Sinornithosaurus. This organism bears feathers that are comparable in every way to those of living birds. And then, curiously, a flying (?) deinonychosaur: Microraptor, covered with flight feathers on its arms and legs (Figure 10.11). At the time of writing, over a dozen specimens of non-flying theropods with feathers have been recovered from Liaoning (see Figure 10.10).

With the discovery of the Liaoning fossils, the development of feathers can be cladisti-cally linked with the fossil record (Figure 10.12 ). It appears that more basal tetanurans (for example, coelurosaurs) bear more basal types of feathers, and more derived tetanurans (for example, eumaniraptorans) bear more derived feathers. Thus the development of feathers appears to track the development of tetanurans.

Figure 10.12. Cladogram with selected tetanurans (Theropoda) with the different stages of feather development superimposed (see text and Figure 10.9). If the authors are correct, primitive feather coats may have graced most derived tetanuran theropods.

This, in turn, provides real insights into what the origin of feathers was all about. The prediction that feathered non-flying dinosaurs would eventually be discovered was correct: feathers likely first provided the insulation that is a prerequisite for warm-bloodedness, allowing theropods to maintain high levels of activity for the extended periods of time that were eventually necessary for flight (see Chapter 12).

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