For over a century, scientists have believed that dinosaurs and birds

For over a century, scientists have believed that dinosaurs and birds are closely related, but more recent evidence suggests that even some non-avian dinosaurs had feathers. Not long after Charles Darwin published The Origin of Species in 1859, Thomas Henry Huxley, a biologist and defender of Darwin's evolutionary theory, pointed out several similarities between dinosaurs and birds. He recognized similarities in their bone structures and drew upon his knowledge of skeletal likenesses between Archaeopteryx fossils and modern birds.

It wasn’t until the last twenty years, however, that scientists found evidence to support over a century of hypothesizing about the relationship between dinosaurs and birds. In the 1990s, several fossils of feathered dinosaurs were found in sedimentary deposit in Liaoning, China. The deposit was particularly rich in well-preserved fossils, as the area had been buried in volcanic ash by eruptions in Mongolia during the early Cretaceous period. From these fossils, scientists have identified at least 17 non-avian dinosaurs that were feathered. In addition to finding feather impressions in fossils, scientists have also drawn conclusions about the relationship between dinosaurs and birds based on skeletal evidence such as the presence of quill knobs, the places where the wing feathers of modern bids attach to the bone. Furthermore, chemical evidence in some species suggests the presence of beta keratin, the primary protein present in bird feathers. Actual fossil feather impressions are rare, but these have allowed scientists to positively identify some of the known feathered dinosaurs. Scientists have also been able to infer the presence of feathers in others through a process called phylogenic bracketing. Phylogenic bracketing allows scientists to make inferences about the likelihood of an unknown trait based what they know about closely related species. Current evidence, such as that found in fossils or identified through chemical analysis, has led that most modern birds contain beta keratin in their feather as did the dinosaurs.

1. According to the passage, chemical evidence has led to which of the following conclusions?

A. non-avian dinosaurs were more numerous than scientists previously thought
B. phylogenic bracketing is an accurate way to infer unknown traits
C. dinosaurs and birds have a similar skeletal structure
D. dinosaur features contained beta keratin, a protein also found in bird feathers
E. the bones of some dinosaurs had quill knobs


2. The author of the passage is primarily concerned with:

A. arguing that new evidence discredits previous e knowledge about the skeletal structure of dinosaurs
B. explaining how phytogenic bracketing allows scientists to infer unknown traits
C. offering evidence to support the idea that chemical evidence is essential in studying extinct species
D. explaining the significance of feather impressions found in the fossils at Liaoning
E. discussing recent evidence supporting the idea that some non-avian dinosaurs had feathers