Archaeopteryx compared to its body length. It could reach up to in body length, with an estimated mass of . "Archaeopteryx" feathers, although less documented than its other features, were very similar in structure to modern-day bird feathers. Despite the presence of numerous avian features, "Archaeopteryx" had many non-avian theropod dinosaur characteristics. Unlike modern birds, "Archaeopteryx" had small teeth, as well as a long bony tail, features which "Archaeopteryx" shared with other dinosaurs of the time. Because it displays features common to both birds and non-avian dinosaurs, "Archaeopteryx" has often been considered a link between them. In the 1970s, John Ostrom,
Archaeopteryx or trunk-climbing lifestyle. This has been interpreted as evidence of theropod ancestry. In 1988, Gregory S. Paul claimed to have found evidence of a hyperextensible second toe, but this was not verified and accepted by other scientists until the Thermopolis specimen was described. "Until now, the feature was thought to belong only to the species' close relatives, the deinonychosaurs." The Thermopolis Specimen was assigned to "Archaeopteryx siemensii" in 2007. The specimen is considered to represent the most complete and best-preserved "Archaeopteryx" remains yet. The discovery of an eleventh specimen was announced in 2011, and it was described in 2014. It