Specimens of Archaeopteryx in 1860 or 1861 and described in 1861 by Christian Erich Hermann von Meyer. The fossil consists of two counterslabs, designated BSP 1869 VIII 1 (main slab) and MB.Av.100 (counterslab). Its two counterslabs are currently located at the Bavarian State Collection of Paleontology and Geology of Munich University and the Natural History Museum in Berlin, respectively. This feather is generally assigned to "Archaeopteryx" and was the initial holotype, but whether it actually is a feather of this species or another, as yet undiscovered, avialan is unknown. There are some indications it is not from the same animal as most of
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