Archaeopteryx

Archaeopteryx, sometimes referred to by its German name, "Urvogel" (lit. Primeval Bird), is a genus of bird-like dinosaurs. The name derives from the ancient Greek ἀρχαῖος (archaīos), meaning "ancient", and πτέρυξ (ptéryx), meaning "feather" or "wing". Between the late 19th century and the early 21st century, Archaeopteryx was generally accepted by palaeontologists and popular reference books as the oldest known bird (member of the group Avialae). Older potential avialans have since been identified, including Anchiornis, Xiaotingia, and Aurornis.

Archaeopteryx lived in the Late Jurassic around 150 million years ago, in what is now southern Germany, during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Similar in size to a Eurasian magpie, with the largest individuals possibly attaining the size of a raven, the largest species of Archaeopteryx could grow to about 0.5 m (1 ft 8 in) in length. Despite their small size, broad wings, and inferred ability to fly or glide Archaeopteryx had more in common with other small Mesozoic dinosaurs than with modern birds. In particular, they shared the following features with the dromaeosaurids and troodontids: jaws with sharp teeth, three fingers with claws, a long bony tail, hyperextensible second toes ("killing claw"), feathers (which also suggest warm-bloodedness), and various features of the skeleton.

History of discovery

The initial discovery, a single feather, was unearthed in 1860 or 1861 and described in 1861 by Hermann von Meyer. It is currently located at the Natural History Museum of Berlin. Though it was the initial holotype, there were indications that it might not have been from the same animal as the body fossils. In 2019 it was reported that laser imaging had revealed the structure of the quill (which had not been visible since some time after the feather was described), and that the feather was inconsistent with the morphology of all other Archaeopteryx feathers known, leading to the conclusion that it originated from another dinosaur. This conclusion was challenged in 2020 as being unlikely; the feather was identified on the basis of morphology as most likely having been an upper major primary covert feather.

Authenticity

Beginning in 1985, an amateur group including astronomer Fred Hoyle and physicist Lee Spetner, published a series of papers claiming that the feathers on the Berlin and London specimens of Archaeopteryx were forged. Their claims were repudiated by Alan J. Charig and others at the Natural History Museum in London. Most of their supposed evidence for a forgery was based on unfamiliarity with the processes of lithification; for example, they proposed that, based on the difference in texture associated with the feathers, feather impressions were applied to a thin layer of cement, without realizing that feathers themselves would have caused a textural difference. They also misinterpreted the fossils, claiming that the tail was forged as one large feather, when visibly this is not the case. In addition, they claimed that the other specimens of Archaeopteryx known at the time did not have feathers, which is incorrect; the Maxberg and Eichstätt specimens have obvious feathers.

Description

Most of the specimens of Archaeopteryx that have been discovered come from the Solnhofen limestone in Bavaria, southern Germany, which is a Lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils laid down during the early Tithonian stage of the Jurassic period, approximately 150.8–148.5 million years ago.

Colouration

In 2011, graduate student Ryan Carney and colleagues performed the first colour study on an Archaeopteryx specimen. Using scanning electron microscopy technology and energy-dispersive X-ray analysis, the team was able to detect the structure of melanosomes in the isolated feather specimen described in 1861. The resultant measurements were then compared to those of 87 modern bird species, and the original colour was calculated with a 95% likelihood to be black. The feather was determined to be black throughout, with heavier pigmentation in the distal tip. The feather studied was most probably a dorsal covert, which would have partly covered the primary feathers on the wings.

Phylogenetic position

Modern palaeontology has often classified Archaeopteryx as the most primitive bird. However, it is not thought to be a true ancestor of modern birds, but rather a close relative of that ancestor. Nonetheless, Archaeopteryx was often used as a model of the true ancestral bird. Several authors have done so. Lowe (1935) and Thulborn (1984) questioned whether Archaeopteryx truly was the first bird. They suggested that Archaeopteryx was a dinosaur that was no more closely related to birds than were other dinosaur groups. Kurzanov (1987) suggested that Avimimus was more likely to be the ancestor of all birds than Archaeopteryx. Barsbold (1983) and Zweers and Van den Berge (1997) noted that many maniraptoran lineages are extremely birdlike, and they suggested that different groups of birds may have descended from different dinosaur ancestors.

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