Archaeopteryx

This article is about the dinosaur. For the ancient plant, see Archaeopteris. For other uses, see Archaeopteryx (disambiguation).

Archaeopteryx, sometimes called by its German name, "Urvogel" (meaning 'Primeval Bird'), is an extinct genus of bird-like dinosaurs. Its name comes from Ancient Greek words meaning 'ancient' and 'feather, wing'. For a long time, from the late 1800s to the early 2000s, many scientists and reference books said that Archaeopteryx was the oldest known bird (a member of the group Avialae). Scientists have since found older possible avialans, including Anchiornis, Xiaotingia, Aurornis, and Baminornis.

Archaeopteryx lived in the Late Jurassic, about 150 million years ago, in what is now southern Germany. Back then, Europe was a chain of islands (an archipelago) in a shallow, warm sea. It was much closer to the equator than it is today. Archaeopteryx was about the size of a Eurasian magpie. The largest kind could grow to about 50 cm (20 in) long, possibly as big as a raven. Even though it was small and had broad wings, Archaeopteryx was more like other small Mesozoic dinosaurs than like modern birds. It shared many features with the dromaeosaurids and troodontids. These included jaws with sharp teeth, three fingers with claws, a long bony tail, and feathers. The feathers also suggest warm-bloodedness.

Because of these features, Archaeopteryx is a strong candidate for a transitional fossil between non-bird dinosaurs and birds. This makes it important for studying the origin of birds, and also for studying dinosaurs. It was named from a single feather in 1861, and scientists still debate what kind of feather it was. That same year, the first complete fossil was announced. Since then, twelve more fossils have been found. These fossils vary, but most experts think they all belong to one species, or at least one genus, though this is still debated.

Most of these 14 fossils show feather impressions. These feathers are an advanced type (flight feathers), so the fossils suggest that feathers began to develop before the Late Jurassic. The type specimen was found just two years after Charles Darwin published On the Origin of Species. Archaeopteryx seemed to support Darwin's ideas. It has since become a key piece of evidence for the origin of birds, for the debate about transitional fossils, and for the proof of evolution. For a long time, it was thought to be the start of the bird family tree. In recent years, though, scientists have found several small, feathered dinosaurs. This has raised new questions about which animals were the ancestors of modern birds and which were their relatives.

History of discovery

Main article: Specimens of Archaeopteryx

Scientists have found fourteen body fossils of Archaeopteryx so far. All of them come from limestone rock near Solnhofen, in Germany. People have dug up this rock for hundreds of years. The first discovery was a single feather. It was found in 1860 or 1861, and Hermann von Meyer described it in 1861. It is now kept in the Natural History Museum of Berlin. The first skeleton, called the London Specimen, was described in 1863 by Richard Owen. The genus name comes from two Ancient Greek words that mean 'ancient' and 'feather, wing'. Other specimens were found later. One is the Berlin Specimen, which is the most complete so far and the first to show a whole head. In 2024, the Field Museum in Chicago announced a fourteenth specimen. A study in 2025 described it.

Starting in 1985, a small group that included Fred Hoyle and Lee Spetner said the feathers on the Berlin and London specimens were fake. Scientists at the Natural History Museum in London, including Alan J. Charig, said these claims were wrong. The people who made them did not understand how fossils form. They also did not explain why the other specimens with feathers were real too. Charig and his team pointed to tiny cracks and mineral growth in the rock. They said these were signs that the feathers were original. Most palaeontologists did not believe the fake idea.

Description

Most Archaeopteryx fossils come from the Solnhofen limestone in Bavaria, southern Germany. This is a rare Lagerstätte, a rock layer known for very detailed fossils from about 150 million years ago. The animal was about the size of a raven. It had broad, rounded wings, a long tail, and small teeth. It could grow to about 50 centimetres long and had a wingspan of about 70 centimetres. Its feathers looked very much like those of modern birds. It had many bird features, but it also had many features of a theropod dinosaur, such as small teeth and a long bony tail. Because it had both, scientists have often seen it as a link between birds and dinosaurs. In the 1970s, John Ostrom followed an idea by Thomas Henry Huxley from 1868. He argued that birds evolved from theropod dinosaurs, and he used Archaeopteryx as important evidence. He found that it was remarkably similar to the Dromaeosauridae family. Each front leg had three separate fingers, and each ended in a claw. Few birds have this, although ducks, swans, Jacanas, and the hoatzin have them hidden under their leg feathers.

Its well-developed flight feathers worked like those of modern birds. The vanes stayed firm because of a barbule and barbicel arrangement. The thumb did not yet have a movable tuft of stiff feathers. Scientists know less about its body feathers. Most of what is known comes from the Berlin specimen, which had "trousers" of feathers on its legs. Some of these feathers lacked barbicels, as in ratites. A patch of pennaceous feathers ran along its back. Fluffy "proto-down", similar to that of Sinosauropteryx, covered much of the rest of its body. Most specimens were buried in anoxic sediment after drifting in the sea. Their bent necks and tails give them the death pose seen in the fossils. In 2011, Ryan Carney and colleagues used scanning electron microscopy and energy-dispersive X-ray analysis to study one feather. It was probably a dorsal covert, and they found melanosomes in it. These showed that the feather was black. A 2020 study confirmed that it was matte black. The rest of its plumage pattern is still unknown.

Classification

Today, fossils of the genus Archaeopteryx are usually sorted into one or two species, A. lithographica and A. siemensii. Its naming history is complicated. The name A. lithographica first referred only to a single flight feather described by Meyer. That feather may belong to a different, smaller feathered theropod. In 1954, Gavin de Beer decided that the London specimen was the holotype. Many early names came from a disagreement between Meyer and Johann Andreas Wagner, and the ICZN later removed many of them. Because the feather was the type specimen, using the name for the skeletons caused nomenclatorial confusion. So on 3 October 2011, the London specimen was made the neotype.

Below is a cladogram published in 2013 by Godefroit et al.

Some researchers think all the specimens belong to one species, while others think there are two. The specimens differ in size, finger shape, snout shape, and possibly the presence of a sternum. Most specimens have been given their own names at some point. In 2007, a review concluded that two species could be supported: A. lithographica and A. siemensii. They are mainly told apart by large flexor tubercles on the claws of A. lithographica. A supposed extra species, Wellnhoferia grandis, seems to differ from A. lithographica only in size. The names are listed in the table below, following zoological nomenclature. A name in parentheses means the taxon was first described in a different genus.

"Archaeopteryx" vicensensis is a nomen nudum for what appears to be an undescribed pterosaur.

Modern scientists have often called Archaeopteryx the most primitive bird. However, it is thought to be a close relative of the true ancestor of modern birds, not that ancestor itself. Some researchers have questioned whether it was the first bird. They have suggested that Avimimus may have been a more likely ancestor. Other studies have noted that many maniraptoran groups were very birdlike. After the discovery of the closely related Xiaotingia in 2011, some analyses placed Archaeopteryx as a deinonychosaur rather than a true bird. A later study returned it to its traditional place at the base of Avialae. Scientists say there is still uncertainty. Studies including Eosinopteryx brevipenna and Jinfengopteryx elegans gave different results. Some work grouped Archaeopteryx with Wellnhoferia, Microraptoria, and Unenlagiinae. One analysis defined Avialae using Passer domesticus, excluding Dromaeosaurus albertensis and Troodon formosus. It placed Archaeopteryx in a grade with Aurornis. Other studies by Hu et al., Wang et al., and Hartman et al. considered it a deinonychosaur. Hartman et al. also suggested that it, like Yi, may have evolved flight independently from bird ancestors, possibly among the flightless "anchiornithids."

Palaeobiology

Like modern birds, the flight feathers of Archaeopteryx were slightly uneven, and its tail feathers were fairly broad. This suggests its wings and tail helped it get lift, but scientists are not sure whether it could flap or only glide. It had no strong bony breastbone, so it was probably not a very strong flier. Its coracoids, a cartilaginous sternum, and the joint between its scapula and humerus may show that it could not raise its wings above its back, which modern flapping flight needs. In 2006, Philip Senter suggested it may have flapped only on the downstroke to help it glide. Its large, short, rounded wings would have let it make tight turns and move through crowded places like trees, similar to crows and pheasants. Its "hind wings," similar to those of Microraptor, may also have helped it move in the air. In 2010, some scientists questioned whether its thin rachises could support powered flight, based on a study of Confuciusornis and Archaeopteryx. Other scientists, including Philip J. Currie and Gregory Paul, disagreed with that study. Some suggested it may have run over water like the basilisk lizard (see Origin of avian flight).

In 2004, scientists studied a detailed CT scan of the braincase of the London Archaeopteryx. They found its brain was much larger than that of most dinosaurs. Its areas for vision, hearing, and muscle control were well developed, which suggests it had the senses needed to fly. Its brain was more advanced than that of non-coelurosaurian dinosaurs such as Carcharodontosaurus or Allosaurus. Newer research shows its brain was not especially large among Maniraptora dinosaurs, which suggests that flight-related brain development was already common in that group. Scientists still debate how Archaeopteryx lived. O. C. Marsh and Samuel Wendell Williston had different ideas about whether it climbed, ran, or did both. A 2002 idea by Elżanowski suggested it used its wings mainly to escape predators. In 2018, scientists reported that it may have flapped in a way closer to maniraptorans than to modern birds.

A histological study in 2009 suggested Archaeopteryx grew relatively slowly, similar to some kiwi birds, and perhaps had a similar basal metabolic rate. It is estimated to have taken at least 970 days to reach adult size. Comparing its scleral rings with those of modern birds and reptiles suggests it was diurnal, like most modern birds.

Palaeoecology

The rocks at the Solnhofen limestones, where every Archaeopteryx fossil has been found, show a Jurassic Bavaria that was very different from today. The area was at a similar latitude to Florida, but it was probably drier. Plants such as cycads and conifers lived there, along with insects, small lizards, pterosaurs, and Compsognathus. The fossils are so well preserved that the animals probably did not travel far. This means Archaeopteryx likely lived on the low islands around the lagoon. Pterosaurs were more common there than Archaeopteryx. One kind was Rhamphorhynchus, from the Rhamphorhynchidae group. These pterosaurs filled the ecological niche that seabirds have today, and they died out at the end of the Jurassic. Pterodactylus was also found. The pterosaurs were common enough that they were unlikely to be vagrants from larger islands 50 km (31 mi) to the north.

The islands were low, semi-arid, and sub-tropical. They had a long dry season and little rain. The closest modern match is said to be Orca Basin in the northern Gulf of Mexico, though that place is much deeper. The flora on the islands was suited to dry conditions. It was mostly low shrubs about 3 m (10 ft) tall. Few tree trunks have been found, and fossilized tree pollen is missing. Researchers disagree about how Archaeopteryx lived. Some think it mostly lived on the ground. Others think it mostly lived in trees, but that idea is based on claw curves that have since been questioned. Some think it was a generalist that could feed in shrubs, on open ground, and along the lagoon shore. It most likely hunted small prey, grabbing it with its jaws or claws.