Compsognathus (; Greek kompsos/κομψός; "elegant", "refined" or "dainty", and gnathos/γνάθος; "jaw") is a genus of small, bipedal, carnivorous theropod dinosaur. Members of its single species Compsognathus longipes could grow to around the size of a chicken. They lived about 150 million years ago, during the Tithonian age of the late Jurassic period, in what is now Europe. Paleontologists have found two well-preserved fossils, one in Germany in the 1850s and the second in France more than a century later. Today, C. longipes is the only recognized species, although the French specimen was once thought to belong to a separate species named C. corallestris.
Many presentations still describe Compsognathus as "chicken-sized" dinosaurs because of the size of the German specimen, which is now believed to be a juvenile. Compsognathus longipes is one of the few dinosaur species whose diet is known with certainty: the remains of small, agile lizards are preserved in the bellies of both specimens. Teeth discovered in Portugal may be further fossil remains of the genus.
Although not recognized as such at the time of its discovery, Compsognathus is the first theropod dinosaur known from a reasonably complete fossil skeleton. Until the 1990s, it was the smallest-known non-avialan dinosaur, with the preceding centuries incorrectly labelling it as the closest relative of Archaeopteryx.
Discovery and species
thumb|left|Joseph Oberndorfer acquired this fossil in Bavaria, Germany, in 1859. Shown here is a cast at the Bavarian State Institute for Paleontology and Historical Geology.
Compsognathus is known from two almost complete skeletons. The German specimen (specimen number BSP AS I 563) stems from limestone deposits in Bavaria and was part of the collection of physician and fossil collector Joseph Oberndorfer. Oberndorfer lent the specimen to paleontologist Johann A. Wagner, who published a brief discussion in 1859, where he coined the name Compsognathus longipes. Wagner did not recognise Compsognathus as a dinosaur, but instead described it as one of the "most curious forms among the lizards". In 1866, Oberndorfer's collection, including the Compsognathus specimen, was acquired by the paleontological state collection in Munich. later authors have suggested that the German specimen was probably discovered during the 1850s. Weathering of the slab on which the fossil is preserved indicates that it was collected from a pile of waste rock left behind by quarrying. All possible localities are part of lagoonal deposits of the Painten Formation, and date to the latest part of the late Kimmeridgian or the earlier part of the early Tithonian.
In two publications in 1868 and 1870, Thomas Huxley, a major proponent of Charles Darwin's theory of evolution, compared Compsognathus with Archaeopteryx, which was considered the earliest known bird. Following earlier suggestions by Carl Gegenbaur and Edward Drinker Cope, Huxley found that Archaeopteryx was closely similar to Compsognathus, and referred to the latter as a "bird-like reptile". He concluded that birds must have evolved from dinosaurs, an assessment that established Compsognathus as one of the most widely known dinosaurs. The specimen has since been studied by many prominent paleontologists, including Othniel Charles Marsh, who visited Munich in 1881. The German paleontologist J.G. Baur, who worked as an assistant of Marsh, removed the right ankle from the slab for illustration and study; this removed part got lost since. Although Baur published a detailed study of the ankle in 1882, which is now the only available source of information of this part of the skeleton, his reconstruction was later found to be inconsistent with corresponding impressions on the slab. A more comprehensive description followed in the same year. According to these authors, the new species differed from the German species in its larger size and modified, flipper-like hand. Ostrom, Jean-Guy Michard and others have since relabeled it as another example of Compsognathus longipes. In 1984, George Callison and Helen Quimby identified the smaller German specimen as a juvenile of the same species.
Collector Heinrich Fischer had originally labeled a partial foot consisting of three metatarsals and a phalanx, from the Solnhofen area, as belonging to Compsognathus longipes. This identification was rejected by Wilhelm Dames, when he described the specimen for the first time in 1884. Friedrich von Huene, in 1925 and 1932, also found that the foot did probably not belong to Compsognathus itself but to a closely related genus. Ostrom, in his 1978 monography, questioned the attribution of this fossil to Compsognathus once more.
Description
thumb|left|Size comparison of the French (orange) and German (green) specimens, with a human
For decades, Compsognathus was known as the smallest known non-avian dinosaur, The German specimen was estimated to be and , Compared to other compsognathids, the larger French specimen would have been similar in size to larger Sinosauropteryx specimens, but smaller than Huaxiagnathus and Mirischia. with the eyes being larger in proportion to the rest of the skull. The lower jaw was slender and had no mandibular fenestra, a hole in the side of the lower jawbone commonly seen in archosaurs.
The teeth were small and pointed, suited for its diet of small vertebrates and possibly other small animals, such as insects. The German specimen had three teeth in each premaxilla (front bone of the lower jaw), 15 or 16 teeth in each maxilla, and 18 teeth in the lower jaw. The French specimen had more teeth, including four in each premaxilla, 17 or 18 in the maxilla, and at least 21 teeth in the dentary. Consequently, many depictions of Compsognathus show them with coverings of downy proto-feathers. However, no feathers or feather-like covering have been preserved with Compsognathus fossils, in contrast to Archaeopteryx, which are found in the same sediments. Karin Peyer, in 2006, reported skin impressions preserved on the side of the tail starting at the 13th tail vertebra. The impressions showed small bumpy tubercles, similar to the scales found on the tail and hind legs of Juravenator. A 2022 review of non-feather integument of non-avialan theropods interprets these structures as aberrant bony growths rather than scales, as the structures are "texturally and mineralogically indistinguishable" from the rest of the fossilized vertebrae. Additional scales had in 1901 been reported by Von Huene, in the abdominal region of the German Compsognathus, but Ostrom subsequently disproved this interpretation; in 2012, Achim Reisdorf postulated that they are plaques of adipocere, corpse wax.
A patch of fossilized skin from the tail and hindlimb of the possible relative Juravenator starki shows mainly scales, though there is some indication that simple feathers were also present in the preserved areas. This may mean that a feather covering was not ubiquitous in this group of dinosaurs, or maybe that some species had fewer feathers than others.
Classification
left|thumb|Outdated restoration of Compsognathus and [[Archaeopteryx by Charles R. Knight]]
Originally classified as a lizard, the dinosaurian affinities of Compsognathus were first noted by Gegenbaur, Cope, and Huxley between 1863 and 1868. Later, both genera were found to belong to other groups of Cope's classification of dinosaurs: Compsognathus to the Gonipoda (equivalent to Theropoda, in which it is now classified), and Ornithotarsus to the Orthopoda (equivalent to Ornithischia). Later, these groups fell into disuse, although a resurrection of the Ornithoscelida was proposed in 2017. The group Compsognatha was used for the last time by Marsh in a 1896 publication, where it was treated as a suborder of Theropoda. In the same publication, Marsh erected the new family Compsognathidae.
The Compsognathidae are a group of mostly small dinosaurs from the late Jurassic and early Cretaceous periods of China, Europe and South America. Huaxiagnathus, Mirischia, Sinosauropteryx, and perhaps Juravenator and Scipionyx. At one time, Mononykus was proposed as a member of the family, but this was rejected by Chen and coauthors in a 1998 paper; they considered the similarities between Mononykus and the compsognathids to be an example of convergent evolution. The position of Compsognathus and its relatives within the coelurosaur group is uncertain. Some, such as theropod expert Thomas Holtz Jr. and co-authors Ralph Molnar and Phil Currie in the landmark 2004 text Dinosauria, hold the family as the most basal of the coelurosaurs, while others as part of the Maniraptora.
For almost a century, Compsognathus longipes was the only well-known small theropod species. This led to comparisons with Archaeopteryx and to suggestions of an especially close relationship with birds. In fact, Compsognathus, rather than Archaeopteryx, piqued Huxley's interest in the origin of birds. The two animals share similarities in shape and proportions, so many in fact that two specimens of Archaeopteryx, the "Eichstätt" and the "Solnhofen", were for a time misidentified as those of Compsognathus.
Here is an alternative phylogeny, published by Cau in 2024, with both specimens in bold.
Paleobiology
thumb|Life restoration
In a 2001 study conducted by Bruce Rothschild and other paleontologists, nine foot bones referred to Compsognathus were examined for signs of stress fracture, but none were found.
Habitat
Bidar and colleagues, in their 1972 description of the French specimen, argued that this specimen had webbed hands which would look like flippers in life. This interpretation was based on a supposed impression of the flipper that consists of several undulating wrinkles running parallel to the forelimb on the surface of the slab. Ostrom debunked this hypothesis, noting that the forelimb of the French specimen is poorly preserved, and that the wrinkles extend well beyond the skeleton and thus are likely sedimentary structures unrelated to the fossil. Ostrom identified the remains as belonging to a lizard of the genus Bavarisaurus, which he concluded was a fast and agile runner owing to its long tail and limb proportions. This in turn led to the conclusion that its predators, Compsognathus, must have had sharp vision and the ability to rapidly accelerate and outrun the lizard. The lizard is in several pieces, indicating that the Compsognathus must have dismembered it while restraining it with its hands and teeth, and then swallowed the remains whole; a similar strategy is used by modern predatory birds. However, later researchers have doubted their connection to the genus because they were found outside the body cavity of the animal. A well-preserved fossil of a Sinosauropteryx, a genus related to Compsognathus, shows two oviducts bearing two unlaid eggs. These proportionally larger and less numerous eggs of Sinosauropteryx cast further doubt on the original identification of the purported Compsognathus eggs.
Speed
In 2007, William Sellers and Phillip Manning estimated a maximum speed of based on a computer model of the skeleton and muscles. This estimate has been criticized by other scholars.
Paleoenvironment
thumb|Restoration of an Archaeopteryx chasing a juvenile Compsognathus
During the late Jurassic, Europe was a dry, tropical archipelago at the edge of the Tethys Sea. The fine limestone in which the skeletons of Compsognathus have been found originated in calcite from the shells of marine organisms. Both the German and French areas where Compsognathus specimens have been preserved were lagoons situated between the beaches and coral reefs of the Jurassic European islands in the Tethys Sea. Contemporaries of Compsognathus longipes include the early avialan Archaeopteryx lithographica and the pterosaurs Rhamphorhynchus muensteri and Pterodactylus antiquus. The same sediments in which Compsognathus have been preserved also contain fossils of a number of marine animals such as fish, crustaceans, echinoderms and marine mollusks, confirming the coastal habitat of this theropod. No other dinosaur has been found in association with Compsognathus, indicating that these little dinosaurs might in fact have been the top land predator in these islands.
Taphonomy
Much discussion revolved around the taphonomy of the German specimen, i.e. how the individual died and became fossilized. Reisdorf and Wuttke, in 2012, speculated about the events that lead to the death and transportation of the specimen to its place of burial. First, the individual must have been brought into the lagoon from its habitat, which probably was on the surrounding islands. It is possible that a flash flood swept the animal into the sea, in which case it likely died by drowning. It is also possible that the animal swam or drifted onto the sea, or that it rafted on plants, and was then transported by surface currents to its place of burial. In any case, the specimen would have arrived on the sea floor within a few hours after its death, as otherwise gases forming in its body cavity would have prevented it from sinking in one piece. Water depth at the burial site would have been large enough to prevent refloating of the carcass after such gases were produced. Rounded structures on the slab might have been formed by the release of these gases. Reisdorf and Wuttke concluded that the death posture indeed resulted from the release of ligaments, more specifically the , which spans the spine from the neck to tail in modern birds. The release of this ligament would have occurred gradually while the surrounding muscle tissue decayed, and only after the carcass was transported to its final site of deposition. The animals have appeared in the Jurassic Park franchise: in the films The Lost World: Jurassic Park, Jurassic Park III, Jurassic World: Fallen Kingdom, Jurassic World Dominion and Jurassic World Rebirth, and the television series Camp Cretaceous and Chaos Theory. In The Lost World: Jurassic Park, the species is incorrectly identified as Compsognathus triassicus, combining the genus name of Compsognathus longipes with the specific name of Procompsognathus triassicus, a distantly related small carnivore that also appears in the Jurassic Park series.