Compsognathus

Compsognathus is an extinct genus of small, bipedal, carnivorous theropod dinosaur. The animal was the size of a turkey and lived around 150 million years ago, the early Tithonian stage 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 larger specimen discovered in France in the 1970s was once thought to belong to a separate species, C. corallestris. Compsognathus was the size of a chicken.

Description
For decades, Compsognathus were famed as the smallest dinosaurs known; the first specimen collected was around 1 m (3.3 ft) in length. However, dinosaurs discovered later, such as Caenagnathasia, Microraptor and Parvicursor, were even smaller. The largest Compsognathus specimen is estimated to have weighed somewhere between 0.83 and 3.5 kg (between 1.8 and 7.7 lb).[3][4]

Compsognathus were small, bipedal animals with long hind legs and longer tails, which they used for balance during locomotion. The forelimbs were smaller than the hindlimbs and featured three digits equipped with solid claws suited for grasping prey. Their delicate skulls were narrow and long, with tapered snouts. The skull had five pairs of fenestrae (skull openings), the largest of which was for the orbit (eye socket).[5] The eyes were large 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 but sharp, suited for its diet of small vertebrates and possibly other small animals, such as insects. Its frontmost teeth (those on the premaxilla) were unserrated, unlike those further back in the jaw which were flattened and more strongly recurved.[6] Scientists have used these dental characteristics to identify Compsognathus and its closest relatives.[7] Reisdorf and Wuttke (2012) described the taphonomical phenomena of the German specimen of Compsognathus.[8]

Integument
Some relatives of Compsognathus, namely Sinosauropteryx and Sinocalliopteryx, have been preserved with the remains of simple feathers covering the body like fur,[9] promoting some scientists to suggest that Compsognathus might have been feathered in a similar way.[10] 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.[11] Additional scales had in 1901 been reported by Von Huene, in the abdominal region of the German Compsognathus, but Ostrom subsequently disproved this interpretation;[12][13] in 2012 they were by Achim Reisdorf seen as plaques of adipocere, corpse wax.[8]

Like Compsognathus, and unlike Sinosauropteryx, 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.[14] This may mean that a feather covering was not ubiquitous in this group of dinosaurs.

Discovery and species
Compsognathus is known from two almost complete skeletons, one from Germany that is 89 cm long (35 in) and another from France that is 125 cm (49 in).[16] The physician and fossil collector Joseph Oberndorfer acquired the German specimen (BSP AS I 563) in 1859, discovered about the same year in the Solnhofen lithographic limestone deposits in the Riedenburg-Kelheim region of Bavaria.[17] The limestone of the Solnhofen area has also yielded such well-preserved fossils as Archaeopteryx with feather impressions and some pterosaurs with imprints of their wing membranes. The German Compsognathus fossil itself most likely came from the Painten Formation of the Kapfelberg locality, specifically dated to the uppermost Kimmeridgian stage (150.8 million years ago);[8] however, alternative possibilities include quarries near Jachenhausen[18] or Goldberg, both from the Tithonian, to which stage Compsognathus has traditionally been dated.[8] Johann A. Wagner discussed the specimen briefly in 1859, when he coined the name Compsognathus longipes,[19] and described it in detail in 1861.[20] In early 1868, Thomas Huxley compared the two species and, following earlier suggestions by Karl Gegenbaur[21] and Edward Drinker Cope,[22] concluded that, apart from its arms and feathers, the Archaeopteryx skeleton was closely similar to Compsognathus, and that the proto-bird was related to the dinosaurs.[23][24] In 1896, Othniel Marsh recognized the fossil as a true member of the Dinosauria.[25] John Ostrom thoroughly redescribed the species in 1978, making it one of the best-known small theropods at that time.[12] The German specimen is on display at the Bayerische Staatsammlung für Paläontologie und historische Geologie (Bavarian State Institute for Paleontology and Historical Geology) in Munich, Germany, which bought the fossil from Oberndorfer in 1865.

The larger French specimen (MNHN CNJ 79) was discovered by quarry owner Louis Ghirardi around 1971 in the Portlandian lithographic limestone of Canjuers near Nice in southeastern France.[26] It dates to the lower Tithonian. Although Alain Bidar originally described the specimen as a separate species called Compsognathus corallestris,[27] Ostrom, Jean-Guy Michard and others have since relabeled it as another example of Compsognathus longipes.[26][28] Quimby identified the smaller German specimen as a juvenile of the same species.[29] In 1983, the Muséum national d'histoire naturelle in Paris acquired the French Compsognathus fossil; Michard thoroughly studied it there.[28]

Collector Heinrich Fischer had originally labelled a partial foot, also from Solnhofen, as belonging to Compsognathus longipes. Though this identification was rejected by Wilhelm Barnim Dames in 1884,[30] Friedrich von Huene nevertheless in 1925 provisionally referred the specimen to Compsognathus.[31] However, Ostrom's study of 1978 has disproven this. Jens Zinke has in 1998 assigned forty-nine teeth from the Kimmeridgian Guimarota formation of Portugal to the genus. These were not identical to those of C. longipes, having serrations on the front edge, but were because of general similarities in form referred to a Compsognathus sp.[32]

In 1997 Virginia Morell renamed a related Chinese form, Sinosauropteryx prima, into a Compsognathus prima;[33] this has found no general acceptance.