Compsognathidae

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Compsognathids
Temporal range: Late Jurassic – Early Cretaceous, 151.5–108 Ma Possible Late Cretaceous record
Compsognathid skeletons to scale
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Neocoelurosauria
Family: †Compsognathidae
Cope, 1871
Type species
†Compsognathus longipes
Wagner, 1861
Genera[3]
Synonyms
  • Sinosauropterygidae Ji & Ji, 1996

Compsognathidae is a family of dinosaurs belonging to the Coelurosauria suborder Theropoda. The group originated in 1861, after Johann A. Wagner published his classification of Compsognathus longpipes.[4][5][6] The family was classified by Edward Drinker Cope in 1875.[7] This classification was accepted by Othniel Charles Marsh in 1882, and added to the Coelurosauria clade by Friedrich von Huene in 1914 after additional fossils had been found.[4] Compsognathids are small carnivorous dinosaurs, generally conservative in form, from the Jurassic and Cretaceous Periods. The bird-like features of this dinosaur, along with other dinosaurs such as Archaeopteryx inspired the idea for the connection between dinosaur reptiles and modern-day avian species.[8] Compsognathids lie at or near the origin of feathers—skin impressions are known from four genera, Compsognathus, Sinosauropteryx, Sinocalliopteryx, and Juravenator, though some of these classifications are still under debate.[9] While Juravenator, Sinosauropteryx, and Sinocalliopteryx show evidence of a covering of simple, primitive feathers, Juravenator and Compsognathus also show evidence of scales on the tail or hind legs.

Fossils have been uncovered across three different continents, specifically in the countries of China,[10] France,[4] Germany,[4][5][6][9] Italy,[11] and Brazil.[5][7] Classification of Compsognathidae is usually determined through examination of the metacarpal, which is used to separate Compsognathidae from other dinosaurs included in the genus Compsognathus.[12] However, classification is still complicated due to similarities to the body of several other theropod dinosaurs, as well as the lack of unifying, stereotypical features that are shared by all compsognathids.[7][13]

The position of the Compsognathidae within the Coelurosaur group is currently still being determined;[5] some hold the family as the basalmost of the coelurosaurs,[14] while others as part of the Maniraptora.[15][16] The evolution of compsognathids, especially Juravenator and Sinosauroptryx, is an important factor in dating and method of feather emersion in dinosaurs.[9]

History of Discovery

The first significant fossil specimen of Compsognathidae was found in the Bavaria region of Germany (BSP AS I 563) and given to collector Joseph Oberndorfer in 1859.[17] The finding was initially significant because of the small size of the specimen. In 1861, after an initial period of review, Johann A. Wagner presented his analysis of the specimen to the public and named the fossil Compsognathus longipes( “elegant jaw”).[18] In 1868, Thomas Henry Huxley, an explorer known for his travels with Charles Darwin and an early supporter of the theory of evolution, used Compsognathus in a comparison to similar feathered dinosaur Archaeopteryx in order to propose the origin of birds. While Huxley noticed that these dinosaurs shared a similar layout to birds and proposed an exploration of the similarities. He is credited as being the first person to do so.[19] This initial comparison sparked the interest into the origin of birds and feathers. In 1882, Othniel Charles Marsh named a new family of dinosaurs for this species Compsognathidae and officially recognized the species as part of Dinosauria.[20] There are currently three accepted dinosaurs that make up the family Compsognathidae- Huaxiagnathus, Sinosauropteryx and Sinocalliopteryx. More have been classified as Compsognathidae, but are less universally accepted.

Anatomy

Compsognathids share a variety of characteristics. The genera in this family demonstrate traits that are characteristic of theropods, such as smaller forelimbs than hind legs. Size, feathers, and metacarpal size are among the most important classifying common characteristics.

Size

Size of different genera of Compsognathidae compared to a human

Compsognathids is considered to be among the smallest dinosaurs ever discovered. Compsognathus longpipes was largely acknowledged to the smallest dinosaur and was around the size of a chicken when fully grown. The specimens found indicate that this species was around 1 m long and weighed 2.5 kg.[21] However, recently other adult dinosaur specimen have now been found that are smaller than Compsognathus, including the dinosaurs Caenagnathasia, Microraptor, and Parvicuror, all of which are estimated to be less than 1m long.[22] Most of these specimen are incomplete, so size determination is still just an estimate.

The other genera in this family are slightly larger than Compsognathus longpipes, but generally similar in

size. The largest member of the Compsognathidae family is Huaxiagnathus, which is estimated from its holotype to be around 5.9 m in length.[23] Sinocalliopteryx measures around 2.4 m in length.[24] Sinosauropteryx is the most similar to Compsognathus, measuring at 1.07 m in length at most.[25]

Feathers

Artistic recreation of Sinosauropteryx with feathers

Compsognathidae have feathers. The phylogeny of Compsognathidae organizes this family near the development of feathers in dinosaurs. In 1998, evidence of filamentous protofeathers was presented in a study on Sinosauropteryx, marking the first time that any sort of feather structure was found outside of birds and their related species.[26] After this, more evidence of feather structure was found in other genera of Compsognathidae. Evidence of protofeathers bearing resemblance to Sinosauropteryx was found on Sinocalliopteryx specimens, including on the foot of the specimen.[27] There have been signs of basic feather structures on Juravenator, but evidence of this is still not definite. Samples of Juravenator skin show scales instead of feathers, leading into debates about Juravenator’s place within the Compsognathidae family.[28] However, a 2010 examination of Juravenator under UV light showed filaments similar to those seen on other compsognathid specimens, indicating that it is likely that these dinosaurs had some sort of feathering.[29]

Diet

Compsognathidae were carnivores and certain specimen have contained the remains of their diet. The German specimen of Compsognathus included remains in the digestive region, which was initially thought to be an unborn embryo.[30] However, further analysis found that the remains belong to a lizard with an elongated tail and stretched legs.[20][31] Other compsognathids, such as Sinosauropteryx, have been shown to eat lizards.[25]

Metacarpal

Another way of classification of Compsognathidae is shared metacarpal morphology. A 2007 study found similarities between compsognathid genera in certain metacarpal I morphologies. The conclusion of this study found that Composgnathidae had a distinct manual morphology where, like theropods, the first digit of the manus is larger than the other digits, but with a distinct metacarpal I morphology where the metacarpal is stocky and short. Compsognathidae also has a projection from the manus that is on this metacarpal.[12]

Species Classification

Classification of Compsognathidae is not very well defined due to a lack of research into specific, defined characteristics shared by all of the species in this family.[12] Therefore, classification of Compsognathidae is mostly dependent upon ancestral characteristics based on where Compsognathidae is placed upon Dinosauria phylogeny, or plesiomorphies. Currently, there is research being done in order to find specific diagnostic traits that can be used for a more accurate classification of Compsognathidae. Compsognathidae is a minute group of dinosaurs, with only three universally accepted groups in this family. These genera are Huaxiagnathus, Sinosauropteryx and Sinocalliopteryx.[32] Most of these species are defined based on singular specimens, some of which are juvenile. Compsognathidae is included in the clade Coelurosauria, which is a group that contains theropods placed closer towards birds and aves.[33] Compsognathids are almost universally placed in this group, usually close to Ornitholestes.[23][34]

Additional Notable Specimen

French Compsognathus longpipes

Comparison of German (green) and French (orange) Compsognathus longpipes specimen

In 1971, a second nearly complete specimen of Composgnathus longpipes was found in the area of Canjuers, which is located in the southeast of France near Nice.[4] This specimen was much larger than the original German specimen, but similarities led to experts categorizing the fossil as an adult Compsognathus longpipes and leading to the further classification of the German specimen as a juvenile.[35] This specimen also contained a lizard in the digestive region, further solidifying the theory that compsognothids consumed small vertebrate species.

Juravenator

Size comparison of Juravenator to human.

Though Juravenator has previously been accepted as a member of Compsognathidae, recent research on the holotype has led some experts to believe that Juravenator does not belong in this group. This is mostly due to the fact that Juravenator could also be classified into a similar group within Coelurosauria, Maniraptoriformes. Maniraptorformes share many similarities with compsognathids and due to the fact that there has been only one verified specimen of Juravenator, experts have disagreed on exactly where to place this genus. Since 2013, Juravenator is still commonly classified as a coelurosaur, but near the family Maniraptorformes instead of Compsognathidae.[32]

Systematics

In his 2003 paper discussing basal theropod relationships, Oliver Rauhut considered compsognathids to be part of Coeluridae.[36] However, subsequent cladistics analyses find Coelurus distantly related to members of Compsognathidae.[37][38]

Timeline

21st century in paleontology20th century in paleontology19th century in paleontology2090s in paleontology2080s in paleontology2070s in paleontology2060s in paleontology2050s in paleontology2040s in paleontology2030s in paleontology2020s in paleontology2010s in paleontology2000s in paleontology1990s in paleontology1980s in paleontology1970s in paleontology1960s in paleontology1950s in paleontology1940s in paleontology1930s in paleontology1920s in paleontology1910s in paleontology1900s in paleontology1890s in paleontology1880s in paleontology1870s in paleontology1860s in paleontology1850s in paleontology1840s in paleontology1830s in paleontology1820s in paleontologySinosauropteryxSinocalliopteryxScipionyxMirischiaJuravenatorHuaxiagnathusCompsognathusAristosuchus21st century in paleontology20th century in paleontology19th century in paleontology2090s in paleontology2080s in paleontology2070s in paleontology2060s in paleontology2050s in paleontology2040s in paleontology2030s in paleontology2020s in paleontology2010s in paleontology2000s in paleontology1990s in paleontology1980s in paleontology1970s in paleontology1960s in paleontology1950s in paleontology1940s in paleontology1930s in paleontology1920s in paleontology1910s in paleontology1900s in paleontology1890s in paleontology1880s in paleontology1870s in paleontology1860s in paleontology1850s in paleontology1840s in paleontology1830s in paleontology1820s in paleontology

References

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