Compsognathidae is a family of theropod dinosaurs. Compsognathids were small , generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other dinosaurs such as Archaeopteryx inspired the idea for the connection between dinosaur reptiles and modern-day avian species.[Etnier, Michael A. "Neptune's Ark: From Ichthyosaurs to Orcas." (2008): 25.] Compsognathid fossils preserve diverse integument — skin impressions are known from four genera commonly placed in the group, Compsognathus, Sinosauropteryx, Sinocalliopteryx and Juravenator.
The first member of the group, Compsognathus, was discovered in 1861, after Johann A. Wagner published his description of the taxon.[Dal Sasso C., Maganuco S. " Scipionyx samniticus (Theropoda: Compsognathidae) from the Lower Cretaceous of Italy: osteology, ontogenetic assessment, phylogeny, soft tissue anatomy, taphonomy and palaeobiology." Memorie, XXXVI-I (2011): 1-283.] and South America.[Brett-Surman, Michael K., Thomas R. Holtz, and James O. Farlow, eds. The complete dinosaur. Indiana University Press, 2012 pp 360.] Some authors have proposed that Compsognathidae is not a monophyletic group, and at least some compsognathids represent juvenile specimens of larger tetanurae theropods, such as carnosaurs and tyrannosaurs.[Cau A. (2024). A Unified Framework for Predatory Dinosaur Macroevolution . Bollettino della Società Paleontologica Italiana, 63(1): 1-19.]
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.
[Wellnhofer, P. (2008). "Dinosaurier". Archaeopteryx — der Urvogel von Solnhofen. Munich: Verlag Dr. Friedrich Pfeil. p. 256. .] 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").
In 1868, Thomas Henry Huxley, an early supporter of
Charles Darwin and his theory of evolution, used
Compsognathus in a comparison to similar feathered dinosaur
Archaeopteryx in order to propose the origin of
. 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.
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
.[Ostrom, J. H. (1978). The osteology of Compsognathus longipes Wagner. Zitteliana.]
Notable Specimens
In 1971, a second nearly complete specimen of
Composgnathus longipes was found in the area of Canjuers, which is located in the southeast of France near Nice.
This specimen was much larger than the original German specimen, but similarities led to experts categorizing the fossil as an adult
Compsognathus longipes and leading to the further classification of the German specimen as a juvenile.
This specimen also contained a lizard in the digestive region, further solidifying the theory that compsognathids consumed small vertebrate species.
The holotype of Juravenator is the only known specimen of the species. Though Juravenator has previously been accepted as a member of Compsognathidae, recent research has led some experts to believe that Juravenator does not belong in this group. This is because Juravenator could also be classified into a similar group within Coelurosauria, Maniraptoriformes. Maniraptoriforms share many similarities with compsognathids and, because 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 group Maniraptoriformes instead of Compsognathidae.
A compsognathid specimen consisting of a single finger bone has been described from Late Jurassic (Tithonian Age, about 150 million years ago) sediments at Port Waikato, New Zealand. It is the first and so far, only dinosaur specimen known from Jurassic New Zealand, as well as being the first New Zealand dinosaur fossil to have been found outside of the Cretaceous marine sediments at Mangahouanga Stream. Possible coprolites have been referred to this specimen, however it is still not an officially classified species.
Description
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
Compsognathids are considered to be among the smallest dinosaurs ever discovered.
Compsognathus longipes was formerly the smallest known dinosaur. It was around the size of a chicken when fully grown: around long and weighing .
[" What was the biggest dinosaur? What was the smallest? " (May 17, 2001)] However, recently discovered adult specimens of other dinosaurs are smaller than
Compsognathus, including
Caenagnathasia,
Microraptor and
Parvicursor, all of which are estimated to be less than 1 m long.
[Paul, G.S. , 2010 The Princeton Field Guide to Dinosaurs, Princeton University Press p. 152] However, most of these specimens are incomplete, so these sizes remain estimates.
The other genera in this family are slightly larger than Compsognathus longipes, but generally similar in size. The largest compsognathid is Huaxiagnathus, which is estimated from its holotype to be around long,[Hwang SH, Norell MA, Ji Q, Gao K-Q (2004) A large compsognathid from the Early Cretaceous Yixian Formation of China. J Syst Pal 2: 13–30. .] while Sinocalliopteryx measures around long.
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.
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.
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 family Compsognathidae.
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.
A 2020 study concluded the "scales" were actually
adipocere, though the same study defended
Juravenator was a
Megalosauroidea and not a compsognathid.
Metacarpals
Another way of classification of Compsognathidae is shared
Metacarpal bones 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.
Classification
The Compsognathidae are a group of mostly small dinosaurs from the late Jurassic and early
Cretaceous periods of China, Europe and South America.
For many years,
Compsognathus was the only member known, but in recent decades paleontologists have discovered several related genera. The
clade includes
Aristosuchus,
,
,
,
and perhaps
Juravenator and
Scipionyx.
At one time,
Mononykus was proposed as a member of the family, but this was rejected by Chen and co-authors in a 1998 paper; they considered the similarities between
Mononykus and the compsognathids to be an example of convergent evolution.
The position of Compsognathidae within the
Coelurosauria 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.
Below is a simplified cladogram showing Compsognathidae by Senter et al. in 2012.
A number of authors have suggested that Compsognathidae is not a monophyletic group as currently defined, and that at least some "compsognathids" represent the juveniles of other tetanurans, including carnosaurs and tyrannosaurs.
Palaeobiology
Diet
Compsognathids were carnivores and certain specimens 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.
[ Report of the 65th Meeting of the British Association for the Advancement of Science, Ipswich, 1895, London, 1895, 743
] However, further analysis found that the remains belong to a lizard with an elongated tail and stretched legs.
Other compsognathids, such as
Sinosauropteryx, have been shown to eat lizards.
