| Sinocalliopteryx | |
|---|---|
 | |
| Holotype specimen JMP-V-05-8-01 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Compsognathidae |
| Genus: | †Sinocalliopteryx Jiet al., 2007 |
| Species: | †S. gigas |
| Binomial name | |
| †Sinocalliopteryx gigas Jiet al., 2007 | |
Sinocalliopteryx (meaning 'Chinese beautiful feather') is agenus of carnivorouscoelurosauriantheropoddinosaurs from theLower CretaceousYixian Formation ofChina (Jianshangou Beds, dating to 124.6 Ma). While similar to the relatedHuaxiagnathus,Sinocalliopteryx were larger. In 2007, thetype specimen was the largest known compsognathid exemplar, at 2.37 metres (7.8 ft) in length. In 2012, an even larger specimen was reported.
Thetype speciesSinocalliopteryx gigas was named and described in 2007 byJi Shu'an,Ji Qiang,Lü Junchang andYuan Chongxi. The generic name is derived fromSinae,Latin for the Chinese and Greek καλός,kalos, "beautiful", and πτέρυξ,pteryx, "feather". The large size of this "giant compsognathid" lentSinocalliopteryx itsspecific name,gigas, meaning 'giant'.[1]
Theholotype, JMP-V-05-8-01, was discovered atHengdaozi, inSihetun, inLiaoning Province, from theJianshangou Beds of theYixian Formation dating from theBarremian-Aptian, about 125 million years old. It consists of a nearly complete skeleton with skull, compressed on a single plate, of an adult individual. Extensive remains of protofeathers have been preserved.[1] In 2012 a second specimen was described, CAGS-IG-T1, of an individual larger than the holotype. The skull was about 10% longer, the feet about a third, a difference explained by positiveallometry. The specimen consists of a partial skull, tail, hands, feet and ribcage. It shows filaments on the tail.[2]
Sinocalliopteryx was a bipedal predator. The preserved length of the holotype specimen is 237 centimetres. Its weight was estimated byGregory S. Paul in 2010 at twenty kilogrammes.[3]Sinocalliopteryx is distinguished fromHuaxiagnathus, as well as other compsognathids, by its relatively long hands in relation to its arms. The arms and hindlimbs were also longer overall than in other compsognathids, a feature possibly related to its size.[1]
Sinocalliopteryx had an elongated head with a pointed snout, showing a convex upper profile. There were four teeth in thepremaxilla which were small but exceptionally had denticles on their front edges. Only six, larger, teeth were present in themaxilla of theholotype specimen but the number of its tooth positions could not be adequately determined. Specimen CAGS-IG-T1 preserves ten maxillary tooth sockets with room for one or two more in damaged areas. Thejugal was a strongly built element with a high-rising front branch that formed part of the lower front edge of the eye socket. The lower jaw lacked an opening in its outer side.[1][2]
The vertebral column consisted of eleven cervical, twelve dorsal, five sacral and at least forty-nine caudal vertebrae. The point of the tail is missing. In the tail, the spines and chevrons strongly inclined to the back. Thegastralia had very short lateral segments.[1]
The arm had a shorthumerus and also the lower arm was short and elegant with anulna showing only a weakly developed olecranon process on its back upper end. The hand was very elongated though, as long as the ulna and upper arm combined. The secondmetacarpal was expanded at the top at the side of the first metacarpal, making the entiremetacarpus more compact. The second claw was elongated, as long as the thumb claw. The third metacarpal was rather short and carried a thin, third, finger.[1]
In the pelvis there was a little notch in the front edge of theilium. The relatively long shaft of theischium curved downwards. The hindlimb was elongated, largely because of a long lower leg, having 90% of the length of the thighbone. The foot was also long, especially in themetatarsus.[1]
Like many othertheropods of the Yixian Formation,Sinocalliopteryx was preserved with "protofeathers," simple filamentousintegument (hairlike structures covering the skin), very similar to that found inSinosauropteryx. The integument ofSinocalliopteryx differ in length across the body, with the longest protofeathers covering the hips, base of the tail, and back of the thighs. These longest protofeathers measured up to ten centimeters (4 in) in length. Protofeathers were also found on the metatarsus (upper part of the foot). While these were not nearly as long or modern as the corresponding feathers of "four-winged" dinosaurs such asMicroraptor andPedopenna, they do indicate that foot-feathers or similar structures first arose in dinosaurs much more basal or "primitive" than previously known.[1]
Sinocalliopteryx was by its describers assigned to theCompsognathidae.[1]
Thiscladogram shows the position ofSinocalliopteryx in the Compsognathidae according to a study bydal Sasso & Maganuco in 2011:[4]
The large size ofSinocalliopteryx compared to its relatives is also notable, and may indicate a trend towards large size among compsognathids (a group well known for their small size compared to other, giant theropod dinosaurs), similar to the trends towards larger sizes in other dinosaurian lineages.[1]
In 2024, Andrea Cau published a study on the phylogenetics of Compsognathids that called the assessment ofSinocalliopteryx into question. The paper recovered the taxon, along with four other proposedCompsognathids in a polytomy within basalCoelurosauria. This polytomy notably did not includeComposognathus proper, which would make none of these speciesCompsognathids.[5]
Qiu et al. (2025) also argued against the monophyly of Compsognathidae and revised the definition of the monophyleticSinosauropterygidae withinCoelurosauria as a family containing all compsognathid-like theropods from the Jehol Biota of China:Sinosauropteryx,Huadanosaurus,Huaxiagnathus andSinocalliopteryx. Their phylogenetic analyses are reproduced below:[6]
The well-preserved skeleton of theSinocalliopteryx holotype contained the partial leg of adromaeosaurid within the abdominal cavity, comprising a complete lower leg and foot with toes and claws in their natural, articulated position.[2] While the leg part, about one foot long, is very large in relation to the abdominal cavity, it is clearly situated within it, lying between the ribs. Ji and colleagues in 2007 suggested that this could indicate it preyed upon the smaller, bird-like dinosaur. This discovery indicated thatSinocalliopteryx may have been an agile, active, "fierce" predator, especially since other compsognathids have been found with (presumably fast-moving) lizards and small mammals in their abdominal cavities.[1] In 2012 the dromaeosaurid was tentatively identified as an individual ofSinornithosaurus with a length of 1.2 metres (3.9 ft). The 2012 study also reported newly discovered remains of prey animals. Above the dromaeosaurid leg, feathers are visible. Below it two clusters of digested food can be seen. It was suggested that the feathers had belonged to a bird and were with the leg still present in thestomach. The digested food would, using the preserved digestive tract ofScipionyx as a reference, have been positioned in theduodenum.[2] The C-shaped abdominal contents of this specimen appear to reflect of the original contour of the digestive tract.[8]
In addition to the dromaeosaurid leg, four irregularly-shaped stones with a diameter between fifteen and twenty millimetres were found in the abdomen, with no similar stones present in any other portions of the skeleton or embedded in the surrounding rock. The authors interpreted these asgastroliths (gizzard stones) similar to those found withNqwebasaurus andBaryonyx. Other theropods, such asCaudipteryx and aMongolianornithomimid, were also found with gastroliths, though in those cases the stones were much more numerous and smaller in size. Ji and colleagues speculated that, since the later two dinosaurs were probably primarily herbivores, the number and size of gastroliths may correspond with diet; that is, herbivores ingested many small stones, while carnivores ingested only a few larger stones to aid in digestion.[1] However, the 2012 study could find no gastroliths with the second specimen and therefore concluded that the stones with the holotype were swallowed by accident. In any case no specialgizzard would have been present.[2]
The second specimen, CAGS-IG-T1, also preserves the remains of several meals. Disarticulated bones were found, in front of the lower ischia, identified as belonging to at least two individuals ofConfuciusornis sanctus, a basal bird that is very common in the formation. Also a 13.5 centimetres long scapula was discovered, belonging to some 1.5 metres (4.9 ft) long herbivorousornithischian, perhapsYueosaurus or aPsittacosaurus species. The bone surface of the scapula looked as if it had been etched by stomach acid for about thirteen days, leading to the conclusion the birds were swallowed later and in quick succession. This again would indicate a high metabolism forSinocalliopteryx, necessitating a regular food intake.[2]
That the second specimen in a short period of time caught two birds, together with the bird feather remains in the holotype stomach, might be an indication thatSinocalliopteryx specialised in such prey. Even theSinornithosaurus might conform to this pattern as the authors considered it a possibly volant form. In 2011 a specimen ofMicroraptor was reported with a bird in its stomach and seen as proof that the former were arboreal. The 2012 study denied the relevance of flying prey for this issue asSinocalliopteryx was in all likelihood cursorial, or ground-dwelling, and yet apparently quite capable of catching birds, e.g. by using stealth attack, a method employed by many modern cursorial predators of fowl.[2]
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