| Shaochilong | |
|---|---|
 | |
| Braincase IVPP V 2885 in right lateral view | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Orionides |
| Clade: | Avetheropoda |
| Genus: | †Shaochilong Brusatte et al.,2009 |
| Species: | †S. maortuensis |
| Binomial name | |
| †Shaochilong maortuensis (Hu, 1964) | |
| Synonyms | |
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Shaochilong (meaning "shark toothed dragon") is anextinctgenus oftetanurantheropoddinosaur from theEarly Cretaceous (Barremian to theAlbian stage)Miaogou Formation ofChina, though a more restrictive suggestion from theAptian to the Albian has been suggested based on faunal composition. It was originally described as acarcharodontosaurid, but other phylogenies have suggested a different position as atyrannosauroid.[2][3] Thetype species,S. maortuensis, was originally namedChilantaisaurus maortuensis, but was re-described and reclassified in 2009.[4][5]
The material referred toShaochilong,IVPP V.2885.1-7, was found in theMiaogou Formation (Maortu locality; originally interpreted as the nearbyUlansuhai Formation).[1] It consists of skull fragments (a braincase, partial skull roof, quadrates, and a right maxilla),axis and six caudal vertebrae. A fragmentary left maxilla was also referred to the species, although it has apparently gone missing as of 2009. Although these are believed to belong to a single individual, alectotype was established in 2010 to accommodate for the possibility that the specimens came from multiple individuals. The lectotype consists of the braincase (IVPP V.2885.1) and partial skull roof (IVPP V.2885.2).[5] All of these specimens were discovered in Inner Mongolia and described by Hu in 1964 as a species ofChilantaisaurus.[6] The genus wasinformally named "Alashansaurus" by Chure in 2000.
Chure (2002) and Rauhut (2001) suggested that it did not belong to that genus, and was probably a primitivecoelurosaur.[7] However, a re-description by Brusatte and colleagues in 2009 found that it was a carcharodontosaurid, the first recognized from Asia, though this has now been disputed. This re-description also provided a new genus name.[4] A more comprehensive description and discussion was published the following year.[5]
The individual which IVPP V2885.1 belonged to was probably adult or nearly adult individual, due to the fusion of many elements of thebraincase.Shaochilong's length – based on the length of the maxillary tooth row – is estimated at 5 to 6 metres (16 to 20 ft). Estimated length of thefemur is 61.5 cm which suggests the whole animal weighed approximately 500 kilograms (1,100 lb). This madeShaochilong an uncharacteristically small for a carcharodontosaurid, in contrast with other members of the family, which were among the largest carnivorous animals on earth. According to the proportions of its maxilla,Shaochilong would have been relatively short-faced if a carcharodontosaur. In combination with its comparatively small size, it could have had a unique ecological role in comparison to other members of this family. The taxa seemed to provide an unambiguous example of a fairly largecarnosaur in Cretaceous Asia at the time of its description, and was considered the youngest known Laurasian allosauroid.[5] However, a 2024 study has interpreted it to come from theMiaogou formation instead of theUlansuhai formation which would make the genusBarremian toAlbian, and phylogenetic studies have cast doubt on its carcharodontosaurid nature.[1][2][3]
Phylogenetic analyses performed by Brusatte and coworkers indicate thatShaochilong is deeply nested within the carcharodontosaurids, the most derived group among theallosauroids.Shaochilong appears to be more closely related to theGondwanan carcharodontosaurians (Tyrannotitan,Carcharodontosaurus,Mapusaurus,Giganotosaurus) than the Laurasian ones (such asNeovenator andAcrocanthosaurus).Shaochilong was distinguished from other carcharodontosaurids due to having the severalautapomorphies, including a reduced and nearly absent maxillaryantorbital fossa, no paradental groove on the medial surface of themaxilla, deep vertical grooves located dorsally on the maxillaryinterdental plates, a pneumatic recess which penetrates to the posterior end of thenasal, a deepsagittal crest on thefrontal, and a large pneumatic foramen in the anterodorsal corner of the prootic's dorsal tympanic recess.[5]
In their description of the largeSouth American carcharodontosauridMeraxes, Canale et al. (2022) recoveredShaochilong as thesister taxon to the Carcharodontosaurinae. The results of theirphylogenetic analyses are displayed in thecladogram below:[8]
However, more recent research has questioned this taxon's position as a carcharodontosaurid. In the description of themetriacanthosauridAlpkarakush,Shaochilong was recovered as a member ofTyrannosauroidea in the phylogenetic analyses oftetanurans.[2] Additionally, in the description of the largeAfrican carcharodontosauridTameryraptor, all analyses recoverShaochilong as a tyrannosauroid as it shares several autapomorphies with the grouping, while many of its listed carcharodontosaurid autapomorphies are either present in other theropods or problematic in their definition.[3]
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