Open Paleo

Monolophosaurus

Zhao & Currie, 1993 MON-oh-LOF-oh-SOR-uhs /ˌmɒnoʊˌlɒfoʊˈsɔːrəs/

From Greek 'monos' meaning 'single' and 'lophos' meaning 'crest', plus Greek 'sauros' meaning 'lizard'; translates as 'single-crested lizard', named for the distinctive single crest on its skull.

168.2–161.5 million years ago Bathonian–Callovian, Middle Jurassic
Middle Jurassic stages

Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5-5.5 meters (16-18 ft) long and weighed 475 kilograms (1,047 lb).

Under dispute

Monolophosaurus jiangi was long regarded as a basal allosauroid, but recent analyses place it outside Allosauroidea among basal tetanurans: as the sister taxon of Avetheropoda (Smith and colleagues, 2007), as a basal tetanuran outside Megalosauroidea and Avetheropoda (Carrano, Benson and Sampson, 2012), as a basal megalosauroid allied with Chuandongocoelurus (Benson, 2010), or as an early-branching spinosaurid within Megalosauroidea (Rauhut and colleagues, 2024). It is placed conservatively at Tetanurae incertae sedis.

Diagnosis

  1. Low, prominent medial crest on skull roof extending from above external naris to point between orbits, formed by paired premaxillary, nasal, lacrimal, and frontal bones
  2. Crest with hollow interior connected to antorbital fossae via several large foramina anterodorsal to orbits
  3. Long, low external naris (155 cm long, 65 cm high) with anteroposteriorly elongate premaxilla and elongate antorbital length (440 mm)
  4. Four premaxillary teeth, with nasal processes of premaxillae deeper along midline than in other theropods

Species

Monolophosaurus jiangi Zhao & Currie, 1993

Type species

Named for Jiangjunmiao, the abandoned desert inn near which the holotype was discovered in Xinjiang, China.

Holotype
IVPP 84019 , Institute of Vertebrate Paleontology and Paleoanthropology
Material
Complete skull and partial skeleton.
Horizon
lower Shishugou Formation, Bathonian–Callovian, Middle Jurassic , 168.2–161.5 million years ago
Locality
34 km northeast of Jiangjunmiao, Xinjiang, China Carrano and colleagues (2012) place the holotype in the lower Shishugou, which they date middle Bathonian to late Callovian.

Synonyms of the genus

Name Type Reason
Jiangjunmiaosaurus nomen nudum Informal name; never met ICZN requirements for formal publication and is treated as referable to Monolophosaurus. Per Olshevsky's Dinosaur Genera List.

References

  1. Zhao, X. J.; Currie, P. J. (1993). A large crested theropod from the Jurassic of Xinjiang, People's Republic of China. Canadian Journal of Earth Sciences 30(10): 2027-2036. Canadian Science Publishing. doi:10.1139/e93-178 zhao1993a
  2. Smith, N. D.; Makovicky, P. J.; Hammer, W. R.; Currie, P. J. (2007). Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society 151(2): 377-421. doi:10.1111/j.1096-3642.2007.00325.x

    Recovered Monolophosaurus as the sister taxon of Avetheropoda.

    smith2007b
  3. Carrano, M. T.; Benson, R. B. J.; Sampson, S. D. (2012). The phylogeny of Tetanurae (Dinosauria: Theropoda). Journal of Systematic Palaeontology 10(2): 211-300. Informa UK Limited. doi:10.1080/14772019.2011.630927

    Recovered Monolophosaurus as a basal tetanuran outside Megalosauroidea and Avetheropoda.

    carrano2012a
  4. Rauhut, O. W. M.; Bakirov, A. A.; Wings, O.; Fernandes, A. E.; Hübner, T. R. (2024). A new theropod dinosaur from the Callovian Balabansai Formation of Kyrgyzstan. Zoological Journal of the Linnean Society 201(4). Oxford University Press (OUP). doi:10.1093/zoolinnean/zlae090

    New Kyrgyzstan theropod description recovered Monolophosaurus as an early-branching spinosaurid.

    rauhut2024a
  5. Benson, R. B. J. (2010). A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158(4): 882-935. Oxford University Press (OUP). doi:10.1111/j.1096-3642.2009.00569.x

    Recovered it as a basal megalosauroid allied with Chuandongocoelurus

    benson2010c