Open Paleo

Micropachycephalosaurus

Dong, 1978 MIEK-ro-PAK-i-SEF-a-lo-SAWR-us

From Greek 'mikros' (small), 'pachys' (thick), 'kephale' (head), and 'sauros' (lizard); meaning 'small thick-headed lizard'.

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

Micropachycephalosaurus is an extinct genus of basal marginocephalian dinosaur, containing only the type species, Micropachycephalosaurus hongtuyanensis. It lived in China during the Late Cretaceous (Campanian) and was found in the Jiangjunding Formation. It has the longest name of any dinosaur, with 23 letters in the genus name alone, while the full binomial contains 37 letters.

Under dispute

Despite its name, Micropachycephalosaurus hongtuyanensis is not confidently a pachycephalosaur. It was described as one (Dong, 1978), but the dedicated redescription found no unambiguous synapomorphies and treated it as Cerapoda incertae sedis (Butler and Zhao, 2009). Butler and colleagues (2008) recovered it with basal ceratopsians, Butler and colleagues (2011) in an unresolved basal polytomy within Marginocephalia, and Fonseca and colleagues (2024) as a pachycephalosaur.

Diagnosis

  1. Parietal and postorbital bones thickened but relatively flat, not strongly domed
  2. Supratemporal fenestra not closed
  3. No prominent sagittal crest on the skull
  4. Teeth slender, arranged in a single row, with central ridge on outer surface and symmetrical small cusps on anterior and posterior edges
  5. Six fused sacral vertebrae with neural spines connected into a plate-like structure
  6. Quadrate with small anterior inclination angle

Species

Micropachycephalosaurus hongtuyanensis Dong, 1978

Type species

Named for the Hongtuyan train station near the discovery site southwest of Laiyang, Shandong Province, China.

Holotype
IVPP V5542 , Institute of Vertebrate Paleontology and Paleoanthropology
Material
Broken parietal (posterior end only); incomplete postorbital and quadrate bones; partial right dentary; series of caudal vertebrae; partial pelvic girdle and hind limbs
Horizon
Wangshi Group, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Red earth cliff southwest of Laiyang Railway Station, Shandong, China

References

  1. Dong, Z. (1978). [A new genus of Pachycephalosauria from Laiyang, Shantung]. Vertebrata PalAsiatica 16(4): 225-228. dong1978b
  2. Fonseca, A. O.; Reid, I. J.; Venner, A.; Duncan, R. J.; Garcia, M. S.; Müller, R. T. (2024). A comprehensive phylogenetic analysis on early ornithischian evolution. Journal of Systematic Palaeontology 22: 2346577. doi:10.1080/14772019.2024.2346577

    Recovered Micropachycephalosaurus's position within their comprehensive ornithischian phylogenetic analysis.

    fonseca2024a
  3. Butler, R. J.; Zhao, Q. (2009). The small-bodied ornithischian dinosaurs Micropachycephalosaurus hongtuyanensis and Wannanosaurus yansiensis from the Late Cretaceous of China. Cretaceous Research 30(1): 63-77. doi:10.1016/j.cretres.2008.03.002

    Redescription found no unambiguous synapomorphies, treating it as Cerapoda incertae sedis.

    butler2009b
  4. Butler, R. J.; Jin, L.; Chen, J.; Godefroit, P. (2011). The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north-eastern China. Palaeontology 55(3): 667-683. doi:10.1111/j.1475-4983.2011.01046.x

    Recovered Micropachycephalosaurus in an unresolved basal polytomy within Marginocephalia.

    butler2011a
  5. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Treats Micropachycephalosaurus as a basal ceratopsian.

    jones2026a
  6. Butler, R. J.; Upchurch, P.; Norman, D. B. (2008). The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6(1): 1-40. doi:10.1017/S1477201907002271

    Recovered Micropachycephalosaurus with basal ceratopsians.

    butler2008b