| Micropachycephalosaurus | |
|---|---|
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| Restoration | |
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| Drawing of theilium | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Marginocephalia |
| Genus: | †Micropachycephalosaurus Dong,1978 |
| Species: | †M. hongtuyanensis |
| Binomial name | |
| †Micropachycephalosaurus hongtuyanensis Dong, 1978 | |
Micropachycephalosaurus (meaning "small thick-headed lizard") is an extinct genus of basalmarginocephaliandinosaur, containing only thetype species,Micropachycephalosaurus hongtuyanensis. It lived inChina during theLate Cretaceous (Campanian) and was found in theJiangjunding Formation.[1] It has the longest name of any dinosaur, with 23 letters in the genus name alone, while the full binomial contains 37 letters.[2]
The holotype, IVPP V5542 was found on a cliff southwest ofLaiyang,Shandong Province, nearHongtuyantrain station.[3] The remains were named and described by Dong Zhiming in 1978, as belonging to the new genus and speciesMicropachycephalosaurus hongtuyanensis,[3] which he incorrectly figured was discovered in theWangshi Formation.
IVPP V5542 consisted of the left quadrate, a partial tooth row with seven teeth, another partial tooth row with no teeth preserved, a single loose tooth, a partialbasioccipital, the centra of three posterior dorsal and two sacral vertebrae, associated with impressions of the neural spines of the posteriormost dorsal and four sacrals, four partial caudal vertebrae preserved in near articulation with associated chevrons, the isolated centra of seven caudals (one with a partial neural arch), a single isolated partial caudal neural arch, a partial left ilium, a left femur, and the proximal portion of the left tibia.[3][4] Dong (1978) briefly described, but did not figure a parietal and squamosal that also supposedly belonged to the holotype,[3] but Butler & Zhao (2009) were unable to locate them.[4]
Micropachycephalosaurus likely only grew up to 1 metre (3.3 ft) long when fully grown.[1] it was abipedal andherbivorous dinosaur.[4]
PaleontologistDong Zhiming originally described it as a member of thePachycephalosauria, a group of bipedal dome-headed herbivores. However, re-evaluation of thefamilyPachycephalosauridae by Sullivan in 2006 cast doubt on this assignment.[5]
Further study of the holotype by Butler and Zhao in 2008 also failed to find any characteristics linkingMicropachycephalosaurus with the pachycephalosaurs. The one piece of evidence that could provide this link, the supposedly thickened skull roof, was missing from the fossil collection the scientists examined, and so could not be used to support or refute its original classification. Butler and Zhao therefore classified it as an indeterminate member of theCerapoda.[4] Acladistic analysis performed by Butler et al. (2011) showed thatMicropachycephalosaurus is a basal member of theCeratopsia.[6] Phylogenetic analyses by Fonseca et al. (2024) instead recovered this taxon as a basal pachycephalosaur.[7]
Micropachycephalosaurus was found in theJiangjunding Formation of the ChineseWangshi Group.[3][8] The Jiangjunding formation consists purpley-grey or reddy-brown sandstones or various consistencies, siltstones and conglomerates. The Wangshi group ofgeologic formations is generally considered to be from theLate Cretaceous, although some regions are older. Based on the discovery ofPinacosaurus, only known elsewhere in theDjadokhta Formation or regions of the same age, the Wangshi Group was presumed to be a similar age of 75-71 million years old. The specific age for theHongtuya Formation has been identified as 73.5-72.9 mya. As the Hongtuya is directly older than the Jiangjunding, it was identified thatTanius sinensis, a contemporary ofMicropachycephalosaurus, lived in the latestCampanian to earliestMaastrichtian by Borinder in 2015.[9]
The Jiangjunding Formation was deposited in a fluvial to lacustrine environment. The climate was warm and humid during the majority of the timespan, although it was beginning to dry out after the Jiangjunding. Taxa that lived alongsideMicropachycephalosaurus in the formation include theankylosaurPinacosaurus cf. grangeri; thehadrosaurTanius sinensis; intermediatesauropods; intermediatecoelurosaurs; and intermediatecheloniids which show similarities toNanhsiungchelyidae. Multiple localities of dinosaur eggs have also been identified.[9]
Media related toMicropachycephalosaurus at Wikimedia Commons
Data related toMicropachycephalosaurus at Wikispecies
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