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Marginocephalia

Marginocephalians
Temporal range: Late Jurassic–Late Cretaceous,
Skull of Triceratops horridus
Skull of Pachycephalosaurus wyomingensis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Neornithischia
Clade: †Cerapoda
Clade: †Marginocephalia
Sereno, 1986
Subgroups

Marginocephalia (/ˌmɑːrdʒənoʊsəˈfæliə/ Latin: margin-head) is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. There are two clades included in Marginocephalia: the thick-skulled Pachycephalosauria and the horned Ceratopsia. All members of Marginocephalia were primarily herbivores (though pachycephalosaurs are speculated to have been omnivorous).[1][2] They basally used gastroliths to aid in digestion of tough plant matter until they convergently evolved tooth batteries in Neoceratopsia (or "new Ceratopsia") and Pachycephalosauria. Marginocephalia first evolved in the Jurassic Period and became more common in the Cretaceous.[3] They are basally small facultative quadrupeds while derived members of the group are large obligate quadrupeds.[4] Primitive marginocephalians are found in Asia, but the group migrated upwards into North America.[5]

Pachycephalosaurs, or "thick-headed reptiles", have primitive features that include basally small sized bodies, obligate bipedalism, and simple teeth with one row in operation at a time that are replaced as they are worn down. As they evolved, pachycephalosaurs evolved much thicker and advanced skull roofs including dome forms with horn-like ornamentation. Some research suggests these domes were used like helmets for protection while head-butting members in intraspecific combat.[6] Some research suggests their necks were not strong enough to support such an impact.[3] Flat-headed pachycephalosaur specimens have been found in Asia, and there is great controversy on the meaning of these flat heads. Recent research suggests the flat heads could be a juvenile state before developing the dome shape in the adult stage. It could also be evidence of sexual dimorphism with the female being more flat-headed.[7][8]

Ceratopsians, or "horned-faces", differ from pachycephalosaurs in the presence of a rostral bone, or beak. They are also known for having a jugal horn and a thin parietal-squamosal shelf that extends back and up into a frill.[9] This frill could have been used for anchoring jaw muscles, as well as for display.[3] The horns were likely used for establishing dominance, or defending territories.[10] It is also possible they were a factor in sexual display and species recognition. One of the basalmost members of this group is Psittacosaurus, which is one of the most species-rich dinosaur genera from Asia. Ceratopsians later evolved into very large quadrupeds with elaborate facial horns such as Triceratops, Styracosaurus, and Centrosaurus. There was no change in richness of species throughout the Cretaceous before the Cretaceous-Paleogene extinction.[11]

  1. ^ "GEOL 104 Marginocephalia: That's Using Your Head!". www.geol.umd.edu. Retrieved 2024-05-14.
  2. ^ Ashley (2020-02-25). "The Real Pachycephalosaurus". Philip J. Currie Dinosaur Museum. Retrieved 2024-05-14.
  3. ^ a b c Fastovsky, David E., Weishampel, David B. (2009). Dinosaurs: A Concise Natural History. New York: Cambridge University Press. pp. 110–132. ISBN 978-0-521-88996-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
  4. ^ Maidment, Susannah C. R.; Linton, Deborah H.; Upchurch, Paul; Barrett, Paul M. (2012-05-22). "Limb-Bone Scaling Indicates Diverse Stance and Gait in Quadrupedal Ornithischian Dinosaurs". PLOS ONE. 7 (5): e36904. Bibcode:2012PLoSO...736904M. doi:10.1371/journal.pone.0036904. ISSN 1932-6203. PMC 3358279. PMID 22666333.Open access icon
  5. ^ Godefroid, Pascal; Lambert, Olivier (2007). "A re-appraisal of Craspedodon llonzeensis DOLLO, 1883 from the Upper Cretaceous of Belgium: the first record of a neoceratopsian dinosaur in Europe?". Sciences de la Terre. 77: 83–93. Retrieved 2016-05-29.
  6. ^ Snively, Eric; Cox, Andres (2008). "Structural Mechanics of Pachycephalosaur Crania Permitted Head-Butting Behavior". Palaeontologia Electronica. 11 (1).
  7. ^ Schott, Ryan K.; Evans, David C.; Goodwin, Mark B.; Horner, John R.; Brown, Caleb Marshall; Longrich, Nicholas R. (2011-06-29). "Cranial Ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria): A Quantitative Model of Pachycephalosaur Dome Growth and Variation". PLOS ONE. 6 (6): e21092. Bibcode:2011PLoSO...621092S. doi:10.1371/journal.pone.0021092. ISSN 1932-6203. PMC 3126802. PMID 21738608.
  8. ^ Horner, John R.; Goodwin, Mark B. (2009-10-27). "Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus". PLOS ONE. 4 (10): e7626. Bibcode:2009PLoSO...4.7626H. doi:10.1371/journal.pone.0007626. ISSN 1932-6203. PMC 2762616. PMID 19859556.
  9. ^ Dodson, P. (1996). The horned dinosaurs: A natural history. Princeton, NJ: Princeton University Press.
  10. ^ Farlow, James O.; Dodson, Peter (1975-01-01). "The Behavioral Significance of Frill and Horn Morphology in Ceratopsian Dinosaurs". Evolution. 29 (2): 353–361. doi:10.2307/2407222. JSTOR 2407222. PMID 28555861.
  11. ^ Farke, Andrew A. (2011-01-20). "Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A". PLOS ONE. 6 (1): e16196. Bibcode:2011PLoSO...616196F. doi:10.1371/journal.pone.0016196. ISSN 1932-6203. PMC 3024410. PMID 21283763.

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