Product Code Database
Marginocephalia ( Latin: margin-head) is a clade of dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. This clade was officially defined in the PhyloCode by Daniel Madzia and colleagues in 2021 as "the smallest clade containing Ceratops montanus, Pachycephalosaurus wyomingensis, and Triceratops horridus". There are two clades included in Marginocephalia: the thick-skulled Pachycephalosauria and the horned Ceratopsia. All members of Marginocephalia were primarily (though pachycephalosaurs are speculated to have been omnivorous). They basally used 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 and became more common in the Cretaceous.Fastovsky, David E., Weishampel, David B. (2025). 9780521889964, Cambridge University Press. ISBN 9780521889964 They are basally small facultative Quadrupedalism while derived members of the group are large obligate quadrupeds. Primitive marginocephalians are found in Asia, but the group migrated upwards into North America.
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. Some research suggests their necks were not strong enough to support such an impact. 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.
, 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. This frill could have been used for anchoring jaw muscles, as well as for display. The horns were likely used for establishing dominance, or defending territories. 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.
Pachycephalosaurs, with their dome-shaped heads, are commonly thought to have used their thick skulls for butting into each other. Their brains and vertebrae are positioned in ways to protect from the impact of head-butting. Also, the columnar structure found in bone remains is consistent with models used to recreate the practice of head-butting. However, some pachycephalosaurs such as Stygimoloch have vascularization in the skull cap that would not have supported head-butting behavior. Thus, the heads could have been used as ornamentation or to butt into the softer flank of other pachycephalosaurs for intraspecific communication or as a form of agonistic behavior.
The frills of ceratopsians are incredibly diverse. They may have been used for protective purposes as the frill sometimes splays over the neck. However, some say that the frill would have provided little protection from other large dinosaurs such as Tyrannosaurus. Other possible functions include intraspecific communication for mating purposes or as a visual display of territorial protection, as seen in many common day organisms such as red-breasted robins. The frills also could have been used for species recognition purposes, as they seem to develop fairly early in life. There has also been evidence that ceratopsians care for their young, as bone-beds have been found of adult individuals with a nest of juveniles, although some refute this as viable evidence of care for young. There have also been bone-beds found with hundreds of adult ceratopsians, indicating herd activity. A few specimens have been found with puncture wounds, supporting the use of horns as protective or combative weapons. Other research examining juvenile ceratopsians reveals a change in horn morphology over time, suggesting frills and horns could have been used for intraspecific communication of age. Horns also could have been used for thermoregulation as indicated by isotope analysis, as aid in knocking down vegetation, or for horn-locking agonistic behavior.
Cladogram after Butler et al., 2011.
|
|
