List of marginocephalian type specimens

This list of specimens is a comprehensive catalogue of all the type specimens and their scientific designations for each of the genera and species that are included in the clade marginocephalia. Marginocephalia is a clade of ornithischian dinosaurs that includes some of the most well-known Mesozoic animals, such as Triceratops and Pachycephalosaurus. The group is united by, and is named for, the presence of a bony margin formed mostly from the parietal and squamosal bones at the posterior end of the skull. Although the first marginocephalian known to scientists, Agathaumas, was described in 1872 by Edward Drinker Cope, the clade itself was not recognized until the latter part of the 20th century when Paul Sereno first united the two major groups, ceratopsians and pachycephalosaurians into a single clade.

Marginocephalians first appeared in the Jurassic period as small bipedal animals. However, they saw an apparent increase in diversity during the Early Cretaceous period which culminated in the emergence of megafaunal forms by the end of the period that weighed in excess of five metric tons. Most of their diversity is known from North America and Asia, with a few remains attributed to the group from Europe, South America, and Australia.

Scope and Terminology
This list will include the type fossils of each marginocephalian species. In paleontology, a type specimen is one which is definitionally a member of a biological taxon. Additional specimens can only be "referred" to these taxa if an expert deems them sufficiently similar to the type and publishes that opinion in the scientific literature.

There is no complete, canonical list of all dinosaur taxa or holotype specimens. Attempts are regularly published in the form of books, such as the Princeton Field Guide to Dinosaurs by Gregory Paul and Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages by Thomas Holtz and Luis Rey. Where appropriate, The Paleobiology Database and |The Fossilworks, which are both online databases of named fossil taxa, are used to supplement the entries from published encyclopedias which are missing or data-deficient.

This list will also be updated regularly as new scientific descriptions are published and new taxa are named. The most recently named marginocephalian is Lokiceratops rangiformis, which was named in June 2024 by Mark Loewen, Joseph Sertich, Scott Sampson, Jingmai O’Connor, Savhannah Carpenter, Brock Sisson, Anna Øhlenschlæger, Andrew Farke, Peter Makovicky, Nick Longrich, and David Evans.

Type System
Types are also used to diagnose higher-level taxa than an individual. One individual might represent the "type specimen" of a particular species. This species would in turn represent the "type species" of a particular genus, unless it is referred to a previously described genus. Most dinosaur genera are monospecific, therefore most type specimens are also the type species of their respective genera. On this list, the type species of a genus is only noted when it belongs to a genus with multiple referred species, such as Psittacosaurus or Chasmosaurus. Furthermore, when an animal is different enough from its close relatives that it is given its own family, it is conventional in dinosaur systematics to name a family after the first described, most famous, or most abundant genus assigned to it. Therefore, on this list, the type species of any type genus for a family or sub-family level taxon is also noted when appropriate.

There are several different varieties of type specimen when referring to fossil animals:
 * Holotype: This is the most common and simplest form of type specimen. A holotype is the first material of a fossil specimen that is described in the scientific literature. In order to qualify as a true holotype, all of the fossils of the type must belong to the same individual animal. All type specimens on this list are holotypes, unless otherwise indicated.
 * Paratype(s): These are described in the same publication as the holotype. A paratype is designated when the fossil material is diagnostic enough to belong to the same species as the holotype, but it is not from the same individual animal. In these cases, the holotype and paratype(s) are collectively called the "type series" for that taxon. On this list, paratypes are noted in the same entry as their associated holotype.
 * Neotype: When a holotype specimen is lost, destroyed, or otherwise unable to be studied further by scientists, a new type specimen for that taxon is required in order to identify future material. On this list, neotypes are only given their own entries when the holotype was never formally given a specimen number, otherwise they are noted in the entry for the holotype.
 * Syntype(s): This is a type series in which no single specimen is selected to serve as a holotype, nor are any designated as paratypes. This is typically done if the fossil material is believed to be from multiple animals, but none of the individual animals were well-preserved enough to provide a complete list of diagnostic characters. These are also sometimes called "cotypes" in publications, although this is discouraged by the ICZN.
 * Lectotype: When a single type specimen from a series of syntypes is designated as the new primary type specimen in a subsequent publication, this is considered to be a lectotype. On this list, lectotypes are given their own entries.
 * Paralectotype(s): When a lectotype is designated from a series of syntypes, the remaining syntypes become paralectotypes as part of a reorganized type series. On this list, paralectotypes are noted alongside the list entry for the lectotype of their respective series.
 * Plastotype: Sometimes, if a cast of a type specimen is made and the original type specimen is lost or destroyed, the cast can be used for the purposes of diagnostic referral to a taxon. Plastotypes are only given their own entries on this list if the holotype was not given a specimen number. Otherwise, they are noted alongside the entry for the holotype.

All name-bearing type specimens (i.e. holotypes, lectotypes, neotypes, and syntypes) have unique entries on this list, and non-name-bearing types (i.e. paratypes, paralectotypes, and topotypes) are noted alongside their name-bearing counterpart.

Validity
Some described species are later determined to be invalid by subsequent scientific publications. However, invalid species are sometimes resurrected, such as in the case of Brontosaurus, and sometimes the validity of a species can be controversial among researchers (e.g. the case of Torosaurus and Triceratops ). For the purposes of neutrality and completeness, all described species and genera of marginocephalians are included, even those that have been subsequently considered invalid by subsequent scientific publications.

Naming conventions and terminology follow the International Code of Zoological Nomenclature (ICZN). Technical terms used include:
 * Junior synonym: A name which describes the same taxon as a previously published name. If two or more taxa are formally designated and the type specimens are later assigned to the same taxon, the first to be published (in chronological order) is the senior synonym, and all other instances are junior synonyms. Senior synonyms are generally used, except by special decision of the ICZN, but junior synonyms cannot be used again, even if deprecated. Junior synonymy is often subjective, unless the genera described were both based on the same type specimen.
 * Nomen dubium (Latin for "dubious name"): A name describing a fossil with no unique diagnostic features. This can be an extremely controversial designation, and as such, they are only notated when their supposedly dubious status has been formally published. Furthermore, if the scientific community has yet to reach a consensus on the validity of a name or taxon, the ongoing nature of the controversy will be stated.
 * Nomen nudum (Latin for "naked name"): A name that has appeared in print but has not yet been formally published by the standards of the ICZN. Nomina nuda (the plural form) are invalid, and are not included on this list.
 * Preoccupied name: A name that is formally published, but which has already been used for another taxon. This second use is invalid (as are all subsequent uses) and the name must be replaced.

Omissions
Some taxa of marginocephalians are not included on this list. Nomina nuda are not included because a type does not become recognized by the ICZN until it is published in a scientific journal with a full description.

Some misidentified taxa are also not included so long as there is a scientific consensus with regard to the specimen in question. If a specimen is later referred to a taxon outside marginocephalia, it is not included on this list. However, specimens that are identified as marginocephalians in publications subsequent to their initial description are included under the name they are given within marginocephalia. For example, Pachycephalosaurus was originally described as a species of the theropod genus Troodon. This is noted where appropriate, but there is no entry on the list under the name Troodon wyomingensis because the specimen itself is now referred to a taxon within marginocephalia.

Referred taxa are only included on the list as separate entries when their initial description includes a unique type specimen (e.g. Triceratops obtusus or Dracorex hogwartsia).

List of Specimens

 * Binomial name: All animals species are given a unique binomial name, typically consisting of Latin or Greek words which are used to formally and scientifically identify each species.
 * Catalogue number: In most museum collections, each fossil specimen will be given a unique catalogue number which is published with the description of the fossils after they are prepared. This serves as a formal name for every single described fossil so that authors are able to refer to individual fossil discoveries in the scientific literature by name.
 * Institution: Most published fossils are stored in museum collections or at universities. This is also true of type specimens, many of which are on display in museums around the world. If a type specimen has been lost, the last known location of the type is listed.
 * Age: The geological stage from which the specimen was recovered is listed, when it is known. The exact age of some geological formations is not known. If this is the case, a range of possible ages is given.
 * Unit: Most fossils are recovered from named geologic formations (e.g. the Morrison Formation or the Hell Creek Formation). When this is not the case, a city or landmark near the locality from which the fossil was recovered is listed.
 * Material: The vast majority of fossils do not preserve the complete skeleton of an animal. In these cases, the specific bones which are fossilized have been listed.
 * Notes: Other general information, such as the validity status of the taxon in question, or any other material in the type series may be listed here.