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 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.
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.
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