This list of informally named Mesozoic reptiles is a listing of prehistoric reptiles from the Mesozoic era (excluding dinosaurs) that have never been given formally published scientific names. This list only includes names that were not properly published ("unavailable names") and have not since been published under a valid name. The following types of names are present on this list:

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 International Commission on Zoological Nomenclature. Nomina nuda (the plural form) are invalid, and are therefore not italicized as a proper generic name would be. Nomen manuscriptum, Latin for "manuscript name": A name that appears in manuscript but was not formally published. A nomen manuscriptum is equivalent to a nomen nudum for everything except the method of publication, and description. Nomen ex dissertationae, Latin for "dissertation name": A name that appears in a dissertation but was not formally published. Nicknames or descriptive names given to specimens or taxa by researchers or the press. This list also includes names published in self-published or predatory journals.

A Addyman plesiosaur

The "Addyman plesiosaur" is an informal name given to a leptocleidid plesiosaur specimen (SAM P15980) discovered by the opal miners John and Molly Addyman in 1967 from the Bulldog Shale near Andamooka, South Australia. Assigned to as cf. Leptocleidus sp. in 2007, probably a juvenile Umoonasaurus, this 80% complete skeleton measures long and represents one of the most immature and smallest known plesiosaur specimens. Housed in the South Australian Museum, the "Addyman plesiosaur" is also dubbed "the finest known opalised skeleton on Earth".

African pterosaur

The "African pterosaur" is an informal name given to a pterosaur specimen from the Early Cretaceous of Niger, which was reported by Paul Sereno's team. The specimen is stated to be a partial wing, which is the first known in Africa, and its life-size reconstruction can be seen in the "GIANTS" exhibit in Chicago; although it is unstated which type of pterosaur this specimen belongs to, it is noted to be a piscivore (fish-eater) based on associated teeth material and similar to the pterosaurs known from Brazil of South America, with an estimated wingspan of . The specimen was later shown in the 2-hour National Geographic special program Sky Monsters (2006), which featured its discovery and life-size reconstruction attempt by Sereno's team. In his update entry of the 2000 Expedition of Niger, Sereno mentioned that his team found evidence of a large pterosaur specimen. In his 2000 interview, David Blackburn who participated in that expedition recounted the pterosaur partial wing discovery. He later discussed about the Elrhaz Formation pterosaur specimens in a 2002 conference abstract, stated to be the "only documented pterosaurian appendicular material from Africa", with the left humerus belonging to a tapejaroid and the partial wing belonging to an anhanguerid.

Aktisaurus

"Aktisaurus" (meaning coast or shoreline lizard) is a nomen ex dissertationae created by Hallie Pritchett Street in her PhD thesis as a new genus to contain the species originally named Mosasaurus conodon (specimen AMNH 1380), which has been of uncertain classification since its naming. The phylogenetic analysis of Street did not recover Mosasaurus as a monophyletic genus, and erected several new genera for species previously assigned to Mosasaurus. "Aktisaurus" was recovered as the sister taxon of Plotosaurus as demonstrated by the similar morphology of the carinae on their teeth.

Amblyrhynchosaurus "Amblyrhynchosaurus wiffeni" (meaning blunt-snouted lizard) is a genus and species of nomen ex dissertationae named by Hallie Pritchett Street in her PhD thesis centered on the taxonomy of Mosasaurus. The designated type specimen is NZGS CD 535, which is a mostly complete mosasaurine skull that was discovered in the Maungataniwha Sandstone on the North Island of New Zealand. "Amblyrhynchosaurus" has similar skull morphology to the genus Prognathodon, but it was recovered as the sister taxon of Moanasaurus and a close relative of Mosasaurus. The species epithet is in honor of Joan Wiffen, although the precise spelling is uncertain. It is spelled both as "wiffeni" and "wiffenae" in the text of the thesis.

Antipodenectes "Antipodenectes" (meaning swimmer from the other side of the world) is a nomen ex dissertationae erected by Hallie Pritchett Street in her PhD thesis to contain the species Mosasaurus mokoroa, which was named by S.P. Welles and D.R. Gregg in 1971. In her phylogenetic analysis, Street did not recover M. mokoroa as being within a monophyletic Mosasaurus genus, so named a new genus to contain this taxon. It was recovered as a close relative of Plotosaurus as well as "Aktisaurus". The type specimen is CM Zfr-1, which was discovered in the Conway Formation from the South Island of New Zealand.

Aust Colossus

The "Aust Colossus" is an informal name given to the giant ichthyosaur specimens (BRSMG Cb3869, BRSMG Cb3870, BRSMG Cb4063 and BRSUG 7007) discovered from the Late Triassic (Rhaetian) Westbury Formation at the Aust Cliff. "Aust Colossus" has been tentatively estimated to be even larger than the long ichthyosaur Ichthyotitan from the same formation, possibly over long, though the authors acknowledge that this is a very speculative estimate.

B Batoremys "Batoremys" is a genus of putative macrobaenid turtle from the Early Cretaceous of Mongolia. The intended type species "Batoremys leptis" was never given formal description, so it remains a nomen nudum.

C

Camel turtle The "camel turtle" is an informal nickname given to an un-described species of turtle, as it sports an unusual protruding ridge along the middle of its carapace, as well as due to its Moroccan origin.

Clidastes moorevillensis Clidastes "moorevillensis" is an informal species of mosasaur from the Late Cretaceous Mooreville Chalk Formation of Alabama. First named in a 1975 thesis, it was never given formal description and lacks sufficient diagnostic characters that differentiate it from the dubious Clidastes liodontus.

Cuers ichthyosaur The "Cuers ichthyosaur" is an informal name given to the giant ichthyosaur specimens (MHNTV PAL-1-10/2012 and MHNTV PAL-2/2010) discovered from the Late Triassic (Rhaetian) locality in Cuers, France. It is suggested to be similar to the Autun ichthyosaur specimens (Ichthyosaurus rheticus and Ichthyosaurus carinatus, both of which are nomen dubium) and Ichthyotitan.

Cystosaurus "Cystosaurus" is a genus of putative teleosaur from France informally named by Étienne Geoffroy Saint-Hilaire in 1831. Because it was never given formal description, "Cystosaurus" remains a nomen nudum. Cryptodraco was used as an unnecessary replacement name for Cryptosaurus by Richard Lydekker (1889) who believed the name Cryptosaurus was already previously in use for "Cystosaurus".

H Hadongsuchus "Hadongsuchus" (crocodile of Hadong County) is an Early Cretaceous (Aptian-Albian) crocodyliform from the Hasandong Formation of South Korea. Known from a long complete skull (KIGAM VP 200401) discovered in 2002, it was informally named as "Hadongsuchus acerdentis" in a 2005 thesis. Certain features of the third premaxillary tooth help distinguish it from other related crocodylomorphs. Like other protosuchians, it is believed to have been a fully terrestrial cursorial animal with a semi-erect posture. Lee (2005) suggested that "Hadongsuchus" and three other crocodyliforms (Shantungosuchus, Sichuanosuchus, and Zosuchus) comprise a new family which represents a sister taxa to the Protosuchidae, with Zosuchus being the closest relative.

Hainosaurus boubker

Hainosaurus "boubker" is an informal species of mosasaur from the Sidi Chennane phosphate quarry in Morocco. The genus Hainosaurus is generally regarded as a synonym of Tylosaurus. In 2025, Bardet and colleagues tentatively recognized H. "boubker" as a valid member of the Tylosaurinae pending more complete specimens; it has been noted that, following ICZN recommendations, the specific name should have been "boubkeri", as it honors Mr. Boubker Chaibi, the discoverer of the specimen. The intended syntype was purportedly reposited in the "Paleontological Museum of the Vancouver Paleontological Society," but Zietlow et al. (2026) were unable to locate the specimen first hand due to the museum being non-existent, indicating that the initial description of this supposed taxon does not conform to ICZN article 72.10 and recommendation 16C; they further argued that the syntype of H. "boubker" is undiagnostic and cannot be distinguished from other tylosaurines, rendering its binomen as a dubious name.

Hitachinaka-ryu "Hitachinaka-ryu" (ヒタチナカリュウ) is the nickname give to single bone of fossil reptile (INM-4-15300) from Campanian-Maastrichtian Nakaminato Group, Ibaraki Prefecture, Japan. It was originally identified as a right scapula of a pterosaur, but it is later re-identified as the right humerus of a trionychid turtle with estimated carapace length around . It has been renamed as "Hitachinaka-oosuppon" in 2021.

Hobetsu-araki-ryu "Hobetsu-araki-ryu", or "Hoppy" is the nickname given to an elasmosaurid plesiosaur (HMG 1) from early Campanian Yezo Group, Hokkaido, Japan. It is known from a considerable number of postcranial materials, although not enough to identify at lower taxonomic levels.

I Induszalim "Induszalim" is an informal genus of crocodyliform named by M.S. Malkani based on fragmentary remains found in the Vitakri Formation of Pakistan in 2005. The proposed type species, "Induszalim bala", was named in a 2014 conference abstract, rendering this name a nomen nudum. A rostrum discovered around 2001 was referred to the theropod dinosaur "Vitakridrinda sulaimani" by Malkani (2006), but it was later referred to "Induszalim" by Malkani (2015a).Malkani M.S. (2015a). Terrestrial mesoeucrocodiles from the Cretaceous of Pakistan. In: Zhang Y., Wu S.Z., Sun G. eds., abstract volume, 12th Symposium on “Mesozoic Terrestrial Ecosystems (MTE 12), and 3rd Symposium of International Geoscience Program (IGCP 608) “Cretaceous Ecosystem of Asia and Pacific” 15–20 August 2015, Paleontological Museum of Liaoning/Shenyang Normal University, Shenyang, China, 242-246.

K

Kaosaurus "Kaosaurus" is an informal genus of turtle from Maastrichtian Mt Indamane (Mont In Daman) site in Niger. It is described in Michaut (2002), but it is not considered as valid under ICZN rules. Michaut described a species of Stratodus ("S. indamanensis") and smaller relative "Ministratodus" from same site, which are also doubtful.

Khuzdarcroco "Khuzdarcroco" is an informal genus of purported mesoeucrocodylians proposed by M.S. Malkani in a 2015 conference abstract based on a rib fragment from the Goru Formation of Pakistan. The proposed type species is, "Khuzdarcroco zahri".

Kitadani goniopholidid

The "Kitadani goniopholidid", also called as "Tetori-wani" (テトリワニ, "Tetori crocodile") is a goniopholidid crocodyliform known from Kitadani Formation of Japan. Nearly complete skeleton was discovered in 1982, which is the first vertebrate record from Kitadani Dinosaur Quarry. Partial materials described in 2024 are likely to belong to the same taxon.

L

Likhoelesaurus