Monotypic prehistoric reptile genera

Terlinguachelys fischbecki is an extinct sea turtle that existed during the Late Cretaceous period some 80 million years ago. It is the sole species in the genus Terlinguachelys and is classified in the family Protostegidae along with other extinct marine turtles.

Santanachelys gaffneyi is an extinct species of sea turtle. It is the only species in the genus Santanachelys, which itself is a member of the extinct family Protostegidae. The species was first described from a 20-centimeter long fossil specimen unearthed in 1998 from the Santana Formation of eastern Brazil. From the rock layer from which it was excavated, it was determined that the specimen was from the Early Cretaceous period (112 million years old). It is therefore one of the oldest known sea turtles. but a new fossil named Desmatochelys padillai in 2015 is estimated to be as old as 120 million years.

Kaganaias (meaning 'Kaga water nymph') is an extinct genus of basal and oldest dolichosaur that lived in what is now Japan during the Early Cretaceous. Kaganaias was semi-aquatic and is the only known aquatic squamate from before the Cenomanian stage of the Cretaceous. It is also the first to be found in an inland area, instead of on the coast where aquatic squamates are commonly found. Its generic name is derived from Kaga Province, the old name for the Ishikawa Prefecture where the specimens were found, while the species name hakusanensis comes from the mountain that gives its name to Hakusan the city near its find site. The geological formation in which the specimens were found, the Kuwajima Formation, stands alongside the Tetori River and has been the site of numerous other finds including molluscs, dinosaurs, fish, and pterosaurs.

Arabemys is an extinct genus of sea turtle. It was first named in 1999, and contains one species, A. crassiscutata. It is known from deposits of Late Paleocene or Early Eocene age near the village of Linah in northern Saudi Arabia (28°44′2″N 43°52′25″E / 28.73389°N 43.87361°E).

Leviathanochelys is an extinct genus of giant sea turtle from the Middle Campanian of northern Spain. Although only known from the rear end of the carapace and the connecting pubic bones, these elements clearly show that they belonged to a turtle of great size, comparable in dimensions to the giant Archelon and Protostega from the Western Interior Seaway of the USA. This makes Leviathanochelys the first giant sea turtle known from Europe and one of the largest known turtles of all time. This great size was evolved independently from the American protostegid turtles and was likely an adaptation to the conditions of the Cretaceous oceans covering much of Europe. Being classified in the superfamily Chelonioidea, Leviathanochelys is likely more closely related to modern sea turtles (families Dermochelyidae and Cheloniidae) than the protostegids, which are thought to be more basal and have a more uncertain relationship to modern sea turtles. Leviathanochelys is thought to have been a pelagic animal. The genus contains a single species, Leviathanochelys aenigmatica.

Archelon is an extinct marine turtle from the Late Cretaceous, and is the largest turtle ever to have been documented, with the biggest specimen measuring 4.6 m (15 ft) from head to tail and 2.2–3.2 t (2.4–3.5 short tons) in body mass. It is known only from the Pierre Shale and has one species, A. ischyros. In the past, the genus also contained A. marshii and A. copei, though these have been reassigned to Protostega and Kansastega, respectively. The genus was named in 1896 by American paleontologist George Reber Wieland based on a skeleton from South Dakota, who placed it into the extinct family Protostegidae. The leatherback sea turtle (Dermochelys coriacea) was once thought to be its closest living relative, but now, Protostegidae is thought to be a completely separate lineage from any living sea turtle.

Proganochelys is a genus of extinct, primitive stem-turtle. Proganochelys was named by Georg Baur in 1887 as the oldest turtle in existence at the time. The name Proganochelys comes from the Greek word ganos meaning 'brightness', combined with prefix pro, 'before', and Greek base chelys meaning 'turtle'. Proganochelys is believed to have been around 1 meter in size and herbivorous in nature. Proganochelys had been known as the most primitive stem-turtle for over a century, until the novel discovery of Odontochelys in 2008. Odontochelys and Proganochelys share unique primitive features that are not found in Casichelydia, such as tooth-like structures on the pterygoid and vomer and a plate-like coracoid.

Melkamter (meaning "winged lizard") is an extinct genus of monofenestratan pterosaurs from the Early Jurassic Cañadón Asfalto Formation of Argentina. The genus contains a single species, M. pateko, known from a partial skull and fragmentary postcranium. Melkamter represents the oldest known monofenestratan pterosaur in the fossil record.

Nipponopterus (meaning "Nippon wing") is a genus of azhdarchid pterosaur that lived during the Turonian and Coniacian ages of the Late Cretaceous period in what is now Japan. Its remains, which consist of a partial cervical (neck) vertebra, were found in the Mifune Group, located in the Kumamoto Prefecture in Kyūshū. It was made the holotype specimen of the genus and type species Nipponopterus mifunensis, named and described by paleontologist Xuanyu Zhou and colleagues in 2025. Nipponopterus represents the first pterosaur to be named from Japan.

Hylonomus (hylo- "forest" + nomos "dweller") is an extinct genus of reptile that lived during the Bashkirian stage of the Late Carboniferous. It is the earliest known crown group amniote and the oldest known unquestionable reptile, with the only known species being Hylonomus lyelli. Despite being amongst the oldest known reptiles, it is not the most primitive member of the group, being a eureptile more derived than either parareptiles or captorhinids.