Protostegidae

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 from head to tail and 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

Protostegidae is a family of extinct marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest Archelon had a head long. Like most sea turtles, they had flattened bodies and flippers for front appendages; protostegids had minimal shells like leatherback turtles of modern times.

Protostega ('first roof') is an extinct genus of sea turtle containing a single species, Protostega gigas. The species lasted from the Coniacian to the Campanian stages of the Late Cretaceous. Its fossil remains have been found in the Smoky Hill Chalk formation of western Kansas (Hesperornis zone, dated to 83.5 million years ago), time-equivalent beds of the Mooreville Chalk Formation of Alabama and Campanian beds of the Rybushka Formation (Saratov Oblast, Russia). It is also known from rocks in Canada, with these sediments dating to the middle Campanian due to them being found in the Pembina

Desmatochelys (from Greek δεσμός desmos 'link' + χέλῡς khelus 'tortoise') is an extinct genus of sea turtles belonging to the family Protostegidae. This genus contains two known species, D. lowii and D. padillai. D. lowii was first discovered in 1895, followed by D. padillai in 2015. Having been estimated at over 120 million years old, D. padillai is currently the oldest known species of sea turtle.

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 mi

Ocepechelon is an extinct genus of giant protostegid sea turtle known from the Late Cretaceous (late Maastrichtian stage, 67 Myr) of Morocco. The feeding apparatus of Ocepechelon, a bony pipette-like snout, is unique among tetrapods and shares unique convergences with both syngnathid fishes (unique long tubular bony snout ending in a rounded and forward directed mouth) and beaked whales (large size and elongated edentulous jaws).

Rhinochelys is an extinct genus of sea turtles belonging to the family Protostegidae.

Chelosphargis is an extinct genus of sea turtle from Upper Cretaceous of Alabama. Only one species has been described, Chelosphargis advena.

Pneumatoarthrus is an extinct genus of sea turtle known from the Late Cretaceous (early Maastrichtian) Mount Laurel Formation of Monmouth County, New Jersey. Many experts consider Pneumatoarthrus a senior synonym of Archelon. If this classification is correct, it would have reached 4-5 meters in length with a fin span of up to 5 meters, and weighed over 2.3 tons. Only a single species, P. peloreus, is known.