Protostegidae

Protostegids Temporal range: Early Cretaceous-Late Cretaceous,120–70 Ma PreЄ Є O S D C P T J K Pg N
Life restoration of Archelon ischyros
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Testudines
Suborder:	Cryptodira
Clade:	Americhelydia
Clade:	Pandermochelys
Family:	†Protostegidae Cope, 1872
Type species
†Protostega gigas Cope, 1872
Genera
†Archelon † †Calcarichelys †Chelosphargis † † † †Protostega †Rhinochelys †Santanachelys †Terlinguachelys

†Archelon
†
†Calcarichelys
†Chelosphargis
†
†
†
†Protostega
†Rhinochelys
†Santanachelys
†Terlinguachelys

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 a meter long. Like most sea turtles, they had flattened bodies and flippers for front appendages; protostegids had minimal shells like leatherback turtles of modern times.

As some of the first marine turtles, the protostegids set the general body plan for future species of sea turtles. They had a generally depressed turtle body plan, complete with four limbs, a short tail, and a large head at the end of a relatively short neck. Like other sea turtles, they possessed oar-like front appendages especially evolved for swimming in the open ocean. Similar to the still-extant, possibly closely related Dermochelyidae, protostegids possessed extremely reduced carapaces. Some specimens had skeletal protrusions from their ribs almost wrapping around their bodies in place of a complete shell. Like modern sea turtles, protostegids had sharp beaks. One of the defining characteristics of the members of the family was their almost-disproportionately large heads. Specifically, some specimens of Archelon have been found with heads a meter long. In addition, the members of the family had somewhat reduced plastrons, as well.

While all members of the family are extinct, palaeoecological studies on the members of the family have provided some insight into the ecological roles of the Protostegidae. Analysis of fossil organs of some protostegids has revealed entire stomachs containing fossilized shellfish. The turtles, in turn, are postulated to have been preyed upon by the major predators of the time. Fossil protostegids have been found with tooth impressions from the large lamnid sharks of the time. Two specimens of Protostega gigas have been discovered to have tooth marks from large sharks. In addition, teeth of the extinct shark Cretoxyrhina mantelli have been found embedded in at least one Protostega skeleton.

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Wikipedia