Protostega

Genus of reptiles

Protostega ('first roof')), time equivalent beds of the Mooreville Chalk Formation of Alabama and Campanian beds of the Rybushka Formation (Saratov Oblast, Russia). Fossil specimens of this species were first collected in 1871, and named by Edward Drinker Cope in 1872. With a total length of , it is the second largest sea turtle that ever lived, second only to the giant Archelon,

The first known Protostega specimen (YPM 1408) was collected on July 4 by the 1871 Yale College Scientific Expedition, close to Fort Wallace and about 5 months before Cope arrived in Kansas. However the fossil that they found was never described or named.

The Late Cretaceous was marked by high temperatures, with large epicontinental seaways. During the Mid to Late Cretaceous period the Western Interior Seaway covered the majority of North America and would connect to the Boreal and Tethyan oceans at times. Within these regions are where the fossil of Protostega gigas have been found.

Protostega is known to have reached up to in length. Cope's Protostega gigas discovery reveled that their shell had a reduction of ossification that helped these huge animals with streamlining in the water and weight reduction. The carapace was greatly reduced and the disk only extending less than half way towards the distal ends of the ribs. Cope described other greatly modified bones in his specimen including an extremely long coracoid process that reached all the way to the pelvis and a humerus that resembled a Dermochelys. Creating better movement of their limbs. Skull Structure: Edward Cope described the uniqued Protostega gigas to have a large jugal that reached to the quadrate along with a thickened pterygoid that reached to the mandibular articulating surface of the quadrate. The fossil featured a reduction in the posterior portion of the vomer where the palatines meet medially. The premaxillary beak was very shorter than that of Archelon.

Examining the bone tissue microstructure (osteohistology) of the Protostega revealed growth patterns similar to modern leatherback sea turtles with rapid growth to large body size. Leatherbacks don't have a typical reptile metabolism, since they have high resting metabolic rates and can hold a body temperature higher than their surroundings. If Protostega had similar bone growth patterns to leatherbacks, it is hypothesized that they both had a similar metabolism. This rapid growth to adult body size in sea turtles would also indicate rapid growth to reproductive maturity, which would have been a great advantage in their survival. However, comparing Protostega to its more basal relative Desmatochelys shows that not all protostegids had the same growth patterns. This indicates that rapid growth to large size evolved late within the lineage, perhaps in response to the evolution of large mosasaurs like Tylosaurus. Given uncertainties in the phylogenetic placement of protostegids relative to living sea turtles, it is unclear if the evolution of rapid growth rates and possible elevated metabolism were convergent with modern leatherbacks or if the two were more closely related.