Protostega is known to have reached up to 3 meters 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.
Another fossilized specimen showed a bony extension, that would have been viewed as a beak, was lacking in the Protostega genus.
The premaxillary beak was very shorted then Archelon.
In front of the orbital region was elongated with broadly roofed temporal region.
The jaws of the fossil showed a large crushing -surfaces.
The quadrato-jugal was triangular with a posterior edge that was concave and the entire bone was convex from distal view.
The squamosal appeared to have a concave formation on the surface at the upper end of the quadrate.
In Cope's fossil the mandible was preserved almost perfectly and from this he recorded that the jaw was very similar to the Chelonidae and the dentary had a broad for above downward with a concave surface, marked by deep pits in the dentary.

Cope concluded that these animals were most likely omnivores and consumed a diet of hard shelled crustacean creatures, due to the long symphysis of its lower jaw.
Along with probably consisted of seaweed and jellyfish or scavenged on floating carcasses as well, like modern turtles.
Protostega is known to have reached up to 3 meters 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. Another fossilized specimen showed a bony extension, that would have been viewed as a beak, was lacking in the Protostega genus. The premaxillary beak was very shorted then Archelon. In front of the orbital region was elongated with broadly roofed temporal region. The jaws of the fossil showed a large crushing -surfaces. The quadrato-jugal was triangular with a posterior edge that was concave and the entire bone was convex from distal view. The squamosal appeared to have a concave formation on the surface at the upper end of the quadrate. In Cope's fossil the mandible was preserved almost perfectly and from this he recorded that the jaw was very similar to the Chelonidae and the dentary had a broad for above downward with a concave surface, marked by deep pits in the dentary.
Cope concluded that these animals were most likely omnivores and consumed a diet of hard shelled crustacean creatures, due to the long symphysis of its lower jaw. Along with probably consisted of seaweed and jellyfish or scavenged on floating carcasses as well, like modern turtles.
Protostega