Cyamodontoidea
- 1 min read
- 2 chapters
Explore on Lably
ToursExplore Lably’s 3D toursDescription
Shell
The shells of cyamodontoids differ from those of turtles in several ways. Turtle shells are fused to their skeletons in several regions, including the vertebrae, ribs, gastralia (belly ribs), and pectoral girdles, but cyamodontoid shells overlie skeletal bones without any fusion. Turtle shells are also composed of two layers of osteoderms, while cyamodontoid shells only have one layer. Cyamodontoids typically have more osteoderms forming their carapaces and plastrons (upper and lower shells) than do turtles, and the osteoderms have less well-defined shapes than the geometric scutes of turtles.
Sign in to keep reading
One more chapter is free with a Lably account.
History
The division of placodonts into two groups was first proposed in 1863 by German paleontologist Christian Erich Hermann von Meyer, who named Macrocephali ("large skulls") and Platycephali ("flat skulls"). Macrocephali would later be known as Placodontoidea, and Platycephali would later become Cyamodontoidea. Complete skeletons of placodonts were not known at the time of von Meyer's proposed classification, and the large shells of cyamodontoids were unknown.