What is the main relationship among archosauria, diapsida, and reptilia clases?

Archosauria (the "ruling reptiles") is a major group of diapsids, differentiated from the other diapsids by the presence of single openings in each side of the skull, in front of the eyes (antorbital fenestrae), among other characteristics. This continues the tetrapod trend of the reduction of skull bones by the fusion of multiple bones and the opening of fenestrae in the skull. This helps to lighten the skull, provides more room for muscles and other tissues, and allows more skull flexibility (kinesis) when eating. Other typical archosaurian characteristics include another opening in the lower jaw (the mandibular fenestra), a high narrow skull with a pointed snout, teeth set in sockets (called thecodont tooth implantation), and a modified ankle joint.

Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period.[1] The diapsids are extremely diverse, and include all crocodilians, lizards, snakes, tuatara, turtles, and birds.[2] Although some diapsids have lost either one hole (lizards), or both holes (snakes and turtles), or have a heavily restructured skull (modern birds), they are still classified as diapsids based on their ancestry. At least 7,925 species of diapsid reptiles[3] exist in environments around the world today (nearly 18,000 when birds are included).

Reptilia, presented as a Class in our classification, includes turtles (Testudines), snakes and lizards (Lepidosauria), crocodiles and their relatives (Crocodilia), and birds (Aves), as well as a number of extinct groups.

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the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

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your spelling is a little off : ]