| 词条 | Cyamodontoidea |
| 释义 |
| fossil_range = Triassic | image = Henodus chelyops 1.JPG | image_caption = Fossil of Henodus chelyops in the Staatliches Museum für Naturkunde Stuttgart | taxon = Cyamodontoidea | authority = Nopsca, 1923 }}Cyamodontoidea is an extinct superfamily of placodont marine reptiles from the Triassic period. It is one of the two main groups of placodonts, the other being Placodontoidea. Cyamodontoids are distinguished from placodontoids by their large shells, formed from fused bony plates called osteoderms and superficially resembling the shells of turtles. Cyamodontoids also have distinctive skulls with narrow, often toothless jaws and wide, flaring temporal regions behind the eyes. Two large temporal openings are positioned at the top of the back of the skull, an arrangement that is known as the euryapsid condition and seen throughout Sauropterygia, the marine reptile group to which placodonts belong. Cyamodontoids are also distinguished by their large crushing teeth, which grow from the palatine bones on the roof of the mouth.[1] DescriptionShellThe 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 overly 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.[1] HistoryThe 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.[1] References1. ^1 2 {{cite journal |last=Rieppel |first=O. |year=2002 |title=The dermal armor of the cyamodontoid placodonts (Reptilia, Sauropterygia): morphology and systematic value |journal=Fieldiana |volume=46 |pages=1–41 |url=https://archive.org/details/dermalarmorofcya46riep}} {{Sauropterygia|P.}}{{Taxonbar|from=Q5197357}}{{Triassic-reptile-stub}} 5 : Triassic sauropterygians|Extinct reptiles|Placodontia|Triassic first appearances|Triassic extinctions |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。