Tanystropheidae is an extinct family of mostly marine archosauromorph reptiles that lived throughout the Triassic Period. They are characterized by their long, stiff necks formed from elongated cervical vertebrae with very long cervical ribs. Some tanystropheids such as Tanystropheus had necks that were several meters long, longer than the rest of their bodies. Relationships among tanystropheid species have been difficult to resolve because most specimens were flattened during fossilization and are preserved two-dimensionally. Three-dimensional fossils are known from Europe and North America.