Tanystropheus hydroides

Adult Tanystropheus hydroides could approach six meters in total body length, with the neck alone accounting for roughly half of that measurement. The neck consisted of only 13 greatly elongated vertebrae, giving it an extreme proportional length relative to the rest of the body.

Tanystropheus hydroides lived during the Middle Triassic period, approximately 240 million years ago. Its fossils have been found in marine deposits in Europe, most notably in the Monte San Giorgio fossil beds on the Swiss-Italian border.

Tanystropheus hydroides is believed to have been a marine or shoreline-dwelling reptile, with fossil evidence and body proportions suggesting it spent significant time in water. Its long neck may have been used for ambush predation from shorelines or shallow-water environments.

Tanystropheus hydroides was distinguished from the smaller Tanystropheus longobardicus by its significantly larger body size and differences in skull and tooth morphology. The species designation was established to separate the large and small forms, which had previously been considered growth stages of a single species.