"Rock of the Month # 229, posted for July 2020" ---

This genus of reptile, a pachypleurosaur, was first discovered in China in 1957 by the versatile scientist Hu Zhengzhi (1917-2018) and the species is named in his honour. The name of the genus is derived from the old Wade-Giles transliteration Kweichow, the home of the type locality is what is now (pinyin transliteration) known in English as Guizhou province, south China. Guizhou is a landlocked province, south of the Yangtze River's course as it passes Chongqing in Sichuan. Variations in transliteration can be ascribed to the efforts to standardize translation of Chinese scripts prior to the development of the pinyin system in the 1950s.

Keichousaurus is preserved in strata dated to the uppermost Middle Triassic (Ladinian stage) to Upper Triassic (Norian stage, circa 227 to 209 Ma) in China and Mongolia. Its family belongs to a Triassic group of marine reptiles named the sauropterygians. Much early work on Chinese dinosaurs was carried out by famed vertebrate palaeontologist Yang Zhongjian (1897-1979),whose name often appears in anglicized form as Chung Chien Young, or simply C-C Young .

The tiny fossils of this genus, often found as complete skeletons, are understandably popular with collectors, and appear to have spawned a home industry in specimens. They are the smallest known examples of such marine reptiles. With their long necks and elongate heads, these were evidently fish-eating predators. The adorable Keichousaurus hui have been nicknamed the "Guizhou dragon". The samples are from Guanling, southwest of Guiyang in western Guizhou. The adults are some 30 cm long. It has been suggested, from their anatomy, that they may have given birth to live young. Fossils of tiny offspring are as small as 3 cm in length. The number of extant skeletal remains is sufficient that paleobiologists have even been able to make inferences about the population represented in museum collections and publications (Mottani et al., 2015). That study was based on 86 specimens, 27 from a single quarry in Nimaigu village, Xingyi City (Huangcaoba), near the Yunnan border in southwest Guizhou. The authors found that the available sample population was some 60% female, suggesting higher mortality of males. It was inferred that the males tended to have larger, more robust forelimbs. Perhaps, then (with a non-expert eye) we can suggest that the individual in Figure 1 is male, and the one in Figure 3 a female (?). These early marine reptiles became extinct at the end of the Triassic period, though some relatives persisted throughout Mesozoic time.

Fig. 3: a second specimen of Keichousaurus hui.