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Species of lizard

Speciesbox
| name = Chinese crocodile lizard
| status = EN
| status system = IUCN3.1
| status ref = A rare and little studied lizard, it is listed in CITES Appendix II, which regulates international trade of specimens. It is the only living member of Shinisauria, a clade of lizards whose fossil record extends back to the Early Cretaceous, over 120 million years ago.

Chinese crocodile lizards are characterized by their green, colored with reddish necks. They often have alternating bands of light and dark patterns. Male Chinese crocodile lizards are more common than females, especially during the breeding season. On average, these lizards are 40 46 cm (16 18 in) long. Perhaps the lizards' most distinctive features are the rows of bony scales down its back and muscular tail, imitating those of a crocodile. Additionally, Chinese crocodile lizards are sexually dimorphic and can be distinguished visually. Adult males are larger and more colorful than females, with their color intensifying during the breeding season.

The composition of gut microbiota is associated with the lizard's metabolism and health. For the Chinese crocodile lizard (as an endangered species), the gut microbiota is an area of concerned study and interest; greater understanding of their diet and dietary functions help contribute to a more stable international, and (ultimately) wild, population. With Chinese crocodile lizards of different ages, there are minimal differences between the adult and juvenile lizards' gut microbial composition; the young will typically seek out the smallest invertebrates they can find, from larvae and young of beetles to spiders, small flies and ants. For mature animals, the crocodile lizards consume prey opportunistically, from earthworms, centipedes, millipedes, and beetles to the larvae from Lepidoptera. Female crocodile lizards have a preference for larval beetles and earthworms, especially during breeding seasons. Within the gut microbiota population, Bacillota and Pseudomonadota are the main microbiota found in the Shinisaurus crocodilurus. These two gut microbes are important across vertebrates and, for crocodile lizards, it benefits and aids in the species' metabolism, environmental information processing, genetic information processing and cellular processing.

In China, Shinisaurus crocodilurus is known to feed on both vertebrates and invertebrates. They are "sit and wait" predators, perched on branches near streams until prey items are sighted. Invertebrates include both terrestrial groups (worms, spiders, katydids, etc.) and aquatic shrimp. Vertebrate prey includes tadpoles, small fish, and occasionally frogs and lizards. The Vietnamese subspecies prefers terrestrial invertebrates, such as cockroaches, crickets, and particularly earthworms. Vertebrates are not known to be part of their diet. They will widen their mouths to establish dominance, which is known as gaping. The frequency of which Shinisaurus crocodilurus gape is thought to establish a dominant subordinate social structure to their conspecifics. Similar to other lizards like Dipsosaurus dorsalis or Tropidurus spp., the Chinese crocodile lizards would also swing their tails and lunge at their competitors. The dominant lizard will lunge and whip its tail, without force, at the subordinate lizard. The result of this is often little to no physical harm done to the subordinate. However, the subordinate lizard will retreat from the dominant's territory. Another interesting dominance establishing behavior for Shinisaurus crocodilurus is push up behavior. The lizard would straighten its forelimbs and level the head. Unlike other lizards, the Shinisaurus crocodilurus would only perform this push up motion with its anterior portion. While they were doing push ups, Shinisaurus crocodilurus would sometimes bob their head in a circular motion. Female crocodile lizards are able to breed annually. Courtship often begins at the end of winter and breeding often occurs in the summer season, mainly July and August. Pre copulation for the Shinisaurus crocodilurus often begins with the adult male appearance changing to a more vibrant coloration.

Surviving subpopulations of Chinese crocodile lizards primarily occupy isolated fragments of land in Guangxi and Guandong provinces of southeastern China. The Vietnamese subspecies is only found on Yên Tử Mountain in Quảng Ninh and Bac Giang provinces of northeastern Vietnam. Shinisaurus crocodilurus live alongside clear streams within subtropical broadleaf evergreen forests. They have a habitual preference for remote streams in undisturbed areas such as mountain ridges and dense forests. The species lives in a relatively cool, monsoonal climate at moderately high elevations, 200 1,500 meters (656 4,921 feet) above sea level. Their preference to occupy less dense habitat is in line with their antipredator trajectory towards flight rather than fight. Shinisaurus crocodilurus utilize tree holes, rocks, vegetated perches as shelter and are rarely found exposed on the forest floor. Its specific name – like the separate genus Crocodilurus – means "crocodile tail".

Shinisaurus was once also regarded as a member of Xenosauridae, but most recent studies of the evolutionary relationships of anguimorphs consider Shinisaurus to be more closely related to monitor lizards and helodermatids than to Xenosaurus. It is now placed as the only living member of the clade Shinisauria within the Anguimorpha. The fossil record of Shinisauria extends back to the Early Cretaceous, over 120 million years ago, with fossils being known from Asia, Europe and North America.

A 2008 study, based on a 2004 survey, estimated that 950 crocodile lizards were left in China, split into eight isolated subpopulations. The largest subpopulation, with around 350 individuals, represents 36% of the entire population in China. A 1978 survey estimated the presence of 6,000 individuals, while a 1990 survey estimated around 2,500 individuals in the entirety of China. This points to severe population decline, on the order of 70 90% per subpopulation, in the 1978 2004 period. Five subpopulations appear to have been extirpated, including the only sites known from Hunan province. The smallest surviving subpopulations are likely unsustainable due to a lack of genetic diversity. Habitat loss will be amplified by climate change: one model argues that forest habitats with a climate suitable for the Chinese subspecies will be eliminated by 2080. The species was introduced into the international pet trade in the 1980s, with exports increasing to several hundred per year by the late 1980s. Population decline linked to increasing exports led to the species being listed on CITES Appendix II in 1990. In 1990, export listings abruptly shifted to the claim that sold individuals were captive bred. However, most exported specimens were likely illegally harvested, as the number of exports has sharply increased with demand despite a lack of evidence for breeding facilities among sellers. The relative number of observed adults in the Vietnamese population sharply declined from 2013 to 2015, even as new sites were discovered. This trend is consistent with illegal collection, as the Vietnamese subspecies was introduced into the pet trade around the same time. In some cases, the number of traded animals approaches or exceeds the wild population estimate, suggesting the presence of undiscovered subpopulations known only to collectors. Isotope analyses have shown that the scales of captive bred individuals are enriched in Carbon 13 and Nitrogen 15, likely a result of being fed with protein loaded feeding insects. This forensic technique may help to differentiate true captive bred individuals from wild caught lizards which are merely labelled as captive bred.