''Philydrosaurus'' is an extinct genus of

choristodera Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the late Miocene (168 to ...

n which existed in China during the

Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...

''P. proseilus'' was named in 2005. ''Philydrosaurus'' was found from the

Jiufotang Formation The Jiufotang Formation ( Chinese: 九佛堂组, pinyin: ''jiǔfótáng zǔ'') is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see ...

and is slightly younger than ''

Monjurosuchus ''Monjurosuchus'' is a genus of choristoderan reptile that lived in what is now China and Japan during the Early Cretaceous. It has large eyes, a rounded skull, robust legs with short claws, and a long, thin tail. Fossils have been found that ...

'', which was found from the

Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ...

Description

Distinct ridges cover the prefrontal and

postfrontal The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

bones of the skull, distinguishing ''Philydrosaurus'' from related genera. The lower temporal fenestra, usually present as a hole in the back of the skull of choristoderes, is closed by bone in ''Philydrosaurus''. The eye sockets are large and spaced close together, similar to ''Monjurosuchus'' and ''

Lazarussuchus ''Lazarussuchus'' (meaning " Lazarus's crocodile") is an extinct genus of amphibious reptile, known from the Cenozoic of Europe. It is the youngest known member of Choristodera, an extinct order of aquatic reptiles that first appeared in the Midd ...

''. ''Philydrosaurus'' is considered more

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

than these choristoderes because its eyes are not as closely spaced and face laterally rather than dorsally. The skull is similar in shape to that of ''

Cteniogenys ''Cteniogenys'' is a genus of choristodere, a morphologically diverse group of aquatic reptiles. It is part of the monotypic family Cteniogenidae. The type and only named species, ''C. antiquus'', was named in 1928 by Charles W. Gilmore. The h ...

'', the most basal choristodere. The shortness of the skull and the laterally facing eye sockets likely represent the ancestral condition for choristoderes, but the closed lower temporal fenestra links the genus with more advanced forms.

Paleobiology

A skeleton of ''Philydrosaurus'' has been found with associated post-hatchling stage juveniles, suggesting that they engaged in post-hatching

parental care Parental care is a behavioural and evolutionary strategy adopted by some animals, involving a parental investment being made to the evolutionary fitness of offspring. Patterns of parental care are widespread and highly diverse across the animal k ...

Phylogeny

Phylogeny from the analysis of Dong and colleagues (2020):

References

Choristodera Prehistoric animals of China Jiufotang fauna Prehistoric reptile genera {{cretaceous-reptile-stub