| Eichstaettisaurus Temporal range:
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| Type and only specimen of E. schroederi | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Family: | †Eichstaettisauridae |
| Genus: | †Eichstaettisaurus Kuhn, 1958 |
| Type species | |
| †Eichstaettisaurus schroederi (Broili, 1938)
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| Other species | |
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| Synonyms | |
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E. schroederi
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Eichstaettisaurus (meaning "Eichstätt lizard") is a genus of lizards from the Late Jurassic and Early Cretaceous of Germany, Spain, and Italy. With a flattened head, forward-oriented and partially symmetrical feet, and tall claws, Eichstaettisaurus bore many adaptations to a climbing lifestyle approaching those of geckoes. The type species, E. schroederi, is among the oldest and most complete members of the Squamata, being known by one specimen originating from the Tithonian-aged Solnhofen Limestone of Germany. A second species, E. gouldi, was described from another skeleton found in the Matese Mountains of Italy. Despite being very similar to E. schroederi, it lived much later, during the Albian stage. Fossils of both species show exceptional preservation due to deposition in low-oxygen marine environments.
Initially named as a species of the genus Ardeosaurus by Ferdinand Broili in 1938, E. schroederi has had a convoluted taxonomic history. It was initially recognized as a relative of night lizards until research in the 1960s identified it and Ardeosaurus as geckoes. However, phylogenetic analyses conducted in the 1990s suggested that it was closer to the ancestor of all squamates. Various conflicting positions were found until the advent of analyses incorporating more species and better data, which resolved E. schroederi as a close relative of geckoes in the Gekkonomorpha. However, the position of Ardeosaurus in relation to E. schroederi remains uncertain: one species, A. digitatellus, has been recovered as its close relative in some analyses, but the other species A. brevipes has been found to be more distantly related.