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.
Discovery and naming
E. schroederi
In 1938, Ferdinand Broili described an exquisitely-preserved specimen of lizard, preserved top-side-up, from Jurassic-aged rock deposits in the municipality of Wintershof, Eichstätt, Germany. The specimen came into the possession of the Bavarian State Collection of Paleontology and Historical Geology (BSPG), where it was prepared by L. Haimerl. It consists of a nearly-complete skeleton, albeit with a crushed skull, a tail missing the tail after the fifth vertebra (probably the result of amputation and replacement by cartilage), and several vertebrae preserved only as impressions (but their presence could still be verified by the associated ribs). A counterslab to the specimen also exists. Today, the rock deposits are known to belong to the Altmühltal Formation, and the specimen and its counterslab are stored under the accession numbers BSPG 1937 I 1a and 1b.
Although he was unable to examine it first-hand, Broili noted from Christian Erich Hermann von Meyer's description of the type specimen of Ardeosaurus brevipes that it bore similarities to this specimen, but also that they had important differences in snout and frontal bone shape, as well as vertebral counts. However, he hesitated to create a new genus due to the preservational state of the skull. Thus, he assigned it to the genus Ardeosaurus with reservations as a new species, A.? schröderi, named after his colleague J. Schröder. (The current specific name is schroederi: by Article 32.5.2.1 of the International Code of Zoological Nomenclature, umlauts in German names published before 1985 must be deleted and be replaced with an "e" inserted as the next letter.)
Robert Hoffstetter formally recognized the distinction between A.? schroederi and A. brevipes in 1953, and established a new generic name, Broilisaurus. However, Oskar Kuhn had already named a stegocephalian amphibian with the same name in 1938; thus, in 1958, he established another generic name for the species, Eichstättisaurus. (Again, due to the ICZN, the current generic name is Eichstaettisaurus.) In 1963, Marguerite Cocude-Michel opined that E. schroederi really represented the same species as Homoeosaurus digitatellus, which had previously been named as a non-type species of Homoeosaurus in 1914 by N.M. Grier. Thus, she created the new combination Eichstaettisaurus digitatellus.