Eichstaettisaurus

Skull

Eichstaettisaurus can be identified by depressed skulls with short, blunt, and rounded snouts. E. schroederi has large nostrils. The tooth-bearing bones of the snout, the uniquely paired premaxilla and the maxilla, were likely connected by a band of soft tissue in E. schroederi. The maxilla has approximately 22 teeth in E. schroederi,^[1] and at least 30 in E. gouldi.^[2] The teeth of both species are small, narrow, conical, and single-cusped; they were fused to the inner side of the jawbone, or pleurodont. Like Ardeosaurus, the lacrimal bone of the eye socket is absent. Also in the eye socket, the postfrontal and postorbital bones are separate elements as opposed to Ardeosaurus, and the rear process of the postorbitals are relatively wide. In E. schroederi, the contact between the latter two bones is unusually far forward compared to most lizards. A rearward-projecting spur or process is missing on the jugal bones of both species. Like most other lizards, the squamosal bones are slender and project downwards to meet the quadrate bones; unlike the Iguania and Teiidae, however, they lack upward processes.^[1][2]

Unlike A. brevipes, E. schroederi lacks bone ornamentation and osteoderms on the skull roof. In both Eichstaettisaurus species, the frontal bones are fused, narrow between the eye sockets (to 25% of the rear of the bone in E. schroederi, and to 20% in E. gouldi), and widen again at the front; they also have well-developed subolfactory processes. The suture between the frontal and parietal bones is slightly convex in E. schroederi and slightly concave in E. gouldi, differing from Ardeosaurus. Unlike E. gouldi and most other lizards, E. schroederi has paired, unfused parietals. The parietals of both species lack rear processes and nuchal fossae. In E. schroederi, the outer edges of the parietals are emarginated, and the supratemporal processes at the rear are short, widely-separated, and bear fossae. On the palate of E. schroederi, the ectopterygoid bones overlap the pterygoid bones at their rear, as in Diploglossus and the gecko Coleonyx. Also in E. schroederi, a pair of crests are present on the supraoccipital bone, likely a result of reduced ossification due to its small size; they are also present in Feylinia, Coleonyx, and Hoplodactylus.^[1][2]

Vertebrae and ribs

Compared to most iguanian, gekkotan, and scincomorphan lizards, which generally have 24-26 vertebrae in front of the sacrum (i.e. presacral vertebrae), E. schroederi has 31, including 7 cervical vertebrae and approximately 24 dorsal vertebrae.^[1] (E. gouldi has 6-7 cervicals, and an unknown number of dorsals;^[2] A. brevipes has 23 presacrals, and A. digitaellus has 27.^[1]) In E. gouldi, the second (axis) and third cervicals are connected to the succeeding vertebra by elements known as intercentra.^[2] In E. schroederi, most of the cervicals do not have cervical ribs, save for the last two. The dorsals have small neural spines, and the last few seem to lack ribs altogether, in the vein of lumbar vertebrae. Zygosphene-zygantrum articulations are present on the dorsals of both species. The ribs are single-headed and have circular articulations.^[1] In E. gouldi, the centra ("bodies") of the caudal (tail) vertebrae are broad, cylindrical, amphicoelous (concave on both ends), and bear strong transverse processes.^[2] Most of the tail in the type specimen of E. schroederi has been replaced by cartilage, having been amputated.^[1]

Limbs and limb girdles

Eichstaettisaurus is characterized by a well-developed acromion process on the scapula, or shoulder blade. The clavicles of E. schroederi do not curve forward, unlike most members of the Autarchoglossa, and also lack rear processes unlike Mabuya and Gerrhosaurus. As in Ardeosaurus, both species of Eichstaettisaurus had relatively stout forelimbs.^[1][2] In E. schroederi, the olecranon process of the ulna is well-developed.^[1] In E. gouldi, the carpal bones were likely incompletely ossified.^[2] The five-digited hand of E. schroederi bears 2, 3, 4, 5, and 3 phalanges on each digit; the penultimate phalanges are relatively long compared to the other phalanges.^[1] E. gouldi appears to have 4 phalanges on the fourth digit, and its claws are short, deep, and sharp, with well-developed flexor tubercle processes.^[2]

In the pelvis of E. schroederi, the expansion of the pubes into the fused pubic apron is relatively narrow; the pubes also lack the forward processes known as the pubic tubercles. The ischia are enlarged and contact each other extensively. The rear expansion of the blade of the ilium is long. The hindlimbs of both Eichstaettisaurus species are also stout, and similar in length to the forelimbs. The femur has a straight shaft, unlike most other lizards where it is sigmoidal. Among the metatarsal bones, the fifth is unusual in that it is short and hooked. In E. schroederi, the foot is also five-digited, with 2, 3, 4, 5, and 4 phalanges on each digit; the penultimate phalanges are also elongated, and the claws are similar as well. Two features are shared by E. schroederi and Gekko gekko: the claws have expansions at their bottom ends; and the articulations between phalanges consist of simple concave-convex joints, instead of bicondylar (i.e. based on two condyles at the end of the phalanx) articulations, which sets them apart from most other lizards.^[1][2]