Dactylosaurus is a genus of nothosaur in the family Pachypleurosauridae. Along with Anarosaurus, Dactylosaurus was one of the earliest known pachypleurosaurs to come from Europe.[1]
Dactylosaurus comes from the Greek daktulos (δακτυλος), "finger" and sauros (σαυρος), meaning "lizard" or "reptile."
Dactylosaurus was a small reptile measuring up to 50 cm (1.6 ft) long.[2] The nasal bones of Dactylosaurus meet and are broadly structured.[3] The upper temporal fenestra is large and kidney-shaped.[3] There are 17 cervical vertebrae[3] and the cervical ribs have anterior processes.[3] The maxillae of Dactylosaurus extended broadly up the side of the snout.[1]
The holotype specimen (MGUWR WR 3871s) of D. gracilis was only a partial skeleton, consisting of the anterior end alone.[1] Because it differed slightly from the fossils of D. gracilis, it was first thought to belong to the species D. schroederi,[1] which is now considered a junior synonym for juvenile D. gracilis.[3] Once this was established, the juvenile fossil, which was found before the adult fossils, became the holotype. The one limb that was found (a left forelimb), was noted to have a slimmer radius and ulna than Neusticosaurus,[1] a similar nothosaur from Europe.[1] D. gracilis is the smallest known species in its family,[1] which includes the much more recognized Keichousaurus, a nothosaur often remembered for its small size.[4] The original holotype of D. gracilis is considered a juvenile,[3] however the size of a nothosaur when its bones harden is used to show size, making the estimate as smallest member of its family still valid.[1]
Dactylosaurus lived in the Early and Middle Triassic period during the Late Olenekian and Anisian[3] faunal stage, of central Europe.[5]
In terms of geology, they are found: 1) in the uppermost Röt (uppermost Buntsandstein; Lower Triassic): e.g. Michałkowice (Siemianowice Śląskie) and Kamień Śląski, S Poland,[3] (the second location is not sure because Röt is not exposed there), 2) in the lowermost Muschelkalk (Middle Triassic), inter alia in the Gogolin Formation - Gogolin and its vicinity, S Poland.[5][6]