|Reproduction||Sexual; lays eggs|
|Prey||Unspecified species of shiny insect|
|Genus||Geiseltaliellus (Oskar Kuhn, 1944)|
|Species||grisolli (Augé, 2005)|
lamandini (Filhol, 1877)
longicaudus (Kuhn, 1944)
maarius (Smith, 2009)
Geiseltaliellus were a genus of iguanian lizards that lived during the Eocene, formerly indigenous to what is now western Europe. Three of the known species —G. grisolli, G. lamandini, the holotype G. longicaudus—are known to have resided in Belgium and France, while G. longicaudus is also found in Geiseltal Valley, Germany, while the only other known species, G. maarius, is instead found in Messel, Germany.
Geiseltalielluses were very similar in internal structure to both the helmeted basilisks and the basilisk lizards, to the extent that G. maarius even possessed a similar prominent crest to that of the basilisk lizards. Their scale pattern was similar to modern day corytophanids too, with large scales covering the top of the skull, smaller overlapping scales covering most of the body, and wide scales covering the toes. Like iguanas their tail was very long in proportion to their body size; while it is common for the various corytophanids to have long tails when compared to other lizards, that of the Geiseltalielluses was much longer proportionately than even those of their cousins—between 2 to 3 times the length of the rest of their body.
Their limbs were typical of corytophanids in that the hind limbs are long and the forelimbs are short, adaptations that may have made Geiseltaliellus an effective jumper and sprinter like the living basilisk lizards. However, although quite similar in appearance to basilisk lizards, they lacked the enlarged scales on the soles of their feet that would have allowed them to temporarily sprint across the surface of the water.
The long legs, short arms, and long tail of Geiseltaliellus would have made it both an effective facultative biped on the ground and climber in trees. Living corytophanids share these features but spend most of their time in trees, with only the juveniles of some species spending significant time on the ground. Long penultimate phalanges (second-to-last toe bones) in Geiseltaliellus, which are common to many other arboreal animals because they allow for better grip on branches, suggest that like living corytophanids it was primarily arboreal rather than terrestrial. This hypothesis fits with the inferred paleoenvironment of the Messel Pit during the Eocene, which was a dense forest.