amniote tetrapods, having descended from terrestrial egg-laying amniotes during the late Permian or the earliest Triassic. However, establishing their position within the amniote evolutionary tree has proven difficult, due to their heavily derived morphology obscuring their ancestry. Several conflicting hypotheses have been posited on the subject. In the second half of the 20th century, ichthyosaurs were usually assumed to be of the Anapsida, seen as an early branch of "primitive" reptiles. This would explain the early appearance of ichthyosaurs in the fossil record, and also their lack of clear affinities with other reptile groups, as anapsids were supposed to be little specialised. This hypothesis has become unpopular for being inherently vague because Anapsida is an unnatural, paraphyletic group. Modern exact quantitative cladistic analyses consistently indicate that ichthyosaurs are members of the clade Diapsida. Some studies showed a basal, or low, position in the diapsid tree. More analyses result in their being Neodiapsida, a derived diapsid subgroup. Until the 1980s, a close relationship was assumed between the Ichthyosauria and the Sauropterygia, another marine reptile group, within an overarching Euryapsida. Today, however, this is usually rejected, with the Euryapsida being seen as an unnatural polyphyletic assemblage of reptiles that happen to share some adaptations to a swimming lifestyle. An exception is a study in 1997 by John Merck, which showed monophyletic archosauromorph euryapsids. Affinity with the Hupehsuchia Since 1959, a second enigmatic group of ancient sea reptiles is known, the Hupehsuchia. Like the Ichthyopterygia, the Hupehsuchia have pointed snouts and show polydactyly, the possession of more than five fingers or toes. Their limbs more resemble those of land animals, making them appear as a transitional form between these and ichthyosaurs. Initially, this possibility was largely neglected because the Hupehsuchia have a fundamentally different form of propulsion, with an extremely stiffened trunk. The similarities were explained as a case of convergent evolution. Furthermore, the descent of the Hupehsuchia is no less obscure, meaning a possible close relationship would hardly clarify the general evolutionary position of the ichthyosaurs. In 2014, Cartorhynchus was announced, a small species with a short snout, large flippers, and a stiff trunk. Its lifestyle might have been amphibious. Motani found it to be more basal than the Ichthyopterygia and named an encompassing clade Ichthyosauriformes. The latter group was combined with the Hupesuchia into the Ichthyosauromorpha. The ichthyosauromorphs were found to be diapsids. The proposed relationships are shown by this cladogram: