Chacaicosaurus

Chacaicosaurus is an extinct genus of long-snouted thunnosaur ichthyosaur known from the northwestern Patagonia area of Argentina.
Description.
"Chacaicosaurus" is known only from the holotype MOZ 5803, an articulated partial skeleton which preserved a partial skull and almost complete forefin. It was collected in the Chacaico Sur locality from the "Emileia giebeli" ammonoid zone of the Los Molles Formation, Cuyo Group, dating to the early Bajocian stage of the Middle Jurassic, about 171.6-170 million years ago. It was found near Zapala city of the Neuquén Basin. "Chacaicosaurus", along with "Mollesaurus periallus", which was found at the same locality, are the only diagnostic ichthyosaur specimens from the Aalenian-Bathonian interval.
In the original description Fernández did not assign "Chacaicosaurus" to a particular family. Maisch and Matzke (2000) and Maisch (2010) regarded it to be an advanced stenopterygiid. However, a recent cladistic analysis found that "Chacaicosaurus" is a basal thunnosaur which is placed outside both Stenopterygiidae and Ophthalmosauridae.
Etymology.
"Chacaicosaurus" was named by Marta S. Fernández in 1994 and the type species is "Chacaicosaurus cayi". The generic name is derived from the name of the Chacaico Sur locality, in which the holotype was collected, and "sauros", Greek for "lizard".