Chacaicosaurus

Chacaicosaurus Temporal range: Middle Jurassic, 171.6–170 Ma PreЄ Є O S D C P T J K Pg N ↓
File:Chacaicosaurus.jpg
Restoration
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Ichthyosauria
Clade:	†Baracromia
Genus:	†Chacaicosaurus Fernández, 1994
Species:	† C. cayi
Binomial name
Chacaicosaurus cayi Fernández, 1994

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".

See also

• List of ichthyosaurs
• Timeline of ichthyosaur research