Content area
Full Text
ABSTRACT-
The ophthalmosaurid Caypullisaurus from the Late Jurassic-Early Cretaceous of the Neuquén Basin, Argentina, is redescribed based on new information from recent discoveries. Cladistic analysis of Caypullisaurus, based on previous ichthyopterygian data sets and using NONA, yielded two most parsimonious trees. Two clades are recognized within the Ophthalmosauridae. Caypullisaurus is found to be nested with Brachypterygius and Platypterygius. Simultaneous, unconstrained analysis, using unambiguous character optimization, is suggested as the best way to analyze data sets with large amounts of missing data.
INTRODUCTION
TITHONIAN-AGE EXPOSURES of the Vaca Muerta Formation in the Neuquén Basin, Argentina, have yielded a rich marine reptile fauna (Gasparini, 1985; Gasparini and Fernández, 1997). Among this fauna, ichthyosaurs are the most common reptiles. Most of the ichthyosaur material is referred to Caypullisaurus bonapartei Fernández, 1997. This species was named based on the holotype, an adult ichthyosaur from Cerro Lotena (early Tithonian, Vaca Muerta Formation) which is the most complete skeleton of a mature ichthyosaur from the Jurassic of South America, as well as on other specimens from the Museo de La Plata collection. Caypullisaurus Fernández, 1997 has been included in cladistic analyses of the Ichthyosauria carried out by Motani (1999) and Maisch and Matzke (2000). Both analyses found Caypullisaurus to be an ophthalmosaurid; but its position within the clade differs between the two. One of the main problems in the analysis of the relationships of Caypullisaurus is that most of the skull sutures cannot be seen in the holotype. Thus, in Motani's (1999) and Maisch and Matzke (2000) data set, a high percentage of characters are scored as missing in Caypullisaurus.
Recently, and as a result of extensive field work carried out in Tithonian and Berriasian exposures of the Vaca Muerta Formation in the Neuquén Basin (32°-41°S, 68°-72°W), Argentina, new material referable to this species has been collected. In addition, our knowledge of the group has significantly increased since the original description of Caypullisaurus. This information about Caypullisaurus allows more extensive description of its morphology and reevaluation of its phylogenetic affinities.
MATERIALS AND METHODS
The following taxa for cladistic analysis were used as terminals: Cymbospondylus piscosus Leidy, 1868; Stenopterygius Jaekel, 1904; Ichthyosaurus de la Beche and Conybeare, 1821; Mollesaurus Fernández, 1999; Brachypterygius Huene, 1922; Aegirosaurus Bardet and Fernández, 2000; Ophthalmosaurus seeley,...