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Ichthyosaurs represent one of the most highly specialized lineages of marine reptiles, but our understanding of the evolution of this group is based on specimens found at a surprisingly small number of stratigraphic intervals and localities. The Lower Jurassic (Toarcian) Posidonia Shale of southwestern Germany is one of the richest ichthyosaur-bearing formations in the world and has produced thousands of skeletons, including specimens with preserved soft tissue, and fetal remains inside the body cavity. The most abundant ichthyosaur genus in the Posidonia Shale isStenopterygius. In spite of almost 200 years of research effort, the number of species in this genus is still a point of active disagreement in the literature. Here, bivariate and multivariate analyses are used to classify both articulated and disarticulated skeletons to the level of species, using measurement data from individual cranial and postcranial elements. Unlike previous classification attempts, this technique pinpoints ontogenetically conserved differences in size and proportion between the species, and so can be applied to adult, subadult, and neonatal specimens. Using this method, three species ofStenopterygius, S. quadriscissus, S. triscissus, andS. uniterare differentiated.

Recent cladistic analyses have all suggested a diapsid origin of ichthyosaurs. However, an intermediate evolutionary stage of the lower temporal region of ichthyosaurian skull between basal diapsids and derived ichthyosaurs has been absent from the fossil record. Here we describe the cranial skeleton of a new mixosaurid ichthyosaur specimen with a well-preserved lower temporal region from the Anisian Guanling Formation of eastern Yunnan. It is characterized by the most primitive lower temporal region within known ichthyosaurs. The primitive characters of the lower temporal region include both external and internal separation between the jugal and the quadratojugal, an anterior process of the quadratojugal, an apparent posteroventral process of the jugal, and a large lower temporal opening surrounded by the jugal, the postorbital, the squamosal, and the quadratojugal. The lower temporal region of this specimen provides the most direct evidence to the diapsid origin of ichthyosaurs. It also suggests that the disappearance of the lower temporal fenestra is caused initially by the reduction of the lower temporal arcade rather than the enlargement of the surrounding bones.

From the Middle Jurassic on, the Tethys basin opened westward; the existence of a Carribean corridor linking the European and Pacific realms now appears well supported by comparison of marine reptile assemblages (e.g., Gasparini and Fernandez, 1997, 2005; Gasparini et al., 2000; Fernandez and Iturralde-Vinent, 2000; Gasparini and Iturralde-Vinent, 2001, 2006; Gasparini et al., 2002). Marine transgression in Mexico began during the Callovian, as evidenced by the evaporites of the Minas Viejas Fm. However, microfossils and invertebrate assemblages indicate that the Mexican Gulf remained isolated from both the European Archipelago and the Pacific, at least temporarily, until the middle Berriasian; the Florida uplift and southward movement of Yucatan were proposed as possibly forming a barrier (Salvador et al., 1993; Adatte et al., 1994, 1996; Goldhammer, 1999; Goldhammer and Johnston, 2001; Gasparini and Iturralde-Vinent, 2006). After almost a decade of field work and examination of collections, the Late Jurassic marine reptile assemblage of north-east Mexico confirms the conclusions drawn from microfossils and invertebrates. Poorly diagnostic ichthyosaur remains, with various thalattosuchians, numerically dominate the assemblage. Sauropterygians are rare, mainly represented by large pliosaurids of unclear affinities, a few vertebrae attributed to elasmosaurids, and a unique cryptoclidid. Turtles are yet to be reported (Frey et al., 2002; Buchy et al., 2003, 2005b, 2006a–d; Buchy, 2007, 2008a, b; material currently under study). The conglomerates, sandstones and siltstones of the Kimmeridgian-Berriasian La Casita Formation characterize the Late Jurassic deltaic and inner shelf paleoenvironments proximal to the Coahuila Peninsula in the area of Saltillo and Monterrey, whereas the shales, siltstones, and phosphorites of the coeval La Caja Formation indicate more distal outer shelf facies further to the south (Fig. 1; e.g., Goldhammer, 1999). Figure …

The family Mixosauridae Baur, 1887 is a dominant group of Middle Triassic ichthyosaurs. Its generic composition has been controversial, but recent findings from southern China enabled Jiang et al. (2006) to recognize two monophyletic taxa within the clade, suggesting the presence of two genera within the family, namely Mixosaurus Baur, 1887 and Phalarodon Merriam, 1910. The latter genus, which was invalidated at one point (Nicholls et al., 1999; McGowan and Motani, 2003), was recently resurrected by Schmitz (2005) by validating its type species. Mixosaurus is Tethyan in distribution, whereas Phalarodon had been known mostly from North America and Spitsbergen, apart from a possible juvenile from Switzerland (Brinkmann, 1997, 1998). More recently, Jiang et al. (2003) reported a largely complete, yet poorly preserved skeleton as the first record of the genus Phalarodon from Asia and referred it to Phalarodon sp. However, important synapomorphies were not clearly identified, and evidence has since emerged that the specimen had been tampered with by farmers after it was collected. In the light of the cladistic analysis by Jiang et al. (2006), the referral of the specimen to the genus Phalarodon is questionable. A new specimen was excavated in Panxian County, near the western border of Guizhou Province, by the Geological Museum and Department of Geology of Peking University. The new material, the authenticity of which is unquestionable, is from the same stratigraphic horizon as the specimen of Jiang et al. (2003). It contains a well-preserved skull and some postcranial bones, and for the first time firmly establishes the presence of the genus Phalarodon in the western Pacific. Also, the skull is preserved in a very unusual condition: it had been split near the sagittal plane, enabling examination of the poorly known interior suture pattern. This illustrates that mixosaurids had extensive …

The ophthalmosaurid Caypullisaurus from the Late Jurassic–Early Cretaceous of the Neuquen 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.

Gastroliths (stomach stones) are frequently reported in association with plesiosaur remains, especially elasmosaurids (e.g., Brown, 1904; Williston, 1904; Welles and Bump, 1949; Darby and Ojakangas, 1980; Everhart, 2000; Cicimurri and Everhart, 2001). Stones are also known from several other fossil and modern aquatic vertebrates, including fishes (Dapples, 1938; Thomson, 1966; Trewin, 1986), penguins (Emery, 1963; Stonehouse, 1967; Boswall and MacIver, 1975), crocodilians (Cott, 1961; Neill, 1971; Keller and Schaal, 1992), and pinnipeds (Fleming, 1951; Mohr, 1963; Bryden, 1999). However, gastroliths are very rarely reported in ichthyosaurs, despite the fact that a large number of articulated skeletons are known from this clade. Some ichthyosaurs show preserved gut contents (e.g., Pollard, 1968; Keller, 1976; Kear et al., 2003), and sand is occasionally found in the gastric area of ichthyosaurs (R. Wild, personal commun., 2000; Wings, personal obs.). Gastroliths with grain sizes >2 mm are only known from two specimens: the one described in detail here and a complete but undescribed skeleton from the famous Upper Jurassic Solnhofen Limestone of Germany (Taylor, 1993; Wings, personal observation). The German specimen is probably referable to the genus Nannopterygius Huene, 1922, so far only known from England. The specimen is preserved as a slab, which is on exhibit at the Jura-Museum, Eichstatt, Germany, and a counterslab, which is accessioned to the collections of the Staatliches Museum fur Naturkunde, Karlsruhe, Germany. A description of the stones found in the perfect holotype specimen (Museum of the Yichang Institute of Geology and Mineral Resources # TR00001) of Panjiangsaurus epicharis described by Chen and Cheng (2003) (Fig. 1) is important not only because of the scarcity of ichthyosaurian gastroliths, the find is also relevant for the interpretation of gastrolith function. Panjiangsaurus epicharis …

A large ichthyosaur from the Los Molles Formation (Early Bajocian) of the Neuquén Basin, Northwestern Patagonia, Argentina, represents a new genus and species,Mollesaurus periallus.The holotype ofM. periallusnew species represents, along with the type ofChacaicosaurus cayithat was found at the same locality, the only diagnostic ichthyosaur specimens from the Aalenian-Bathonian interval.

Utatsusaurus hataii, an Early Triassic ichthyosaur from Japan, is represented by exceptionally well preserved materials but is poorly known because of incomplete preparation. Further preparation of the holotype and one of the paratype specimens has revealed nearly complete forefins that are pentadactyl, with no more than five phalanges in any of the digits. The first digit is not well developed, and the fifth distal carpal appears to be absent. The phalanges along the fin margin tend to be lunate; others are flattened cylinders. These findings indicate that the relationship of Utatsusaurus with other Early Triassic ichthyosaurs must be reconsidered.

A large ichthyosaur from the Early Tithonian (Late Jurassic) of the Neuquén province, Argentina, represents a new genus and species, Caypullisaurus bonapartei, within the family Ichthyosauridae. The holotype is the most complete skeleton of a mature ichthyosaur known to date from the Jurassic of South America. In comparison with other Late Jurassic ichthyosaurs, the new taxon shares a long and slender rostrum, degenerate dentition in adults, and the enlargement of the orbit with Ophthalmosaurus. Unlike Ophthalmosaurus, the forefin of Caypullisaurus has four major digits composed of tightly packed, polygonal phalanges, and pre- and post-axial accessory digits. Caypullisaurus demonstrates that ichthyosaurs were more diverse during the Late Jurassic than thought previously.

ichthyosaur finds, and a number of new genera and species were described from this state. Based on a few vertebrae, Leidy (1868) erected a new Middle Triassic ichthyosaur genus, Cymbospondylys, with two species, C. petrinus and C. piscosus. The type material of C. petrinus came from the Prida Formation of the southern Humboldt Range, and that of C. piscosus from the Favret Formation of the New Pass Range. Much ichthyosaur material was collected by University of California field parties around the turn of the century (Merriam, 1902, 1905, 1906, 1908, 1910). Most of the finds again came from the Prida Formation of the southern Humboldt Range and overwhelmingly pertained to Cymbospondylus petrinus (Merriam, 1908). Additional ichthyosaur taxa based on the same collections from the Prida of the Humboldt Range are Cymbospondylus(?) natans Merriam, 1908, Omphalosaurus nevadanus Merriam, 1906, and Phalarodon fraasi Merriam, 1910. All three species are known from rare and scanty material only. Cymbospondylus(?) natans turned out to be a species of Mixosaurus (Sander and Bucher, 1990), while Phalarodon appears to be a junior synonym of Mixosaurus (Brinkman et al., 1992). Another species based on very fragmentary material, C. nevadanus, was described by Merriam (1908) from the Favret Formation of the New Pass Range. Together with the Late Triassic Shonisaurus (Camp, 1980), the Middle Triassic Cymbospondylus is the best known Triassic ichthyosaur. Both genera were large pelagic predators similar in their ecology to moder odontocetes (Massare, 1988). Characteristically, in Nevada these ichthyosaurs are found together with a rich ammonite fauna but few other vertebrate fossils.

The occurrence of the large ichthyosaur Cymbospondylus in the Middle Triassic of Spitsbergen is recognized based on two different specimens. One consists of a semiarticulated string of 17 dorsal vertebrae with associated ribs and the other of an anterior dorsal vertebral centrum and possibly a caudal vertebral centrum. Both specimens can only be identified as Cymbospondylus sp. This record fills a gap in the distribution of Cymbospondylus, establishing this genus as the second most widespread Triassic ichthyosaur after Mixosaurus.

A partial skeleton, including a skull with part of the axial skeleton, part of a second skull, and fragments of ribs have been recovered from the Sinemurian of the Sandilands Formation exposed at Kennecott Point in the northwestern Queen Charlotte Islands. This material is the most complete Early Jurassic collection from North America reported to date; other occurrences include a forefin from the Nordegg Formation (Sinemurian) of Alberta positively identified as Ichthyosaurus (McGowan, 1978) and vertebral centra from the Nicely Formation (Pliensbachian), Oregon, not assigned conclusively to a genus (McGowan, 1978). The discovery of ichthyosaurs in the allochthonous insular belt of British Columbia adds weight to the contention that ichthyosaurs were cosmopolitan in their distribution (McGowan, 1978; Orr, 1986).

The small ichthyosaurMixosaurusis the most widely distributed ichthyosaur. It is known from Lower Triassic rocks of British Columbia, Canada (Callaway and Brinkman, 1989), and Middle Triassic rocks of northwestern North America (Alaska, British Columbia), China, Timor, the western Tethys (Switzerland, Italy, Turkey), the Germanic Triassic, and the high Arctic (Spitsbergen, Exmouth Island) (Mazin, 1986; Callaway and Brinkman, 1989; Callaway and Massare, 1989). The presence ofMixosaurusin one of the richest ichthyosaur provinces, the Middle Triassic of Nevada (Merriam, 1908), has been difficult to establish. The history of this problem is very colorful and is the topic of this note together with the description of a new specimen from the Nevada Middle Triassic.