Mesozoic Sea Dragons by Olivier Rieppel

Author:Olivier Rieppel
Language: eng
Format: epub
ISBN: 9780253040145
Publisher: Indiana University Press
Published: 2019-02-21T16:00:00+00:00

The Genus Lariosaurus

In his survey of the fossil biota of Monte San Giorgio, Kuhn-Schnyder illustrated a small lariosaur that was collected in 1971 in Val Mare near Meride, which he referred to Lariosaurus balsami (1974:65, fig. 42). The specimen came from the top of the upper Meride Limestone, that is, the late Ladinian Kalkschieferzone, and thus qualifies as the geologically youngest fossil reptile so far collected at Monte San Giorgio. In his monographic description of the specimen, Kuhn-Schnyder referred it to a new species, Lariosaurus lavizzarii, named after Luigi Lavizzari (1814–1875), an influential naturalist and politician of Canton Ticino, the Italian-speaking part of Switzerland where Monte San Giorgio is located (1987:19). The species is described as differing from Lariosaurus balsami in the contours of the skull (a slightly offset rostrum), and a relatively shorter humerus. With a glenoid-acetabular length of only 60 to 62 mm, the specimen was recognized as a juvenile individual by Kuhn-Schnyder (1987:7). This raises questions regarding the diagnostic value of these characters, in particular relative humerus length, although Sanz had characterized the relation of humerus to femur growth as isometric in Lariosaurus (1983).

The specimen was later revisited by Tschanz, who declared Lariosaurus lavizzarii a subjective junior synonym of L. balsami (1989). He noted that the rostrum is even more distinctly set off from the orbital region of the skull in the Munich specimen of L. balsami, which was designated the neotype of its species by Kuhn-Schnyder (1987:19; see Peyer, 1933, pl. 32, fig. 1; Rieppel, 1998b:12, fig. 10A). The relative humerus length in L. lavizzarii corresponds to that of small individuals of L. balsami (Tschanz, 1989:157). However, in 1993, Renesto described a juvenile specimen of Lariosaurus from the Kalkschieferzone at Ca’ del Frate near Viggiù that he found to be not diagnostic at the species level and which therefore cannot be referred to any species of Lariosaurus with certainty. Comparing this new specimen with Lariosaurus lavizzarii from the Kalkschieferzone of a nearby locality, he drew the same conclusion with respect to the latter specimen (Renesto, 1993). Otherwise, the Kalkschieferzone near Ca’ del Frate has yielded a beautifully preserved lariosaur described as Lariosaurus valceresii by Tintori and Renesto (1990). Renesto’s conclusion was that it is impossible to decide whether the juvenile specimens from the Kalkschieferzone should be referred to the latter species or to Lariosaurus balsami instead (1993). Lariosaurus lavizzarii thus becomes a nomen dubium (Rieppel, 2000a:91).

In September 1961, a small nothosaurian reptile was collected in layer 97 at Point 902. This renders the specimen of uppermost Anisian age and hence, as was later found, the earliest record of lariosaurs at Monte San Giorgio (Brack and Rieber, 1986, 1993; Tschanz, 1989; Furrer, 2003). Kuhn-Schnyder illustrated the specimen, which he referred to as a “small nothosaurid” (1974:31, figs. 9 through 12; see also Kuhn-Schnyder, 1963b). At the time, the description of this new find did not constitute “one of the urgent tasks of the Paleontological Institute,” of which he was director (Kuhn-Schnyder, 1990:314). The specimen was eventually described by Tschanz as a new species, Lariosaurus buzzii (fig.

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