Swiss Journal of Palaeontology最新文献

Switzerland is an ichthyosaur country: it has a rich record of marine reptile fossils, particularly the fish-shaped ichthyosaurs, and the according research. Here, we provide an overview over the 12 or more genera and at least 13 species plus numerous fragmentary remains of ichthyosaurs from the Triassic to the Cretaceous that have been discovered in twelve cantons thus far, of which four species are based on Swiss holotypes. This wealth of ichthyosaur species can be explained by their abundance in the Middle Triassic conservation deposits (Konservat Lagerstätte) of Monte San Giorgio, as well as occasional discoveries in strata of Middle Triassic to Early Cretaceous age. The moderate abundance of outcrops in reasonable conditions in combination with the long history of palaeontological research in Switzerland explains this good fossil record. In addition to this unique overview, we provide more data for further studies and update the knowledge of these taxa.

Placodonts were durophagous reptiles of the Triassic seas with robust skulls, jaws, and enlarged, flat, pebble-like teeth. During their evolution, they underwent gradual craniodental changes from the Early Anisian to the Rhaetian, such as a reduction in the number of teeth, an increase in the size of the posterior palatal teeth, an elongation of the premaxilla/rostrum, and a widening of the temporal region. These changes are presumably related to changes in dietary habits, which, we hypothesise, are due to changes in the type and quality of food they consumed. In the present study, the dental wear pattern of a total of nine European Middle to Late Triassic placodont species were investigated using 2D and 3D microwear analyses to demonstrate whether there could have been a dietary shift or grouping among the different species and, whether the possible changes could be correlated with environmental changes affecting their habitats. The 3D analysis shows overlap between species with high variance between values and there is no distinct separation. The 2D analysis has distinguished two main groups. The first is characterised by low number of wear features and high percentage of large pits. The other group have a high feature number, but low percentage of small pits. The 2D analysis showed a correlation between the wear data and the size of the enlarged posterior crushing teeth. Teeth with larger sizes showed less wear feature (with higher pit ratio) but larger individual features. In contrast, the dental wear facet of smaller crushing teeth shows more but smaller wear features (with higher scratch number). This observation may be related to the size of the food consumed, i.e., the wider the crown, the larger food it could crush, producing larger features. Comparison with marine mammals suggests that the dietary preference of Placochelys, Psephoderma and Paraplacodus was not exclusively hard, thick-shelled food. They may have had a more mixed diet, similar to that of modern sea otters. The diet of Henodus may have included plant food, similar to the modern herbivore marine mammals and lizards.

Supplementary information: The online version contains supplementary material available at 10.1186/s13358-024-00304-x.

In the wake of the greatest mass extinction in Earth's history, the End-Permian Mass Extinction, the Triassic was a time of recovery and innovation. Aided by warm climatic conditions and favorable ecological circumstances, many reptilian clades originated and rapidly diversified during this time. This set the stage for numerous independent invasions of the marine realm by several reptilian clades, such as Ichthyosauriformes and Sauropterygia, shaping the oceanic ecosystems for the entire Mesozoic. Although comparatively less speciose, and temporally and latitudinally more restricted, another marine reptile clade, the Thalattosauriformes, stands out because of their unusual and highly disparate cranial, dental and skeletal morphology. Research on Thalattosauriformes has been hampered by a historic dearth of material, with the exception of rare material from Lagerstätten and highly fossiliferous localities, such as that from the UNESCO world heritage site of Monte San Giorgio. Consequently, their evolutionary origins and paleobiology remain poorly understood. The recent influx of new material from southwestern China and North America has renewed interest in this enigmatic group prompting the need for a detailed review of historic work and current views. The earliest representatives of the group may have been present from the late Early Triassic onwards in British Columbia. By the Ladinian the group had achieved a wide distribution across the northern hemisphere, spanning the eastern Panthalassic as well as the eastern and western Tethyan provinces. Distinct morphological and likely ecological differences exist between the two major clades of Thalattosauriformes, the Askeptosauroidea and the Thalattosauroidea, with the latter showing a higher degree of cranial and skeletal morphological disparity. In-group relationships remain poorly resolved beyond this bipartition. Overall, thalattosaurs may be closely related to other marine reptile groups such as ichthyopterygians and sauropterygians. However, their exact position within Diapsida remains elusive. Future focal points should utilize modern digital paleontological approaches to explore the many fragmentary specimens of otherwise poorly sampled localities.

Only a few Swiss fossil localities are known globally and of which, the UNESCO World Heritage Site Monte San Giorgio, which extends from Switzerland into Italy, is the most important one. Following the discovery of the occurrence of articulated skeletons of marine reptiles in the local mines, large excavations were organized by Bernhard Peyer from the University of Zurich starting 1924. With this collection of articles, we commemorate the successful excavations and research, which initiated the publication of a series of monographies, mostly on the vertebrates but also on the invertebrates of this locality. Especially with the discovery of several remarkably similar Konservat-Lagerstätten in China, the discoveries from Monte San Giorgio gained global relevance. New methodologies such as computed tomography produced a wealth of new data, particularly on endocranial anatomy of several tetrapods.