Palaeoecology of the marine reptiles of the Redwater Shale Member of the Sundance Formation (Jurassic) of central Wyoming, USA

Abstract

The Redwater Shale Member (Oxfordian) of the Sundance Formation was deposited in the foreland basin of the Cordillera during the last and largest marine transgression of the Jurassic in North America. One ichthyosaur (Ophthalmosaurus natans), two cryptocleidoid plesiosaurs (Tatenectes laramiensis, Pantosaurus striatus) and one pliosauromorph (Megalneusaurus rex) are known from the Redwater Shale Member. Ichthyosaurs are much more abundant than plesiosaurs, making up almost 60% of the fauna. No actinopterygian fish have been found, although four species have been identified from the lower Sundance Formation. At least one hybodont shark and one neoselachian are known from rare isolated teeth. The main food source for the marine reptiles was belemnoids, as indicated by preserved gut contents for all four species. In comparison, the better known and slightly older Peterborough Member of the Oxford Clay Formation of England, has a much higher taxonomic and ecological diversity, especially in the plesiosaurs, marine crocodiles, and fish. The lower diversity in the Redwater Shale Member probably reflects a much lower primary productivity in the Sundance Sea, as well as restricted migration from the open ocean to the north.

Structural, functional, and physiological signals in ichthyosaur vertebral centrum microanatomy and histology

“…As opposed to what was described for some ribs Massare et al 2014) and long bones (Houssaye et al 2014b), no general or local increase in bone compactness is observed in ichthyosaur vertebral centra, which are exclusively spongious, as compared to what is observed in most amniotes (Houssaye et al 2014a). As noted above, there is no peripheral layer of compact cortex as in most amniotes (Dumont et al 2013;Hayashi et al 2013;Houssaye et al 2014b).…”

High evolutionary rates and the origin of the Rosso Ammonitico Veronese Formation (Middle-Upper Jurassic of Italy) reptiles

“…The Rosso Ammonitico Formation is primarily representative of deep water column deposition (depth >110 m, Martire 1992;Martire et al 2006;Cau and Fanti 2011), thus significantly deeper than the epieric seas deposits where most metriorhynchoids and plesiosaurians are usually recovered (depth <50 m; Hudson and Martill 1991;Young et al 2010;Massare et al 2013). The taphonomy of both type specimens of Anguanax and Neptunidraco suggests that they did not suffer substantial transport neither disarticulation before burial (Cau andFanti 2011, 2014).…”

Skeletal microstructure of Stenopterygius quadriscissus (Reptilia, Ichthyosauria) from the Posidonienschiefer (Posidonia Shale, Lower Jurassic) of Germany

“…The dorsal ribs show variation in structure with length along the shaft as is also seen in mosasaurs, cetaceans and the ichthyopterygian Utatsusaurus hataii and ichthyosaurian Ophthalmosaurus natans (Houssaye & Bardet ; Massare et al . ; Nakajima et al . ; D'Emic et al .…”