Palaeoecology of the marine reptiles of the Redwater Shale Member of the Sundance Formation (Jurassic) of central Wyoming, USA
2014
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.
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