J�rn Geister

Academic paper

FACIES

39

105-124

Numerous gutter-like furrows, up to 60 cm wide and up to 9 m long are preserved at the interface "Macrocephalus Beds" I "Callovian Marl" over a surface of 20 by 200 m. They are interpreted as feeding traces made by large marine vertebrates, most likely plesiosaurs and ichthyosaurs searching for food in the lime mud of the shallow Middle Jurassic sea floor. Possible prey animals were in faunal invertebrates (crustaceans) which produced an intricate meshwork of burrows (mainly Rhizocoralliurn irregulare and Thalassinoides) in the bottom sediments, as well as infaunal bivalves. Evidence from coprolites of predatory pelagic reptiles (ichthyosaurs, plesiosaurs) as well as reptile regurgitalites indicate that these animals fed not only on fast-swim-ming vertebrates and cephalopods but also on epi- and endobenthic invertebrates. In addition, the cololites show that the predators ingested considerable amounts of bottom sediment. Different sizes and shapes of the traces suggest that the gutters were produced by different reptiles or age groups. Candidates for the widest gutters are pliosaurs. Of the marine vertebrates known from Jurassic time, only the snout of adult pliosaurs of the genus Liopleurodon was broad enough to produce gutters more than 40 cm wide. Smaller, less than 15 cm wide gutters, could have been made by plesiosauroids or by the narrow pointed snouts of ichthyosaurs.
Almost identical traces described from the Oxfordian of Spain and similar but smaller traces from the Lower Devonian of Prague are equally interpreted as feeding traces on the sea floor. Feeding traces of vertebrates in bottom sediments may give detailed information on the hunting behaviour of the predators. However, the attribution of the traces to definite vertebrate taxa remains uncertain.

Trace Fossils - Feeding Traces - Vertebrates - Marine Saurians - Jura Mountains (Switzerland) - Jurassic (Callovian)

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