VERTEBRATE BROMALITES FROM EOCENE LACUSTRINE STRATA – COMPARISON OF ICHNOFAUNAS FROM THE GREEN RIVER FORMATION OF THE WESTERN UNITED STATES AND THE MESSEL LAGERSTÄTTEN IN GERMANY

The predominantly early Eocene Green River Formation of the western United States and the middle Eocene Messel Lagerstätte of southwestern Germany both preserve extensive vertebrate fossils and associated ichnotaxa. The Green River was deposited in areally extensive lakes, whereas Messel represents a relatively small crater lake. The majority of Green River body fossils are fish, whereas Messel preserves a higher proportion of terrestrial mammals, birds, bats, crocodilians, amphibians, snakes, turtles and lizards. Regurgitalites. Messel has well-documented regurgitalites produced by birds (strigilites), snakes and possibly lizards, including one yielding a skeleton of the hyaenodontid mammal Lesmesodon edingeri. There are no described regurgitalites from the Green River, but they undoubtedly exist. Consumulites. The Green River Formation produces a number of fish consumulites, including several aspirationalites. A notable specimen is an example of a matryoshkalite (consumulite within a consumulite) as Amia uintaensis consumed Diplomystus, which, in turn, had consumed Knightia. Mioplosus labracoides has yielded the most consumulites in the Green River. Messel has yielded many consumulites, notably from multiple mammals and birds. Eleven taxa of birds yield gastrolites and cropalites. Two lizards and two snakes contain gastrolites. One specimen of Eoconstrictor fisheri has the lizard Geiseltaliellus maarius in its stomach that, in turn, contains an insect in its digestive trac (matryoshkalite). Several bat and fish skeletons yield consumulites. Coprolites. The most common coprolites in both the Green River and at Messel represent fish, with fewer derived from crocodilians. Messel includes spiral coprolites that are absent from the Green River. Pabulites. Multiple isolated feet of medium-large size birds occur at Messel, and the majority of these exhibit broken leg bones with missing ends, suggesting incomplete predation by crocodilians. Both Messel and the Green River yield diverse and important bromalites, and two of the three known matryoshkalites are from these units. The bromalite diversity reflects that of the body fossils – most Green River specimens pertain to fish and at Messel more pertain to tetrapods. More work is needed on all Green River bromalites and on Messel coprolites.