PALEOHABITAT OF MIDDLE DEVONIAN (EIFELIAN) FISHES OF NORTH AMERICA WITH NOTES ON DEINODUS BENNETTI

Eifelian-age fishes from the Onondaga (New York), Columbus and Delaware (Ohio) limestones were examined and their paleohabitats inferred. Within the Onondaga, Deinodus, Onychodus and Machaeracanthus preferred the shallow water conditions of the lower Moorehouse Member. The lower part of the Moorehouse is fine-grained and fossils are not common. Because of an overlying unconformity, the lower Moorehouse may represent a lagoonal area with poor circulation. Macropetalichthys and Ptyctodus are found in the more open water facies of the upper Moorehouse and the Seneca Member. These units are course-grained, extremely fossiliferous and represent open shelf environments near wave base. Onychodus, Machaeracanthus, Palaeomylus, Rhynchodus and Eczematolepis preferred the shallow waters of the Delaware Limestone. The Delaware is a fine-grained rock with numerous, fossiliferous lag deposits and shaly partings. Like the lower Moorehouse, it represents a low-energy environment, with intermittent increases in energy, and poor circulation. As in the upper Moorehouse, Macropetalichthys lived in more open water units, as in the facies of the upper Columbus. Macropetalichthys was probably an open water predator. Tooth morphology indicates that Onychodus and Rhynchodus were ambush predators of the shallow waters. The life habits of Machaeracanthus can only be speculated upon as only spines are found. The other taxa, all ptyctodonts, possessed dental plates for crushing hard-shelled invertebrate prey. The enigmatic Deinodus bennetti shares similar characteristics with the ptyctodonts. Its anterior ventral lateral plates are most similar to those of ptyctodonts and are associated with broad spinous plates. As with most other ptyctodonts, its dentition is designed for crushing.